A Study to Investigate the Use of VH3810109 With or Without Fostemsavir (FTR) to Reduce the Size and Activity of the Viral Reservoir in People Living With HIV

Inclusion Criteria: * Age between 18 years and 70 years old at the time of obtaining informed consent. * Persons of any sex or gender are eligible. Note: Participants of childbearing potential (POCBP) are eligible to participate if not pregnant, not lactating, and agreeing to adhere to study requirements for use of contraception and pregnancy avoidance. * Participant has a documented diagnosis of HIV-1 infection Note: Participants in Population 1 must have a documented positive HIV antibody result available for Screening. Population 1 only: * Plasma HIV-1 RNA \>=2000 copies/milliliter (c/mL) at Screening. * CD4+ T cell count \>=300 cells/microliter (μL) at Screening. * Antiretroviral treatment naïve, defined as no exposure to ART after a diagnosis of HIV-1 infection, prior to enrollment. Population 2 only: * Participant is stably virologically suppressed (plasma HIV-1 RNA \<50 c/mL). * Documented evidence of uninterrupted treatment with oral non-boosted INSTI-based ART for at least 6 months prior to Screening, as well as uninterrupted treatment with ART (any guideline-recommended oral regimen) for at least 24 months prior to Screening. * CD4+ T cell count \>=450 cells/μL at Screening. * Body weight \>=50 kg to \<=115 kg. * Participant is capable of giving written informed consent, which includes adherence to the requirements and restrictions listed in the consent form and in the protocol. Exclusion Criteria: CONCURRENT MEDICAL CONDITIONS \& MEDICAL HISTORY * Participa…