Date of Award

2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Joseph A. Fraietta

Abstract

Chimeric antigen receptor (CAR) T-cells have not induced meaningful clinical responses in solid tumor indications. Loss of T-cell stemness, poor expansion capacity and exhaustion during prolonged tumor antigen exposure are major causes of CAR T-cell therapeutic resistance. scRNA-sequencing analysis of CAR T-cells from a first-in-human trial in metastatic prostate cancer identified two distinct and independently validated cell states associated with antitumor potency or lack of efficacy. Low levels of the PRDM1 gene encoding the BLIMP1 transcription factor defined highly potent TCF7+CD8+ CAR T-cells, while enrichment of TIM3+CD8+ T-cells with elevated PRDM1 expression predicted poor outcome. PRDM1 single knockout promoted TCF7-dependent CAR T-cell stemness and proliferation resulting in marginally enhanced leukemia control. However, in the setting of PRDM1 deficiency, a negative epigenetic feedback program of NFAT-driven T-cell dysfunction characterized by compensatory upregulation of NR4A3 and multiple other genes encoding exhaustion-related transcription factors hampered effector function in solid tumors. PRDM1 and NR4A3 combined ablation skewed CAR T-cell phenotypes away from TIM3+CD8+ and toward TCF7+CD8+ to counter exhaustion of tumor-infiltrating CAR T-cells and improve in vivo antitumor responses, effects that were not achieved with BLIMP1 or NR4A3 single disruption alone. These data reveal a novel molecular targeting strategy to enrich stem-like CAR T-cells resistant to exhaustion and underscore dual inhibition of PRDM1/NR4A3 expression or activity as a promising approach to advance adoptive cell immuno-oncotherapy.

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