Abstract B077: Spatially-resolved gene signatures of long-term anti-tumor immunity in ultra- and hypermutated Endometrial Cancer

Abstract Spatially-resolved gene signatures of long-term anti-tumor immunity in ultra- and hypermutated Endometrial CancerHans W. Nijman 1,± , Koen Brummel1,*, Marta Requesens1,*, Nienke van Rooij1, #, Annechien Plat1, #, Annegé Vledder1, René Wardenaar2, Diana C.J. Spierings2, Eugene Berezikov2, Joost Bart3, Marco de Bruyn1,±. 1Department of Obstetrics and Gynaecology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. 2European Research Institute for the Biology of Ageing, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. 3Department of Pathology, Leiden University Medical Centre, Leiden, The Netherlands. Background: Long-term protection against cancer recurrence is believed to rely on the formation of immunologic memory. However, the characteristics that define T cells capable of developing long-term memory in cancer patients remain poorly understood. This study aimed to characterize the transcriptional and spatial signatures of long-term immunity in ultra- and hypermutated endometrial cancer (EC) and to determine how neoadjuvant immune checkpoint inhibition (neoICI) influences these signatures and cells. Methods: We conducted single-cell RNA sequencing of T cells from ultramutated polymerase epsilon (POLE) mutant patients, hypermutated mismatch repair deficient (MMRd) patients, and MMRd patients treated with neoICI. Long-term immunity was assessed by pairing tumor single-cell RNA sequencing data with deep peripheral blood sequencing collected up to 8 years post-primary treatment. Spatial transcriptomics enabled analysis of the intratumoral distribution of long-term memory gene signatures. Finally, gene signatures indicative of long-term memory were evaluated during clinically effective neoICI in MMRd EC. Results: By integrating RNA expression data with antigen specificity mapping to T cell receptors (TCRs), we stratified intratumoral T cells with and without long-term memory potential as tumor-reactive or bystander cells. We identified a gene signature for tumor-reactive CD8 T cell clones with long-term memory potential (LTM cells), which included genes such as IL7R and TCF7. Through a spatial transcriptomics dataset of eight EC patients, we mapped the association of LTM cells with intratumoral structures like tertiary lymphoid structures (TLSs). Finally, using label transfer to ICI-responsive and nonresponsive tumor-infiltrating T cells, we pinpointed ICI-responsive CD8 T cells that had migrated to tumor-draining lymph nodes (TDLN) as the most likely to form long-term memory. Conclusion: This study offers a comprehensive analysis of the long-term memory potential of tumor-reactive T cell clones in ultra- and hypermutated EC and reveals how neoICI may shape the long-term memory pool. Furthermore, our findings suggest potential biomarkers for ICI response at both gene and tumor microenvironment levels. Citation Format: Hans W. Nijman, Marta Requesens, Koen Brummel, Nienke van Rooij, Annechien Plat, Annegé Vledder, René Wardenaar, Diana C.J. Spierings, Eugene Berezikov, Joost Bart, Marco de Bruyn. Spatially-resolved gene signatures of long-term anti-tumor immunity in ultra- and hypermutated Endometrial Cancer [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B077.