Date

July 2013

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Molecular Microbiology and Immunology

Institution

Oregon Health & Science University

Abstract

Cytomegaloviruses establish a lifelong, latent/persistent infection in their hosts, tactfully avoiding the many redundant components of the innate and adaptive immune system. In so doing, they provoke a large, functional CD8 T-cell response directed against a subset of viral epitopes. This reponse is maintained for the life of the host and is termed “memory inflation.” Inflationary responses are comprised primarily of cells with an effector phenotype, which retain cytotoxic capacity and the ability to produce cytokines upon antigen stimulation. Because of the immunogenic properties of this virus, immunologists anticipate that CMV-vectored vaccines will have the capacity to generate robust, long-lived and fast-acting cellular immunity against defined antigens from pathogens and tumor cells. How and why certain epitopes within the virus are chosen as targets for memory inflation is not fully understood. This knowledge is essential for the intelligent design of CMV-based vaccines. Additionally, the capacity to modulate inflationary responses to individual CD8 T-cell epitopes could greatly enhance the application of this technology. Here I have used Murine CMV (MCMV) as a model in which to explore the selection and behavior of inflationary CD8 T-cell responses in Human CMV (HCVM) infection. I have used a recombinant MCMV encoding the ovalbumin-derived epitope SIINFEKL as a model antigen. I show that when SIINFEKL occupied the IE2 locus of MCMV, T-cells specific for the SIINFEKL epitope inflated and profoundly dominated T-cells specific for endogenous, MCMV-derived epitopes. The immunodominance of the SIINFEKL epitope could not be altered by modulating the proportion of SIINFEKL or MCMV-specific T-cells available prior to infection. Instead, coinfection with this virus and a WT MCMV enabled co-inflation of T-cells specific for both SIINFEKL and MCMV-derived antigens. Because coinfection allows presentation of xi SIINFEKL and MCMV-derived antigens by different cells within the same animal, these data show that competition for, or availability of, antigen at the level of the antigen presenting cell influences the selection of inflationary response during chronic MCMV infection. These findings emphasize the need to select and place exogenous epitopes within CMV vectors such that they have competitive expression kinetics and biochemical properties. I also found that the SIINFEKL-specific response during chronic infection could be boosted by the intravenous administration of soluble peptide-eptitope. This was true for inflationary responses generated during infection with WT MCMV as well, and for smaller central-memory responses in the same infection. I found, for all but one epitope, that inflationary and central memory responses proliferated and remained expanded as a result of what is traditionally a tolerizing stimulus. These findings suggest a method for boosting T-cell populations in a vaccine setting. Additionally, they contradict recent evidence suggesting that memory and effector T-cells are susceptible to peptide-induced tolerance.

Identifier

doi:10.6083/M4H41PGS

School

School of Medicine

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