Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.

Date of Award

9-2012

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Animal Biotechnology and Biomedical Sciences

First Advisor

Cynthia Baldwin

Second Advisor

Samuel Black

Third Advisor

Barbara Osborne

Subject Categories

Immunology and Infectious Disease

Abstract

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.

Share

COinS