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Understanding & optimizing human T regulatory cell function in patients with autoimmunity and/or undergoing transplantation MacDonald, Katherine Grace

Abstract

CD4⁺FOXP3⁺ T regulatory cells (Tregs) are potent suppressors of inflammatory immune activity. Cellular therapy with Tregs is a promising way to induce antigen specific tolerance in transplantation and autoimmunity, as it would allow the reduction of nonspecific immunosuppression. Currently, Tregs are being tested in clinical trials; however, outstanding questions regarding stability, specificity, and longevity of transferred cells remain. The aim of this research was to better understand the potential plasticity of Tregs, develop novel methods of creating antigen specific Tregs, and determine the optimal signals for Tregs to persist after transfer. To better understand the pathological conversion of Tregs to inflammatory cells, I examined the phenotype of Tregs in systemic sclerosis, a Th2-biased disease. I found that Tregs in patient skin and blood had acquired Th2-cytokine and homing marker expression, respectively, and that both tissue-localized and homing cells express the receptor for IL-33, which was expressed in patient skin. This work suggests that sub-populations of Tregs have the capacity to become pathogenic upon encountering tissue-specific inflammatory signals. Next, in order to create antigen specific Tregs, I developed a novel chimeric antigen receptor (CAR) against HLA-A2 and tested its function. A2CAR-Tregs were highly activated and proliferative in response to HLA-A2, but they retained their suppressive capacity and expression of the transcription factors FOXP3 and Helios, and the effector molecules CD25 and CTLA-4. A2CAR-Tregs were also superior to polyclonal Tregs at preventing xenoGVHD in mice, even at low doses. Thus, A2CAR-Treg cell therapy is a promising new technology to create potent Tregs for antigen-specific transplant tolerance. Finally, to optimize Treg activity and persistence in patients, I developed a series of CARs containing different co-stimulatory domains. Four TNFR superfamily domains were cloned, from 4-1BB, OX40, GITR and TNFR2, and three signalling domains were cloned from the B7/CD28 superfamily, from ICOS, PD-1, and CTLA-4. 4-1BB, OX40, ICOS, and PD-1 containing CARs were expressed on the surface of cells. These tools will provide valuable information in future research on Treg survival in vivo. Collectively, these studies have provided insights to improve both the safety and efficacy of Treg cell therapy.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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