ASSEMBLY BIOSCIENCES, INC.

Previous wording

We are a biotechnology company developing innovative therapeutics targeting serious viral and liver diseases with the potential to improve the lives of patients worldwide. Our pipeline includes multiple clinical-stage investigational therapies, including: (1) two long-acting helicase-primase inhibitors (HPI) for the treatment of recurrent genital herpes, GS-5366 (5366) and GS-1179 (1179), which have been exclusively licensed to Gilead Sciences, Inc. (Gilead); (2) an orally bioavailable sodium taurocholate co-transporting peptide (NTCP) inhibitor, ABI-6250 (6250), for the treatment of (a) chronic hepatitis delta virus (HDV) infection and (b) primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), both cholestatic liver diseases (CLD); and (3) a highly potent next-generation capsid assembly modulator (CAM) designed to disrupt the replication cycle of hepatitis B virus (HBV) at several key points, ABI-4334 (4334). Our pipeline also includes a novel, oral broad-spectrum non-nucleoside polymerase inhibitor (NNPI) for the treatment of transplant-related herpesviruses, ABI-7272 (7272), which is currently undergoing studies to enable a regulatory filing, and we have additional research programs against multiple viral and liver disease targets. In December 2025, pursuant to our collaboration with Gilead (the Gilead Collaboration), Gilead exercised its option to license our HPI program for the treatment of recurrent genital herpes, including our long-acting investigational candidates 1179 and 5366. For additional information regarding Gilead’s exercise of its option, see “Collaboration and License Agreement—Gilead Sciences, Inc.—Option Exercise.”

Current wording

Our pipeline includes multiple clinical-stage investigational therapies, including: (1) two long-acting helicase-primase inhibitors (HPI) for the treatment of recurrent genital herpes, GS-1179 (1179) and GS-5366 (5366), which have been exclusively licensed to Gilead Sciences, Inc. (Gilead); (2) an orally bioavailable sodium taurocholate cotransporting peptide (NTCP) inhibitor, ABI-6250 (6250), for the treatment of (a) chronic HDV infection and (b) primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), both CLDs; and (3) a highly potent next-generation capsid assembly modulator (CAM) designed to disrupt the replication cycle of HBV at several key points, ABI-4334 (4334). Our pipeline also includes a novel, oral broad-spectrum non-nucleoside polymerase inhibitor (NNPI) for the treatment of transplant-related herpesviruses, ABI-7272 (7272), which is currently undergoing studies to enable a regulatory filing, and we have additional research programs against multiple viral and liver disease targets.

Previous wording

Our Clinical Programs and Regulatory Filing-Enabling Program

Current wording

Our Clinical Programs and Regulatory Filing-Enabling Programs

Previous wording

4334 – Continuing process to identify potential partners that was initiated in the first quarter; we do not plan to advance 4334 further without a partner.

Current wording

4334 – Continuing process to identify potential partners that was initiated in the first quarter of 2026; we do not plan to advance 4334 further without a partner.

Previous wording

Most people with initial symptomatic genital herpes who are infected with HSV-2 have frequent recurrences, generally between three and 15 per year, impacting over four million people in the United States and France, Germany, Italy and Spain (collectively, the EU4) and the United Kingdom (UK). Currently, there are three antiviral drugs (all nucleoside analogs) that have been approved in the United States and the EU4/UK for the treatment of genital herpes. However, no new drugs have been approved in these regions to treat genital herpes for more than 25 years. In addition to the approved nucleoside analogs, agents such as local anesthetics or analgesics may be used to alleviate local symptoms of minor pain and discomfort.

Current wording

Most people with initial symptomatic genital herpes who are infected with HSV-2 have frequent recurrences, generally between three and 15 per year, impacting over four million people in the United States and France, Germany, Italy and Spain (collectively, the EU4) and the United Kingdom (UK). Currently, there are three antiviral drugs (all nucleoside analogs) that have been approved in the United States and the EU4/UK for the treatment of genital herpes. However, only one new drug, which was approved in the United States for the treatment of acyclovir-resistant HSV in immunocompromised adults, has been approved in these regions to treat genital herpes for more than 25 years. In addition to the approved nucleoside analogs, agents such as local anesthetics or analgesics may be used to alleviate local symptoms of minor pain and discomfort.

Previous wording

Based on the limitations of current therapies, we see a path to advancing the treatment paradigm for people suffering from recurrent genital herpes. To reach that goal, we discovered and began the clinical development of a novel, potent, long-acting HPI for recurrent genital herpes, 5366, which demonstrated low nanomolar potency in vitro against both HSV-1 and HSV-2 clinical isolates and a favorable nonclinical safety profile in the FDA's Good Laboratory Practice (GLP) toxicology studies. In addition, we began development of a second novel, potent, long-acting HPI for genital herpes, 1179, which was in-licensed to us as part of our collaboration with Gilead. As Gilead has exercised its option to exclusively license our HPI program, including 5366 and 1179, development is now in Gilead’s sole control following completion of the Phase 1a/b studies of 5366 and 1179. For additional information regarding the option exercise, see “Collaboration and License Agreements—Gilead Sciences, Inc.—Option Exercise.”

