Date of Graduation

5-2014

Document Type

Dissertation (PhD)

Program Affiliation

Immunology

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Laurence J.N. Cooper, M.D., Ph.D.

Committee Member

Joya Chandra, Ph.D.

Committee Member

Gianpietro Dotti, Ph.D.

Committee Member

Dean A. Lee, M.D., Ph.D.

Committee Member

Bradley McIntyre, Ph.D.

Committee Member

Cliona Rooney, Ph.D.

Abstract

Tethered IL-15 to augment the therapeutic potential of T cells expressing chimeric antigen receptor: Maintaining memory potential, persistence, and antitumor activity

Adoptive immunotherapy can retarget T cells to CD19, a tumor-associated antigen (TAA) expressed on B-cell malignancies, by the expression of a chimeric antigen receptor (CAR). Infusion of CAR-modified T cells for the treatment B-cell malignancies has demonstrated promise in preclinical and clinical trials. These data highlight the ability of infused CD19-specific T cells to be synchronously activated by large burdens of CD19+ leukemia and lymphoma. This can lead to dramatic antitumor effects, but also exposes the recipient to toxicity associated with tumor-cell lysis and cytokine storm. Clinical trials will now be addressing the targeting of minimal burdens of CD19+ malignancy as patients are enrolled earlier in their disease course and receive concomitant chemotherapy. It is likely that the existing populations of CAR T cells generated ex vivo to address relapsed disease may not be able to address minimal residual disease (MRD). Therefore, we have developed a clinically appealing approach to sustaining the persistence of CAR T cells independent of TAA by providing signaling through the common gamma chain receptor (gc). Administration of exogenous soluble recombinant cytokines that signal through the gc, such as interleukin (IL)-2, have been used clinically to sustain the persistence of adoptively transferred T cells. However, systemic high-dose administration has resulted in dose-limiting toxicities. Unlike IL-2, IL-15 possesses numerous attributes desirable for adoptive therapy and has been ranked among the most valuable immunotherapeutic agent for cancer treatment. It is a pro-survival cytokine that promotes the survival of long-lived T-cell memory subsets and in vivo antitumor activity. Unlike other gc family cytokines, IL-15 is transpresented to responding T cells in the context of IL-15 receptor alpha (IL-15Ra). Therefore, we hypothesized that a membrane-bound IL-15 fusion protein (mIL15) tethered to the cell surface would enhance T-cell costimulation to support persistence independent of CAR activation by preserving T-cell memory potential and maintain antitumor activity in the presence of low TAA. Using clinically compliant methods, the generated mIL15-CAR T cells mimicked the physiologic mechanism of transpresentation to sustain costimulation via phosphorylation of signal transducer and activator of transcription (pSTAT5). In contrast to conventional CD19-specific CAR T cells, mIL15-CAR T cells persisted in mice independent of the presence of TAA and mediated potent rejection of a systemically distributed CD19+ leukemia. The potential for sustained immunity against B-cell malignancies was shown as, in the absence of antigen, mIL15-CAR T cells were long-lived and adopted a desirable CD45ROnegCCR7+ “low-differentiation” state with a memory-like molecular profile and phenotype. These results have direct implications for the design of an adoptive immunotherapy clinical trial evaluating mIL15-CAR T cells in the setting of MRD and warrants further investigation of mIL15 to engineer T cells targeting other tumor cells that have sequestered or low levels of TAA.

Keywords

immunotherapy, cytokines, IL-15, chimeric antigen receptor, T-cell persistence, memory, memory stem cell, leukemia, B-ALL

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