Adoptive cell therapy (ACT), including the use of T cells engineered to express chimeric antigen receptors (CARs), has produced unprecedented clinical outcomes and represents a new paradigm in cancer immunotherapy. However, the therapeutic efficacy is often limited by poor in vivo persistence and function of adoptively transferred T cells. How T cell fate decisions between robust effector function and long-term persistence are regulated in the tumor microenvironment (TME) remains poorly understood. Moreover, T cells undergo extensive metabolic reprograming during their activation and differentiation, but how metabolic fitness is linked to T cell function and longevity is unclear. In our preliminary studies, through an in vivo pooled CRISPR- Cas9 mutagenesis screening of metabolism-associated factors, we identified the enzyme Regnase-1 (Reg1) as a major negative regulator of antitumor CD8 T cell responses. Deletion of Reg1 resulted in drastically improved intratumoral CD8 T cell accumulation and therapeutic efficacies against mouse solid and blood cancers. Reg1- null CD8 T cells were reprogrammed in TME to acquire better persistence, survival advantage and nave/memory cell-associated gene signatures, but also retain potent effector function and enhanced mitochondrial metabolism. To explore the underlying mechanisms and additional targets, we performed a secondary in vivo genome-scale CRISPR-Cas9 screening in Reg1-null CD8 T cells and uncovered BATF as the key functional target of Reg1 in shaping mitochondrial metabolism and effector function of CD8 T cells. We also identified additional factors as putative targets for combinatorial therapy, as their co-deletion further potentiated the antitumor activity of Regnase-1-null cells. Our central hypothesis is that tumor-specific CD8 T cells can be reprogrammed to be long-lived effector T cells with adaptive metabolic and transcriptional programs, and targeting Regnase- 1 and associated pathways is an innovative strategy for cancer immunotherapy.
Aim 1. Establish Reg1- BATF-dependent mitochondrial metabolism in tumor-specific CD8 T cells.
Aim 2. Dissect mechanistic basis underpinning the stemness features of tumor-specific CD8 T cells.
Aim 3. Explore the therapeutic potential of targeting Reg1 and combinatorial factors. We predict our studies will establish a new paradigm in understanding fundamental mechanisms of T cell fate decisions and immunometabolism and provide new avenues to improve ACT efficacy in cancer immunotherapy.

Public Health Relevance

Statement Adoptive cell therapy using engineered T cells has produced unprecedented clinical outcomes and represents a new paradigm in cancer immunotherapy. CD8 T cells play a pivotal role in the control of cancer and their antitumor activity critically depends upon the longevity and differentiation state, but how T cell fate decisions are regulated in the tumor microenvironment remains elusive. Hence, a better understanding of the underlying metabolic pathways and signaling mechanisms may open new avenues for therapeutic intervention of cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Special Emphasis Panel (ZRG1)
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Mccarthy, Susan A
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St. Jude Children's Research Hospital
United States
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