Current wording

Based on the limitations of current therapies, we see a path to advancing the treatment paradigm for people suffering from recurrent genital herpes. To reach that goal, we discovered and began the clinical development of a novel, potent, long-acting HPI for recurrent genital herpes, 5366, which demonstrated low nanomolar potency in vitro against both HSV-1 and HSV-2 clinical isolates and a favorable nonclinical safety profile in the FDA's GLP toxicology studies. In addition, we began development of a second novel, potent, long-acting HPI for genital herpes, 1179, which was in-licensed to us as part of our collaboration with Gilead. As Gilead has exercised its option to exclusively license our HPI program, including 1179 and 5366, development is now in Gilead’s sole control. Initiation of a Phase 2 study of 1179 is expected by the end of 2026. We do not expect that Gilead will develop 5366 further at this time. For additional information regarding the option exercise, see “Collaboration and License Agreement—Gilead Sciences, Inc.”

Previous wording

We also conducted a Phase 1a/b clinical study of 1179, a structurally-differentiated HPI, which has single digit nanomolar potency against HSV-1 and HSV-2 and a nonclinical PK and safety profile that is supportive of a potential long-acting treatment by once-weekly oral administration. We reported interim data from two oral weekly dose cohorts in the Phase 1b portion of the 1179 study in December 2025. For the powered antiviral endpoint, HSV-2 shedding rate, highly potent antiviral activity was observed with a 98% reduction in HSV-2 shedding rate compared to placebo (p<0.01) over the 29-day evaluation period in the 50 mg weekly dose cohort. This reduction exceeded our target for the study of an 80-85% reduction in HSV-2 shedding rate. Further, data revealed a 91% reduction in virologically confirmed lesion rate compared to placebo (p<0.01) with the 50 mg weekly dose. There was also a >99% reduction in the number of samples with high viral load, a potential surrogate for HSV-2 transmission and a secondary endpoint.

Current wording

We conducted a Phase 1a/b clinical study of 1179, which has single digit nanomolar potency against HSV-1 and HSV-2 and a nonclinical pharmacokinetics (PK) and safety profile that is supportive of a potential long-acting treatment by once-weekly oral administration. For the powered antiviral endpoint, HSV-2 shedding rate, highly potent antiviral activity was observed with a 97% reduction in HSV-2 shedding rate compared to placebo (p<0.01) over the 29-day evaluation period in the 50 mg weekly dose cohort. This reduction exceeded our target for the study of an 80-85% reduction in HSV-2 shedding rate. Further, data revealed a 92% reduction in virologically confirmed lesion rate compared to placebo (p<0.01) with the 50 mg weekly dose. There was also a 100% reduction in the number of samples with high viral load, a potential surrogate for HSV-2 transmission and a secondary endpoint.

Previous wording

Across both oral weekly dose cohorts, 1179 demonstrated a PK profile that continues to support once-weekly dosing. 1179 was observed to be well-tolerated at both doses. Overall, the proportion of participants reporting treatment-emergent AEs was similar between 1179 and placebo recipients. Of the treatment-emergent AEs reported, the majority were Grade 1 or Grade 2. The most common AEs were upper respiratory tract infection and headache. There have been no serious AEs reported to date. One Grade 3 AE of migraine was reported in a participant enrolled in the 50 mg/placebo cohort.

Current wording

Across all oral weekly dose cohorts, 1179 demonstrated a PK profile that continues to support once-weekly dosing. 1179 was observed to be well-tolerated at both doses. Overall, the proportion of participants reporting treatment-emergent adverse events (AEs) was similar between 1179 and placebo recipients. Of the treatment-emergent AEs reported, the majority were Grade 1 or Grade 2. The most common AEs were upper respiratory tract infection and headache. No serious AEs have been reported to date. One Grade 3 AE of migraine was reported in a participant enrolled in the placebo cohort.

Previous wording

All participants in the Phase 1b portion of the 1179 study have completed dosing and follow up. With these data, 1179 can move directly into a Phase 2 study for a once-weekly treatment regimen, subject to the completion of chronic toxicology studies, which are underway. The 1179 data reported in December 2025 was presented in a poster presentation at ESCMID in April 2026.

Current wording

The Phase 1b portion of the 1179 study is complete. With these data, 1179 can move directly into a Phase 2 study for a once-weekly treatment regimen, and additional chronic toxicology studies are currently being conducted by Gilead. The 1179 data reported in December 2025 was presented in a poster presentation at The Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) in April 2026. Gilead presented final Phase 1b data in two posters at IDWeek in October 2026.

Previous wording

We reported interim data from the Phase 1b portion of the 5366 study in August 2025, focused on two different oral doses of 5366 administered on a once-weekly basis. For the powered antiviral endpoint, HSV-2 shedding rate, highly potent antiviral activity was observed with a 94% reduction compared to placebo (p<0.01) over the 29-day evaluation period in the cohort evaluating a 350 mg weekly dose. This reduction exceeded our target for the study of an 80-85% reduction in the rate of HSV-2 shedding. For a secondary clinical endpoint of virologically confirmed genital lesion rate, a 97% reduction compared to placebo (p<0.05) was observed with the 350 mg weekly dose. The rate of genital swabs with high viral load (i.e., >104 copies/mL HSV DNA), a potential surrogate for HSV-2 transmission and a secondary endpoint, was reduced by 98% compared to placebo (p<0.05) in this cohort.

