Our research focuses on human cytomegalovirus (CMV) latency. CMV is a beta herpesvirus that infects the majority of the population worldwide and is the leading cause of infectious-disease related birth defects. CMV replicates in a variety of cell types, but its genome is uniquely maintained without the production of progeny in hematopoietic cells. This latent state enables the virus to persist for a lifetime in healthy individuals without causing disease. However, reactivation of CMV from latency can cause life-threatening disease in immunocompromised patients such as stem cell and solid organ transplant recipients and AIDS patients. In spite of its critical importance to the infectious cycle and pathogenesis, the mechanisms underlying CMV latency have remained obscure. Latency is a delicate balance dependent on complex interactions between the virus and the host at the molecular, cellular, and systemic levels. Primary impediments to understanding CMV latency have been the lack of suitable in vitro and in vivo models for CMV latency. Recently, we have developed a novel in vitro system for studying hematopoietic progenitor cells giving a great deal of attention to hematopoietic cell biology. Using this system, we have identified a hematopoietic progenitor subpopulation (CD34+/CD38-) that uniquely supports a latent infection when infected in vitro. Our work seeks to identify and characterize viral and cellular determinants of CMV latency using this system.
Clinical strains of CMV, but not highly-passaged laboratory-adapted strains, can establish a latent infection in hematopoietic cells infected in vitro. Interestingly, laboratory-adapted strains are missing a 15 kilobase segment of DNA (termed the ULb’ region) that is found in all clinical strains. From these findings, we hypothesize that viral determinants exist that contribute to the latent infection in hematopoietic progenitor cells. We have identified a 5 kilobase sequence, and more specifically the UL138 open reading frame (ORF), within the ULb’ region unique to clinical strains that promotes a latent infection in hematopoietic cells. Currently, our focus is to determine the mechanism by which viral determinants function in promoting latency using molecular, genetic, and biochemical approaches.
We are also interested in developing an in vivo model for studying CMV infection and latency in human hematopoietic cells. We propose to develop a physiologically relevant mouse model using immunocompromised mice engineered to support human hematopoiesis. The mouse will serve as a sophisticated incubator, providing a microenvironment for differentiation of CMV-infected human hematopoietic cells that cannot be recapitulated in culture systems. This mouse model will allow us to analyze complex interactions between CMV-infected hematopoietic cells and their microenvironment as they pertain to CMV latency. Using this system, we will determine the effects of CMV infection on hematopoietic reconstitution following transplantation and the ability of infected progenitor cells to disseminate latently infected cells through differentiation. Our studies will define key mechanisms governing CMV latency and identify molecular targets for improved antiviral treatments to prevent CMV disease. Elucidating the mechanisms underlying CMV latency is critical to controlling CMV disease in immunocompromised patients and to prevent congenital infection.