Spatiotemporal immune landscape and long-term immune memory in POLE-mutant endometrial cancer at the single-cell level
Brummel K., Requesens M., van Rooij N., Workel HH., Eggink FA., Plat A., Wardenaar R., Spierings DCJ., Foijer F., Church DN., Bart J., Nijman HW., de Bruyn M.
Abstract Polymerase epsilon mutant (POLE-mut) endometrial cancers (EC) are characterized by a near 100% disease-specific survival rate, even when treated by surgery alone. This spectacular survival, combined with the ultramutated genome and high level of neoantigens in these tumors, indicates a substantial degree of immune control in preventing disease spread and recurrence. Although these features are intriguing, the immune infiltration of POLE-mut EC has predominantly been confined to immunohistochemistry studies. Here, we used state of the art single-cell RNA and TCR sequencing to characterize the immune landscape of POLE-mutant ECs. Moreover, we uniquely analyzed patient blood samples taken two to eight years after curative treatment to assess formation of long-term immune memory in circulation. We identified specialized tumor-infiltrating myeloid subsets at different stages of maturation, an array of lymphocytes ranging from immature to cytotoxic and adaptive natural killer (NK) as well as tumor-reactive exhausted and effector T cells, contributing to a highly inflammatory anti-tumor response. Remarkably, our analysis of blood samples taken years after curative treatment uncovered the presence of tumor-reactive T cell clones that matched the primary tumor. This indicates the formation of systemic long-term memory immune responses in POLE-mut EC survivors. Our study highlights the distinctive immunogenicity of POLE-mut EC and identifies key features associated with persistent anti-tumor immunity that may contribute to prolonged, relapse-free survival.