Current wording

We also conducted a Phase 1 a/b study of 5366, a structurally-differentiated HPI, and we reported interim data from the Phase 1b portion of the study in August 2025, focused on two different oral doses of 5366 administered on a once-weekly basis, and in December 2025, which included a once-monthly cohort. For the powered antiviral endpoint, HSV-2 shedding rate, highly potent antiviral activity was observed with a 94% reduction compared to placebo (p<0.01) over the 29-day evaluation period in the cohort evaluating a 350 mg weekly dose. This reduction exceeded our target for the study of an 80-85% reduction in the rate of HSV-2 shedding. For a secondary clinical endpoint of virologically confirmed genital lesion rate, a 97% reduction compared to placebo (p<0.05) was observed with the 350 mg weekly dose. The rate of genital swabs with high viral load (i.e., >104 copies/mL HSV DNA), a potential surrogate for HSV-2 transmission and a secondary endpoint, was reduced by 98% compared to placebo (p<0.05) in this cohort. In the 5366 monthly dose cohort, potent antiviral activity was observed, with a 76% reduction in HSV-2 shedding rate compared to placebo (p<0.01) over the 29-day evaluation period. The majority of positive swabs (89%) were collected in the last two weeks of the evaluation period when drug levels were declining. We observed an 88% reduction in virologically confirmed genital lesion rate (p=0.01), along with an 81% reduction in the number of samples with high viral load (p<0.01) compared to placebo in the monthly dose cohort.

Previous wording

Across the two weekly oral dose cohorts and the monthly oral dose cohort of the Phase 1b study, 5366 demonstrated a pharmacokinetic (PK) profile that continues to support once-weekly and potentially once-monthly dosing.

Current wording

Across the two weekly oral dose cohorts and the monthly oral dose cohort of the Phase 1b study, 5366 demonstrated a PK profile that continues to support once-weekly and potentially once-monthly dosing.

Previous wording

5366 was observed to be well-tolerated at all dose levels tested in the Phase 1b portion of the study. The two weekly oral cohorts as well as the monthly oral cohort are complete and unblinded safety data has been reported. Across all cohorts, the proportion of participants reporting treatment-emergent adverse events (AEs) was similar between 5366 and placebo recipients, and all were Grade 1 or Grade 2. One Grade 3 AE was reported, hypertriglyceridemia, in a participant with relevant medical history who had Grade 4 elevated triglycerides pre-dose on Day 1. This AE resulted in study discontinuation but was not considered treatment related. The proportion of participants reporting treatment-emergent lab abnormalities was similar in 5366 and placebo recipients with the majority being Grade 1 or Grade 2. There were three participants with treatment-emergent Grade 3 lab abnormalities across all cohorts, all of which are considered unrelated to assigned treatment; one participant with exercise-associated elevation in creatine kinase (150/30 mg QW); one participant with an elevation of cholesterol in the follow up period, which participant had a Grade 2 elevation at baseline (350 mg QW); and one participant, who was dosed with placebo, with decreased neutrophils. There did not appear to be a dose-response relationship in either the frequency or severity of the treatment-emergent AEs or lab abnormalities. No serious AEs have been reported to date.

Current wording

5366 was observed to be well-tolerated at all dose levels tested in the Phase 1b portion of the study. The two weekly oral cohorts as well as the monthly oral cohort are complete and unblinded safety data has been reported. Across all cohorts, the proportion of participants reporting treatment-emergent AEs was similar between 5366 and placebo recipients, and all were Grade 1 or Grade 2. One Grade 3 AE was reported, hypertriglyceridemia, in a participant with relevant medical history who had Grade 4 elevated triglycerides pre-dose on Day 1. This AE resulted in study discontinuation but was not considered treatment related. The proportion of participants reporting treatment-emergent lab abnormalities was similar in 5366 and placebo recipients with the majority being Grade 1 or Grade 2. There were three participants with treatment-emergent Grade 3 lab abnormalities across all cohorts, all of which are considered unrelated to assigned treatment; one participant with exercise-associated elevation in creatine kinase (150/30 mg QW); one participant with an elevation of cholesterol in the follow up period, which participant had a Grade 2 elevation at baseline (350 mg QW); and one participant, who was dosed with placebo, with decreased neutrophils. There did not appear to be a dose-response relationship in either the frequency or severity of the treatment-emergent AEs or lab abnormalities. No serious AEs have been reported to date.

Previous wording

All participants in the Phase 1b portion of the 5366 study have completed dosing and follow up. The observed PK profile continues to support once-weekly dosing and the potential for once-monthly oral dosing regimens. Additionally, all chronic toxicology studies have been completed. With these data, 5366 is ready to move into a Phase 2 clinical study; however, 5366 development is in Gilead's sole control and Gilead does not intend to develop 5366 further at this time.

