CD8+ T cell effector differentiation and memory formation during vaccination under physiological and pathophysiological conditions

The goal of this thesis is to further the understanding of CD8+ T cell effector differentiation in response to vaccination. CD8+ T cell effector differentiation occurs under many different settings including physiological settings in which healthy patients are vaccinated to protect against future disease and pathophysiological settings where the immune system is suppressed such as during cancer or HIV. Therefore we studied CD8+ T cell priming and effector differentiation in both physiological and pathophysiological conditions focusing on limiting terminal differentiation to promote the development of memory CD8+ T cells. Interestingly, during vaccination we observed that CD8+ T cells promote their own terminal differentiation by modulating their priming environment causing the upregulation of T-bet expression by CD8+ T cells. Further in the tumor setting, we demonstrate that blocking TGF-beta combined with vaccination concomitant with surgical resection of the primary tumor results in reduced expression of T-bet by tumor specific CD8+ T cells leading to enhanced protection against recurrent and residual tumor disease. Finally, we show that NKG2D ligation of CD8+ T cells during vaccination rescues the secondary responses of unhelped CD8+ T cells, in both human and murine models, by reducing expression of T-bet.;Chapter III: CD8+ T cells sabotage their own memory potential: CD8+ T cell responses have been shown to be regulated by dendritic cells (DCs) and CD4+ T cells leading to the tenet that CD8+ T cells play a passive role in their own differentiation. In contrast, by using a DNA vaccination model, to separate the events of vaccination from those of CD8+ T cell priming, we demonstrate that CD8+ T cells, themselves, actively limit their own memory potential through CD8+ T cell-derived IFN-gamma-dependent modification of the IL-12/IL-15R&agr; axis on DCs. Such CD8+ T cell-driven cytokine alterations result in increased T-bet and decreased Bcl-2 expression, and thus decreased memory progenitor formation. These results identify an unrecognized role for CD8+ T cells in the regulation of their own effector differentiation fate and a previously uncharacterized relationship between the balance of inflammation and memory formation.;Chapter IV: Perioperative immunotherapy generates anti-tumor CD8 memory: A main goal of cancer immunology research is the formation of antigen-specific memory T cell immunity capable of activation upon tumor re-encounter. The requirements necessary to overcome the inhibitory signals present in the tumor microenvironment and form such memory T cell responses are unknown. In contrast to previous studies targeting tumors expressing highly immunogenic "model antigens," we demonstrate that alleviating tumor-induced suppression along with vaccination against authentic antigens during the perioperative period provides long-lasting protection against a highly suppressive and poorly immunogenic melanoma. Here, we employed DNA vaccination with an immunologically optimized mouse melanoma-shared antigen, Trp1ee/ng, combined with systemic TGF-beta blockade during the perioperative period of primary tumor resection, to confer protection against B16 melanoma, and against JBRH, an independently-derived melanoma unrelated to B16. Importantly, we demonstrate that correlative to memory responses, perioperative immunotherapy increases the formation of tumor infiltrating and tumor-reactive CD8+ T cells expressing low levels of the transcription factor T-bet, defined as memory precursor effector cells (MPECs). We show that conditions for an "immunologically-fertile environment" are met when TGF-beta blockade and vaccination are applied during the perioperative period of primary tumor resection. These findings address limitations of current CD8+ T cell immunotherapies against cancer by generating effective CD8+ T cell memory recall responses.;Chapter V: NKG2D on unhelped CD8+ T cells rescues memory response: CD4-unhelped CD8+ T cells are functionally defective cells primed in the absence of CD4+ T cell help and present a critical problem. Based on the co-stimulatory and non-canonical roles of NKG2D on CD8+ T cells, we investigated its ability to rescue these immunologically impotent cells. We demonstrate that augmented co-stimulation through NKG2D during priming paradoxically rescues memory, but not effector, responses. NKG2D-mediated rescue is characterized by reversal of elevated T-bet expression and recovery of IL-2 and IFN-gamma production and cytolytic responses. Rescue is abrogated in CD8+ T cells lacking NKG2D. Augmented co-stimulation through NKG2D confers a high rate of survival to mice lacking CD4+ T cells in a CD4-dependent influenza model and rescues HIV-specific CD8+ T cell responses from CD4-deficient HIV-positive donors. These findings demonstrate that augmented co-stimulation through NKG2D is effective in rescuing CD4-unhelped CD8+ T cells from their pathophysiological fate and may provide therapeutic benefits.;Conclusion: These studies demonstrate novel cellular interactions and relationships between cytokines and surface receptors that direct CD8+ T cell effector differentiation through the regulation of T-bet expression. Additionally, these results provide the groundwork for future anti-tumor immunotherapies that require long-lived CD8+ T cells for protection.