Key Inclusion Criteria:

Cohort 1 (treatment-experienced switch)

   - Must not have a history of known resistance to elvitegravir (EVG), tenofovir
   disoproxil fumarate (TDF), or emtricitabine (FTC)

   - Plasma HIV-1 RNA concentrations (at least two measurements) at undetectable levels
   (according to the local assay being used) in the 6 months preceding the screening
   visit and have HIV-1 RNA < 50 copies/mL at screening

   - Estimated glomerular filtration rate (GFR) 30-69 mL/min according to the
   Cockcroft-Gault formula for creatinine clearance, using actual weight

   - May be currently enrolled in Gilead studies GS-US-236-0102, GS-US-236-0103, and
   GS-US-216-0114, but will be eligible to enroll only after the Week 144 visit for that
   study is complete; or currently receiving Stribild® (STB) or atazanavir
   (ATV)/cobicistat (COBI) + Truvada (TVD) in Gilead studies GS-US-236-0104 or
   GS-US-216-0105, but will be eligible to enroll only after the Week 48 visit for that
   study is complete.

Cohort 2 (treatment-naive)

   - Plasma HIV-1 RNA levels ≥ 1,000 copies/mL at screening

   - Screening genotype report provided by Gilead Sciences must show sensitivity to EVG,
   FTC, and TDF

   - No prior use of any approved or investigational antiretroviral drug for any length of
   time, except the use for pre-exposure prophylaxis (PrEP), or post-exposure prophylaxis
   (PEP), up to 6 months prior to screening

   - Estimated GFR 30-69 mL/min according to the Cockcroft Gault formula for creatinine
   clearance, using actual weight

All Cohorts:

All individuals must meet all of the following inclusion criteria to be eligible for
participation in this study:

   - The ability to understand and sign a written informed consent form, which must be
   obtained prior to initiation of study procedures

   - CD4+ count of ≥ 50 cells/μL

   - Stable renal function: serum creatinine measurements to be taken at least once (within
   three months of screening)

   - Cause of underlying chronic kidney disease (eg hypertension, diabetes) stable, without
   change in medical management, for 3 months prior to baseline

   - Normal electrocardiogram (ECG)

   - Hepatic transaminases (AST and ALT) ≤ 5 x upper limit of normal (ULN)

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

   - Adequate hematologic function

   - Serum amylase ≤ 5 x ULN

   - Females of childbearing potential must agree to utilize highly effective contraception
   methods (two separate forms of contraception, one of which must be an effective
   barrier method, or be non-heterosexually active, practice sexual abstinence) from
   screening throughout the duration of study treatment and for 30 days following the
   last dose of study drug

   - 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 throughout the study period and for 30 days following
   discontinuation of investigational medicinal product. A highly effective method of
   contraception is defined as two separate forms of contraception, one of which must be
   an effective barrier method, or males must be non-heterosexually active, or practice
   sexual abstinence

Key Exclusion Criteria:

   - A new AIDS-defining condition (excluding CD4 cell count and percentage criteria)
   diagnosed within the 30 days prior to screening,with the exception of the first two
   bullet points

   - Hepatitis C virus (HCV) antibody positive. Individuals who are HCV positive, but have
   a documented negative HCV RNA, are eligible

   - Hepatitis B surface antigen (HBVsAg) positive

   - Individuals receiving drug treatment for Hepatitis C, or individuals who are
   anticipated to receive treatment for Hepatitis C during the course of the study

   - Individuals experiencing decompensated cirrhosis (eg, ascites, encephalopathy, etc.)

   - Females who are breastfeeding

   - Positive serum pregnancy test

   - Have an implanted defibrillator or pacemaker

   - Current alcohol or substance use judged by the Investigator to potentially interfere
   with study compliance

   - A history of malignancy within the past 5 years or ongoing malignancy other than
   cutaneous Kaposi's sarcoma, basal cell carcinoma, or resected, non-invasive cutaneous
   squamous carcinoma

   - Active, serious infections (other than HIV-1 infection) requiring parenteral
   antibiotic or antifungal therapy within 30 days prior to baseline

   - Individuals on hemodialysis, other forms of renal replacement therapy, or on treatment
   for underlying kidney diseases (including prednisolone and dexamethasone)

   - Individuals receiving ongoing therapy with any medications not to be used with EVG,
   COBI, FTC, or TAF or individuals with any known allergies to the excipients of
   E/C/F/TAF

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