Current wording

The Phase 1b portion of the 5366 study is complete. Additionally, all chronic toxicology studies have been completed. With these data, 5366 is ready to move into a Phase 2 clinical study; however, 5366 development is in Gilead's sole control, and we do not expect that Gilead will develop 5366 further at this time.

Previous wording

The 5366 data reported in August and December 2025 were presented in an oral presentation and two poster presentations at the Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) in Munich, Germany in April 2026.

Current wording

The 5366 data reported in August and December 2025 were presented in an oral presentation and two poster presentations at ESCMID in Munich, Germany in April 2026.

Previous wording

In December 2025, Gilead exercised its option early to license our HPI program for the treatment of recurrent genital herpes, including 5366 and 1179. We received Gilead’s clinical development plan and budget for the HPI program in June 2026. The plan indicates that 1179 has been selected to advance, with a Phase 2 clinical study in participants with recurrent genital herpes expected to initiate by the end of 2026. Gilead is also considering the possible evaluation of 1179 as part of a combination strategy with HIV PrEP. Our decision regarding the Profit-Share (as defined below) will be made after receipt and review of Gilead's commercial cost estimates, which will complete the opt-in package. For more information regarding Gilead’s exercise of its option, see “Collaboration and License Agreement—Gilead Sciences, Inc.—Option Exercise.”

Current wording

In December 2025, Gilead exercised its option early to license our HPI program for the treatment of recurrent genital herpes, including 1179 and 5366. Following receipt and review of the CDP for the HPI program, we exercised our Profit-Share option in the third quarter of 2026. Under the CDP, Gilead is expected to advance 1179 into a Phase 2 clinical study in participants with recurrent genital herpes by the end of 2026, and potentially evaluate 1179 as part of a combination strategy with HIV PrEP. For more information regarding Gilead’s exercise of its option and our exercise of our option related to the Profit-Share, see “Collaboration and License Agreement—Gilead Sciences, Inc."

Previous wording

HDV is a “satellite virus” of HBV because it can only infect people (1) who are already infected with HBV or (2) at the same time as a person is infected with HBV. HDV affects a subset of approximately 12 million HBV infected people. These individuals infected with HDV, which comprise an estimated nearly 5% of hepatitis B surface antigen (HBsAg) positive individuals, experience a substantially increased disease burden, as they account for 18% of cirrhosis and 20% of hepatocellular carcinoma associated with HBV. HDV is considered the most severe form of hepatitis, as 70% of individuals infected with HDV progress to cirrhosis within ten years. While HDV is less prevalent in the United States, it is a significant and serious health problem with inadequate treatment in many parts of Europe, Africa, the Middle East, East Asia and parts of South America. HDV may be significantly underdiagnosed, because there were no HDV-targeted therapies approved until very recently, and the first HDV-targeted therapy is only approved in the European Economic Area (EEA), the UK, Switzerland, Australia, Canada and the United States. HDV is known to accelerate disease progression and increase the incidence of liver cirrhosis and liver cancer, which results in higher morbidity and mortality rates than HBV alone.

Current wording

HDV is a “satellite virus” of HBV because it can only infect people (1) who are already infected with HBV or (2) at the same time as a person is infected with HBV. HDV affects a subset of approximately 12 million HBV infected people. These individuals infected with HDV, which comprise an estimated nearly 5% of hepatitis B surface antigen (HBsAg) positive individuals, experience a substantially increased disease burden, as they account for 18% of cirrhosis and 20% of hepatocellular carcinoma associated with HBV. HDV is considered the most severe form of hepatitis, as 70% of individuals infected with HDV progress to cirrhosis within ten years. While HDV is less prevalent in the United States, it is a significant and serious health problem with inadequate treatment in many parts of Europe, Africa, the Middle East, East Asia and parts of South America. HDV may be significantly underdiagnosed, because there were no HDV-targeted therapies approved until the last few years, and the first HDV-targeted therapy is only approved in the European Economic Area (EEA), the UK, Switzerland, Australia, Canada and the United States.

Previous wording

One Grade 2 alanine transminase (ALT) elevation was observed in the cohort evaluating the highest single-dose level of 25 mg. In this cohort, off-target engagement of other liver transporters was also seen as indicated by elevated CP-1 levels. Grade 1 ALT elevations were observed at a low frequency across the other cohorts, including placebo. All ALT elevations were self-limited, and none were accompanied with elevations in bilirubin or other markers of liver injury. The elevations resolved in the study period with ongoing drug exposure due to 6250's four-day half-life.

Current wording

One Grade 2 alanine transaminase (ALT) elevation was observed in the cohort evaluating the highest single-dose level of 25 mg. In this cohort, off-target engagement of other liver transporters was also seen as indicated by elevated CP-1 levels. Grade 1 ALT elevations were observed at a low frequency across the other cohorts, including placebo. All ALT elevations were self-limited, and none were accompanied with elevations in bilirubin or other markers of liver injury. The elevations resolved in the study period with ongoing drug exposure due to 6250's four-day half-life.

