Abstract B003: p53 promotes anti-tumor immunity of human CD8+ T cells

Abstract Cell-based immunotherapies using chimeric antigen receptors (CARs) or T-cell receptor (TCR)-engineered T cells have emerged as potent treatments for hematological and solid tumors. The efficacy of receptor-engineered T cells is limited, however, by poor persistence and T cell exhaustion following adoptive transfer. Unfortunately, conventional manufacturing processes for CAR- or TCR-engineered T cells tend to drive terminal differentiation and exhaustion, undermining their longevity and anti-tumor potential. One therapeutic strategy to improve T-cell anti-tumor efficacy is to promote the formation of immunological memory during cell manufacturing with pharmacological approaches. Here, we focus on p53 because of its canonical role in key cellular processes such as apoptosis, survival, and stem cell maintenance. Although the p53-MDM2 pathway in malignant cells has been extensively studied, its function in human CD8+ T cells is relatively unexplored. In this study, we investigated inhibitors of the MDM2–p53 interaction in human CD8+ T cells. We show that p53 is minimally expressed in quiescent naïve CD8+ T cells but rapidly upregulated upon T-cell receptor activation and clonal expansion. There are at least 12 isoforms encoded by the TP53 gene on chromosome 17p13 that arise through alternative splicing, promoter usage, and translation initiation. We performed RT-qPCR after stimulation to assess mRNA levels of p53 isoforms, including full-length p53, Δ40p53, Δ133p53, p53β, and p53γ isoforms. We found a nearly 40-fold increase in full-length p53 and Δ40p53 mRNA levels in memory compared to exhausted CD8+ T cells. Having observed that p53 is enriched in memory T cells compared to terminally differentiated and exhausted T cells, we explored whether we could pharmacologically induce p53 in CD8+ T cells and whether this would promote the expansion of the memory subset. Pharmacologic inhibition of MDM2 resulted in elevated p53 protein levels that correlate with enhanced phenotypic and transcriptional features of T cell memory and constrained exhaustion, improved metabolic fitness with increased spare respiratory capacity, and augmented polyfunctionality with increased interferon gamma and granzyme B production. Crucially, receptor-engineered T cells (TCR MAGE-A4+) generated in the presence of an MDM2 inhibitor show increased p53 and superior tumor-killing capacity (M407 melanoma tumor cells) compared to conventionally manufactured T cells using real-time imaging (IncuCyte). Together, these findings support the induction of p53 using MDM2 inhibitors as a novel and clinically-feasible therapeutic strategy to manufacture large numbers of receptor-modified human T cells with memory features and superior antitumor efficacy. Citation Format: Alexandra Boix de Jesus, Hy B. Dao, Anthony Imani, Gabriel Abril Rodriguez, Michael S. Shehata, Rachana R. Chandran, Stuart A. Fine, Sin Yee Lim, Michelle To, Serena Y. Lofftus, Fritz C. Eilber, Brigitte N. Gomperts, Tyler R. McCaw, Cristina Puig-Saus, Joseph G. Crompton. p53 promotes anti-tumor immunity of human CD8+ T cells abstract. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B003.