Annexon, Inc. (ANNX) Business

Item 1. Business.

In this Annual Report on Form 10-K, “we,” “our,” “us,” “Annexon” and the “Company” refer to Annexon, Inc. and its consolidated subsidiary. Annexon, Annexon, Inc., the Annexon logo and other trade names, trademarks or service marks of Annexon are the property of Annexon, Inc. This report contains references to our trademarks and to trademarks belonging to other entities. Trade names, trademarks and service marks of other companies appearing in this report are the property of their respective holders. We do not intend our use or display of other companies’ trade names or trademarks to imply a relationship with, or endorsement or sponsorship of us by, any other companies.

Overview

We are a biopharmaceutical company advancing the next generation platform of targeted immunotherapies aimed at complement-mediated neuroinflammatory diseases that impact nearly 10 million people worldwide. The classical complement pathway is a core component to the body’s immune system that activates a powerful inflammatory cascade. We believe that by stopping the classical complement pathway at its start by targeting C1q, the initiating molecule of the classical complement pathway, our approach may have the potential to provide more complete protection against complement-mediated disorders of the body, brain and eye.

Using our proprietary platform, we are identifying and characterizing the role of the classical complement pathway in three therapeutic areas—autoimmune, neurodegeneration and ophthalmology. In so doing, we are advancing a pipeline of product candidates designed to block the early classical cascade and all downstream pathway components and their tissue-damaging functions. Our goal is to suppress excessive or aberrant classical complement activity that contributes to chronic inflammation and tissue damage to slow or even halt disease progression, while preserving the beneficial immune functions of the lectin and alternative complement pathways involved in the clearance of pathogens and damaged cells. Building on more than a decade of expertise stopping acute and chronic neuroinflammation at its source, we have demonstrated robust target engagement in the body, brain and eye, and clinical proof of concept in multiple diseases.

Our strategic priorities include advancing two late-stage registrational programs: tanruprubart, toward our first potential approval in Guillain-Barré Syndrome, or GBS, and vonaprument, toward pivotal data in geographic atrophy, or GA, as well as developing ANX1502, a novel oral small molecule for autoimmune conditions.

Tanruprubart is an investigational targeted immunotherapy delivered in a single infusion to rapidly halt aggressive neuroinflammation and damage in GBS, an acute, rare, neuromuscular emergency that annually affects ~150,000 people worldwide. There are currently no therapies approved by the FDA for GBS and no substantial evidence of effectiveness from the current standard of care. In the placebo-controlled Phase 3 trial, approximately 90% of GBS patients treated with tanruprubart improved by week 1 and more than twice as many treated patients achieved a normal state of health at week 26. Tanruprubart has consistently demonstrated rapid and sustained functional improvements across a comprehensive data package that includes successful placebo-controlled proof-of-concept, or POC, and Phase 3 data, Real-World Evidence, or RWE, indirect comparison data of tanruprubart’s treatment effect versus current standard of care, and drug-drug interaction safety data with tanruprubart with current standard of care. Completed placebo-controlled studies were conducted in Southeast Asia given GBS’ sudden and debilitating disease course and lack of approved comparator in the U.S. The open-label FORWARD study in the U.S. and Europe is ongoing and designed to support a broad intended label for the treatment of GBS and further expand the use of tanruprubart across geographies.

We filed the Marketing Authorization Application, or MAA, with the European Medicines Agency, or EMA, for tanruprubart for the treatment of GBS in January 2026, and we continue to engage with EU regulators through the MAA review process. Tanruprubart has been granted orphan designation from the EMA. Tanruprubart has also been granted Fast Track and orphan drug designation for the treatment of GBS from the FDA. The currently ongoing open-label U.S./EU FORWARD study is designed to broaden Western experience with tanruprubart, and we anticipate initial pharmacokinetics, or PK, pharmacodynamics, or PD, biomarker and functional data in 2026 to supplement our comprehensive data package for tanruprubart in GBS. Following such data, we plan to engage with the FDA with the

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goal of reaching alignment on our current and supplemental data package and information supporting the generalizability of tanruprubart in Western patients for submission of a biologics license application, or BLA, in 2026.

Vonaprument is an investigational neuroprotective inhibitor of C1q and the classical complement cascade delivered intravitreally for dry AMD with GA, a leading cause of blindness affecting more than eight million people worldwide. There are no approved therapies for GA targeting the preservation of vision. Vonaprument is the only investigational therapy in GA to show significant vision preservation on assessments of best corrected visual acuity, or BCVA, and low luminance visual acuity, or LLVA, demonstrating significant protection from vision loss in both normal and low light conditions, as well as significant preservation of central retinal photoreceptors necessary for visual acuity. In the Phase 2 ARCHER trial, vonaprument also reduced risk of 15-letter vision loss by more than 70%.

In July 2025, we completed enrollment of 659 patients in ARCHER II, a global, sham-controlled, double-masked Phase 3 trial for patients with GA. The primary endpoint of ARCHER II is the gold standard for visual acuity, measuring proportion of patients with confirmed BCVA ≥15-letter loss at any two consecutive visits through month 15. A secondary endpoint is ellipsoid zone, or EZ, loss, which is a key anatomic measure of photoreceptor health and function. We plan to report topline data in the fourth quarter of 2026.

We have established a global registration path with the FDA and EMA, which supports the potential of vonaprument to be the first treatment approved in both Europe and the U.S. for the protection of vision in patients with GA. The single-study program will be analyzed as two sub-studies in the U.S. in accordance with the FDA’s two-trial recommendation. Vonaprument is the first and only therapeutic candidate for the treatment of GA to receive Priority Medicine, or PRIME, designation by the EMA, which provides early and proactive support to developers of promising medicines that may offer a major therapeutic advantage over existing treatments or benefit to patients without treatment options. Vonaprument was also selected by the EMA for the Product Development Coordinator Pilot launched in July 2025 to help PRIME designation holders efficiently navigate regulatory interactions including expedited scientific advice, MAA submission readiness activities, and ad-hoc queries throughout the development program.

ANX1502 is a novel oral small molecule inhibiting the activated form of C1s, an enzyme carried by C1q to initiate the classical cascade, which we believe is first-in-kind and has the potential to offer the advantages of selective upstream classical complement inhibition with the convenience and flexibility of oral administration. In a Phase 1 single-ascending dose, or SAD, and multiple-ascending dose, or MAD, clinical trial in healthy volunteers designed to evaluate the safety, tolerability, PK and PD, ANX1502 was generally well tolerated across cohorts with no serious adverse events, achieved target levels of active drug and showed supportive impact on a PD biomarker of complement activity. We are evaluating an enteric-coated tablet formulation of ANX1502 in an ongoing POC study in patients with cold agglutinin disease, or CAD. We have observed drug levels at and exceeding the pre-defined target in fasted CAD patients. Dosing is ongoing to enhance our understanding of ANX1502’s profile and we plan to provide an update upon study completion in 2026.

Annexon was co-founded by the late Dr. Ben Barres, former member of the National Academy of Sciences, Chair of Neurobiology at Stanford University and a pioneer in complement-mediated neurodegeneration, and Dr. Arnon Rosenthal, a world-renowned scientist and industry executive. We have assembled a seasoned and accomplished management team that has been involved in the discovery, development, approval and commercialization of numerous marketed drugs, and has been studying the complement pathway and autoimmune and neurodegenerative disorders for decades. Our team is further supported by an experienced scientific advisory board, board of directors and leading healthcare investors that share our commitment to developing disease-modifying medicines for patients with neuroinflammatory diseases of the body, brain and eye.

We hold worldwide development and commercialization rights, including through exclusive licenses, to all of our product candidates, which allows us to strategically maximize value from our product portfolio over time. Our patent portfolio includes patent protection for our targeted immunotherapy platform and each of our product candidates.

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Our Pipeline

Our pipeline includes diverse drug candidates designed to address neuroinflammatory diseases with significant unmet medical need and where we have the potential to provide a first-in-class treatment opportunity. Our pipeline is summarized below:

Beyond our flagship programs, our “next wave” programs are supported by a strong scientific and clinical rationale, and provide additional potential portfolio growth and diversification opportunities subject to availability of resources and ongoing evaluation of further development options.

We have evaluated tanruprubart in patients with Huntington’s Disease, or HD, and amyotrophic lateral sclerosis, or ALS, chronic neurodegenerative disorders in which aberrant classical complement activation drives neuroinflammation and has been shown to be associated with disease progression. In a completed Phase 2 clinical trial in patients with manifest HD, chronic dosing of tanruprubart was generally well-tolerated, demonstrated rapid and sustained target engagement of C1q in both blood and cerebrospinal fluid, or CSF, reduced downstream complement markers in CSF, and showed promising efficacy signals on standard measures of disease progression in patients with higher levels of classical complement activity at baseline.

In a completed signal-finding open-label Phase 2a trial in patients with ALS, chronic dosing of tanruprubart was generally well-tolerated, showed rapid and sustained target engagement of C1q in blood, and reduced downstream pharmacodynamic complement markers in blood. Consistent with what has been shown in other neuroinflammatory diseases, including HD, exploratory analyses indicated that patients with higher baseline classical complement activation who enrolled within 12 months of diagnosis achieved better outcomes, including less functional decline on the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale, or ALSFRS-R, and stabilization of neurofilament light chain, or NfL. These analyses support a precision medicine approach to identify patients most likely to respond to anti-C1q therapy in clinical trials with recently diagnosed ALS patients who have elevated baseline levels of classical complement activity.

In addition, we have developed ANX009, a C1q-blocking Fab formulated for subcutaneous delivery, for patients with lupus nephritis, or LN, who have high baseline complement activity. LN is an autoimmune disease for which pathogenic anti-C1q antibodies, or PACAs, enhance activity and uniquely amplify kidney inflammation and damage. In a completed Phase 1b signal-finding trial, ANX009 was well tolerated, demonstrated plasma C1q target engagement and complement inhibition, and rapidly increased free/circulating PACA levels (consistent with decreased deposition

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in the kidney) and improved all downstream markers of complement consumption and activation (C4, as well as C3 and C5b-9).

Our Strategy

Our goal is to develop disease-modifying medicines for patients with neuroinflammatory diseases of the body, brain and eye. Key elements of our strategy include:

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Vonaprument: Establish the First Potential Vision-Preserving Therapy for Dry AMD with GA. We are advancing vonaprument towards pivotal data and a global registration path to approval for GA to address the unmet needs of more than eight million patients worldwide. Vonaprument’s well-tolerated, differentiated profile is the only program to show significant protection against vision loss as well as significant protection of central retinal photoreceptors necessary for visual acuity. Vonaprument is the first and only therapeutic candidate for the treatment of GA to receive PRIME designation in the EU, which provides early and proactive support to developers of promising medicines that may offer a major therapeutic advantage over existing treatments or benefit to patients without treatment options.

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Tanruprubart: Establish the First Potential Targeted Rapid-Acting Treatment for GBS. We are advancing tanruprubart as a first-line monotherapy treatment option to address the global unmet needs of approximately 150,000 patients annually diagnosed with GBS. Tanruprubart’s well-tolerated, differentiated profile showing rapid and durable improvement in muscle strength, has received both Fast Track and orphan drug designations from the FDA, as well as orphan drug designation by the EMA.

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Expand Our Targeted Immunotherapy Platform. We are leveraging learnings and data from our two late-stage registrational programs to inform clinical development in “next wave” neuroinflammatory diseases. We are also advancing a first-in-kind oral small molecule program with the aim of providing efficacy with enhanced dosing flexibility and convenience for long-term treatment of chronic autoimmune conditions. We plan to efficiently prosecute opportunities across our portfolio to create near-term value for patients, physicians and stakeholders.

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Leadership in Neuroinflammatory Diseases with C1q Inhibition. We believe our C1q inhibition platform creates a unique competitive advantage and has the potential to provide a transformative therapeutic approach to halting neuroinflammation in a broad range of well-characterized neuroinflammatory diseases. Our product candidates are designed to yield enhanced efficacy and safety by blocking all classical cascade neuroinflammation and have shown differentiated clinical outcomes across multiple diseases of the body, brain and eye.

