Mechanisms of memory CD8+ T cell protection from an acuute lethal viral disease

Abstract

CD8+ T cells are important mediators of adaptive immunity that work to eliminate certain pathogenic viruses. Antigen-specific CD8 + T cells exert their antiviral effects via direct cytolysis of infected cells and through the production of cytokines and chemokines. The experiments described in this dissertation identify the essential components in memory CD8+ T cell mediated protection against an acute lethal viral infection. The two major anti-viral effector mechanisms of CD8+ T cells are thought to be perforin (Prf)-mediated cell lysis and interferon gamma (IFN-γ)-mediated induction of an anti-viral state. By affecting the expression of proteins involved in antigen presentation, IFN-γ is also thought to shape the magnitude and specificity of the CD8+ T cell response. Therefore, in our first manuscript, we studied the role of Prf and IFN-γ in shaping the effector and memory CD8+ T cell response to vaccinia virus (VACV). We found that the virus loads are the main reason for the increased strength of the CD8 response in IFN-γ and Prf deficient mice and that neither Prf nor IFN-γ deficiency had an effect on the immunodominance hierarchy of 5 Kb-restricted CD8+ T cell determinants during either acute infection or after recovery. Thus, our work demonstrated that neither IFN-γ nor Prf are essential for the control of VACV. Moreover, we showed that CD8+ T cell immunodominance during VACV infection was unaffected by the effects of IFN-γ on the antigen presentation machinery. Memory CD8+ T cells induced by immunization with VACV, the virus in the smallpox vaccine, protect from mousepox, the mouse homolog of human smallpox. In our second manuscript, we showed that the ability of memory CD8+ T cells to protect from mousepox depended on their initial frequency and required the presence of IFN-γ. However, while memory CD8+ T cells could provide all the IFN-γ necessary for protection, their ability to produce IFN-γ was dispensable. Thus, the capacity of memory CD8+ T cells to protect from a viral infection was dependent on their frequency but independent of their ability to produce IFN-γ. To follow-up on these findings, in our third manuscript we demonstrated that the protective ability of memory CD8+ T cells was dependent on the secretory perforin-dependent granule exocytosis pathway. Hence, the effector to target cell ratio is greater when the initial memory CD8+ T cell frequency is high. This results in more infected cells being killed by the Prf/granzyme pathway and the survival of the host. We have previously shown that the adoptive transfer of multispecific memory CD8+ T cells can protect from an acute lethal viral disease. Therefore, in our fourth manuscript we determined whether CD8 + T cells specific for single ID or SD peptides could be protective. We found that complete protection from mousepox could be achieved by memory CD8+ T cells specific for single ID or SD determinants induced by immunization with peptide-pulsed dendritic cells. Our data suggests that it is feasible to produce effective anti-viral CD8+ T cell vaccines using single CD8+ T cell determinants. Additionally, we showed that the protective ability of monospecific memory CD8+ T cells was not compromised in the absence of natural killer cells, which are essential for resistance to mousepox in non-immune mice. Together, the work presented in this dissertation contribute to the efforts of rational vaccine development by providing information about mechanisms of acquired protection that may be applicable to other pathogenic viruses that cause acute or chronic viral diseases