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May, Christopher Galen

University of British Columbia

Chimeric antigen receptor (CAR) T cells are regarded as a major breakthrough for treating hematological malignancies. Through expression of a receptor comprising an extracellular antigen-binding domain and intracellular stimulatory domains, CAR T cells can be re-directed to target cells expressing the antigen of choice where they are activated to proliferate and kill their targets. Despite representing a major advancement in the treatment of “liquid” tumours, the success of CAR T cells in solid tumours has been hampered in part by the immunosuppressive tumour microenvironment. Tumours form a complex network of cells and signaling molecules that promote tumour growth while suppressing the immune response. One of these mechanisms of immunosuppression is indoleamine 2,3-dioxyganse (IDO). IDO degrades tryptophan into a set of immunosuppressive metabolites called kynurenines. Through these actions, IDO activates suppressive immune cells while inhibiting anti-tumour immunity. In CAR T-cell therapy, IDO expression can suppress T-cell mediated killing and compromise treatment efficacy. The aim of this thesis is to enhance the ability of CAR T cells to contend with IDO-mediated immunosuppression in the tumour microenvironment. This engineering strategy involves the enzymatic degradation of suppressive kynurenines, which first requires knowledge of the specific kynurenines involved. Herein I show that of all kynurenines, kynurenine itself most strongly suppresses CAR T cells through the aryl hydrocarbon receptor, and I demonstrate the ability of T cells expressing kynureninase (KYNase) to degrade kynurenine in vitro. I outline the optimization of a model system to assess IDO-mediated immunosuppression of human CAR T cells in vivo, and use this system to evaluate the therapeutic effect of KYNase modification. I show that, while KYNase expression is ineffective at rescuing human CAR T-cell suppression in a subcutaneous tumour model in vivo, the modification of the CAR itself may influence its ability to withstand the immunosuppressive milieu produced by IDO. Furthermore, I identify the solvents used in in vitro assays as a possible confounding factor that may influence the interpretation of decades of research into kynurenine. This thesis contributes towards a better appreciation of the variability in IDO-mediated immunosuppression in vitro and in vivo, between species, and across diverse model systems.

Text

2024-01-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87153

Interdisciplinary Oncology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/