A Study to Evaluate Efficacy, Safety and Tolerability in Antiretroviral Therapy (ART)-Experienced Participants of at Least 50 Years of Age Living With Human Immunodeficiency Virus (HIV) With Virologic Suppression Who Switch to DTG/3TC FDC From BIC/FTC/TAF

Inclusion criteria

• Participants living with HIV-1 and had documented plasma HIV-1 RNA <50 c/mL within 3 months prior to Screening.
• Participants had been on uninterrupted ART for ≥1 year (except for brief periods [less than 30 days] where all ART had been stopped due to tolerability and/or safety concerns).
• Participants had been on uninterrupted BIC/FTC/TAF for at least 6 months prior to Screening.
• Participants had plasma HIV-1 RNA <50 c/mL at Screening.
• Participants had no known prior regimen switches due to documented virologic failure (defined as a confirmed plasma HIV-1 RNA ≥200 c/mL).
• Participants with unknown full treatment/clinical history beyond 5 years prior to Screening may have been eligible upon discussion and agreement with the medical monitor.

Exclusion criteria

• Women participants were pregnant or breastfeeding or planned to become pregnant or breastfeed during the study.
• Participants had any evidence of an active Centers for Disease Control and Prevention (CDC) Stage 3 disease, EXCEPT cutaneous Kaposi's sarcoma not requiring systemic therapy. Historical or current CD4 cell counts less than 200 cells/cubic millimetre (mm^3) were not exclusionary.
• Participants had signs and symptoms which, in the opinion of the investigator, were suggestive of active severe acute respiratory syndrome-related coronavirus (SARS-CoV-2) infection within 14 days prior to enrolment.
• Participants had severe hepatic impairment (Class C) as determined by Child-Pugh classification.
• Evidence of hepatitis B virus (HBV) infection was based on the results of testing at Screening for hepatitis B surface antigen (HBsAg), hepatitis B core antibody (anti-HBc), hepatitis B surface antibody (anti-HBs) and HBV deoxyribonucleic acid (DNA) as follows:

• Participants positive for HBsAg were excluded;
• Participants negative for anti-HBs but positive for anti-HBc (negative HBsAg status), whether negative or positive for HBV DNA, were excluded;
• Participants positive for anti-HBc (negative HBsAg status) and positive for anti-HBs (past and/or current evidence) were immune to HBV and were not excluded.
• Participants had unstable liver disease (as defined by any of the following: presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or gastric varices, or persistent jaundice or cirrhosis), known biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones or otherwise stable chronic liver disease per investigator assessment).
• Participants had a history of liver cirrhosis with or without hepatitis viral co-infection.
• Participants had untreated syphilis infection (positive rapid plasma reagin [RPR] at Screening without clear documentation of treatment). Participants who were at least 7 days post completed treatment were eligible.
• Participants had a history or presence of allergy or intolerance to the study treatment or their components or drugs of their class or a history of drug or other allergy that, in the opinion of the investigator or Medical Monitor, contraindicated their participation.
• Participants had ongoing malignancy other than cutaneous Kaposi's sarcoma, basal cell carcinoma, or resected, non-invasive cutaneous squamous cell carcinoma, or cervical, anal or penile intraepithelial neoplasia.
• Participants who, in the investigator's judgment, posed a significant suicidality risk. Participant's history of suicidal behavior and/or suicidal ideation was considered when evaluating for suicide risk.
• Participants had any evidence of any major 3TC resistance associated mutations (M184V/I and/or K65R and/or MDR) or presence of any major Integrase strand transfer inhibitor (INSTI) resistance associated mutation in any available prior resistance genotype assay test result. All available historical resistance reports with HIV-1 reverse transcriptase or integrase genotypic data were provided to ViiV after screening and before enrollment for review by ViiV Virology.
• Participants had any verified Grade 4 laboratory abnormality with the exception of Grade 4 lipid abnormalities.

Alanine aminotransferase (ALT) was ≥5 times the upper limit of normal (ULN) or ALT was ≥3×ULN and bilirubin was ≥1.5×ULN (>35% direct bilirubin).

• Participants had estimated creatine clearance <30 mL/min per 1.73 square meter (m^2) using the refitted, race-neutral Chronic Kidney Disease Epidemiology Collaboration (CKD-EPIcr_R) method.