Switching From a Tenofovir Disoproxil Fumarate (TDF) Containing Regimen to Elvitegravir/Cobicistat/Emtricitabine/ Tenofovir Alafenamide (E/C/F/TAF) Fixed-Dose Combination (FDC) in Virologically-Suppressed, HIV-1 Infected Adults Aged ≥ 60 Years

Key Inclusion Criteria: * Currently receiving a TDF and FTC or 3TC-containing 'backbone' (maximum 2 NRTIs) regimen plus a third agent for ≥ 6 consecutive months prior to screening visit. For individuals with 3 or more ART regimens, a regimen history must be provided for approval by the Sponsor. Refer to assigned interventions for allowed third agents of the current regimen. * Documented plasma HIV-1 RNA levels \< 50 copies/mL for ≥ 6 months preceding the screening visit (measured at least twice using the same assay). In the preceding 6 months prior to screening, one episode of "blip" (HIV-1 RNA \> 50 and \< 400 copies/mL) is acceptable, only if HIV-1 RNA is \< 50 copies/mL immediately before and after the "blip". * Plasma HIV-1 RNA level \< 50 copies/mL at screening visit * Adequate renal function * Estimated glomerular filtration rate ≥ 30 mL/min according to the Cockcroft-Gault formula (eGFRCG) and are on ARVs that are appropriately dose adjusted for renal function per package insert * All documented historical plasma genotype(s) must not show resistance to TDF or FTC, including, but not limited to the presence of reverse transcriptase resistance mutations K65R, K70E, M184V/I, or thymidine analog-associated mutations (TAMs) that include M41L, L210W, D67N, K70R, T215Y/F, K219Q/E/N/R. If historical plasma prior to first ART is not available or individual has 3 or more ART regimens, individuals will have proviral genotype analysis prior to Day 1 to confirm absence of archived resistance to TDF or FTC. * Study performed dual energy x-ray absorptiometry (DXA) scan and T-score received prior to Day 1 Key Exclusion Criteria: * Previous use of any approved or experimental integrase strand transfer inhibitor (INSTI) (for any length of time) if the current regimen contains a PI/r * Individuals will have no evidence of previous virologic failure on a PI/r or INSTI-based regimen (with or without resistance to either class of ARV) * A new AIDS-defining condition diagnosed within the 30 days prior to screening (except CD4+ cell count and/or percentage criteria) * Hepatitis C virus that would require therapy during the study * Individuals receiving ongoing treatment for bone disease (eg, osteoporosis), including bisphosphonates, denosumab, and strontium ranelate Note: Other protocol defined Inclusion/ Exclusion criteria may apply.