Efficacy of Tenofovir Alafenamide Versus Placebo Added to a Failing Regimen Followed by Treatment With Elvitegravir/Cobicistat/Emtricitabine/Tenofovir Alafenamide Plus Atazanavir in HIV-1 Positive, Antiretroviral Treatment-Experienced Adults

The primary objective of this study is to evaluate the efficacy of tenofovir alafenamide (TAF) versus placebo, each administered with the existing, failing antiretroviral (ARV) regimen. There are 2 parts to this study: Part 1 and Part 2. Part 1 consists of 2 cohorts, starting with a sentinel cohort, in which participants will be enrolled to receive open-label TAF in addition to their current failing ARV regimen. This cohort will then be followed by a randomized, double-blind, cohort to compare the addition of TAF or placebo in HIV-1 positive adults who are failing their current ARV regimen. In Part 2, all participants who complete Part 1 of the study will discontinue their failing ARV regimen and TAF or placebo for a 14-day washout period. Following the washout period, all participants who received TAF in Part 1 and have a \> 0.5 log10 decline in HIV-1 RNA will receive elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide (E/C/F/TAF) single-tablet regimen (STR) plus atazanavir (ATV) once daily for 48 weeks. Participants who received TAF who have a ≤ 0.5 log10 decline in HIV-1 RNA will be discontinued from the study and will not be eligible to continue into Part 2 of the study. All participants who received placebo in Part 1 will be eligible to participate in Part 2 regardless of their viral load change. After completion of Part 2, all participants will be eligible to continue to receive E/C/F/TAF plus ATV in the extension phase until E/C/F/TAF becomes commercially available, or until Gilead Sciences terminates development of E/C/F/TAF in the applicable country.