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Maximizing the value of our product candidates. We currently hold worldwide development and commercialization rights, including through exclusive licenses, to all of our product candidates. We have secured broad intellectual property protection for our targeted immunotherapy platform and intend to leverage our intellectual property and know-how to protect and enhance our leading position in developing novel therapeutics that target the classical complement cascade. We intend to pursue independent development and commercialization in indications and markets we can address with a focused sales and marketing organization. We plan to explore licensing agreements, collaborations or partnerships to advance our product candidates in indications and markets where we could accelerate and expand development and commercialization leveraging the resources of larger biopharmaceutical companies.

Overview of the Complement System and C1q Biology

The Complement System—three main complement pathways

The complement system is an integral component of the immune system that consists of many circulating and locally-produced molecules. This system evolved to enhance, or complement, other components of the adaptive and innate immune systems. The complement system, also known as the complement cascade, rapidly responds to pathogens, damaged cells and unwanted tissue components to facilitate their removal by the immune system.

There are three main complement pathways (also called cascades)—the classical, lectin and alternative pathways. Each pathway is initiated by different molecules that respond to distinct triggers. When activated, the

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initiating molecules set in motion a cascade of enzymatic reactions that greatly amplify, or complement, an inflammatory response. The classical pathway is initiated by C1q, which recognizes antibody complexes, specific pathogens, damaged cells or unwanted cellular components. The lectin pathway is triggered by carbohydrates on the surface of pathogens or cells. The alternative pathway amplifies the action of the other two pathways and also self-activates to eliminate pathogens or cells that are not specifically shielded by the body’s built-in self-protective systems. While these three pathways are initiated by distinct molecules, they converge downstream on common pathway components known as C3 and C5.

Aberrant activation of the complement system can result in a range of diseases characterized by an attack on healthy tissue, such as red blood cells, nerve cells or kidney components. A broad range of neuroinflammatory diseases are known to be associated with pathological activation of the complement cascade in the body, brain and eye, including GBS, CAD, lupus nephritis, glaucoma, GA, HD, ALS, frontotemporal dementia and Alzheimer’s disease. We believe intervening in the activation of the complement cascade offers a potent and selective mechanism for specifically slowing or reversing these disease processes.

Specific activated components of the complement cascade have important immune functions that contribute to three key outcomes:

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Immune cell recruitment and inflammation. Specific activated molecules from the cascade serve as soluble signals to make blood vessels leaky and attract immune cells into tissues.

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Directed immune cell attack. Several complement components, including C1q, bind directly to the pathogen and serve as receptors that direct immune cell attack and pathogen engulfment.

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Membrane damage. Downstream components of the cascade directly puncture the pathogen or cell surface, causing membrane damage and lysis.

Broad potential for classical complement pathway targeted therapeutics in neuroinflammatory diseases

The classical complement cascade has a well-established role in augmenting antibody function within the immune system. C1q recognizes antibodies bound to pathogens or cells and activates the classical pathway to trigger their removal and clearance by the immune system. C1q can also directly recognize pathogens, damaged cells or unwanted cellular components leading to similar downstream clearance. A more recent finding made by the laboratory of Dr. Ben Barres, our scientific founder, is that C1q also directly interacts with neuronal connections, or synapses, during early development. Recognition of weaker synapses by C1q triggers the classical complement cascade and directs immune cells to “prune” the synapses away from neurons, thereby reinforcing stronger synapses to establish appropriate neuronal connections.

Because of its central role in immune function, aberrant activation of C1q can lead to damage of healthy tissue and destruction of functioning synapses. In GBS, pathogenic antibodies react with components of the peripheral nerve system, or PNS, to cause widespread peripheral nerve damage and paralysis. This disease process is also evident in antibody-mediated autoimmune disease involving blood components, such as CAD, characterized by auto-reactive antibodies that trigger destruction of red blood cells, and in a subset of patients with systemic lupus erythematosus where endogenous pathogenic antibodies against C1q itself drive aberrant C1q activation and are highly associated with kidney damage, or lupus nephritis.

Aberrant activation of C1q at synapses in aging and disease can lead to excessive synapse loss and neuronal damage, driving disease progression in multiple neurodegenerative disorders regardless of the initiating factor. In animal models, C1q accumulated on synapses with age, building up to 300-fold higher levels than in younger animals. It did not activate with normal aging, but other inflammatory stimuli, including misfolded proteins, metabolic dysfunction or increases in intraocular pressure, appeared to aberrantly reactivate C1q’s developmental role in synapse elimination. Complement activation and aberrant synapse pruning in disease may lead to neuroinflammation, loss of synaptic neuronal connections and neurodegeneration. In support of this hypothesis, we and other investigators have observed that C1q inhibition was protective in numerous models of neurodegenerative disease, including diseases of the eye, such as glaucoma and age-related macular degeneration, or AMD, chronic diseases of the central nervous system, such as frontotemporal dementia, Alzheimer’s, HD and Spinal Muscular Atrophy and acute injury, such as traumatic brain injury and stroke.

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Our differentiated approach to treating complement-mediated neuroinflammatory diseases through inhibition of C1q

We believe that in order to selectively inhibit aberrant activation of the classical complement pathway implicated in driving certain complement-mediated autoimmune and neurodegenerative diseases, it is important to target the early components of the classical cascade, particularly C1q, C4 and C3. Activated fragments of C4 and C3 induce vascular leakiness and immune cell recruitment into the tissue, while other fragments of C4 and C3, as well as C1q, work together to direct immune cell attack to the cell or synapse surface. Furthermore, C1q inhibition blocks downstream classical pathway activation of C5 and its membrane damaging effects. We believe that inhibition of C1q does not block the activity of these components in the lectin or alternative complement pathways, and both of these pathways will continue to perform their normal immune functions.

Our Platform

Our targeted immunotherapy platform is designed to completely inhibit classical complement activity for the treatment of neuroinflammatory diseases in the body, brain and eye. We believe there are potential advantages to our approach of upstream inhibition of the classical complement cascade, which include:

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Full inhibition of the classical cascade while preserving healthy immune function of the other complement pathways. Inhibition of C1q fully inhibits the classical cascade, including components downstream of C1q such as C4, C3, C5 and the downstream membrane attack complex. As a result, we believe our approach is designed to block all classical complement activity that can contribute to disease pathology, including immune cell recruitment, directed immune cell attack and membrane damage. By targeting upstream tissue-damaging components of the classical complement pathway, our approach leaves the lectin and alternative pathways to perform their normal immune function, which may aid both clinical improvement and safety. Our approach is also distinct from inhibiting C3 or C5. Inhibition of C5 will not affect the upstream components of the classical pathway involved in pathology (C1q, C4 and C3), while inhibition of C3 will block downstream components in all three complement pathways.

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Broad applicability across many indications. We believe our approach has broad utility for the treatment of diseases in which full inhibition of the entire classical complement cascade may be beneficial. We believe our approach is distinguishable from those that target only downstream complement components. Our initial indications represent our beachhead within antibody-mediated autoimmune and complement-mediated neurodegenerative diseases, and we will selectively pursue both orphan and larger patient population diseases with clear biological evidence of classical complement activation.

Our Flagship Programs

Guillain-Barré Syndrome

Overview of Guillain-Barré Syndrome

GBS is a serious and life-threatening condition that continues to be associated with significant long-term morbidity and mortality in patients despite use of IVIg treatment as standard of care. GBS is a rare disease, but is also the most common, most severe, and well understood acute paralytic inflammatory disease of the peripheral nervous system. GBS generally occurs post-infection in otherwise healthy persons. Antibodies generated against an infectious agent cross-react with components of peripheral nerves, leading to a complement mediated attack on nerve components, including myelin sheath and axonal tissue. The ensuing peripheral nerve damage is acute and rapidly progressive, leading to acute severe paralysis, significant morbidity, disability and mortality. The neuronal destruction progresses until titers of the cross-reactive, complement-activating antibodies have diminished (van den Berg et al., 2014). GBS impacts approximately 150,000 people annually worldwide, 22,000 in the United States and EU, and approximately 8,000 are hospitalized each year in the United States. The prevalence of GBS continues to increase with advancing age. The annual economic cost of GBS in the United States was estimated to have reached over $7 billion in 2025, largely due to the permanent disability and mortality it can cause.

There are currently no FDA-approved or targeted therapies for the treatment of GBS. Treatment guidelines published by the American Academy of Neurology recommend early initiation of IVIg or plasma exchange in patients diagnosed with GBS. Although IVIg and plasma exchange are the established standards of care in the western world

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and parts of Asia, significant unmet need still exists, and many patients, despite receiving the standard of care, are left with residual neurological disability, accompanied by chronic pain and fatigue.

The clinical course of GBS usually involves rapidly progressive weakness in the limbs culminating in neuromuscular paralysis within two to four weeks of onset. According to 2011 estimates, 20 to 30% of patients require mechanical ventilation, over 20% have permanent motor or sensory disability and 2 to 20% of cases result in death globally. Many patients with GBS require extensive monitoring and supportive care and will seek treatment in a hospital within a few days of onset of the disease. Because approximately a quarter of patients need mechanical ventilation due to respiratory muscle weakness, and many develop autonomic disturbances, admission in an intensive care unit is frequently necessary. Symptoms peak within four weeks as the auto-antibody response declines, followed by a recovery period that can last months or years, as the nervous system repairs itself. The development of targeted treatments for GBS is crucial to improve outcomes and quality of life for those affected by this debilitating condition.

C1q is a key driver of pathogenesis in GBS

GBS is an acute, autoimmune disease driven by antibodies that lead to activation of the classical complement cascade. Pathological nerve-targeting auto-antibodies, which may be triggered by an infection, lead to the activation of C1q and the classical complement cascade. Studies have shown that pathogenic auto-antibodies are present in the serum and CSF, and that activated components of the complement cascade are deposited on peripheral nerve tissue from GBS patients. Peripheral nerve roots are immersed in CSF as they emerge from the spinal cord and are prominent sites of damage in GBS. The figure below illustrates the activation of the classical complement pathway within peripheral nerves in GBS patient samples from autopsy. The left image shows a low magnification view of a peripheral nerve with numerous individual nerve fibers coated with membrane-damaging complement activation products (C5b-9; dark staining). The middle image shows a high magnification view of an individual nerve fiber with deposition of C3d (dark staining), a complement activation product that directs immune cell attack. The right image shows a high power image of an individual nerve fiber being probed by an infiltrating immune cell (macrophage).

We believe that by blocking the activity of C1q early in the onset of the disease, we can minimize the neuronal damage caused by these pathogenic auto-antibodies, in turn reducing the patients’ symptoms and accelerating their neurological recovery.

Tanruprubart Development Background in GBS

Since 2015, we have developed tanruprubart as the potential first targeted therapy for patients with GBS, an acute neurological emergency for which there is no FDA approved treatment. Tanruprubart is being developed as a first-line monotherapy treatment option to address the unmet needs of GBS patients and healthcare providers, leveraging our expertise and leadership in classical complement-mediated diseases. A robust data package has been generated over the nine year development path that includes a placebo-controlled Phase 1b trial that established POC for tanruprubart as a first-line treatment for GBS, a successful Phase 3 trial showing that tanruprubart was generally well-tolerated and resulted in faster and more complete functional recovery versus placebo, a RWE study that showed improved outcomes against current standards of care in matched patient populations, and a drug-drug interaction study with tanruprubart and IVIg strengthening the safety profile for tanruprubart in GBS. Importantly, to ethically provide

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a placebo-controlled dataset, we conducted tanruprubart’s clinical development for GBS outside of the U.S. in jurisdictions where IVIg treatment is not readily available. In addition, we have generated real-world evidence to support the generalizability of tanruprubart to a matched Western patient population and compared tanruprubart treatment outcomes from a single infusion of tanruprubart versus standard of care IVIg given as a 5-day infusion or PE.

