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

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.