Maternal Fc-mediated non-neutralizing antibody responses correlate with protection against congenital human cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common congenital infection and a leading cause of stillbirth, neurodevelopmental impairment, and pediatric hearing loss worldwide. Development of a maternal vaccine or therapeutic to prevent congenital infection has been hindered by limited knowledge of the immune responses that protect against placental HCMV transmission in maternal primary and nonprimary infection. To identify protective antibody responses, we measured anti-HCMV IgG binding and anti-viral functions in maternal and cord blood sera from HCMV transmitting (n=41) and non-transmitting (n=40) mother-infant dyads identified via a large U.S.-based public cord blood bank. In a predefined immune correlate analysis, maternal monocyte-mediated antibody-dependent cellular phagocytosis (ADCP) and high avidity IgG binding to HCMV envelope glycoproteins were associated with decreased risk of congenital HCMV infection. Moreover, HCMV-specific IgG engagement of Fc{gamma}RI and Fc{gamma}RIIA, which mediate non-neutralizing antibody responses, was enhanced in non-transmitting mother-infant dyads and strongly correlated with ADCP. These findings suggest that Fc effector functions including ADCP protect against placental HCMV transmission. Taken together, our data indicate that future active and passive immunization strategies to prevent congenital HCMV infection should target Fc-mediated non-neutralizing antibody responses.