Characterization of Early Viral Populations in Infants Acquiring HIV Through Perinatal and Breastmilk Transmission: A Review of what is Currently Known and the Gaps that Need to be Addressed to Guide Passive HIV Immunization of Breastfeeding Infants.

Newborns represent only 1% of the population. Yet, HIV vertical transmissions represent 10% of all new infections globally, even though antiretroviral therapy (ART) has been shown to reduce the risk of vertical transmission to less than 2%. While vaccines still represent the most efficient and cost-effective intervention to eradicate new infections, HIV immunogens that can effectively elicit broad-spectrum protection are still at least a decade away. In contrast, passive immunization with broadly neutralizing antibody (bnAb) combinations has the potential to provide a more immediate pathway to HIV prophylaxis. Early-phase infant trials are underway to establish the safety and pharmacokinetics of bnAb combinations selected for their potency against viruses acquired via adult transmissions. However, the specific characteristics and phenotypic differences of vertically transmitted viruses in infants compared to those in adults remain uncertain, including their susceptibility to known broadly neutralizing antibodies (bnAbs). We review the current knowledge of vertically transmitted HIV viruses, including their genetics and phenotypic features. Differences in immunity between adults and infants lead us to hypothesize that distinct selection and evolutionary pressures act on the virus at the time of transmission and during the early phases of infection, and these may in turn affect the choice of bnAb combinations needed for protection against vertical transmission of HIV.