Efficacy of CMV vFcR vaccines to prevent congenital CMV transmission

ABSTRACT – PROJECT 3 Congenital cytomegalovirus (cCMV) is the most common in utero infection, affecting approximately 1 in every 200 newborns and causing devastating neurologic impairment in 1 in 5 infected infants. Placental transmission of CMV is significantly reduced in women experiencing reinfection (3-4%) compared to women experiencing CMV infection for the first time during pregnancy (30-40%), suggesting that maternal CMV-specific adaptive immunity can protect against cCMV infection. However, to effectively reduce cCMV prevalence, the protective effects of vaccine-elicited immunity must supersede that of natural immunity. Several challenges have limited CMV vaccine development, including the numerous immune evasion mechanisms of the virus. One of these mechanisms is viral Fc receptors (vFcγRs) that bind the Fc region of IgG, which our team showed in vitro to interfere with host Fc-mediated antibody effector functions that we showed to be critical immune factors for preventing cCMV transmission. In our model of primary CMV infection in pregnant rhesus macaques (RM), we identified three vFc?Rs encoded by rhesus CMV (RhCMV). Utilizing an engineered vFcγR-deleted RhCMV, we determined that while the ΔvFcγR virus could reach a similar peak viremia as the parental full-length virus (FL-RhCMV), it was cleared from the blood significantly earlier. Conversely, CD4+ T cell depletion of pregnant RM dams and subsequent infection with ΔvFcγR restored viremia to FL-RhCMV levels. While this revealed that placental transmission does not require the presence of vFcγRs, it highlights their role in limiting antibody effectiveness in vivo. Therefore, the goal of this project is to develop and test CMV vaccine strategies that will interrupt the action of vFcγRs in cCMV transmission in the RM model. We hypothesize that addition of passive or active vaccination against RhCMV vFcγRs to an entry glycoprotein-based vaccine strategy will enhance plasma Fc receptor-mediated IgG functions and protect against cCMV transmission in a nonhuman primate model. Specifically, we will define immunity against vFcγRs in natural immunity and after immunization (Aim 1), define the impact of passive antibodies against vFcγRs on the protective effect of pre-existing anti-RhCMV antibodies on cCMV transmission (Aim 2), and determine the ability of inclusion of vFcγR antigens with a viral entry glycoprotein (gB) mRNA-LNP vaccine to enhance protection against cCMV in the RM model (Aim 3). This preclinical assessment of a novel CMV vaccine strategy will inform and de-risk potential human clinical trials seeking to reduce the most common infectious cause of birth defects and brain damage.