We have closely coordinated our clinical efforts with leading researchers of the International GBS Outcome Study, or IGOS, in pursuing a novel therapy for GBS. With the goal of aiding the development of effective treatments for GBS, practitioners established IGOS in May 2012 and have collected natural history data from 2,000 GBS patients worldwide. IGOS is a prospective, observational, multicenter cohort study that aims to identify the clinical and biological determinants and predictors of disease onset as well as the subtype, course and outcome of GBS. IGOS was established to help develop a better understanding of the mechanism of disease progression and recovery and to conduct selective therapeutic trials to improve patient outcomes. This natural history database is an invaluable resource to clinical development, facilitating the design of clinical trials, optimal selection of endpoints, and patient follow-up for one to three years. We initiated our GBS clinical development in Bangladesh, a country where the incidence of GBS is several times higher than in North America and Europe and where 17% of patients die from the disease and 20% suffer permanent disability and are unable to walk. Additionally, our site in Bangladesh is well situated to conduct clinical research in GBS in a manner compliant with good clinical practice, or GCP, requirements.

Phase 1b Trial of tanruprubart in GBS

We conducted a Phase 1b placebo-controlled, dose escalation trial (n=50) of tanruprubart in GBS patients at a tertiary care hospital in Bangladesh, in compliance with GCP as described above. The trial objectives included safety and tolerability, dosing levels and target engagement, and included a follow up of eight weeks. The dosing levels of tanruprubart delivered in this trial ranged from 3 mg/kg to 75 mg/kg. Tanruprubart was well tolerated, and no drug-related serious adverse events or drug-related discontinuations occurred. The most common adverse events were acute infusion-related reactions, or IRRs, which occurred in the majority of patients and presented as low grade, non-serious, transient skin rash. These acute IRRs were mitigated by standard anti-inflammatory pre-medications.

Results from the Phase 1b trial showed increasing serum levels of tanruprubart and its duration in the circulation at increasing dose levels, and that the drug was present in the serum for up to three weeks at a dose of 75 mg/kg. When tanruprubart was present in the circulation, C1q function was fully inhibited and rapidly returned to normal levels as tanruprubart serum levels declined.

Much of the proximal weakness in GBS patients is due to involvement of peripheral nerve roots that are immersed in CSF as they exit the spinal cord. Hence, we believe product candidate levels and target inhibition in CSF may be an important contributor to efficacy. We observed that tanruprubart entered the CSF of GBS patients treated with doses of 18-75 mg/kg of tanruprubart, resulting in full engagement of C1q inhibition in the CSF.

In the Phase 1b trial in GBS patients, tanruprubart treatment at doses that engaged C1q in both serum and CSF (i.e., 18-75 mg/kg dose) resulted in a statistically significant early decline in serum NfL levels compared to placebo (two to four-week post treatment p-value 0.05). In this Phase 1b trial, we also explored the administration of tanruprubart on multiple validated clinical disability measures including GBS-Disability Score, or GBS-DS, Medical Research Council Muscle Strength Scale, or MRC, and Inflammatory Rasch-built Overall Disability Scale, or I-RODS, over an eight-week period. We observed that early decline in NfL correlated with improvement in the GBS-DS at the end of the study (two to eight-week post treatment p-value 0.05). We believe these results suggest that tanruprubart had a rapid impact on the disease process by ameliorating antibody-induced nerve damage, likely within the first two weeks of dosing.

Though the trial was not powered for statistical significance, treatment with tanruprubart resulted in consistent, positive numerical trends, including an improvement in MRC score and the number of days of ventilation. We observed a dose-dependent trend for improvement in MRC within the first week of treatment.

Early improvement in MRC is known to have strong prognostic implications on long-term functional recovery (modified Erasmus GBS Outcome Score). In line with this published data, we found that early improvement in MRC correlated with patients’ disability scores at the end of the Phase 1b trial (GBS-DS at week eight). This result is

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important because GBS-DS is typically used as the primary endpoint in GBS registrational studies. In addition, using a responder analysis, 28% of patients treated with high dose tanruprubart (18-75 mg/kg) improved by at least three points on GBS-DS by week eight compared to 0% of placebo-treated patients.

Following the completion of the Phase 1b treatment cohorts (through 75 mg/kg), two unblinded exploratory cohorts were enrolled to establish higher dose and multiple dose safety and PK/PD to inform subsequent chronic dosing trials. These two exploratory cohorts were a single dose of 100 mg/kg, and two doses of 75 mg/kg separated by one week (150 mg/kg total). At these higher dose levels, tanruprubart was well-tolerated, and no drug-related serious adverse events or drug-related discontinuations occurred; moreover, we did not reach a maximum tolerated dose. Similarly, we observed full inhibition of C1q in serum and CSF, a reduction in NfL and trends of improvement in clinical measures when compared to placebo; however, there was no additional impact on these clinical measures beyond that seen at 75 mg/kg.

The results of the Phase 1b dose-ranging trial in GBS showed that tanruprubart was well-tolerated, fully inhibited C1q in the blood and CSF at target doses, and demonstrated an early reduction in NfL levels. Drug treatment was associated with a trend for early improvement in MRC, and early changes in MRC significantly correlated with improved clinical measures in GBS patients. An additional key learning from the study is the importance of using baseline MRC for patient stratification at the time of hospitalization and study entry. Accounting for baseline MRC strengthened the impact of tanruprubart treatment in the biomarker and clinical measures, demonstrating that MRC will be an important stratification tool in future GBS trials.

Phase 3 Trial of tanruprubart in GBS

Based on the positive findings from our Phase 1b trial, we conducted a randomized, double-blind, placebo-controlled, multi-center Phase 3 trial to evaluate the efficacy, safety, PK and PD of tanruprubart administered by a single intravenous, or IV, infusion. The Phase 3 trial enrolled 241 patients in Bangladesh and the Philippines diagnosed with GBS according to the National Institute of Neurological Disorders and Stroke Diagnostic Criteria for Guillain-Barré Syndrome at the onset of GBS-related weakness ≤10 days prior to the start of treatment. Patients were stratified for leading prognostic factors including muscle strength and time from symptom onset.

In June 2024, we presented topline results from the Phase 3 trial demonstrating that a single infusion of tanruprubart at 30 mg/kg met the trial’s primary endpoint of a meaningful improvement in GBS-disability scale at week 8. Specifically, tanruprubart 30 mg/kg achieved a highly statistically significant 2.4-fold improvement on the GBS-DS (p = 0.0058), utilizing a proportional odds methodology to assess the proportion of patients who shift to better outcomes on the GBS-DS with tanruprubart treatment compared to placebo at week 8. Tanruprubart 30 mg/kg treatment also demonstrated improvements versus placebo on key secondary endpoints, including early gains in muscle strength by Medical Research Council, or MRC, sum score at day 8 (p 0.0001*) and at week 8 (p = 0.0351*), and a median of 28 fewer days on mechanical ventilation through week 26 (p = 0.0356*). Additionally, tanruprubart 30 mg/kg demonstrated a 31-day reduction in the median time to walk independently versus placebo (p = 0.0211*) in a prespecified analysis. Tanruprubart 30 mg/kg treated patients got better sooner on each of these assessments, presenting important clinical care outcomes for patients and the healthcare community.

* nominal p-values

The Phase 3 trial evaluated two doses of tanruprubart, 30 mg/kg and 75 mg/kg, both of which delivered rapid and complete suppression of complement activity but differed in duration of C1q inhibition. The 30 mg/kg dose suppression lasted one week and the 75 mg/kg dose suppression lasted two to three weeks. Tanruprubart 75 mg/kg outperformed placebo on multiple endpoints; however, it was not statistically significant on the primary endpoint of GBS-DS at week 8 (p = 0.5548). The two dose levels were evaluated based on findings in the earlier Phase 1b proof-of-concept study, which showed efficacy in pooled analysis of both shorter and longer duration of tanruprubart C1q inhibition. Because classical complement drives tissue damage in the early phase of disease, while facilitating nerve repair after acute nerve injury, the strong positive Phase 3 results with the 30 mg/kg dose resulting in one week of C1q inhibition appeared to define the optimal treatment window.

The clinical safety and tolerability findings of tanruprubart at both doses in the Phase 3 study support a generally well-tolerated profile with no new safety signals. The majority of adverse events were mild Grade 1 to moderate Grade

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2 events. The most common treatment-related adverse events were infusion related reactions (30.4%) that were mostly mild transient rashes. There were no autoimmune related adverse events, and no drug-related deaths or serious infections were observed.

Real World Evidence Study of tanruprubart in GBS

To support these Phase 1b and Phase 3 clinical trials conducted at sites outside the United States and based on feedback from the FDA, we conducted a RWE study in collaboration with IGOS investigators to establish comparability between Phase 3 participants and western patients.

IGOS investigators and we established a cohort of 79 real-world patients from the IGOS global patient registry that was matched based on key prespecified prognostic factors to the cohort of 79 patients treated with tanruprubart 30 mg/kg from our completed Phase 3 study. Patients in the tanruprubart Phase 3 population had moderate to severe disease, and the matching level demonstrates that the Phase 3 population is represented within the global GBS patient spectrum captured in IGOS.

This RWE study also provided the first insights comparing tanruprubart with the standard of care IVIg or PE. Patients treated with tanruprubart showed faster and greater improvement in muscle strength and disability compared to patients in the matched IGOS cohort treated with IVIg or PE. The comparison also showed that fewer patients treated with tanruprubart required mechanical ventilation. Further, tanruprubart-treated patients were observed to spend less time on ventilation and less time in the intensive care unit, or ICU. These findings indicate that tanruprubart may decrease the overall burden of GBS care.

Some key findings comparing tanruprubart 30 mg/kg to IVIg or PE included:

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By week 1, patients treated with tanruprubart showed more than 10-point improvement in muscle strength over patients treated with IVIg or PE, a clinically meaningful benefit as measured by MRC sumscore and an indicator for future recovery potential (p 0.0001).

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Patients treated with tanruprubart were approximately twice as likely to be in a better state of health than patients on IVIg or PE on the GBS-DS at multiple timepoints throughout the study, including at week 8, the primary endpoint for the Phase 3 trial (p = 0.0459).

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Approximately half the number of patients treated with tanruprubart (n=15 of 79) required mechanical ventilation compared with patients treated with IVIg or PE (n=32 of 79) (p = 0.022).

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Tanruprubart-treated patients were observed to spend fewer days on mechanical ventilation and fewer days in the ICU (median of 12 fewer days for each measure, p = n.s.).

FORWARD Study of tanruprubart in GBS

We are currently conducting the ongoing open-label FORWARD study in the U.S. and Europe, designed to support a broad intended label for the treatment of GBS and further expand the use of tanruprubart across geographies. We anticipate initial PK, PD, biomarker and functional data in 2026 to supplement our comprehensive data package for tanruprubart in GBS.

In January 2026, we filed an MAA with the EMA for tanruprubart for the treatment of GBS, and we continue to engage with EU regulators through the MAA review process. Tanruprubart has been granted orphan designation from the EMA. Tanruprubart has also been granted Fast Track and orphan drug designation for the treatment of GBS from the FDA. Following initial U.S. and EU data from the FORWARD study, we plan to engage with the FDA with the goal of reaching alignment on our current and supplemental data package and information supporting the generalizability of tanruprubart in Western patients for submission of a BLA in 2026.

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Geographic Atrophy

Overview of Geographic Atrophy

GA is an advanced form of dry AMD, an eye disease that is the leading cause of blindness in the elderly. GA is a chronic progressive neurodegenerative disorder of the retina involving the loss of photoreceptor synapses and cells in the outer retina. GA affects more than an estimated one million people in the United States and eight million people worldwide, severely limiting their independence and causing frustration, anxiety and emotional hardship. Effective treatments that preserve vision are still needed, as no currently approved therapies have been shown in clinical trials to significantly prevent vision loss.

