Around 7–10% of endometrial carcinomas are characterized by polymerase-ε-(POLE) exonuclease-domain-mutations, an ultra-mutated-phenotype and a favorable prognosis. It is currently unknown whether POLE ultra-mutated-tumors are more immunogenic when compared to the other groups of endometrial cancers.

We used autologous-dendritic-cells (DC) pulsed with whole-tumor-extracts to assess the level of CD8 + and CD4 + T-cell-activation induced by POLE-ultramutated (+) and POLE wild-type (−) endometrial cancer cells in vitro. T-lymphocyte-proliferations were evaluated using CFSE and/or ^[3H]thymidine-incorporation-assays while the ability to specifically kill autologous-tumor-cells by cytotoxic-T-lymphocyte (CTL) was tested in standard 4-h-⁵¹Cr-cytotoxicity-assays. In order to correlate cytotoxic activity and proliferation by CD4 + and CD8 + T-lymphocytes, respectively, with a particular lymphoid subset, two-color-flow-cytometric analysis of intracellular-cytokine-expression (IFN-γ vs IL-4) at the single cell level was also performed.

DC-pulsed with tumor extracts were able to induce CTL-responses against autologous-tumor-cells in both POLE (+) and POLE (−) cancer patients (P = 0.305). These CD8 + T-cell-populations were cytotoxic against tumor-cells but they did not lyse PHA-stimulated-autologous-lymphocytes or autologous-EBV-transformed-lymphoblastoid-control-cell-lines. In contrast, only POLE (+) tumor-lysate-pulsed-DC were able to induce significant proliferation and high IFN-γ expression (i.e., Th1-cytokine-bias) in autologous in vitro DC-stimulated CD4 + T-cells as well as naïve CD4 + and CD8 + T-cells from patients-peripheral-blood (P < 0.05).

POLE ultra-mutated-tumors are significantly more immunogenic when compared to POLE (−) tumors, in particular to the helper arm of the immune system. These data lend support to the hypothesis that the better prognosis of patients with POLE (+) tumors may at least in part be linked to their enhanced immunogenicity.