Previous wording

A Phase 1a study demonstrated that 4334 was well-tolerated when administered orally as single or multiple doses. During the second quarter of 2024, we dosed our first participant in a Phase 1b clinical study of 4334. We reported interim clinical results from the initial 150 mg cohort in December 2024, and topline clinical results, including a subsequent 400 mg cohort in June 2025. In both the 150 mg and 400 mg cohorts, 4334 continued to show a half-life supportive of once-daily oral dosing. In addition, results for both cohorts indicated that 4334 maintained clinical exposures multiple folds above those anticipated to be required for potent viral activity and inhibition of cccDNA formation. Mean declines in HBV DNA of 2.9 log10 IU/mL and 3.2 log10 IU/mL were observed over 28 days in a population of predominately HBeAg negative participants receiving 150 mg and 400 mg, respectively. Among the subset of participants with detectable HBV RNA at baseline, mean declines of 2.5 log10 U/mL and 2.3 log10 U/mL were observed over 28 days in the participants receiving 150 mg and 400 mg, respectively. As anticipated, limited changes in viral antigens were observed for the study population over the 28-day treatment period. These antiviral data are consistent with the high potency seen preclinically for 4334. The safety data also demonstrated that 4334 was well-tolerated with a favorable safety profile observed. The 400 mg cohort was the final cohort for this Phase 1b study and final data was presented at the American Association for the Study of Liver Disease, The Liver Meeting® in November 2025.

Current wording

A Phase 1a study demonstrated that 4334 was well-tolerated when administered orally as single or multiple doses. We reported interim Phase 1b clinical results from the initial 150 mg cohort in December 2024, and topline clinical results, including a subsequent 400 mg cohort in June 2025. In both the 150 mg and 400 mg cohorts, 4334 continued to show a half-life supportive of once-daily oral dosing. In addition, results for both cohorts indicated that 4334 maintained clinical exposures multiple folds above those anticipated to be required for potent viral activity and inhibition of cccDNA formation. Mean declines in HBV DNA of 2.9 log10 IU/mL and 3.2 log10 IU/mL were observed over 28 days in a population of predominately HBeAg negative participants receiving 150 mg and 400 mg, respectively. Among the subset of participants with detectable HBV RNA at baseline, mean declines of 2.5 log10 U/mL and 2.3 log10 U/mL were observed over 28 days in the participants receiving 150 mg and 400 mg, respectively. As anticipated, limited changes in viral antigens were observed for the study population over the 28-day treatment period. These antiviral data are consistent with the high potency seen preclinically for 4334. The safety data also demonstrated that 4334 was well-tolerated with a favorable safety profile observed. Final data for this Phase 1b study was presented at AASLD in November 2025.

Previous wording

PBC affects intrahepatic bile ducts, with complications including cirrhosis and hepatocellular carcinoma. PBC is also associated with Sjogren’s Syndrome. There are approximately 150,000 adults diagnosed with PBC in the United States, and approximately 40% of patients fail first line therapy. There are multiple therapies available for the treatment of PBC; however, a significant percentage of individuals have an inadequate response to these treatments, and there remains an unmet medical need for improved treatment of PBC.

Current wording

PBC affects intrahepatic bile ducts, with complications including cirrhosis and hepatocellular carcinoma. PBC is also associated with Sjogren’s Syndrome. There are approximately 150,000 adults diagnosed with PBC in the United States, and approximately 40% of patients fail first line therapy. In 2024, two peroxisome proliferator-activated receptor (PPAR) agonists were approved in the European Union and the United States as second-line therapy for PBC. However, at least one-third of patients receiving these treatments failed to achieve biochemical responses in Phase 3 studies. Therefore, there remains an unmet medical need for improved treatment of PBC.

Previous wording

In May 2026, we announced that we expanded 6250 clinical development beyond HDV into CLD, targeting PBC and PSC. Further, we conducted a pre-IND meeting with the FDA to discuss our planned development of 6250 in CLD. Official meeting minutes support advancement of the CLD program. We are preparing for Phase 2 clinical studies, with Phase 2 initiation expected in the first quarter of 2027.

Current wording

In May 2026, we announced that we expanded 6250 clinical development beyond HDV into CLD, targeting PBC and PSC. Further, in May 2026, we conducted a pre-IND meeting with the FDA to discuss our planned development of 6250 in CLD. In September 2026, we received a Study May Proceed letter from the FDA for the Phase 2 study in PBC and PSC. We are preparing for Phase 2 clinical studies, with Phase 2 initiation expected in the first quarter of

Previous wording

7272, our development candidate in our NNPI program, is currently in regulatory filing-enabling nonclinical studies.

Current wording

7272, our development candidate in our NNPI program, has completed GLP toxicology studies and is currently completing other regulatory filing-enabling nonclinical studies.

Previous wording

In addition to our investigational therapy programs that have nominated development candidates and have advanced into clinical studies or regulatory-filing enabling studies, our research team continues to actively focus on proprietary research to discover and nominate novel molecules to treat serious viral and liver diseases.