Role of C1q and Complement in Geographic Atrophy

Genome-wide association studies have strongly implicated multiple components of the complement cascade in AMD and geographic atrophy. For example, specific alleles of the gene for C3 can increase the likelihood of developing AMD by 50%. Histopathological investigations have also observed the presence of complement components in geographic atrophy. These studies largely point to a role of excessive C3 activity in disease, but do not indicate how C3 is being activated (classical, lectin or alternative pathways). We have identified a potential dual role of C1q and the classical cascade as an important complement-activating system in geographic atrophy. First, we found that C1q strongly accumulated on photoreceptor cell synapses with normal age or disease, as shown below (left panel), implicating C1q’s role in excessive synapse pruning and complement-mediated neurodegeneration. Second, C1q and C1q ligands, such as C-reactive protein, also accumulated in the retina below photoreceptor cells in association with drusen (extracellular membrane and protein debris associated with geographic atrophy; right panel). These results suggest that the photoreceptor neurons and pigmented retinal epithelial cells – cell types that are both lost in GA – are sandwiched between deposits of C1q and that the classical complement cascade may have an ongoing and pathogenic role in GA by activating C3.

In support of this hypothesis, we found that either deletion or pharmacologic inhibition of C1q was protective in an animal model of photoreceptor neuron loss induced by photo-oxidation, as shown below. Further, components of the classical complement cascade have been associated with photoreceptor cells in human GA tissue (C4 and C3) and implicated in photoreceptor cell targeting with an in vitro assay. Finally, C1q is locally produced within the retina during disease by infiltrating immune cells, indicating that its pathogenic role may be amenable to local inhibition of C1q. As described above, we believe inhibition of C1q would block all key components of the classical cascade, including C1q, C4, and C3 involved in immune cell attack and synapse pruning, as well as C5 involved in direct membrane damage.

C1q inhibition was shown to be protective of photoreceptor cells and retinal function in a model of photoreceptor cell damage induced by light.

Phase 1b Trial of vonaprument in Glaucoma to Support Development in GA

We completed single-ascending dose (n=9) and sham-controlled multiple dose (n=17) studies of intravitreal vonaprument in patients with glaucoma to evaluate safety, tolerability, pharmacokinetics and target engagement. These patients had aqueous humor taps so that ocular fluid could be analyzed for levels of vonaprument and free C1q

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immediately prior to first dose (day 1) and prior to second dose (day 29). The studies showed that vonaprument was well-tolerated at all doses (1 mg, 2.5 mg and 5 mg) and achieved complete suppression of C1q at 2.5 mg and 5 mg.

Phase 2 ARCHER Trial of vonaprument in GA

We conducted the randomized, multi-center, double-masked, sham-controlled Phase 2 ARCHER trial to compare the safety and efficacy of vonaprument in patients with GA. The study enrolled a total of 270 patients, stratified by GA lesion size, location and choroidal neovascularization, or CNV, in the fellow eye at the time of enrollment. Patients were nearly equally split between foveal (49.4% to 57.3%) and non-foveal groups, had an average age of 80 years and were balanced between female and male. Ninety-six percent of patients enrolled were from the United States. Patients were randomized to receive an intravitreal dose of 5mg vonaprument monthly (n=89), 5mg vonaprument every other month (n=92) or sham monthly or every other month (pooled n=89) for a treatment period of 12 months, followed by a six-month off-treatment period.

The primary outcome measure of the study was the rate of change in GA lesion growth (slope) from baseline as measured by fundus autofluorescence through 12 months for the study eye. The study included multiple pre-specified visual function measures to assess the effects of vonaprument on vision: change from baseline in BCVA; change from baseline in low-luminance best corrected visual acuity; and change in baseline from low-luminance visual acuity deficit, or LLVD.

In the Phase 2 ARCHER trial, vonaprument demonstrated consistent protection against vision loss in a broad population of patients with GA. Specifically, topline data from the Phase 2 ARCHER trial reported in May 2023 and presented at the American Society of Retina Specialists Annual Meeting in July 2023 showed that vonaprument provided significant, time and dose-dependent protection from vision loss in patients with GA, measured by BCVA ≥ 15-letter loss, the widely accepted and clinically meaningful functional endpoint assessing visual acuity.

Monthly treatment with vonaprument demonstrated nominally statistically significant reduction in BCVA ≥15-letter loss (p=0.0021) compared to sham. The persistent ≥15-letter BCVA loss through month 12 hazard was reduced 72% in the monthly arm (p=0.006) and 48% in the every other month arm (p=0.064). Protection from vision loss was also shown in multiple additional prespecified measures of BCVA and visual function, including in standard and low light conditions. Protection from vision loss was enhanced in a subpopulation of patients with less advanced disease defined by LLVD 30 at baseline and in patients with more intact vision as defined by 80% ellipsoid zone, or EZ, loss. Vonaprument’s treatment effect increased over the course of the on-treatment portion of the study, suggesting that vonaprument may provide a growing and durable treatment effect over time. While benefit gained against vision lost was maintained during the subsequent six-month off-treatment period, the rate of decline for BCVA ≥ 15-letter vision began to parallel that of sham, providing additional support for the observed on-treatment protection.

While the primary endpoint of mean rate of change (slope) in GA lesion area compared to sham at 12 months did not reach statistical significance, greater impact on retinal pigment epithelium loss was observed in the second six months of treatment versus the first. Consistent with its proposed mechanism, vonaprument reduced photoreceptor EZ loss and showed more pronounced effect in reducing total EZ loss and protection of photoreceptors in the central fovea that are associated with visual acuity.

Vonaprument treatment was generally well-tolerated, with no increase in CNV rates between the treated and sham arms and no events of retinal vasculitis reported.

Phase 3 ARCHER II Trial of vonaprument in GA

In July 2025, we completed enrollment of 659 patients in the Phase 3 ARCHER II trial, a global, sham-controlled, double-masked trial for patients with GA. The single-study program will be analyzed as two sub-studies in the U.S. in accordance with the FDA’s two-trial recommendation. The primary endpoint of ARCHER II is the gold standard for visual acuity, measuring proportion of patients with confirmed BCVA ≥15-letter loss at any two consecutive visits through month 15. A secondary endpoint is an objective structural measure of EZ loss. We have established a global registration path with the FDA and EMA, which supports the potential of vonaprument to be the

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first treatment approved in both Europe and the U.S. for the protection of vision in patients with GA. We plan to report topline data in the fourth quarter of 2026.

Vonaprument is the first and only therapeutic candidate for the treatment of GA to receive PRIME designation by the EMA, which provides early and proactive support to developers of promising medicines that may offer a major therapeutic advantage over existing treatments or benefit to patients without treatment options. Vonaprument was also selected by the EMA for the Product Development Coordinator Pilot launched in July 2025 to help PRIME designation holders efficiently navigate regulatory interactions including expedited scientific advice, MAA submission readiness activities, and ad-hoc queries throughout the development program.

ANX1502

Overview of ANX1502

ANX1502 is a novel small molecule inhibitor of classical complement designed for oral administration in a range of chronic autoimmune diseases. ANX1502 converts to the active compound, ANX1439, on administration and delivers a highly potent and selective inhibitor of the activated form of C1s—part of the C1 complex that initiates the classical pathway. The active compound has been shown to have a high affinity to C1s and demonstrate a robust functional inhibition of the classical pathway.

Role of C1s in Complement-Mediated Autoimmune Diseases

The C1 complex is responsible for the activation of the classical pathway and is comprised of C1r, C1s and C1q. As part of the disease process, once activated, C1s is responsible for cleaving C4 and C2, key amplification components of the classical cascade. We believe that by stopping C1s from cleaving C4 and C2 with ANX1502, we will be able to block the classical cascade to reduce levels of inflammation, slow disease progression and potentially impact disease outcomes for patients.

Phase 1 SAD/MAD Trial of ANX1502

We completed the randomized, double-blind, placebo-controlled Phase 1 SAD/MAD trial of ANX1502 to assess the safety, tolerability, PK and PD of ANX1502 liquid suspension formulation in healthy adults. The study evaluated single ascending doses of ANX1502 ranging from 25 mg to 1050 mg (6 patients treated with ANX1502 plus 2 placebo subjects per cohort) and multiple ascending doses of ANX1502 ranging from 200 mg twice-daily to 525 mg twice-daily (9 patients treated with ANX1502 plus 3 placebo subjects per cohort).

In the SAD/MAD study, dose-proportional PK and targeted levels of active drug were observed across both cohorts, and single doses of 525-1025 mg ANX1502 suppressed C4d serum levels in healthy volunteers with higher than median baseline C4d. Across all doses evaluated, ANX1502 was generally well tolerated with mild to moderate

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treatment-emergent adverse events, which included gastro-intestinal events such as nausea, emesis and diarrhea. No serious adverse events were reported, and there were no significant clinical or lab findings.

Ongoing Development of ANX1502 in Autoimmune Diseases

We are evaluating an enteric-coated tablet formation of ANX1502 in an ongoing open-label, single arm POC study in patients with CAD for up to four weeks to assess tolerability, pharmacokinetics, pharmacodynamic, and clinical efficacy endpoints (e.g., hemolysis as measured by reduction of elevated bilirubin). We have observed drug levels at and exceeding the pre-defined target in fasted CAD patients. Dosing is ongoing to enhance our understanding of ANX1502’s profile and we plan to provide an update upon study completion in 2026.

Following the successful completion of the proof-of-concept study, we intend to evaluate ANX1502 in serious complement-mediated diseases, with the aim of providing enhanced efficacy and offering convenient dosing administration for long-term treatment of chronic autoimmune conditions.

Our Next Wave Programs

Tanruprubart for Huntington’s Disease

We completed a Phase 2 trial of tanruprubart in patients with HD (28 patients were enrolled with safety data measured from all 28 patients and efficacy data measured from 23 patients that completed both six-months of treatment and subsequent three-month follow-up period), which showed that treatment with tanruprubart was generally well-tolerated, with full target engagement of C1q in both serum and CSF observed throughout the six-month treatment period and well into the three-month follow-up period. Disease progression stabilized for the entire nine months of the study, as assessed by both Composite Unified Huntington's Disease Rating Scale, or cUHDRS, and Total Functional Capacity, or TFC, the two primary clinical measurement scales for HD. Additionally, HD patients with higher baseline complement activity, as measured by elevated levels of C4a/C4 in CSF, demonstrated a rapid clinical benefit as early as week 6, as assessed by both cUHDRS and TFC, that was sustained over the entire nine months of the study. Plasma and CSF NfL levels remained generally consistent through the nine-month study and were comparable to NfL levels described in published natural history data for HD patients. Based on these findings and productive engagement with the FDA, we are assessing opportunities for late-stage development of tanruprubart in HD.

Tanruprubart for ALS

We completed a Phase 2a signal-finding trial evaluating tanruprubart in patients with ALS, designed to assess safety, tolerability, and target engagement (13 patients were enrolled and treated for 12 weeks, of which 7 patients continued on treatment for 24 weeks). Chronic dosing of tanruprubart was generally well-tolerated, showed rapid and sustained target engagement of C1q in blood, and reduced downstream pharmacodynamic complement markers in blood. Consistent with what has been shown in other neurodegenerative diseases, including HD, exploratory analyses indicated that patients with higher baseline classical complement activation who enrolled within 12 months of diagnosis achieved better outcomes, including less functional decline on the ALSFRS-R and stabilization of NfL. These analyses support a precision medicine approach to identify patients most likely to respond to anti-C1q therapy in clinical trials with recently diagnosed ALS patients who have elevated baseline levels of classical complement activity.

ANX009 for Lupus Nephritis

ANX009, an investigational C1q Fab formulated for subcutaneous delivery, which was most recently evaluated in a Phase 1b signal-finding trial using a precision medicine approach for patients with LN who have high baseline complement activity. LN is an autoimmune disease for which PACAs enhance activity and uniquely amplify kidney inflammation and damage. We designed ANX009 with a goal of enabling chronic dosing for patients with antibody-mediated autoimmune disorders where anti-C1q may have a disease-modifying effect and where we can utilize our targeted biomarker-driven approach. In a first-in-human clinical trial, ANX009 was well-tolerated (7 patients were enrolled, of which 6 patients completed treatment) at all dose levels tested and no drug-related safety signals were observed. The trial showed that ANX009 led to sustained C1q inhibition at multiple doses, supporting the potential

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for twice-weekly subcutaneous administration with the current formulation, and advancement into the Phase 1b signal-finding trial for patients with LN.

