Reactivation of latent human cytomegalovirus (HCMV) remains a significant cause of morbidity and mortality in transplant recipients, despite the use of antiviral drugs. Therefore, new approaches are required to reduce the complications from this pathogen. Due to the species specificity of HCMV, we have developed a clinically relevant transplant model using the highly related murine CMV (MCMV) as a model to study CMV latency and reactivation in the context of organ transplantation. In this model, MCMV latently infected kidneys are transplanted into B6 mice, inducing transcriptional reactivation of Immediate Early (IE) genes. Addition of a clinically relevant immunosuppression (IE) regimen results in reactivation of latent virus in the donor kidney, which disseminates into other organs of the recipient. Our preliminary data shows that IL-1/IL-18, IL-6/CD40, and TNF signaling are associated with IE gene expression following transplantation, presenting candidate pathways that can be targeted for therapeutic intervention. The central hypothesis of this proposal is that the inflammatory response elicited by the transplanted kidney results a signaling cascade that stimulates epigenetic reprogramming of latent viral genomes, transcriptional reactivation of IE genes, and in immunosuppressed recipients, re-entry of latent virus into the lytic replication program. To test this hypothesis, in Aim 1 we will investigate the requirement for candidate factors identified in our preliminary studies, and their downstream signaling intermediates, in inducing reactivation. We have also shown that transplant-induced reactivation of IE expression is associated with epigenetic reprogramming. Previous studies by our collaborator, Dr. Thomas Kristie, have identified epigenetic inhibitors that suppress reactivation of latent herpes simplex virus.
In Aim 2 we will investigate these promising therapeutic interventions for their ability to prevent reactivation of latent MCMV in our model.
In Aim 3 we will investigate a new in vitro model of differentiation- induced reactivation of bone-marrow derived murine hematopoietic progenitor cells from latently infected mice. This complementary in vitro model will be exceptionally useful for defining molecular mechanisms in the absence of the complexity of our in vivo model, and for corroborating data from in vitro studies of HCMV latency and reactivation. Upon completion, our studies will have identified signaling pathways that lead to epigenetic reprogramming of viral chromatin to reactivate latent MCMV and potential therapeutic targets. This project has considerable synergy with Project 2, which will investigate inflammatory and epigenetic factors that control HCMV latency and reactivation, and Project 3, which will investigate complications due MCMV infection and inflammation on tolerance to donor-specific antigens.
