Antibody-mediated prevention of vaginal HIV transmission is dictated by IgG subclass in humanized mice
HIV broadly neutralizing antibodies (bNAbs) are capable of both blocking viral entry and recruiting innate immunity to HIV-infected cells through their fragment crystallizable (Fc) region. Vaccination or productive infection results in a polyclonal mixture of class-switched IgG antibodies comprised of four subclasses, each encoding distinct Fc regions that differentially engage innate immune functions. Despite evidence that innate immunity contributes to protection, the relative contribution of individual IgG subclasses is unknown. Here we use vectored immunoprophylaxis (VIP) in humanized mice to interrogate the efficacy of individual IgG subclasses during prevention of vaginal HIV transmission by VRC07, a potent CD4-binding site directed bNAb. We find that VRC07-IgG2, which lacks Fc-mediated functionality, exhibits significantly reduced protection in vivo relative to other subclasses. However, even low concentrations of highly functional VRC07-IgG1 yields substantial protection against vaginal challenge, suggesting that interventions capable of eliciting modest titers of functional subclasses may provide meaningful benefit against infection.