Initial results from the Phase 1b trial were presented at the American Society of Nephrology’s Kidney Week 2023 conference, which showed subcutaneous ANX009 was well tolerated and demonstrated plasma C1q target engagement and complement inhibition. Importantly, inhibition of C1q rapidly increased free/circulating PACA levels (consistent with decreased deposition in the kidney) and improved all downstream markers of complement consumption and activation (C4, as well as C3 and C5b-9). These results indicate that C1q and the classical pathway are key drivers of complement activation in LN, independent of the alternative and lectin pathways, and that PACAs are a component of the classical complement activation pathway. Consistent with the short duration of this signal-finding study (3 weeks), changes in urinary protein excretion were not observed as anticipated. We are evaluating options for future development of ANX009 in LN.

Intellectual Property

Our intellectual property is critical to our business and we strive to protect it, including by obtaining and maintaining patent protection in the United States and internationally for our product candidates, new therapeutic approaches and potential indications, and other inventions that are important to our business. Our policy is to seek to protect our proprietary and intellectual property position by, among other methods, filing U.S. and foreign patent applications related to our proprietary technology, inventions and improvements that are important for the development and implementation of our business. We also rely on the skills, knowledge and experience of our scientific and technical personnel, as well as that of our advisors, consultants and other contractors. To help protect our proprietary know-how that is not patentable, we rely on confidentiality agreements to protect our interests. We generally require our employees, consultants, scientific advisors and contractors to enter into confidentiality agreements prohibiting the disclosure of confidential information and requiring disclosure and assignment to us of the ideas, developments, discoveries and inventions important to our business.

Our patent portfolio includes patents that are licensed to us from Stanford University; patents and patent applications that are co-owned by us with a number of partners, including The J. David Gladstone Institutes, Fondazione Telethon and Universita’ degli Studi di Trento, and the University of California; and patents and patent applications that are owned by us. Our proprietary technology has been primarily developed by in-house research and development programs, and to a lesser extent through acquisitions, relationships with academic research centers and contract research organizations.

For our product candidates, we will, in general, initially pursue patent protection covering compositions of matter and methods of use. Throughout the development of our product candidates, we seek to identify additional means of obtaining patent protection that would potentially enhance commercial success, including by protecting inventions related to additional methods of use, processes of making, formulation and dosing regimens.

We hold worldwide development and commercialization rights, including through exclusive licenses, to all of our product candidates, which allows us to strategically maximize value from our product portfolio over time. Our patent portfolio includes patent protection for our targeted immunotherapy platform and each of our product candidates.

As of March 13, 2026, our patent portfolio, including patents licensed from our partners, comprised 19 different patent families filed in various jurisdictions worldwide. Our patent portfolio includes issued patents and patent applications in the United States and in other jurisdictions.

One patent family, which we exclusively license from Stanford University, includes nine granted U.S. patents covering various methods of treating neurodegeneration and related medical conditions by inhibiting the C1 complex or its components, such as by using an anti-C1q antibody. The U.S. patents in this family include claims covering uses of tanruprubart, vonaprument and ANX009. These U.S. patents will expire between 2026 and 2030, absent any additional disclaimers, extensions or adjustments of patent term. There are no pending applications or foreign patents in this family.

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Two other patent families, which we own, are directed to anti-C1q antibodies and methods of using them. These families include seven granted U.S. patents, two pending U.S. patent applications, 34 granted foreign patents and four pending foreign patent applications. The patents in these families cover tanruprubart, vonaprument and ANX009. These patents will expire between 2034 and 2037, absent any additional disclaimers, extensions or adjustments of patent term.

Other patent families that we own include:

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two granted U.S. patents, one pending U.S. patent application, 13 granted foreign patents, and four pending foreign patent applications. The granted U.S. patents and pending patent applications in this family include claims directed to vonaprument. The granted U.S. patents and patents that may be issued from this family expire between 2036 and 2038, absent any additional disclaimers, extensions or adjustments of patent term;

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one pending U.S. patent application and 17 pending foreign patent applications. The pending patent applications in this family include claims covering a pharmaceutical formulation comprising anti-C1q antibodies, including tanruprubart, vonaprument and ANX009. Patents that may be issued from this family would expire in 2043, absent any disclaimers, extensions or adjustments of patent term;

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two granted U.S. patents, one pending U.S. patent application, one pending U.S. reissue application; one granted foreign patent and 36 pending foreign patent applications. The granted patents and pending patent applications in this family include claims covering certain small molecule modulators of the classical pathway, including ANX1502. The granted patents from this family expire in 2041, absent any additional disclaimers, extensions or adjustments of patent term, and patents that may issue from this family would expire in 2041, absent any disclaimers, extensions or adjustments of patent term;

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one granted U.S. patent, one pending U.S. patent application, and 17 pending foreign applications. The granted U.S. patent and pending applications in this family include claims covering certain small molecule modulators of the classical pathway. The granted U.S. patent from this family expires in 2043, absent any disclaimers, extensions, or adjustments of patent term; and patents that may issue from this family would expire in 2043, absent any disclaimers, extensions or adjustments of patent term; and

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one pending PCT application. The pending PCT application in this family includes claims covering a dosing regimen for tanruprubart. Patents that may be issued from this family would expire in 2046, absent any disclaimers, extensions or adjustments of patent term.

Our patent portfolio also includes 11 patent families, owned by us solely or jointly with the University of California or The J. David Gladstone Institutes or Fondazione Telethon and Universita’ degli Studi di Trento, directed to compositions or treatments of certain medical conditions using anti-C1q antibodies, including tanruprubart, vonaprument and ANX009. These families include one granted U.S. patent, nine pending U.S. patent applications, six granted foreign patents, and 83 pending foreign patent applications. The granted patents and patents that may issue from these families would expire between 2034 and 2043, absent any disclaimers, extensions or adjustments of patent term.

Exclusive (Equity) Agreement with The Board of Trustees of the Leland Stanford Junior University

In November 2011, we and The Board of Trustees of the Leland Stanford Junior University, or Stanford, entered into an exclusive licensing agreement, or the Stanford Agreement. Under the Stanford Agreement, Stanford granted to us an exclusive, worldwide, royalty-bearing, sublicensable license, under certain patent rights, or the Licensed Patents, to make, use, offer for sale, sell, import and otherwise commercialize products covered by the Licensed Patents for human or animal diseases, disorders or conditions. We are required to meet certain development and funding milestones for the licensed products.

Under the Stanford Agreement, we are obligated to pay Stanford an upfront payment, license maintenance fees ranging from the single digit to tens of thousands of dollars per year, and milestone payments totaling up to $675,000. We also agreed to make royalty payments at a rate equal to a low single-digit percentage of worldwide net sales of licensed products and a portion of certain sublicensing income we receive from sublicensees at a rate in the low double digit percentages, subject to a specified maximum total payment.

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Additionally, in accordance with the terms of the Stanford Agreement, upon closing our first financing event that raised at least $2.0 million, we granted Stanford $150,000 in shares of our redeemable convertible preferred stock, which were automatically converted into shares of our common stock prior to the completion of the initial public offering, or IPO, in July 2020. We may also have to pay a fee to Stanford if we assign our rights under the Stanford Agreement to a third party.

We may terminate the Stanford Agreement in its entirety, or as to a particular Licensed Patent or licensed product, for convenience on thirty days’ prior written notice. Stanford may terminate the Stanford Agreement for our breach that remains uncured for forty-five days or if we provide any false report, are delinquent on any report or payment, fail to achieve a milestone or fail to diligently develop and commercialize a licensed product.

Patent Term and Term Extensions

Generally, utility patents issued for applications filed in the United States are granted a term of 20 years from the filing date of the earliest non-provisional patent application to which a claim of priority is made. In addition, in certain instances, the term of a U.S. patent can be extended to recapture a portion of any delay caused by the United States Patent and Trademark Office, or USPTO, in issuing the patent (patent term adjustment), as well as a portion of the term of a granted patent that is effectively lost as a result of the FDA regulatory review period (patent term extension, or PTE). For PTE, the restoration period cannot be longer than five years and the restoration period cannot extend the patent term beyond 14 years from FDA approval for the product covered by that patent. In addition, only one patent applicable to an approved drug may receive PTE, and the extension applies only to coverage for the approved drug, methods for using it and methods of manufacturing it, even if the claims cover other products or product candidates. Where one patent covers multiple products or product candidates, it may only receive PTE for one of the covered products; any PTE available to a second product or product candidate must be applied to a different patent. The duration of foreign patents varies in accordance with provisions of applicable local law, but typically is also 20 years from filing date of the earliest non-provisional patent application to which a claim of priority is made, such as a PCT application. All taxes, annuities or maintenance fees for a patent, as required by the USPTO and various foreign jurisdictions, must be timely paid in order for the patent to remain in force during this period of time.

The actual protection afforded by a patent may vary on a product by product basis, from country to country, and can depend upon many factors, including the type of patent, the scope of its coverage, the availability of regulatory-related extensions and the availability of legal remedies in a particular country and the validity and enforceability of the patent.

Our patents and patent applications may be subject to procedural or legal challenges by others. We may be unable to obtain, maintain and protect the intellectual property rights necessary to conduct our business, and we may be subject to claims that we infringe or otherwise violate the intellectual property rights of others, which could materially harm our business. For more information, see the section titled “Risk Factors—Risks Related to Our Intellectual Property.”

Trademarks and Know-How

In connection with the ongoing development and advancement of our products and services in the United States and various international jurisdictions, we seek to create protection for our marks and enhance their value by pursuing trademarks and service marks where available and when appropriate.

In addition to patent and trademark protection, we rely upon know-how and continuing technological innovation to develop and maintain our competitive position. We seek to protect our proprietary information, in part, by using confidentiality agreements with our commercial partners, collaborators, employees and consultants, and invention assignment agreements with our employees and consultants. These agreements are designed to protect our proprietary information and, in the case of the invention assignment agreements, to grant us ownership of technologies that are developed by our employees and through relationships with third parties. These agreements may be breached, and we may not have adequate remedies for any breach. In addition, our trade secrets may otherwise become known or be independently discovered by competitors. To the extent that our contractors, commercial partners, collaborators, employees and consultants use intellectual property owned by others in their work for us, disputes may arise as to the

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rights in related or resulting know-how and inventions. For more information, see the section titled “Risk Factors—Risks Related to Our Intellectual Property.”

Sales and Marketing

We hold worldwide commercialization rights, including through exclusive licenses, to our product candidates. Given our stage of development, we have established a small commercial organization and have not established distribution capabilities. Should any of our product candidates be approved for commercialization, we intend to develop a plan to commercialize them in the United States and other key markets, through internal infrastructure and/or external partnerships in a manner that will enable us to realize the full commercial value of our programs.

Manufacturing

Our success as a company will depend on our ability to deliver reliable, high-quality drug supply. We do not currently own or operate facilities for product manufacturing, storage and distribution, or testing. We contract with third parties for the manufacture of our product candidates. Because we rely on contract manufacturers, we employ personnel with extensive technical, manufacturing, analytical and quality experience. Our staff has strong project management discipline to oversee contract manufacturing and testing activities, and to compile manufacturing and quality information for our regulatory submissions.

Manufacturing is subject to extensive regulation that imposes various procedural and documentation requirements and that governs record keeping, manufacturing processes and controls, personnel, quality control and quality assurance, and more. Our systems and our contractors are required to be in compliance with these regulations, and compliance is assessed regularly through monitoring of performance and a formal audit program.

Our current supply chains for our lead drug candidates involve several manufacturers that specialize in specific operations of the manufacturing process, specifically, raw materials procuring, drug substance manufacturing and drug product manufacturing. We currently operate under work order programs for our drug candidates with Master Services and Quality agreements in place that include specific supply timelines, volume and quality specifications. We are in discussions with our current manufacturers regarding preparation of a BLA in the near future and our MAA filed in January 2026. This involves technology transfers, process characterization, and process validation to establish commercial manufacturing capabilities.

