ASSEMBLY BIOSCIENCES, INC.

Previous wording

We are a biotechnology company developing innovative therapeutics targeting serious viral 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, ABI-5366 (5366) and ABI-1179 (1179); (2) an orally bioavailable hepatitis delta virus (HDV) entry inhibitor, ABI-6250 (6250); 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 antiviral targets. In December 2025, pursuant to our collaboration with Gilead Sciences, Inc. (Gilead and 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

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.”

Previous wording

2025 was a pivotal year for us, as we reported data readouts for 5366, 1179, 6250 and 4334. We also nominated 7272 and advanced it into regulatory-enabling studies. In 2026, we continued to progress each of these investigational product candidates.

Current wording

In the second quarter of 2026, we continued to progress each of our investigational product candidates, 5366, 1179, 6250 and 4334.

Previous wording

4334 – Initiated process to identify potential partners 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; we do not plan to advance 4334 further without a partner.

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 U.S. Food and Drug Administration's (FDA) 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 will be in Gilead’s sole control following completion of the Phase 1a/b studies of 5366 and 1179, which we are managing until they are complete. 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 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.”

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 genital lesion rate, a 94% reduction compared to placebo (p<0.01) 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 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.

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.

Current 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.

Previous wording

The 5366 data reported in August and December 2025 was 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 the Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) in Munich, Germany in April 2026.

Previous wording

In addition to 5366, 1179, a structurally-differentiated HPI with single digit nanomolar potency against HSV-1 and HSV-2 and a nonclinical PK and safety profile to date that is supportive of a potential long-acting treatment by once-weekly oral administration is also in clinical development. 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 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.

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 20 mg/placebo cohort.

Current 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.

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 Phase 2 enabling studies 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 at ESCMID in April 2026.

Current 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.

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 expect to receive Gilead’s development plan and budget for the HPI program and make our decision regarding the Profit-Share (as defined below) by mid-2026. We anticipate Gilead will initiate a Phase 2 clinical study for the HPI program in 2026. 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 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.”

Previous wording

The World Health Organization (WHO) estimates that 254 million people worldwide are chronically infected with HBV as of 2022, and 1.2 million new infections occur each year. HBV is a leading global cause of chronic liver disease and liver transplants, and the WHO estimates that 1.1 million people died in 2022 from HBV, mostly due to cirrhosis and hepatocellular carcinoma. Of the 254 million people living with chronic HBV infection, only approximately 33 million, or 13%, were aware of their infection, and only approximately 7 million, or 3%, of those diagnosed received treatment. HBV is a highly prevalent disease that infects almost three times the number of people infected with hepatitis C virus and HIV infections combined, according to the WHO.

Current wording

The World Health Organization (WHO) estimates that 240 million people worldwide were chronically infected with HBV as of 2024, and 0.9 million new infections occur each year. HBV is a leading global cause of chronic liver disease and liver transplants, and the WHO estimates that 1.1 million people died in 2024 from HBV, mostly due to cirrhosis and hepatocellular carcinoma (primary liver cancer). Of the 240 million people living with chronic HBV infection, only approximately 65 million, or 27%, were aware of their infection, and only approximately 10 million, or 4%, of those diagnosed received treatment. HBV is a highly prevalent disease that infects almost three times the number of people infected with hepatitis C virus and HIV infections combined, according to the WHO.

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 to 72 million HBV infected people. These individuals infected with HDV, which comprise an estimated 4.5% 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 therapy approved is only approved in the European Economic Area (EEA), the UK, Switzerland, Australia and Canada. 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 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.

Previous wording

The current standard of care treatment for HDV is off-label pegylated interferon-α (IFN-α) injected weekly or, in the EEA, the UK, Switzerland, Australia and Canada, a large, complex peptide inhibitor that requires daily injections, bulevirtide. There are no approved HDV treatments in the United States. We believe a safe and effective oral small molecule entry inhibitor would be a significant innovation for people living with HDV, who face a significant and immediate disease burden.