Current wording

Our research team continues to actively focus on proprietary research to discover and nominate novel molecules to treat serious viral and liver diseases. In October 2026, we nominated a development candidate, 8914, targeting the respiratory virus space. Discovered by the research team, 8914 is currently advancing into regulatory filing-enabling studies.

Previous wording

If Gilead exercises its opt-in right to any current or future program under the collaboration, we are eligible to receive up to $330.0 million in potential regulatory and commercial milestones on that program, in addition to royalties ranging from the high single-digits to high teens, depending on the clinical stage of the program at the time of the opt-in. Following Gilead’s exercise of its option for each program, we may opt-in to cover 40% of the research and development costs in the United States and share 40% of the profits and operating loss in the United States for products within the program in lieu of receiving milestones and royalties for that program in the United States, unless we later opt out of the cost/profit share for the program. Prior to Gilead’s potential exercise of its opt-in, we are primarily responsible for all discovery, research and development on both our programs and the two Gilead-contributed programs. Following Gilead’s opt-in, Gilead will control the further discovery, research, development and commercialization on any optioned programs, and is responsible for all related costs unless we opt in to share 40% of all costs and profits in the United States. During the term, Gilead will continue to support the collaboration through extension fees of $75.0 million in each of the third, fifth and seventh anniversaries of the collaboration.

Current wording

Following Gilead’s exercise of its option for each program, we may elect to cover 40% of the research and development costs in the United States and share 40% of the profits and operating losses in the United States for products within the program in lieu of receiving milestones and royalties for that program in the United States. For programs for which we do not participate in the Profit-Share, we are eligible to receive up to $330.0 million in development, regulatory and commercial milestone payments and tiered royalties ranging from the high-single digits to the high teens, depending on the timing of Gilead's option exercise. For programs for which we participate in the Profit-Share, we remain eligible to receive up to $280.0 million in development, regulatory and commercial milestone payments, as well as royalties outside the United States. Prior to Gilead’s exercise of its option, we are primarily responsible for all discovery, research and development activities for our programs. Following Gilead’s exercise of its option, Gilead controls further discovery, research, development and commercialization of any optioned programs, and is responsible for all related costs unless we opt in to the Profit-Share. We also retain certain co-promotion rights for future programs not identified at the time we entered into the Gilead Collaboration Agreement.

Previous wording

Also in October 2023, we and Gilead entered into a Common Stock Purchase Agreement and an Investor Rights Agreement (together, the Gilead Equity Agreements), which were both amended in June 2024. The Gilead Equity Agreements include a three-year standstill provision and a two-year lockup provision (which has expired), each with customary exceptions, and provide Gilead with certain other stock purchase rights and registration rights, as well as the right to designate two directors (or, alternatively, board observers at Gilead’s election) to our board of directors. In December 2023, Gilead designated Tomas Cihlar, Ph.D. to serve on our board of directors, and in March 2024, Gilead designated Robert D. Cook II to serve on our board of directors.

Current wording

Also in October 2023, we and Gilead entered into a Common Stock Purchase Agreement and an Investor Rights Agreement (together, the Gilead Equity Agreements), which were both amended in June 2024. The Gilead Equity Agreements provide Gilead with certain stock purchase rights and registration rights, as well as the right to designate two directors (or, alternatively, board observers at Gilead’s election) to our board of directors.

Previous wording

As of June 30, 2026, Gilead held (1) approximately 25.1% of our outstanding common stock, (2) a warrant to purchase up to 179,500 shares of our common stock at a price of $17.00 per share, which was acquired in a financing transaction in 2024 (the 2024 Warrant), (3) a Class A warrant to purchase up to 1,147,960 shares of our common stock at a price of $21.60 per share (Class A Warrant), which was acquired in a financing transaction in 2025 (the 2025 Financing) and (4) a Class B Warrant to purchase up to 1,147,960 shares of our common stock at a price of $21.60 per share (Class B Warrant), which was also acquired in the 2025 Financing. The 2024 Warrant is exercisable and expires on June 18, 2029. The Class A Warrant is also exercisable and expires on or prior to the earlier of (a) August 11, 2030 (five years from the date of issuance) and (b) the date that is 30 days after the public announcement that we have completed enrollment of at least 200 patients for our Phase 2 clinical study evaluating 5366 versus valacyclovir. The Class B Warrant is exercisable between November 15, 2026 and December 31, 2026, provided that if, prior to November 15, 2026, we publicly announce that we have received at least $75.0 million in the aggregate of non-dilutive capital in connection with a collaboration agreement, then the Class B Warrant automatically terminates in full.

Current wording

As of September 30, 2026, Gilead held approximately 24.4% of our outstanding common stock and warrants to purchase up to 179,500 shares of our common stock at a price of $17.00 per share that expires on June 18, 2029 and a warrant to purchase up to 1,147,960 shares of our common stock at a price of $21.60 per share that expires on August 11, 2030. Neither of the warrants are currently exercisable due to certain blocker provisions in the warrant agreements. As of September 30, 2026, Gilead also held a warrant to purchase an additional 1,147,960 shares of our common stock at a price of $21.60 per share, which was cancelled in November 2026 following our public announcement that we received the first $75.0 million extension fee under the Gilead Collaboration Agreement.

