A Study of GS-3242 in Combination With Lenacapavir Versus Biktarvy in Virologically Suppressed People With HIV-1

The study will have two parts: Part A and Part B. In Part A, the goal of the study is to compare the effectiveness of switching to the study drugs GS-3242 plus Lenacapavir (LEN) versus continuing Biktarvy (bictegravir/emtricitabine/tenofovir alafenamide (B/F/TAF)), in virologically suppressed people with HIV-1 (PWH) in treatment Group 1, 2 and 3 at Week 35. In Part B the goal of the study is to compare the effectiveness of switching to the study drugs, GS-3242 and LEN versus continuing B/F/TAF in Groups 4 and 3 at Week 26. The primary objective of part A is to evaluate the efficacy of switching to intramuscular (IM) GS-3242 plus IM LEN versus continuing on B/F/TAF PWH who are virologically suppressed in treatment Groups 1, 2, and 3 at Week 35 and Part B is to evaluate the efficacy of switching to IM GS-3242 plus IM LEN versus continuing on B/F/TAF in PWH who are virologically suppressed in Treatment Groups 4 and 3 at Week 26.

Key Inclusion Criteria: * Documented human immunodeficiency virus type 1 (HIV-1) ribonucleic acid (RNA) \< 50 copies/mL for ≥ 6 months before screening. * Plasma HIV-1 RNA levels \< 50 copies/mL at screening. * Receiving bictegravir/emtricitabine/tenofovir alafenamide (coformulated; Biktarvy®) (B/F/TAF) for ≥ 6 months prior to screening. * No documented resistance to GS-3242 (integrase mutation Q148H/K/R plus at least 2 of the following integrase mutations: L74I/M, T97A, E138A/K/T, or G140A/C/S). Key Exclusion Criteria: * Prior use of, or exposure to GS-3242 or LEN. * History of virologic failure while on an integrase strand transfer inhibitor (INSTI)-based regimen. * Prior use of any long-acting parenteral antiretroviral therapy (ART) medications such as monoclonal antibodies or broadly neutralizing antibodies targeting HIV-1, injectable cabotegravir (including oral cabotegravir lead-in), or injectable rilpivirine. Note: Other protocol defined Inclusion/Exclusion criteria may apply.