Current wording

The current standard of care treatment for HDV is off-label pegylated interferon-α (IFN-α) injected weekly or, in the EEA, the UK, Switzerland, Australia, Canada and the United States, a large, complex peptide inhibitor that requires daily injections, bulevirtide. We believe a safe and effective oral small molecule entry inhibitor would be a significant innovation for people living with HDV, who face a significant and immediate disease burden.

Previous wording

HDV is a small RNA virus that encodes just two viral proteins and relies on host enzymes as well as the HBsAg from HBV to replicate, which limits the number of HDV-specific antiviral targets. Similar to HBV, HDV utilizes HBsAg to enter hepatocytes by binding the cellular transmembrane protein sodium taurocholate co-transporting peptide (NTCP). NTCP is highly expressed on human hepatocytes, where it serves as one of several proteins involved in the transport of bile acids. The binding of specific small or large molecules to NTCP has been shown to effectively inhibit the interaction of HBsAg with NTCP, which prevents HBV and HDV from infecting hepatocytes.

Current wording

HDV is a small RNA virus that encodes just two viral proteins and relies on host enzymes as well as the HBsAg from HBV to replicate, which limits the number of HDV-specific antiviral targets. Similar to HBV, HDV utilizes HBsAg to enter hepatocytes by binding the cellular transmembrane protein, NTCP. NTCP is highly expressed on human hepatocytes, where it serves as one of several proteins involved in the transport of bile acids. The binding of specific small or large molecules to NTCP has been shown to effectively inhibit the interaction of HBsAg with NTCP, which prevents HBV and HDV from infecting hepatocytes.

Previous wording

The inhibition of HBV and HDV infection by molecules that bind NTCP has been demonstrated in vitro, in animal models and clinically. Notably, bulevirtide, a peptide inhibitor of NTCP, is the only approved therapy for HDV. 6250 has the same clinically-validated MOA as bulevirtide. The binding of NTCP-targeted HBV/HDV entry inhibitors to NTCP has also been shown to inhibit the transport of certain bile acids into cells, which results in plasma elevations of bile acids; this effect has been well-tolerated clinically and may serve as a biomarker of pharmacologically active concentrations of drug in the plasma.

Current wording

The inhibition of HBV and HDV infection by molecules that bind NTCP has been demonstrated in vitro, in animal models and clinically. Notably, bulevirtide, a peptide inhibitor of NTCP, is the only approved therapy for HDV. 6250 has the same clinically-validated MOA as bulevirtide. The binding of HBV/HDV entry inhibitors to NTCP has also been shown to inhibit the transport of certain bile acids into cells, which results in plasma elevations of bile acids; this effect has been well-tolerated clinically and may serve as a biomarker of pharmacologically active concentrations of drug in the plasma.

Previous wording

A Phase 1a clinical study of 6250 was initiated in the fourth quarter of 2024, and in August 2025, we announced interim PK, biomarker and safety data from single-ascending and multiple-ascending doses cohorts in healthy participants. Across the cohorts evaluated to date, a mean half-life of approximately four days was observed for 6250 when dosed orally, supporting the once-daily oral dosing profile target. Given this half-life, accumulation was observed in the multiple-dose cohorts with exposures on the last day of dosing generally reaching six- to seven-fold higher than the exposure seen after the first dose.

Current wording

Top-line clinical data, including PK, biomarker and safety data for the Phase 1a study of 6250 was presented at the European Association for the Study of the Liver Congress that took place in Barcelona, Spain in May 2026. Across all cohorts , a mean half-life of approximately four days was observed for 6250 when dosed orally, supporting the once-daily oral dosing profile target. Given this half-life, accumulation was observed in the multiple-dose cohorts with exposures on the last day of dosing generally reaching six- to eight-fold higher than the exposure seen after the first dose.

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. 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 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.

Previous wording

All participants in the Phase 1a study have completed dosing and follow up. The chronic toxicology studies to enable longer term dosing are complete, and we are preparing for Phase 2 clinical studies, with Phase 2 initiation expected in the fourth quarter of 2026.

