The primary purpose of this study is to assess safety, tolerability of the different vaccine schedules (different regimen durations and different number of dose administrations) with Ad26.Mos.HIV and Clade C Glycoprotein (gp) 140 and to assess Envelope (Env)-binding Antibody (Ab) responses of the different vaccine schedules.

This is a phase 1 single-center, randomized (the study drug is assigned by chance), parallel group (each group of participants will be treated at the same time), placebo-controlled (study in which the experimental treatment or procedure is compared to a pretend treatment with no drug in it to test if the drug has a real effect), and double-blind (neither physician nor participant knows the treatment that the participant receives) study. Participants will be randomized in to 3 groups and will receive study vaccines or placebo. Group 1 will have 4 vaccination time points during 48 weeks, Groups 2 and 3 will have 3 vaccination time points during 24 weeks. The study comprises a Screening Period (up to 4 weeks), a Vaccination Period (maximum 48 weeks), and a Follow-up Period (up to 72 weeks). Participants' safety will be monitored throughout the study. An optional Long-term Extension (LTE) phase (approximately 1 year after Week 72) will be performed for participants randomized to receive study vaccine, who have received all planned vaccinations and are negative for HIV infection at Week 72. The duration of the participation will be approximately 124 weeks for participants participating to the optional LTE phase.

Inclusion Criteria:

• Each participant must sign an informed consent form (ICF) indicating that he or she understands the purpose of and procedures required for the study and is voluntarily willing to participate in the study
• Participant must be healthy on the basis of physical examination, medical history, electrocardiogram (ECG), and vital signs measurement performed at Screening
• Participants are negative for Human Immunodeficiency Virus (HIV) infection at Screening
• All female participants of childbearing potential must have a negative serum pregnancy test (beta human chorionic gonadotropin [beta hCG]) at the Screening visit, and a negative urine pregnancy test pre-dose on Day 1
• Participants are willing/able to adhere to the prohibitions and restrictions specified in the protocol and study procedures

Exclusion Criteria:

• Participant has chronic hepatitis B or active hepatitis C, active syphilis infection, chlamydia, gonorrhea, or trichomonas . Active syphilis documented by serology unless positive serology is due to past treated infection
• In the 12 months prior to randomization, participant has a history of newly acquired herpes simplex virus type 2, syphilis, gonorrhea, non-gonococcal urethritis, chlamydia, pelvic inflammatory disease, trichomonas, mucopurulent cervicitis, epididymitis, proctitis, lymphogranuloma venereum, chancroid, or hepatitis B
• Participant has any condition for which, in the opinion of the investigator, participation would not be in the best interest of the participant (example, compromise the well-being) or that could prevent, limit, or confound the protocol-specified assessments
• Participant has had major surgery within 4 weeks prior to Screening or planned major surgery through the course of the study
• Participant has had a thyroidectomy or active thyroid disease requiring medication during the last 12 months