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.

Key Inclusion Criteria:

• Ability to understand and sign a written informed consent form, which must be obtained prior to initiation of study procedures

• Currently taking a failing ARV regimen

• Plasma HIV-1 RNA ≥ 500 copies/mL but ≤ 100,000 copies/mL at screening

• Normal ECG

• Estimated glomerular filtration rate (eGFR) ≥ 50 mL/min according to the Cockcroft-Gault formula for creatinine clearance

• Alanine aminotransferase (AST)/aspartate aminotransferase (AST) ≤ 5 × the upper limit of the normal range (ULN)

• Total bilirubin ≤ 1.5 mg/dL, or normal direct bilirubin

• Adequate hematologic function

• Serum amylase ≤ 5 × ULN

• Females may enter the study if it is confirmed that she is:

  • Not pregnant or nursing

  • Of non-childbearing potential (ie, have had a hysterectomy, both ovaries removed, medically documented ovarian failure, or are postmenopausal women > 54 years of age with cessation [for ≥ 12 months] of previously occurring menses), or

  • Of childbearing potential and agrees to utilize highly effective contraception methods or be non-heterosexually active or practice sexual abstinence from screening throughout the duration of study treatment and for 30 days following study drug dosing

    • Females who utilize hormonal contraceptive as one of their birth control methods must have used the same method for at least three months prior to study dosing.

• Males must agree to utilize a highly effective method of contraception during heterosexual intercourse or be non-heterosexually active, or practice sexual abstinence from first dose throughout the study period and for 30 days following the last study drug dose.

• Males must agree to refrain from sperm donation from first dose until at least 30 days after the last study drug dose.

Key Exclusion Criteria:

• A new AIDS-defining condition diagnosed within the 30 days prior to screening
• Hepatitis B surface antigen (HBsAg) positive
• Hepatitis C antibody positive (individuals with positive hepatitis C virus (HCV) antibody and without detectable HCV RNA are permitted to enroll)
• History of integrase inhibitor use
• Screening or historical genotype reports shows Q151M or T69ins or more than 3 TAMs.
• Screening or historical genotype report shows resistance to integrase inhibitors
• Individuals experiencing decompensated cirrhosis
• Current alcohol or substance use
• History of malignancy within the past 5 years (prior to screening) or ongoing malignancy other than cutaneous Kaposi's sarcoma (KS), basal cell carcinoma, or resected, non-invasive cutaneous squamous carcinoma. Individuals with cutaneous KS are eligible, but must not have received any systemic therapy for KS within 30 days of Part 1, Day 1 and must not be anticipated to require systemic therapy during the study.
• Active, serious infections (other than HIV-1 infection) requiring parenteral antibiotic or antifungal therapy within 30 days prior to Part 1, Day 1
• Any other clinical condition or prior therapy that would make the individual unsuitable for the study or unable to comply with dosing requirements
• Participation in any other clinical trial (including observational trials) without prior approval from the sponsor is prohibited while participating in this trial
• Receiving ongoing therapy with any disallowed medications, including any drugs not to be used with elvitegravir, cobicistat, emtricitabine and tenofovir alafenamide or known allergies to the excipients of E/C/F/TAF STR

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Qualified external researchers may request IPD for this study after study completion. For more information, please visit our website at http://www.gilead.com/research/disclosure-and-transparency.

18 months after study completion

A secured external environment with username, password, and RSA code.

Part 1 Sentinel Cohort: Open-label, non-randomized Part 1 Randomized Cohort: Double-blind, randomized Part 2: Open-label, non-randomized