? Project 2: Viral determinants of fetal RhCMV transmission Human cytomegalovirus (HCMV) is the leading infectious cause of congenital disease in newborns, and the development of treatments and preventative measures requires a better understanding of the viral determinants enabling fetal transmission in CMV-nave and CMV-immune individuals. Since HCMV is highly species-restricted, animal models of congenital infection by the corresponding animal CMVs are used to study congenital infection. Recent advances in non-human primate models for the first time enable the study of fetal transmission in a host that is anatomically very similar to humans by a virus that is highly homologous to HCMV. The goal of this project is therefore to use this model to identify and characterize viral determinants facilitating fetal transmission to ultimately support the development of specific countermeasures. Specifically, we will examine whether fetal transmission correlates with viremia and viral dissemination in the pregnant female. We will further examine the role of viral cell tropism in fetal infection and examine the hypothesis that the efficacy of antiviral antibodies is limited by viral Fc receptors. To enable the genetic manipulation of RhCMV that is required to address these questions we generated a bacterial artificial chromosome (BAC) clone representative of a low passage isolate and demonstrated fetal transmission of BAC-derived RhCMV. Using this BAC we will take advantage of our observation that RhCMV lacking the immunodominant major tegument protein pp65 displayed dramatically increased replication and dissemination in RhCMV-nave animals to examine the role of viremia and viral dissemination in fetal transmission (Aim 1). We will further experimentally address the role of the cell tropism-determining pentameric glycoprotein complex gH/gL/UL128/UL130/UL131A in maternal/fetal transmission (Aim 2). The pentameric complex is currently a major target for vaccine development, but preliminary data unexpectedly revealed increased transmission of virus lacking this complex. Finally, we will determine whether viral Fc-Receptors limit the efficacy of hyperimmunoglobulin treatment to limit viral dissemination (Aim 3). This project will both benefit from and impact the studies described in Project 1 and require the services of all four cores. We anticipate that this project will impact the design of prophylactic and therapeutic CMV vaccines and that it will reveal novel approaches to improve antibody-based therapy.