A Study to Assess Change in Disease Activity, Adverse Events, and How the Drug Moves Through the Body in Adult Participants Living With Human Immunodeficiency Virus (HIV) Receiving Intravenous (IV) Infusion or Subcutaneous (SC) Injection of Budigalimab and/or ABBV-382

Human immuno-deficiency virus (HIV) is the virus that causes Acquired Immuno-Deficiency Syndrome (AIDS). HIV disease is considered to be a chronic disease requiring lifelong therapy. The purpose of this study is to assess change in disease activity, adverse events, tolerability, and how the drug moves through the body.

Budigalimab and ABBV-382 are investigational drugs being developed for the treatment of HIV disease. In Part 1, participants are placed in 1 of 5 groups, called treatment arms. Each group receives a different treatment. There is a 1 in 7 chance that participants will be assigned to placebo (A placebo is not a drug and it is not expected to have any chemical effects on your body and it is not designed to treat any disease or illness). In Part 2, eligible participants will be placed in an open-label arm to receive Budigalimab. Approximately 160 adult participants living with HIV disease on stable antiretroviral therapy (ART) willing to undergo Analytical Treatment Interruption (ATI) will be enrolled at approximately 90 sites worldwide.

In Part 1, participants will receive 4 doses of intravenous (IV) budigalimab or placebo combined with 3 doses of IV ABBV-382 or placebo for an 8 week dosing period. In Part 2, participants will receive 4 doses of open-label subcutaneous (SC) Budigalimab for a 6 week dosing period. Participants need to be stable on antiretroviral therapy to participate in the study. If participant qualifies to the study, on the day they receive the first injection, participants will be asked to stop antiretroviral medications (also referred to as analytical treatment interruption or ATI) for 112 weeks or until meeting specific criteria to restart antiretroviral medications. Participants will undergo a closely monitored ART interruption. Protocol-defined ART restart criteria includes participant's request. Participants will be followed for up to approximately 112 weeks.

There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. There will be an option for virtual or home health visits for some of the follow-up visits. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.