This is a Phase 1 study to evaluate the safety, tolerability, pharmacokinetics and anti-viral efficacy of the PGDM1400 and PGT121 mAbs for HIV prevention and therapy. PGDM1400 mAb and PGT121 mAb are recombinant human IgG1 monoclonal antibodies that target a V1V2 (PGDM1400) and a V3 glycan-dependent (PGT121) epitope region of the HIV envelope protein (Jardine, Julien et al. 2013, Sok, Doores et al. 2014). PGT121 and PGDM1400 mAb were chosen for this study because they are potent, neutralize a wide array of HIV viruses, and can prevent and treat simian-human immunodeficiency virus (SHIV) in rhesus monkeys.