We intend to establish long-term supply agreements in the future. We believe our current manufacturers have the scale, the system, and the experience to supply our currently planned clinical trials and commercial launch. To ensure continuity in our supply chain, we plan to establish supply arrangements with alternative larger scale suppliers for certain portions of our supply chain, as appropriate.

Competition

The pharmaceutical, biopharmaceutical and biotechnology industries are characterized by rapidly advancing technologies, intense competition and a strong emphasis on proprietary products. While we believe that our technology, the expertise of our executive and scientific team, research, clinical capabilities, development experience and scientific knowledge provide us with competitive advantages, we face potential competition from many different sources, including pharmaceutical, biopharmaceutical and biotechnology companies, academic institutions, governmental agencies and public and private research institutions. Product candidates that we successfully develop and commercialize may compete with existing therapies and new therapies that may become available in the future.

Our competitors may have significantly greater financial resources, established presence in the market, expertise in research and development, manufacturing, preclinical and clinical testing, and experience in obtaining regulatory approvals and reimbursement and marketing approved products than we do. These competitors also compete with us in recruiting and retaining qualified scientific, sales, marketing and management personnel, establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies complementary to, or necessary for, our programs. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

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Guillain-Barré Syndrome

There are currently no approved therapies for GBS in the United States. IVIg and PE are the most commonly used therapies in the Western world and parts of Asia. Currently, two investigational products are in development. Hansa Biopharma AB is conducting an open label Phase 2 trial of imlifidase in GBS patients in Europe and the United Kingdom for which it released topline results in December 2023 and real-world comparison data in December 2024. AstraZeneca/Alexion completed a Phase 3 trial of SOLIRIS (eculizumab) in Japan that did not meet its primary endpoint. Additionally, a primary investigator sponsored Phase 2 trial with argenx’s efgartigimod is listed as an active trial.

Geographic Atrophy

Two treatments are currently FDA-approved for GA, both receiving approval in 2023: Apellis’s Syfovre, a C3 inhibitor as well as Astellas’s avacincaptad pegol, a C5 inhibitor. There are currently no approved therapies for GA in the EU. There is currently one combination complement cascade-targeted therapy in Phase 3 development for GA—Regeneron’s pozelimab, a C5 inhibiting monoclonal antibody combined with cemdisiran, a C5-targeted siRNA molecule dosed subcutaneously. In Phase 2, there are currently four complement-targeting agents: Aviceda Therapeutics’s AVD-104, a nanoparticle molecule that inhibits complement cascade amplification and inflammation pathways, Janssen’s JNJ-1887, a gene therapy candidate which expresses soluble CD59, a complement protein, Novartis’s iptacopan, an oral factor B inhibitor, and Perceive Bio’s VOY-101 molecule, the detailed mechanism of action of which has not been fully disclosed. Other products that do not target the complement cascade currently in Phase 2 or 3 clinical trials are being developed by Roche, Alkeus, Belite Bio, Stealth BioTherapeutics, Boehringer Ingelheim, Galimedix Therapeutics, Cognition Therapeutics, ONL Therapeutics, and Ocugen. Astellas, Roche and Inflammasome Therapeutics each have an asset in Phase 1 of development.

Cold Agglutinin Disease, a type of autoimmune hemolytic anemia

Sanofi’s Enjaymo was approved by the FDA for CAD in February 2022, and in October 2024, Sanofi sold global rights to Enjaymo to Italy-based Recordati. There are currently two investigational agents in clinical trials for CAD: Alpine Immune Sciences, Inc. is developing povetacicept, a fusion protein that blocks the function of two cytokines and Sanofi completed a phase I trial of BIVV020 in November 2023 with positive results with a single dose delivery in CAD patients.

Government Regulation

The FDA and other regulatory authorities at federal, state and local levels, as well as in foreign countries, extensively regulate, among other things, the research, development, testing, manufacture, quality control, import, export, safety, effectiveness, labeling, packaging, storage, distribution, record keeping, approval, advertising, promotion, marketing, post-approval monitoring and post-approval reporting of product candidates such as those we are developing. A new drug must be approved by the FDA through the approval process and a new biologic must be approved by the FDA through the BLA process before it may be legally marketed in the United States. We, along with third-party contractors, will be required to navigate the various preclinical, clinical manufacturing and commercial approval requirements of the governing regulatory agencies of the countries in which we wish to conduct studies or seek approval or licensure of our product candidates. The process of obtaining regulatory approvals and the subsequent compliance with applicable federal, state, local and foreign statutes and regulations require the expenditure of substantial time and financial resources.

U.S. Biologics Regulation

In the United States, the FDA regulates drugs under the federal Food, Drug, and Cosmetic Act, or FDCA, and in the case of biologics, also under the Public Health Service Act, or PHSA, and their implementing regulations. The process required by the FDA before a drug or biologic may be marketed in the United States generally involves the following:

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completion of preclinical laboratory tests and animal studies performed in accordance with the FDA’s Good Laboratory Practice requirements, or GLP requirements and other applicable regulations;

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submission to the FDA of an Investigational New Drug application, or IND, which must become effective before clinical trials may begin;

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approval by an institutional review board, or IRB, or ethics committee, or EC, at each clinical site before the trial is commenced at such site;

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performance of adequate and well-controlled human clinical trials in accordance with GCP requirements to establish the safety and efficacy of the proposed drug, or the safety, purity and potency of the proposed biologic for its intended purpose;

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preparation of and submission to the FDA of an NDA or BLA after completion of all required clinical trials;

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satisfactory completion of an FDA Advisory Committee review, if applicable;

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a determination by the FDA within 60 days of its receipt of an NDA or BLA whether to file the application for review;

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satisfactory completion of an FDA pre-approval inspection of the manufacturing facility or facilities at which the proposed drug or biologic is produced to assess compliance with current Good Manufacturing Practices, or cGMPs, and to assure that the facilities, methods and controls are adequate to preserve the product’s continued safety, purity and potency, and of selected clinical investigation sites to assess compliance with GCP; and

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FDA review and approval of the BLA or NDA to permit commercial marketing of the product for specific indication(s) for use in the United States.

Preclinical studies include laboratory evaluation of product chemistry, toxicity and formulation, as well as animal studies to assess potential safety and efficacy. Prior to beginning the first clinical trial with a product candidate in the United States, a sponsor must submit an IND to the FDA, which is a request for authorization from the FDA to administer an investigational new drug product to humans. The central focus of an IND submission is on the general investigational plan and the protocol(s) for the proposed clinical trial(s). The IND also includes results of animal and in vitro studies assessing the toxicology, pharmacokinetics, pharmacology and pharmacodynamic characteristics of the product; chemistry, manufacturing and controls information; and any available human data or literature to support the use of the investigational product. An IND must become effective before human clinical trials may begin. The IND automatically goes into effect 30 days after receipt by the FDA, unless the FDA, within the 30-day time period, raises safety concerns or questions about the proposed clinical trial. In such a case, the IND may be placed on clinical hold and the IND sponsor and the FDA must resolve any outstanding concerns or questions before the clinical trial can begin. Submission of an IND therefore may or may not result in FDA authorization to begin a clinical trial.

Clinical trials involve the administration of the investigational product to human subjects under the supervision of qualified investigators in accordance with GCP, which include the requirement that all research subjects provide their informed consent for their participation in any clinical trial. Clinical trials are conducted under protocols detailing, among other things, the objectives of the study, the parameters to be used in monitoring safety and the effectiveness criteria to be evaluated. A separate submission to the existing IND must be made for each successive clinical trial conducted during product development and for any subsequent protocol amendments. While the IND is active, progress reports summarizing the results of the clinical trials and nonclinical studies performed since the last progress report, among other information, must be submitted at least annually to the FDA, and written IND safety reports must be submitted to the FDA and investigators for serious and unexpected suspected adverse events, findings from other studies suggesting a significant risk to humans exposed to the same or similar drugs, findings from animal or in vitro testing suggesting a significant risk to humans, and any clinically important increased incidence of a serious suspected adverse reaction compared to that listed in the protocol or investigator brochure.

Furthermore, an independent IRB or EC for each site proposing to conduct the clinical trial must review and approve the plan for any clinical trial and its informed consent form before the clinical trial begins at that site, and must monitor the trial until completed. Some studies also include oversight by an independent group of qualified experts organized by the clinical trial sponsor, known as a Data Safety Monitoring Board, which provides authorization for whether or not a trial may move forward at designated check points based on access to certain data from the study and may halt the clinical trial if it determines that there is an unacceptable safety risk for subjects or

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other grounds, such as no demonstration of efficacy. Regulatory authorities, the IRB/ethics committee or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the subjects are being exposed to an unacceptable health risk or that the trial is unlikely to meet its stated objective(s). There are also requirements governing the reporting of ongoing clinical trials and clinical trial results to public registries.

For purposes of BLA or NDA approval, human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

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Phase 1—The investigational product is initially introduced into healthy human subjects or patients with the target disease or condition. These trials are designed to test the safety, dosage tolerance, absorption, metabolism and distribution of the investigational product in humans, the side effects associated with increasing doses, and, if possible, to gain early evidence on effectiveness.

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Phase 2—The investigational product is administered to a limited patient population with a specified disease or condition to evaluate the preliminary efficacy, optimal dosages and dosing schedule and to identify possible adverse side effects and safety risks. Multiple Phase 2 clinical trials may be conducted to obtain information prior to beginning larger and more expensive Phase 3 clinical trials.

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Phase 3—The investigational product is administered to an expanded patient population to further evaluate dosage, to provide statistically significant evidence of clinical efficacy and to further test for safety, generally at multiple geographically dispersed clinical trial sites. These clinical trials are intended to establish the overall risk/benefit ratio of the investigational product and to provide an adequate basis for product approval.

In some cases, the FDA may require, or companies may voluntarily pursue, additional clinical trials after a product is approved to gain more information about the product. These so-called Phase 4 trials may also be made a condition to approval of the BLA or NDA.

Concurrent with clinical trials, companies may complete additional animal studies and develop additional information about the biological characteristics of the product candidate and must finalize a process for manufacturing the product in commercial quantities in accordance with cGMPs. The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things, must develop methods for testing the identity, strength, quality and purity of the final product. Additionally, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

FDA Review and Approval Process

Assuming successful completion of all required testing in accordance with all applicable regulatory requirements, the results of product development, nonclinical studies and clinical trials are submitted to the FDA as part of a BLA or NDA requesting approval to market the product candidate for one or more indications. The BLA or NDA must include all relevant data available from preclinical studies and clinical trials, including negative or ambiguous results as well as positive findings, together with detailed information relating to the product’s chemistry, manufacturing, controls and proposed labeling, among other things. Data can come from company-sponsored clinical trials intended to test the safety and effectiveness of a use of the product candidate or from a number of alternative sources, including studies and trials initiated by investigators. The submission of a BLA or NDA requires payment of a substantial user fee to the FDA, and the sponsor of an approved BLA or NDA is also subject to an annual program fee. A waiver of user fees may be obtained under certain limited circumstances. Additionally, no user fees are assessed on BLAs or NDAs for products designated as Orphan Drugs, unless the application also seeks a non-orphan-designated indication.

Within 60 days following submission of the application, the FDA reviews a BLA or NDA submitted to determine if it is substantially complete before the FDA accepts it for filing. The FDA may refuse to file any BLA or NDA that it deems incomplete or not properly reviewable at the time of submission and may request additional information. In this event, the Sponsor may meet with the FDA to confirm the additional information required to resubmit the BLA or NDA. Once a BLA or NDA has been accepted for filing, the FDA’s goal is to review standard applications within ten months after it accepts the application for filing, or, if the application qualifies for priority

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review, six months after it accepts the application for filing. Priority review designation will direct overall attention and resources to the evaluation of applications for products that, if approved, would represent significant improvements in the safety or effectiveness of the treatment, diagnosis or prevention of serious conditions. In both standard and priority reviews, the review process is often significantly extended by FDA requests for additional information or clarification. The FDA reviews an NDA to determine, among other things, whether a product is safe and effective for its intended use and whether its manufacturing is cGMP‑compliant to assure and preserve the product’s identity, strength, quality and purity. The FDA reviews a BLA to determine, among other things, whether a product is safe, pure and potent and the facilities in which it is manufactured, processed, packed or held meet standards designed to assure the product’s continued safety, purity and potency. The FDA may also convene a public Advisory Committee to provide additional expert insight on application review questions. The FDA is not bound by recommendations of an Advisory Committee, but it considers such recommendations when making decisions regarding approval.