Current wording

All participants in the Phase 1a study have completed dosing and follow up. The chronic toxicology studies to enable longer term dosing are complete, and we are preparing for Phase 2 clinical studies, with Phase 2 initiation expected in the fourth quarter of 2026. In addition, we expect to initiate additional Phase 1 pharmacology studies to support labeling anticipated to start in the fourth quarter of 2026.

Previous wording

In March 2026, Gilead declined to either exercise its option to license 4334 or defer its option until completion of Phase 2 studies. As a result, we retain full control of 4334, including the right to evaluate partnering opportunities for 4334 outside of the Gilead Collaboration. We are actively evaluating partnering opportunities for 4334 and have initiated a process to find potential partners. We do not plan to advance 4334 further without a partner.

Current wording

In March 2026, Gilead declined to either exercise its option to license 4334 or defer its option until completion of Phase 2 studies. As a result, we retain full control of 4334, including the right to evaluate partnering opportunities for 4334 outside of the Gilead Collaboration. We are actively evaluating partnering opportunities for 4334 and do not plan to advance 4334 further without a partner.

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 antivirals to treat serious viral diseases.

Current 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.

Previous wording

In October 2023, we entered into an Option, License and Collaboration agreement (the Gilead Collaboration Agreement) with Gilead pursuant to which Gilead (1) exclusively licensed to us its HPI program and its NNPI program, while retaining opt-in rights to these programs, and (2) has an option to take an exclusive license, on a program-by-program basis, to all of our other current and future pipeline programs. During the 12-year collaboration term (subject to payment of certain extension fees) and for a specified period thereafter, Gilead may exercise its opt-in rights, on a program-by-program basis, at one of two timepoints—completion of a certain Phase 1 study or, upon payment of a deferral fee and completion of a certain Phase 2 study for the first product within the program—upon payment of an opt-in fee ranging from $45.0 million to $125.0 million per program depending on the type of program and when the option is exercised. Pursuant to the Gilead Collaboration Agreement, Gilead made an $84.8 million upfront cash payment to us. In December 2024, we and Gilead entered into the First Amendment to the Gilead Collaboration Agreement, which restructured the timing of specific options exercisable and the fees payable to us under the terms of the Gilead Collaboration Agreement due to an agreed upon development plan for 6250. To facilitate this development plan, (1) we received a payment of $10.0 million from Gilead and (2) the opt-in fee payable by Gilead in connection with 6250 was restructured, though it remains in the range of opt-in fees detailed above. The $10.0 million payment received in connection with the First Amendment to the Gilead Collaboration Agreement is creditable towards future collaboration-related payments payable by Gilead. This credit was applied toward Gilead’s opt-in fee paid for the HPI program in December 2025.

Current wording

In October 2023, we entered into an Option, License and Collaboration agreement (the Gilead Collaboration Agreement) with Gilead pursuant to which Gilead (1) exclusively licensed to us its HPI program and its NNPI program, while retaining opt-in rights to these programs, and (2) has an option to take an exclusive license, on a program-by-program basis, to all of our other current and future pipeline programs. During the 12-year collaboration term (subject to payment of certain extension fees) and for a specified period thereafter, Gilead may exercise its opt-in rights, on a program-by-program basis, at one of two timepoints—completion of a certain Phase 1 study or, upon payment of a deferral fee and completion of a certain Phase 2 study for the first product within the program—upon payment of an opt-in fee ranging from $45.0 million to $125.0 million per program depending on the type of program and when the option is exercised. Pursuant to the Gilead Collaboration Agreement, Gilead made an $84.8 million upfront cash payment to us. In December 2024, we and Gilead entered into the First Amendment to the Gilead Collaboration Agreement, which restructured the timing of specific options exercisable and the fees payable to us under the terms of the Gilead Collaboration Agreement due to an agreed upon development plan for 6250. To facilitate this development plan, (1) we received a payment of $10.0 million from Gilead and (2) the opt-in fee payable by Gilead in connection with 6250 was restructured, though it remains in the range of opt-in fees detailed above. The $10.0 million payment received in connection with the First Amendment to the Gilead Collaboration Agreement was creditable towards future collaboration-related payments payable by Gilead and was applied toward Gilead’s opt-in fee paid for the HPI program in December 2025.

