A Study of Safety and Drug Levels of ePGT121v1-LS, PGDM1400LS, and VRC07-523LS in Adult Participants Without HIV-1

This study is testing a lab-made antibody called ePGT121v1-LS that targets a specific part of HIV. Researchers will give it by vein (IV) and under the skin (SC), both on its own and together with two other antibodies, VRC07-523LS and PGDM1400LS, which target different parts of the virus. They will assess safety and side effects, determine the right dose, study how the body processes the drug (pharmacokinetics or PK), and measure how well it neutralizes HIV in the blood (serum neutralizing activity). The expectation is that ePGT121v1-LS, whether given alone or with PGDM1400LS and VRC07-523LS, by IV or SC, will be safe in generally healthy adults and that the antibodies will not interfere with each other when used together. Approximately 83 volunteers in overall good health and without HIV-1 will be enrolled into two parts (A and B). Part A has six groups. In Groups 1-3, participants will get ePGT121v1-LS given by IV at one of three dose levels: 5 mg/kg, 20 mg/kg, or 40 mg/kg. In Groups 4-6, participants will receive three antibodies-first ePGT121v1-LS, then PGDM1400LS and VRC07-523LS-given by IV at two separate visits that are 24 weeks apart. The total study duration for participants in Part A is 48 weeks of scheduled clinic visits. Part B has two groups. In Group 7, people will get ePGT121v1-LS as SC shots at two visits 12 weeks apart. Each visit will give a total of 375 mg, split into three injections of 125 mg each. In Group 8, people will also have two visits 12 weeks apart and will receive three antibodies as SC shots in this order: first ePGT121v1-LS (125 mg), then PGDM1400LS (100 mg), and then VRC07-523LS (100 mg). The total study duration for participants in Part B is 24 weeks of scheduled clinic visits.