Previous wording

Research and development expenses were $14.9 million for the three months ended June 30, 2026 compared to $16.1 million for the same period in 2025. The $1.2 million decrease was primarily driven by lower external program expenses, particularly for 5366, reflecting the completion of clinical trials and lower manufacturing and toxicology study costs, partially offset by increases in our research and discovery efforts and higher employee-related expenses due to increased headcount, annual salary adjustments and stock-based compensation expense related to performance-based restricted stock units granted in mid-2025.

Current wording

Research and development expenses were $20.2 million for the three months ended September 30, 2026 compared to $16.6 million for the same period in 2025. The $3.6 million increase was primarily driven by higher external program expenses, reflecting the start-up of multiple clinical trials for 6250 and increases in our research and discovery efforts, as well as higher employee-related expenses due to increased headcount, annual salary adjustments and stock-based compensation expense related to restricted stock units granted in 2026. These increases were partially offset by lower external program expenses for 1179 and 5366 following completion of their Phase 1 clinical trials.

Previous wording

General and administrative expenses were $9.5 million for the six months ended June 30, 2026 compared to $9.1 million for the same period in 2025. The $0.4 million increase was primarily driven by higher stock-based compensation expense associated with performance-based restricted stock units granted in mid-2025, partially offset by lower professional fees related to patent filings.

Current wording

General and administrative expenses were $6.1 million for the three months ended September 30, 2026 compared to $5.1 million for the same period in 2025. The $1.1 million increase was primarily driven by higher stock-based compensation expense related to restricted stock units granted in 2026 and increased commercial planning and market research expenses.

Previous wording

Interest and other income, net was $2.5 million for the three months ended June 30, 2026, compared to $0.9 million for the same period in 2025. The $1.6 million increase was primarily due to a larger portfolio balance resulting from the investment of cash proceeds from financing transactions completed in August 2025 and May 2026 and the collaboration transaction completed in December 2025.

Current wording

Interest and other income, net was $3.2 million for the three months ended September 30, 2026, compared to $1.7 million for the same period in 2025. The $1.5 million increase was primarily due to a larger portfolio balance resulting from the investment of cash proceeds from our financing completed in May 2026 and the payment received from Gilead in December 2025 for a license to our HPI program.

Previous wording

Collaboration revenue was $13.4 million for the three months ended June 30, 2026 compared to $9.6 million for the same period in 2025. The $3.7 million increase reflects the timing of activities performed and progress toward completion of services under the Gilead Collaboration Agreement, and includes a $5.1 million cumulative catch-up adjustment recognized during the three months ended June 30, 2026 related to updated estimates of future activities under the collaboration.

Current wording

Collaboration revenue was $24.5 million for the nine months ended September 30, 2026 compared to $29.8 million for the same period in 2025. The $5.3 million decrease was primarily driven by an $11.3 million reduction in the transaction price of the HPI program license, reflecting research and development costs we estimate are probable of being reimbursed to Gilead under the Profit-Share. This decrease was partially offset by an increase in research and development activities we performed under the Gilead Collaboration Agreement, and includes a $6.7 million cumulative catch-up adjustment recognized during the nine months ended September 30, 2026 related to updated estimates of future activities under the collaboration.

Previous wording

Research and development expenses were $29.8 million for the six months ended June 30, 2026 compared to $31.0 million for the same period in 2025. The $1.2 million decrease was primarily driven by lower external program expenses, particularly for 5366, reflecting the completion of clinical trials and lower manufacturing and toxicology study costs, partially offset by increases in our research and discovery efforts and higher employee-related expenses due to increased headcount, annual salary adjustments and stock-based compensation expense related to performance-based restricted stock units granted in mid-2025.

Current wording

Research and development expenses were $50.1 million for the nine months ended September 30, 2026 compared to $47.6 million for the same period in 2025. The $2.5 million increase was primarily driven by higher external program expenses for 6250, reflecting the start-up of multiple clinical trials, and increased research and discovery efforts, as well as higher employee-related expenses due to increased headcount, annual salary adjustments and stock-based compensation expense related to restricted stock units granted in 2026. These increases were partially offset by lower external program expenses for 5366, 1179 and 4334 following the completion of their Phase 1 clinical trials.

Previous wording

General and administrative expenses were $4.8 million for the three months ended June 30, 2026 compared to $4.6 million for the same period in 2025. The $0.2 million increase was primarily driven by higher stock-based compensation expense associated with performance-based restricted stock units granted in mid-2025, partially offset by lower professional fees related to patent filings.

Current wording

General and administrative expenses were $15.6 million for the nine months ended September 30, 2026 compared to $14.2 million for the same period in 2025. The $1.4 million increase was primarily driven by higher stock-based compensation expense associated with restricted stock units granted in June 2026.

Previous wording

Interest and other income, net was $4.8 million for the six months ended June 30, 2026, compared to $2.0 million for the same period in 2025. The $2.8 million increase was primarily due to a larger portfolio balance resulting from the investment of cash proceeds from financing transactions completed in August 2025 and May 2026 and the collaboration transaction completed in December 2025.