Previous wording

As of March 31, 2026, Gilead held (1) approximately 28.4% 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 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.

Previous wording

We remain eligible to receive up to $330 million in regulatory and commercial milestones, as well as tiered royalties on net sales ranging from the high single-digits to low teens. We will also have the right to opt in to share 40% of all costs and profits in the United States (the Profit-Share) in lieu of receiving milestones and royalties for that program in the United States after receipt of a development plan and budget from Gilead.

Current wording

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 whether to exercise our right to opt in to share 40% of all costs and profits in the United States (the Profit-Share) in lieu of receiving milestones and royalties for that program in the United States will be made after receipt and review of Gilead's commercial cost estimates, which will complete the opt-in package. If we opt in to the Profit-Share, we remain eligible to receive up to $280 million in regulatory and commercial milestones, as well as tiered royalties on net sales ranging from the high single-digits to low teens.

Previous wording

Collaboration revenue was $8.2 million for the three months ended March 31, 2026 compared to $9.4 million for the same period in 2025. The $1.2 million decrease reflects the timing of activities performed and progress toward completion of services under the Gilead Collaboration Agreement.

Current 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.

Previous wording

Research and development expenses consist primarily of employee-related expenses, fees paid to contract resource organizations and contract manufacturing organizations, lab supplies and other third-party expenses that support our research and discovery, nonclinical and clinical activities. External program costs represent a significant portion of our research and development expenses, which we track by product candidate once it has been nominated. We use our employee and infrastructure resources, as well as certain third-party costs, across multiple research and development programs, and we do not specifically allocate these costs to our programs.

Current wording

Research and development expenses consist primarily of employee-related expenses, fees paid to contract research organizations and contract manufacturing organizations, lab supplies and other third-party expenses that support our research and discovery, nonclinical and clinical activities. External program costs represent a significant portion of our research and development expenses, which we track by product candidate once it has been nominated. We use our employee and infrastructure resources, as well as certain third-party costs, across multiple research and development programs, and we do not specifically allocate these costs to our programs.

Previous wording

Research and development expenses remained flat at $14.9 million for both the three months ended March 31, 2026 and 2025. Employee-related expenses increased due to higher headcount, annual salary adjustments, and stock-based compensation expense associated with performance-based restricted stock units granted in mid-2025. This increase was partially offset by external program expenses, which mostly decreased due to the completion of clinical trials, partially offset by increases in our research and discovery efforts.

Current 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.

Previous wording

General and administrative expenses were $4.7 million for the three months ended March 31, 2026 compared to $4.5 million for the same period in 2025. The $0.2 million increase was primarily driven by an increase in stock-based compensation expense associated with performance-based restricted stock units granted in mid-2025.

Current 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.

Previous wording

Interest and other income, net was $2.3 million for the three months ended March 31, 2026, compared to $1.1 million for the same period in 2025. The $1.2 million increase was primarily due to a larger portfolio balance following the investment of proceeds from our financing transaction in August 2025, as well as proceeds received from the $35.0 million payment from Gilead for an exclusive license to our HPI program in December 2025.

Current 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.

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 March 31, 2026 principally through equity financings, raising an aggregate of $821.8 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 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.

Previous wording

Cash Flows for the Three Months Ended March 31, 2026 and 2025

Current wording

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

Previous wording

Net cash used in investing activities was $5.4 million for the three months ended March 31, 2026, compared to net cash provided by investing activities of $6.6 million for the same period in 2025. The change was primarily due to our purchases of marketable securities during the current period as we invested excess cash and cash equivalents, including proceeds received in December 2025 from the $35.0 million payment from Gilead for an exclusive license to our HPI program. In contrast, during the prior year, proceeds from maturing securities were primarily used to fund operations.

Current 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.

Previous wording

As of March 31, 2026, we held cash, cash equivalents and marketable securities of $226.6 million. Based on our current operating plan, we believe we have sufficient funds to meet our operating requirements into 2028. 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 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.