Before approving a BLA or NDA, the FDA will typically inspect the facility or facilities where the product candidate is manufactured. The FDA will not approve an application unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product candidate within required specifications. Additionally, before approving a BLA or NDA, the FDA will typically inspect one or more clinical sites and/or the sponsor to assure compliance with GCP.

After the FDA evaluates a BLA or NDA and conducts inspections of clinical trial sites and manufacturing facilities where the investigational product and/or its drug substance will be produced, the FDA may issue an Approval Letter or a Complete Response Letter. An Approval Letter authorizes commercial marketing of the product with specific prescribing information for specific indications. A Complete Response Letter indicates that the BLA or NDA is not ready for approval in its present form and ends the current review cycle, and will describe all of the deficiencies that the FDA has identified in the BLA or NDA. The FDA may issue the Complete Response Letter without first conducting required inspections, testing submitted product lots, and/or reviewing proposed labeling. In issuing the Complete Response Letter, the FDA may recommend actions that the applicant might take to place the BLA or NDA in condition for approval, including requests for additional information or clarification. The FDA may delay or refuse approval of a BLA or NDA if applicable regulatory criteria are not satisfied, require additional testing or information and/or require post-marketing testing and surveillance to monitor safety or efficacy of a product.

If regulatory approval of a product is granted, such approval will be granted for particular indications and may entail limitations on the indicated uses for which such product may be marketed. Additionally, the FDA may approve a BLA or NDA with a Risk Evaluation and Mitigation Strategy, or REMS, to ensure the benefits of the product outweigh its risks. A REMS is a safety strategy to manage a known or potential serious risk associated with a medicine and to enable patients to have continued access to such medicines by managing their safe use, and could include medication guides, physician communication plans, or elements to assure safe use, such as restricted distribution methods, patient registries, and other risk minimization tools. Once approved, the FDA may withdraw the product approval if compliance with pre- and post- marketing requirements is not maintained or if problems occur after the product reaches the marketplace. The FDA may also require one or more Phase 4 post-marketing studies and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization, and may limit further marketing of the product based on the results of these post-marketing studies.

Expedited Development and Review Programs

A sponsor may seek approval of its product candidate under programs designed to accelerate FDA’s review and approval of product candidates that meet certain criteria. Specifically, drugs and biologics are eligible for Fast Track designation if they are intended to treat a serious or life-threatening disease or condition and demonstrate the potential to address unmet medical needs for the disease or condition. For a Fast Track product candidate, the FDA may consider sections of the BLA or NDA for review on a rolling basis before the complete application is submitted, if the sponsor provides a schedule for the submission of the sections of the application, the FDA agrees to accept sections of the application and determines that the schedule is acceptable and the sponsor pays any required user fees upon submission of the first section of the application. A BLA or NDA for a Fast Track-designated product candidate may also qualify for priority review, under which the FDA sets the target date for FDA action on the BLA or NDA at six months after the FDA accepts the application for filing. Priority review is granted when there is evidence that the product candidate, if approved, would provide a significant improvement in the safety or effectiveness of the treatment, diagnosis, or

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prevention of a serious disease or condition. If criteria are not met for priority review, the application is subject to the standard FDA review period of 10 months after FDA accepts the application for filing.

A product candidate intended to treat a serious or life-threatening disease or condition may also be eligible for Breakthrough Therapy designation to expedite its development and review. A product candidate can receive Breakthrough Therapy designation if preliminary clinical evidence indicates that the product candidate, alone or in combination with one or more other drugs or biologics, may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. The designation includes all of the Fast Track program features, as well as more intensive FDA interaction and guidance beginning as early as Phase 1 and an organizational commitment to expedite the development and review of the product candidate, including involvement of senior reviewers at FDA.

In addition, a product candidate may be eligible for accelerated approval. Drugs and biologics intended to treat serious or life threatening diseases or conditions may be eligible for accelerated approval upon a determination that the drug or biologic has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit or a clinical endpoint that can be measured earlier than irreversible morbidity or mortality that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the availability or lack of alternative treatments. As a condition of approval, the FDA generally requires sponsors of products receiving accelerated approval to conduct well-controlled confirmatory required to verify or characterize the drug or biologic’s predicted clinical benefit. In addition, the FDA currently requires as a condition for accelerated approval pre-approval of promotional materials, which could adversely impact the timing of the commercial launch of the product. The FDA may withdraw approval of a product or indication approved under accelerated approval if, for example, the sponsor fails to conduct any required confirmatory studies in a timely manner, or if such studies fail to verify the predicted clinical benefit of the product.

Fast Track designation, priority review, accelerated approval and Breakthrough Therapy designation do not change the standards for approval but may expedite the development or approval process. Even if a product qualifies for one or more of these programs, the FDA may later decide that the product no longer meets the conditions for qualification or decide that the time period for FDA review or approval will not be shortened.

Orphan Drug Designation and Exclusivity

Under the Orphan Drug Act, the FDA may grant Orphan designation to a drug or biologic intended to treat a rare disease or condition, defined as a disease or condition with a patient population of fewer than 200,000 individuals in the United States, or a patient population greater than 200,000 individuals in the United States and when there is no reasonable expectation that the cost of developing and making available the biologic in the United States will be recovered from sales in the United States for that drug or biologic. Orphan Drug designation must be requested before submitting a BLA or NDA. After the FDA grants Orphan Drug designation, the generic identity of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA. Orphan designation does not convey any advantage in or shorten the duration of the regulatory review and approval requirements or process.

If a product candidate that has Orphan Drug designation subsequently receives the first FDA approval for the disease or condition for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications, including a full BLA or NDA, to market the same biologic or chemical entity for the same disease or condition for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with Orphan Drug exclusivity or if the FDA finds that the holder of the Orphan Drug exclusivity has not shown that it can assure the availability of sufficient quantities of the Orphan Drug to meet the needs of patients with the disease or condition for which the drug was designated. Orphan Drug exclusivity does not prevent the FDA from approving a different drug or biologic for the same disease or condition, or the same drug or biologic for a different disease or condition. Among the other benefits of Orphan Drug designation are tax credits for certain research and development activities and a waiver of the BLA or NDA application user fee.

A designated Orphan Drug may not receive Orphan Drug exclusivity if it is approved for a use that is broader than the indication for which it received Orphan designation. In addition, Orphan Drug exclusive marketing rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or, as noted above, if the second applicant demonstrates that its product is clinically superior to the approved product with

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Orphan exclusivity or the manufacturer of the approved product is unable to assure sufficient quantities of the product to meet the needs of patients with the rare disease or condition.

Post-Approval Requirements

Any drugs or biologics manufactured or distributed pursuant to FDA approvals are subject to pervasive and continuing regulation by the FDA, including, among other things, requirements relating to record-keeping, reporting of adverse experiences, periodic reporting, product sampling and distribution, and advertising and promotion of the product. After approval, most changes to the approved product, such as adding new indications or other labeling claims, are subject to prior FDA review and approval. There also are continuing, annual program fees for any marketed products. Drug and biologic manufacturers and their subcontractors are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMPs, which impose certain procedural and documentation requirements upon us and our third-party manufacturers. Changes to the manufacturing process are strictly regulated, and, depending on the significance of the change, may require prior FDA approval before being implemented. FDA regulations also require investigation and correction of any deviations from cGMPs and impose reporting requirements upon us and any third-party manufacturers that we may decide to use. Accordingly, manufacturers must continue to expend time, money and effort in the area of production and quality control to maintain compliance with cGMPs and other aspects of regulatory compliance.

The FDA may withdraw approval if compliance with regulatory requirements and standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product, including adverse events of unanticipated severity or frequency, or with manufacturing processes, or failure to comply with regulatory requirements, may result in revisions to the approved labeling to add new safety information; imposition of post-market studies or clinical studies to assess new safety risks; or imposition of distribution restrictions or other restrictions under a REMS program. Other potential consequences include, among other things:

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restrictions on the marketing or manufacturing of the product, complete withdrawal of the product from the market, or product recalls;

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fines, Warning Letters, or untitled enforcement letters;

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clinical holds on clinical studies;

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refusal of the FDA to approve pending applications or supplements to approved applications, or suspension or revocation of product approvals;

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product seizure or detention, or refusal to permit the import or export of products;

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consent decrees, corporate integrity agreements, debarment or exclusion from federal healthcare programs;

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mandated modification of promotional materials and labeling and the issuance of corrective information;

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the issuance of safety alerts, Dear Healthcare Provider letters, press releases and other communications containing warnings or other safety information about the product; or

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injunctions or the imposition of civil or criminal penalties.

The FDA closely regulates the marketing, labeling, advertising and promotion of drugs and biologics. A company can make only those claims relating to safety and efficacy, purity and potency that are approved by the FDA and in accordance with the provisions of the approved label. The FDA and other agencies actively enforce the laws and regulations prohibiting the promotion of so-called “off-label” uses. Failure to comply with these requirements can result in, among other things, adverse publicity, Warning Letters, corrective advertising and potential civil and criminal penalties. Physicians may prescribe legally available products for uses that are not described in the product’s labeling and that differ from those tested by us and approved by the FDA. Such off-label uses are common across medical specialties. Physicians may believe that such off-label uses are the best treatment for many patients in varied

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circumstances. The FDA does not regulate the behavior of physicians in their choice of treatments. The FDA does, however, restrict manufacturer’s communications on the subject of off-label use of their products.

Biosimilars and Exclusivity

The Patient Protection and Affordable Care Act, as amended by the Health Care and Education Reconciliation Act, or collectively the ACA, signed into law in 2010, includes a subtitle called the BPCIA, which created an abbreviated approval pathway for biological products that are biosimilar to, or interchangeable with, an FDA-licensed reference biological product. The FDA has issued several guidance documents outlining an approach to review and approval of biosimilars. Biosimilarity, which requires that there be no clinically meaningful differences between the biological product and the reference product in terms of safety, purity and potency, can be shown through analytical studies, animal studies and a clinical study or studies. Interchangeability requires that a product is biosimilar to the reference product and the product must demonstrate that it can be expected to produce the same clinical results as the reference product in any given patient and, for products that are administered multiple times to an individual, the biologic and the reference biologic may be alternated or switched after one has been previously administered without increasing safety risks or risks of diminished efficacy relative to exclusive use of the reference biologic.

Under the BPCIA, an application for a biosimilar product may not be submitted to the FDA until four years following the date that the reference product was first licensed by the FDA. In addition, the approval of a biosimilar product may not be made effective by the FDA until 12 years from the date on which the reference product was first licensed. During this 12-year period of exclusivity, another company may still market a competing version of the reference product if the FDA approves a full BLA for the competing product containing that applicant’s own preclinical data and data from adequate and well-controlled clinical trials to demonstrate the safety, purity and potency of its product. The BPCIA also created certain exclusivity periods for biosimilars approved as interchangeable products. At this juncture, it is unclear whether products deemed “interchangeable” by the FDA will, in fact, be readily substituted by pharmacies, which are governed by state pharmacy law.

