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Date of Award
Doctor of Philosophy (PhD)
Animal Biotechnology and Biomedical Sciences
Immunology and Infectious Disease
NKG2D is a unique immunoreceptor of key significance to immune surveillance of tumor cells, and it represents an attractive candidate in the development of both molecular and cell-based immunotherapies. NKG2D is a stimulatory receptor expressed by human natural killer (NK) cells, cytokine induced killer/lymphokine activated killer (CIK/LAK) cells, γδ T cells and CD8 + αβ T cells. The NKG2D receptor plays a pivotal role in both innate and adaptive immunity, where it stimulates the cytotoxic function of (NK) cells and CD8 + T cells upon recognition of a diverse array of MHC-related ligands. In turn, these ligands are specifically induced under pathological conditions.Current research has established a prominent role for the NKG2D receptor in the modulation of tumor immunity by both NK cells and T cells. We discovered a novel genetic modifier that limits the effectiveness of NK/T cell immunotherapy in human cancer patients. Our objective of this study was to investigate how these genetic modifiers affect NK receptor-ligand interactions and ultimately tumor cell recognition, immunity, and immune evasion.
We characterized an alternate splice variant of human NKG2D that encodes a truncated receptor lacking the ligand-binding ectodomain. This truncated NKG2D variant (NKG2DTR ) does not activate cytotoxicity in a ligand-dependent manner, and its enforced expression inhibits killing mediated by the full-length NKG2D isoform (NKG2DFL ). Enforced expression of NKG2DTR resulted in the retention of NKG2DFL in intracellular compartments. The relative abundance of NKG2DTR transcripts varies among PBMC and activated LAK/CIK cells and NK cells of diverse donors and inversely correlates with the killing capacity of expressing cells. Furthermore, specific shRNA-mediated knockdown of the endogenous NKG2D TR isoform in human CIK cells and NK cells enhances endogenous NKG2D FL -mediated cytotoxicity. Co-immunoprecipitation studies revealed that NKG2DTR pairs with DAP10 and heterodimerizes with NKG2D FL , suggesting that its dominant negative impact on cytotoxicity is due to the formation of heterodimeric NKG2DTR/FL receptor complexes incapable of ligand binding. Thus, competitive interference via an alternatively spliced NKG2D variant constitutes a novel mechanism for regulation of NKG2D-mediated signaling and cytotoxicity in LAK/CIK cells and NK cells.
Karimi, Mobin A, "The Role of Human NKG2D Receptor-Ligand Function in Tumor Immunity and Immune Escape" (2012). Doctoral Dissertations 1896 - February 2014. 412.