July 22, 2026 – Gilead Sciences and Merck (known as MSD outside the United States and Canada) have announced encouraging Phase 3 results for their investigational once-weekly oral HIV treatment regimen combining islatravir and lenacapavir (ISL/LEN). The findings, which will be presented at the 26th International AIDS Conference (AIDS 2026), showed that the once-weekly single-tablet regimen maintained virological suppression through 48 weeks in adults living with HIV who switched from standard daily antiretroviral therapy.

The results come from the ISLEND-1 and ISLEND-2 Phase 3 clinical trials, which evaluated the safety and efficacy of the investigational regimen in adults whose HIV was already virologically suppressed on existing treatment. According to the companies, the data will support future regulatory submissions.

If approved, ISL/LEN could become the first once-weekly oral treatment for HIV, offering an alternative to daily antiretroviral therapy and expanding treatment options for people living with the virus.

In the ISLEND-1 study, participants who switched from BIKTARVY® to the once-weekly regimen maintained virological suppression at rates comparable to those who continued their daily treatment. None of the participants receiving ISL/LEN had HIV-1 RNA levels of 50 copies/mL or higher at Week 48, compared with 0.3% of those who remained on BIKTARVY.

Similarly, the ISLEND-2 trial demonstrated that the once-weekly regimen was non-inferior to other standard daily oral antiretroviral therapies. Only 0.3% of participants receiving ISL/LEN experienced virological rebound at Week 48, compared with 1.3% of those continuing standard-of-care treatment.

Across both studies, the investigational regimen demonstrated a safety profile broadly comparable to existing therapies, with no new safety concerns identified. The most commonly reported treatment-related adverse events included headache, nausea and diarrhoea, while discontinuation rates due to adverse events remained low. CD4+ T-cell and lymphocyte counts remained stable throughout the 48-week follow-up period.

Participants who switched to the once-weekly regimen also reported greater treatment satisfaction and a lower treatment burden compared with those taking daily oral HIV medications, according to patient-reported outcomes collected during the studies.

The investigational therapy combines islatravir, Merck's next-generation nucleoside analogue, with lenacapavir, Gilead's first-in-class HIV capsid inhibitor. Together, the two medicines are designed to provide sustained antiviral activity that enables once-weekly dosing.

Although the findings are promising, the combination of islatravir and lenacapavir remains investigational and has not yet been approved by regulatory authorities. There is currently no cure for HIV or AIDS, and antiretroviral therapy remains the standard approach for long-term viral suppression.

The detailed Phase 3 results will be presented during late-breaking sessions at AIDS 2026 on 29 July 2026.