Drug Product Marketing Exclusivity

Market exclusivity provisions authorized under the FDCA can delay the submission or the approval of certain marketing applications. For example, the FDCA provides a five-year period of non-patent data exclusivity within the United States to the first applicant to obtain approval of an NDA for a new chemical entity. A drug is a new chemical entity if the FDA has not previously approved any other new drug containing the same active moiety, which is the molecule or ion responsible for the action of the drug substance. During the exclusivity period, the FDA may not approve or even accept for review an abbreviated new drug application, or ANDA, or an NDA submitted under Section 505(b)(2), or 505(b)(2) NDA, submitted by another company for another drug based on the same active moiety, regardless of whether the drug is intended for the same indication as the original innovative drug or for another indication, where the applicant does not own or have a legal right of reference to all the data required for approval. However, an application may be submitted after four years if it contains a certification of patent invalidity or non-infringement to one of the patents listed with the FDA by the innovator NDA holder.

The FDCA alternatively provides three years of marketing exclusivity for an NDA, or supplement to an existing NDA if new clinical investigations, other than bioavailability studies, that were conducted or sponsored by the applicant are deemed by the FDA to be essential to the approval of the application, for example new indications, dosages or strengths of an existing drug. This three-year exclusivity covers only the modification for which the drug received approval on the basis of the new clinical investigations and does not prohibit the FDA from approving ANDAs or 505(b)(2) NDAs for drugs containing the active agent for the original indication or condition of use. Five-year and three-year exclusivity will not delay the submission or approval of a full NDA. However, an applicant submitting a full NDA would be required to conduct or obtain a right of reference to any preclinical studies and adequate and well-controlled clinical trials necessary to demonstrate safety and effectiveness.

Pediatric exclusivity is another type of marketing exclusivity available in the United States. Pediatric exclusivity provides for an additional six months of marketing exclusivity attached to another period of exclusivity if a sponsor conducts clinical trials in children in response to a written request from the FDA. The issuance of a written request does not require the sponsor to undertake the described clinical trials. In addition, orphan drug exclusivity, as described above, may offer a seven-year period of marketing exclusivity, except in certain circumstances.

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Other Healthcare Laws and Compliance Requirements

Pharmaceutical companies are subject to additional healthcare regulation and enforcement by the federal government and by authorities in the states and foreign jurisdictions in which they conduct their business. Such laws include, without limitation, U.S. federal and state fraud and abuse laws, including false claims, civil monetary penalties, consumer protection and transparency laws regarding drug pricing and payments or other transfers of value made to physicians and other licensed healthcare professionals, as well as similar foreign laws in the jurisdictions outside the United States. Violation of any of such laws or any other governmental regulations that apply may result in penalties, including, without limitation, significant administrative, civil and criminal penalties, damages, fines, disgorgement, additional reporting obligations, contractual damages, the curtailment or restructuring of operations, exclusion from participation in governmental healthcare programs and imprisonment.

Data Privacy and Security Laws

Numerous state, federal and foreign laws, regulations, and standards govern the collection, use, access to, confidentiality and security of health-related and other personal data, including clinical trial data, and apply now or could apply in the future to our operations or the operations of those with whom we work. In the United States, numerous federal and state laws and regulations, including data breach notification laws, health information privacy and security laws and consumer protection laws and regulations govern the collection, use, disclosure, and protection of health-related and other personal data. In addition, certain foreign laws govern the privacy and security of personal data, including health-related data. For example, the European Union General Data Protection Regulation, or the EU GDPR, imposes strict requirements for processing the personal data of individuals within the European Economic Area, or the EEA. Companies that must comply with the EU GDPR and similar data protection frameworks face increased compliance obligations and risk, including more robust regulatory enforcement of data protection requirements and potentially significant fines and processing penalties for noncompliance. Privacy and security laws, regulations, and other obligations globally are evolving, may conflict with each other (which complicate compliance efforts and increases compliance cost), and can result in investigations, proceedings, and other actions that can lead to significant civil and/or criminal penalties and fines.

Coverage and Reimbursement

Sales of any pharmaceutical product depend, in part, on the extent to which such product will be covered by third-party payors, such as federal, state and foreign government healthcare programs, commercial insurance and managed healthcare organizations, and the level of reimbursement for such product by third-party payors. No uniform policy exists for coverage and reimbursement for products exists among U.S. third-party payors. Therefore, decisions regarding the extent of coverage and amount of reimbursement to be provided are made on a plan-by-plan basis. The process for determining whether a third-party payor will provide coverage for a product typically is separate from the process for setting the price of such product or for establishing the reimbursement rate that the payor will pay for the product once coverage is approved. Third-party payors may limit coverage to specific products on an approved list, also known as a formulary, which might not include all of the FDA-approved products for a particular indication, or place products at certain formulary levels that result in lower reimbursement levels and higher cost-sharing obligation imposed on patients. One third-party payor’s decision to cover a particular medical product or service does not ensure that other payors will also provide coverage for the medical product or service. As a result, the coverage determination process will often require us to provide scientific and clinical support for the use of our product candidates to each payor separately and can be a time-consuming process, with no assurance that coverage and adequate reimbursement will be applied consistently or obtained in the first instance. For products administered under the supervision of a physician, obtaining coverage and adequate reimbursement may be particularly difficult because of the higher prices often associated with such drugs. Additionally, separate reimbursement for the product itself or the treatment or procedure in which the product is used may not be available, which may impact physician utilization.

Moreover, there has recently been heightened governmental scrutiny over the manner in which manufacturers set prices for their marketed products, which has resulted in several Congressional inquiries and proposed and enacted legislation designed, among other things, to bring more transparency to product pricing, review the relationship between pricing and manufacturer patient programs and reform government program reimbursement methodologies for pharmaceutical products. For example, the U.S. Department of Health and Human Services, or HHS, imposes rebates on many Medicare Part B and Medicare Part D products to penalize price increases that outpace inflation on

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an annual basis. In addition, HHS has been empowered to negotiate the price of certain single-source drugs that have been on the market for at least 7 years and single-source biologics that have been on the market for at least 11 years covered under Medicare as part of the Medicare Drug Price Negotiation Program. Each year up to twenty (20) products will be selected by HHS for the Medicare Drug Price Negotiation Program. Products subject to the Medicare Drug Price Negotiation Program are expected to experience a significant reduction in reimbursement from the Medicare program on a per unit basis.

In international markets, reimbursement and healthcare payment systems vary significantly by country, and many countries have instituted price ceilings on specific products and therapies. For example, the European Union provides options for its member states to restrict the range of medicinal products for which their national health insurance systems provide reimbursement and to control the prices of medicinal products for human use. A member state may approve a specific price for the medicinal product or it may instead adopt a system of direct or indirect controls on the profitability of the company placing the medicinal product on the market. Pharmaceutical products may face competition from lower-priced products in foreign countries that have placed price controls on pharmaceutical products. Furthermore, there can be no assurance that a product will be considered medically reasonable and necessary for a specific indication, that a product will be considered cost-effective by third-party payors, that an adequate level of reimbursement will be established even if coverage is available or that the third-party payor’s reimbursement policies will not adversely affect the ability to sell a product profitably.

Healthcare Reform

In the United States and certain foreign jurisdictions, there have been, and we expect there will continue to be, a number of legislative and regulatory changes to the healthcare system. In March 2010, The Patient Protection and Affordable Care Act, or ACA, was signed into law, which substantially changed the way healthcare is financed by both governmental and private insurers in the United States and significantly affected the pharmaceutical industry. The ACA contains a number of provisions, including those governing enrollment in federal healthcare programs, reimbursement adjustments and fraud and abuse changes. Since its enactment, there have been amendments to and judicial, Congressional and executive branch challenges to certain aspects of the ACA. For example, on July 4, 2025, the One Big Beautiful Bill Act, or the OBBBA, was signed into law, which narrowed access to ACA marketplace exchange enrollment and declined to extend the ACA enhanced advanced premium tax credits that expired at the end of 2025, which, among other provisions in the law, are anticipated to reduce the number of Americans with health insurance. The OBBBA also is expected to reduce Medicaid spending and enrollment by implementing work requirements for some beneficiaries, capping state-directed payments, reducing federal funding, and limiting provider taxes used to fund the program. Congress is considering proposed legislation intended to further reduce healthcare costs with alternatives to replace the expired ACA subsidies.

Other legislative changes have been proposed and adopted since the Affordable Care Act was enacted, including aggregate reductions of Medicare payments to providers, which will remain in effect through 2032, absent additional Congressional action.

The current administration is pursuing policies to reduce regulations and expenditures across government agencies including at HHS, the FDA, the Centers for Medicare & Medicaid Services, or CMS, and related agencies. These actions, presently directed by executive orders or memoranda from the Office of Management and Budget, may propose policy changes that create additional uncertainty for our business. For example, the current administration has announced agreements with several pharmaceutical companies that require the drug manufacturers to offer, through a direct-to-consumer platform, U.S. patients and Medicaid programs prescription drug Most-Favored Nation pricing equal to or lower than those paid in other developed nations, with additional mandates for direct-to-patient discounts and repatriation of foreign revenues. Other recent actions, for example, include (1) directing agencies to reduce agency workforce and cut programs; (2) directing HHS and other agencies to lower prescription drug costs through a variety of initiatives, including by improving upon the Medicare Drug Price Negotiation Program and establishing Most-Favored-Nation pricing for pharmaceutical products; (3) imposing tariffs on imported pharmaceutical products; and (4) as part of the Make America Healthy Again Commission’s Strategy Report released in September 2025, working across government agencies to increase enforcement on direct-to-consumer pharmaceutical advertising. Additionally, the current administration recently called on Congress to enact “The Great Healthcare Plan,” to codify and expand Most-Favored Nation pricing, lower government subsidies to private insurance companies, increase healthcare price transparency, expand pharmaceutical drugs available for over-the-counter purchase, and enact restrictions on

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pharmacy benefit manager payment methodologies, among other things. These actions and policies may significantly reduce U.S. drug prices, potentially impacting manufacturers’ global pricing strategies and profitability, while increasing their operational costs and compliance risks. In June 2024, the U.S. Supreme Court’s Loper Bright decision greatly reduced judicial deference to regulatory agencies, which could increase successful legal challenges to federal regulations affecting our operations. Congress may introduce and ultimately pass health care related legislation that could impact the drug approval process and make changes to the Medicare Drug Price Negotiation Program.

Individual states in the United States have also become increasingly active in implementing regulations designed to control pharmaceutical product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure and transparency measures and, in some cases, mechanisms to encourage importation from other countries and bulk purchasing. Furthermore, there has been increased interest by third-party payors and governmental authorities in reference pricing systems and publication of discounts and list prices.

We expect that additional state and federal healthcare reform measures will be adopted in the future, any of which could limit the amounts that federal and state governments will pay for healthcare product candidates and services, which could result in reduced demand for our product candidates once approved or additional pricing pressures.

Human Capital Resources

As of December 31, 2025, we had 96 full-time employees, 77 of whom were primarily engaged in research and development activities. A total of 35 employees have an M.D., Ph.D. or Pharm.D. degree. Most of our employees are based in our Brisbane, California facility, subject to hybrid and remote work arrangements.

We believe that our future success will depend, in part, on our ability to continue to attract, hire, and retain qualified personnel. We continue to seek additions to our science and technical staff. Through our experience with technological innovation, we appreciate the importance of retention, growth and development of our employees. We believe we offer competitive compensation (including salary, incentive bonus, and equity) and benefits packages. None of our employees is represented by a labor union, and we consider our employee relations to be good.

Corporate Information

We were incorporated under the laws of the State of Delaware on March 3, 2011. Our principal executive offices are located at 1400 Sierra Point Parkway, Bldg C, Suite 200, Brisbane, California 94005, and our telephone number is (650) 822-5500. Our corporate website address is www.annexonbio.com. Information contained on, or accessible through, our website shall not be deemed incorporated into and is not a part of this Annual Report on Form 10-K.

Available Information

We file Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, proxy statements, and related amendments, exhibits and other information with the Securities and Exchange Commission, or the SEC. You may access and read our filings without charge through the SEC’s website at www.sec.gov or through our website at https://ir.annexonbio.com/financial-information/sec-filings, as soon as reasonably practicable after such materials are electronically filed with or furnished to the SEC pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act. Information contained on, or accessible through, our website shall not be deemed incorporated into and is not a part of this Annual Report on Form 10-K.