Title: Transcriptional regulation of normal and neoplastic leukocyte physiology
Description: This dissertation addresses two distinct areas of tumor/host interactions: the processes of initiation and propagation of Snf5-deficient lymphoma; and immunosurveillance of solid tumors in the absence of T-bet. Until recently, suitable models for the study of initiation and progression of mature T cell lymphomas, a heterogeneous group of non-Hodgkin's lymphomas of poor clinical prognosis, were lacking. As a model of this class of tumors we studied the rapidly arising mature CD3 + CD8 + CD4 - T cell lymphoma in mice conditionally deficient for Snf5. We show that Snf5 inactivation within the T cell lineage before TCR-dependent development is not oncogenic, while loss of Snf5 after expression of TCR leads to the appearance of lymphomas. Snf5-deficient CD8 + CD3 + lymphomas require TCR signaling for propagation, but not IL-15, suggesting that IL-15-independent memory CD8 + T cells are the target of transformation. We show a lineage-specific role of Snf5 in lymphoid development and tumor suppressor activity, since Snf5 loss impairs αβ but not γδ T cell development and exclusively leads to transformation of CD3 + CD8 + T lymphocytes. Snf5-deficient lymphomas rely on TCR signaling for initiation and self-renewal; therefore its pharmacological interruption may be an effective therapy for this class of tumors.

We also studied the regulation of anti-tumor immunity in a second murine model. Mice deficient in the transcription factor T-bet (T-bet -/- ) and prone to prostate cancer development show a normal incidence of tumors despite their inability to control tumor metastasis. The mechanism underlying this susceptibility is not understood. Here we show that T-bet plays a role in the inhibition of B16F10 lung-colony growth by regulating the longevity and function of NK cells. Our data demonstrate that the absence of a NK-driven immune response in T-bet -/- mice precludes the initiation of a potent adaptive immune response to tumors. Adoptive transfer of wildtype activated NK cells protects T-bet -/- animals after melanoma challenge whereas transfer of T-bet -/- activated NK cells fails to do so, due to their reduced in vivo survival, inefficient lysis of cancer cells and poor interferon-γ production. Taken together, these results show an irreplaceable role for T-bet in NK-mediated cross-talk between innate and adaptive immune responses to metastatic disease.