Graduation Date

Fall 12-16-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Cancer Research

First Advisor

Hamid Band, M.D., Ph.D.

Abstract

Adaptive T cell immunity is essential for defense against foreign antigens and immune surveillance against cancer. Tight regulation of T cell activation is required to avoid autoimmunity to self-antigens or protracted inflammation after foreign antigens are cleared. Incomplete or inappropriate stimulation leads to an active shutdown of T cell activation called anergy. The Casitas B-lineage Lymphoma (CBL)-family of ubiquitin ligases (E3s) are essential negative regulators of T cell activation that impinge on thymic selection as well as anergy induction programs. Single gene studies show that CBL is critical during T cell development while CBL-B plays an essential role in peripheral T cells; however, a more severe inflammatory-autoimmune disease is observed upon T cell-specific deletion of CBL in CBL-B null mice indicating redundant roles of CBL proteins. Mutations in CBL-B have been linked with increased susceptibility in a number of autoimmune diseases, and CBL-B null mice exhibit constitutive tumor rejection. The mechanisms by which CBL proteins regulate T cells in autoimmunity and antitumor immunity are not fully understood. It was previously not feasible to test the functional redundancy of CBL proteins in specific populations of T cells using existing models because their generalized CBL-B deficiency leads to altered and/or enhanced function of all T cell subsets and other immune cells, including B cells, macrophages, mast cells, neutrophils, and NKT cells. Here, we generated the first CBL-Bflox/flox mouse which allows conditional CBL and CBL-B deletion in a cell type-specific manner. By crossing this new mouse strain with the previously generated CBLflox/flox mouse and to a CD4-Cre transgene, we obtained concurrent CBL and CBL-B double knockout (DKO) in all T cell subsets, with altered T cell development, widespread organ infiltration by immune cells and rapid lethality, consistent with a redundant functional role of CBL and CBL-B. Unexpectedly, CD4-Cre-induced deletion in a small fraction of hematopoietic stem cells led to expansion of certain non-T-cell lineages, suggesting caution in the use of CD4-Cre for T-cell-restricted gene deletion.

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