Evaluating the Safety and Immunogenicity of EnvSeq-1 and CH505 M5 gp120 Envs Adjuvanted With GLA-SE in Healthy, HIV-Uninfected Adults

This study will evaluate the safety, tolerability, and immunogenicity of EnvSeq-1 and CH505 M5 gp120 Envs adjuvanted with GLA-SE in healthy, HIV-uninfected adults. The three individual EnvSeq-1 HIV vaccine Envs used in this study are called CH505TF gp120, CH505w53 gp120, and CH505w78 gp120. This study will take place in two parts: Part A and Part B. Participants in Part A will be randomly assigned to one of four groups. Participants in each group will receive CH505TF (admixed with GLA-SE) or placebo by intramuscular (IM) injection at Months 0, 2, 4, 8, and 12. Study researchers will evaluate participant data from Part A of the study prior to enrolling participants into Part B of the study. Researchers will also evaluate data from Part A to determine the dosing for Part B. Participants in Part B will be randomly assigned to one of four groups. Participants in each group will receive IM injections at Months 0, 2, 4, 8. GLA-SE will be admixed with all the CH505 gp120 vaccines. Part B, Group 5 will follow a sequential approach to EnvSeq-1 vaccine administration with administration of the CH505TF vaccine at Month 0, then CH505w53 at Month 2, and CH505w78 at Months 4, and 8. Part B, Group 6 participants will follow an additive approach to EnvSeq-1 administration with administration of the CH505TF vaccine at Month 0; then the CH505TF and CH505w53 vaccines at Month 2; then the CH505TF, CH505w53 and CH505w78 vaccines at Month 4; then the CH505w53 and CH505w78 vaccines at Month 8. Part B, Group 7 participants will receive CH505 M5 at Months 0, 2, 4, and 8. Part B, Group 8 participants will receive placebo injections at each time point. Additional study visits will occur through Month 18 for participants in Part A and through Month 14 for participants in Part B. Visits may include physical examinations and clinical assessments; blood, urine, and stool collection; HIV testing; risk reduction counseling; and interviews/questionnaires. Study staff will contact participants for follow-up health monitoring at Month 24 for participants in Part A and at Month 20 for participants in Part B. Part C will be an open-label study arm using the EnvSeq-1 proteins in sequential administration (CH505TF, CH505w53, and CH505w78 gp120s) at the same dose as in Part B (400 mcg) to allow for in-depth analysis of B cell precursor frequency.