Serum samples for PK (pharmacokinetic) measurements will be collected before the start of the first mAb infusion. Peak PK sampling for 3BNC117 will occur following the completion of the 3BNC117 infusion and prior to the start of the 10-1074 infusion. Peak PK sampling for 10-1074 will occur following the completion of the 10-1074 infusion. Additional samples for PK assessments will be collected at multiple time points during study follow up.