Current wording

Interest and other income, net was $7.9 million for the nine months ended September 30, 2026, compared to $3.7 million for the same period in 2025. The $4.2 million increase was primarily due to a larger portfolio balance resulting from the investment of cash proceeds from our financings completed in August 2025 and May 2026 and the payment received from Gilead in December 2025 for a license to our HPI program.

Previous wording

As a result of our significant research and development expenditures and the lack of any FDA-approved products to generate product sales revenue, we have not been profitable and have generated operating losses since we were incorporated in October 2005. We have funded our operations through June 30, 2026 principally through equity financings, raising an aggregate of $929.8 million in net proceeds, and strategic collaborations, raising an aggregate of $236.2 million.

Current wording

As a result of our significant research and development expenditures and the lack of any FDA-approved products to generate product sales revenue, we have not been profitable and have generated operating losses since we were incorporated in October 2005. We have funded our operations through September 30, 2026 principally through equity financings, raising an aggregate of $940.2 million in net proceeds, and strategic collaborations, raising an aggregate of $238.0 million.

Previous wording

Cash Flows for the Six Months Ended June 30, 2026 and 2025

Current wording

Cash Flows for the Nine Months Ended September 30, 2026 and 2025

Previous wording

Net cash used in operating activities was $37.6 million for the six months ended June 30, 2026, compared to $40.2 million for the same period in 2025. The decrease was primarily attributable to lower clinical development expenditures resulting from the completion of multiple clinical trials, as well as approximately $1.5 million received under the letter agreement we entered into with Gilead in July 2025.

Current wording

Net cash used in operating activities was $54.7 million for the nine months ended September 30, 2026, compared to $55.3 million for the same period in 2025. The decrease was primarily attributable to approximately $1.8 million received under the Gilead Collaboration Agreement in 2026.

Previous wording

Net cash used in investing activities was $97.5 million for the six months ended June 30, 2026, compared to net cash provided by investing activities of $23.6 million for the same period in 2025. The change was primarily due to our purchases of marketable securities following the underwritten offering in May 2026, as we invested the $108.1 million net proceeds received from the offering.

Current wording

Net cash used in investing activities was $94.0 million for the nine months ended September 30, 2026, compared to net cash used in investing activities of $134.7 million for the same period in 2025. The decrease was primarily due to higher maturities of marketable securities, partially offset by higher purchases of marketable securities, as we invested the $108.1 million net proceeds received from our underwritten offering in May 2026.

Previous wording

Net cash provided by financing activities was $108.9 million for the six months ended June 30, 2026, compared to $2.3 million for the same period in 2025. The increase was primarily attributable to the net proceeds received from the underwritten offering in May 2026, which exceeded the proceeds received from sales of common stock under the Company's "at-the-market" offering program during 2025.

Current wording

Net cash provided by financing activities was $119.3 million for the nine months ended September 30, 2026, compared to $174.2 million for the same period in 2025. The decrease was primarily attributable to lower net proceeds from our underwritten offering in May 2026, compared to the net proceeds from our underwritten offering and concurrent private placement with Gilead in August 2025, partially offset by larger proceeds from the exercise of warrants in 2026.

Previous wording

We expect our future operating expenses to increase over the coming years as we continue to expand our pipeline and advance our candidates. We monitor our cash needs and the status of the capital markets on a continuous basis. From time to time, we opportunistically raise capital and have done so numerous times since our initial public offering by issuing equity securities. We expect to continue to raise capital when and as needed and at the time and in the manner most advantageous to us.

Current wording

We expect our future operating expenses to increase over the coming years as we continue to advance our candidates and expand our pipeline. We monitor our cash needs and the status of the capital markets on a continuous basis. From time to time, we opportunistically raise capital and have done so numerous times since our initial public offering by issuing equity securities. We expect to continue to raise capital when and as needed and at the time and in the manner most advantageous to us.

Previous wording

As of June 30, 2026, we held cash, cash equivalents and marketable securities of $320.4 million, which based on our current operating plan, we believe will be sufficient to fund our operating requirements into late 2028. We believe our cash runway will extend into 2029 with the receipt of the $75.0 million extension fee due from Gilead in the fourth quarter of 2026, following the third anniversary of the Gilead Collaboration Agreement. We have based our estimate on assumptions that may prove to be wrong, and we may utilize our available capital resources sooner than we currently expect.

Current wording

As of September 30, 2026, we held cash, cash equivalents and marketable securities of $314.3 million. Based on our current operating plan and including the $75.0 million collaboration extension payment we received from Gilead in November 2026, we believe we have sufficient funds to meet our operating requirements into 2029. We have based our estimate on assumptions that may prove to be wrong, and we may utilize our available capital resources sooner than we currently expect.

Previous wording

the scope, progress, results and costs of our ongoing drug discovery, nonclinical development, laboratory testing and clinical studies of our product candidates and any additional clinical studies we may conduct in the future;

Current wording

the scope, progress, results and costs of our ongoing drug discovery, nonclinical development, laboratory testing and clinical studies of our product candidates and any additional clinical studies we may conduct in the future, including studies conducted by Gilead;