Ontogeny and Function of Tumor-Resident Innate Lymphocytes and Innate-Like T Cells

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Project Summary Cancer immunosurveillance ascribes a role of the immune system in repressing tumor development. Cancer immunotherapy approaches such as checkpoint blockade that revives this function of exhausted T cells have revolutionized cancer patient care. Nonetheless, many patients do not respond to this modality of cancer treatment, calling for investigation of a broader spectrum of tumor-elicited immune responses. We have recently shown that tumor growth induces expansion of tissue-resident cytotoxic innate lymphocytes and innate-like T cells that share a gene expression program distinct from that of NK cells and exhausted T cells. Characterized by high expression of the transcription factor Hobit and cytolytic granzymes, these cells are herein named killer innate lymphoid cells (ILCk) and killer innate-like T cells (ILTCk). Notably, genetic depletion of ILCk and ILTCk results in accelerated tumor growth. Furthermore, tumor cells express high levels of IL-15 and lose E-cadherin polarity, and IL-15 or E-cadherin deficiency depletes ILCk and ILTCk resulting in accelerated tumor growth. Based on these findings, we hypothesize that ILCk and ILTCk are novel lineages of cytotoxic lymphocytes, and they function as sentinels of cell transformation by sensing tumor cell-derived IL-15 and E-cadherin. To test this hypothesis, we will first define the developmental pathways of ILCk and ILTCk. By performing cell transfer and cell fate-mapping experiments as well as using mice deficient in lineage-specifying transcription factors, we will assess whether ILCk are differentiated along the innate lymphoid cell lineage. In addition, we will generate T cell receptor (TCR) retrogenic mice and perform TCR “swapping” experiments to determine whether distinct thymic selection promotes ILTCk differentiation. Parabiosis and inducible hematopoietic stem cell-targeted cell fate-mapping experiments will also be performed to determine whether ILCk and ILTCk are continuously generated throughout tumor progression. Secondly, we will define the function and regulation of ILCk and ILTCk by initially assessing whether Hobit expression marks a stage of functional specification, and whether Hobit controls a gene expression program essential for ILCk and ILTCk- mediated cancer surveillance. In addition, we will utilize conditional null alleles of Il15 and Il2rb and a gain-of- function allele encoding an active form of the transcription factor Stat5b to determine whether tumor IL-15 functions as an alarmin for ILCk and ILTCk, and whether IL-15 signaling constitutes a rate-limiting step of the ILCk and ILTCk response. Finally, we will investigate the interactions between tumor cells and ILCk and ILTCk by intravital imaging, and assess whether E-cadherin is sensed by the TGF-b-induced integrin CD103, and whether patient CDH1 hot-spot missense mutations promote tumor evasion from ILCk and ILTCk-mediated cancer surveillance. Successful completion of this project will not only generate mechanistic insights into the lineage commitment and regulation of tumor-resident ILCk and ILTCk, but also guide the targeting of this novel cancer immunosurveillance pathway for therapy of a wide range of malignancies.