This is a clinical research study in which 2 experimental study products either given separately or together are being tested to see if they are safe, and to understand how long they stay in the human body. We hope to learn what kind of side effects one may experience after receiving the study product(s). The two study products being tested are called 3BNC117-LS-J and 10-1074-LS-J. They are human antibodies against HIV that have been made in a laboratory. HIV is the virus that causes Acquired Immunodeficiency Syndrome (AIDS). Scientists are hoping that one day, these antibodies can be used to help prevent HIV infection in people

This is a Phase 1/2 study to evaluate the safety and tolerability of two broadly neutralizing monoclonal human antibodies (bNAbs), 3BNC117-LS-J, which targets the CD4 binding site on HIV-1 envelope protein, and 10-1074-LS-J which targets the V3 loop of HIV-1 envelope protein. The hypothesis is that the two antibodies will be safe for healthy American and African adults when co-administered subcutaneously or intravenously and, after subcutaneous administration in the optimal ratio, each antibody will maintain trough serum levels >10 µg/ml at steady state. Primary Objectives 1.To evaluate the safety and tolerability of two broadly neutralizing monoclonal human antibodies, 3BNC117-LS-J and 10-1074-LS-J, when given alone and in combination, intravenously (IV) or subcutaneously (SC) to healthy American and African adults. 2.To evaluate the pharmacokinetic profile of two broadly neutralizing monoclonal human antibodies, 3BNC117-LS-J and 10-1074-LS-J, when given alone or in combination, IV or SC to healthy American and African adults. 3.To identify a regimen of the two antibodies that, when given SC every 3 months, will maintain a trough level of > 10 µg/ml for each antibody in >80% of study population. Secondary Objectives 1.To evaluate the effect of participant characteristics (e.g. sex, body weight or body mass index ) on pharmacokinetic parameters. 2.To conduct pharmacokinetic modelling to assess the effect of dose, dose ratio, dosing frequency and loading dose on serum trough levels of each antibody. 3.To assess the incidence and titers of anti-drug antibodies (ADA) against each antibody