Project 3

Reactivation of latent Cytomegalovirus (CMV) continues to be a significant infectious complication following transplantation. The specific molecular mechanisms that lead to reactivation of latent CMV are not well understood, at least in part, due to the species specificity of CMV, which has precluded the use of animal models, necessary to understand the complex interactions between the virus and host, to study the establishment of human CMV (HCMV) latency and reactivation from latency. Thus, mechanistic observations derived from clinically relevant animal models that allow the study of murine CMV (MCMV) latency and reactivation in the context of transplantation need to be reconciled with in vitro studies of HCMV latency and reactivation. This Program Project proposes to do just that, building on a central theme emanating from two sets of important observations that have been made from a combination of studies of molecular virology, clinical studies, cell culture models of infection, and animal models: 1) expression of viral genes involved in lytic replication is repressed by epigenetic factors that induce heterochromatinization of viral genomes; and 2) signaling pathways activated by an inflammatory immune response induce reactivation of the virus through epigenetic reprogramming of viral DNA, such that the immediate early genes are released from transcriptional repression. We propose to use a number of complementary models and approaches to identify common cellular and molecular mechanisms that lead to CMV latency and reactivation. The overarching objective is to develop novel therapeutic interventions to prevent, rather than treat CMV reactivation in transplant recipients. The unifying hypothesis is that reactivation of latent CMV is induced by inflammatory mediators, which activate signaling pathways, leading to epigenetic reprogramming of viral genomes, resulting in induction of immediate early (IE) gene expression, and ultimately, to reactivation of infectious virus. Thus, we propose three distinct but inter-related and synergistic projects designed to test whether blockade of these signaling pathways, either by interfering with specific signaling pathways, blocking epigenetic modifications, or by donor-specific tolerance, prevent reactivation of CMV.