Antigen presentation potential is variable among human ovarian tumour and syngeneic murine models and dictates pre-clinical outcomes of immunotherapy

High grade serous ovarian carcinoma (HGSC) is a fatal gynaecological malignancy with limited therapeutic options. Immunotherapies targeting MHC-I-dependent antigen presentation offer potential. Currently, the antigen presentation machinery (APM) of widely used syngeneic murine HGSC models remains poorly characterised, limiting translational relevance. Here, we systematically evaluate APM gene expression in syngeneic murine and patient samples. Tap1 and Psmb8 were identified as critical APM markers, deficient in murine models and strongly correlating with MHC-I expression. Hierarchical clustering correlation analysis using these markers revealed that ID8-p53^⁻/⁻BRCA1^⁻/⁻ was the most strongly correlated model and aligned with the largest patient subset. Moreover, ID8-ip1 correlated to the smaller second patient subset strongly. The low MHC-I expressing IG10 model was unique clustering alongside patient derived LP28 tumour and not fitting either patient subset. In vivo test of a novel combination immune therapy consisting of Flt3L, Poly(I:C), and paclitaxel therapy demonstrated significantly reduced tumour burden in high APM models (p53⁻/⁻BRCA1⁻/⁻, ID8-ip1; p < 0.01), but not IG10. Furthermore, high expressing MHC-I models were linked to enhanced DC expansion, CD8⁺ T-cell infiltration, and effector differentiation (131 % increase in ID8-ip1), alongside improved CD8⁺ T-cell activation and CD86⁺ B-cell co-stimulation. These findings establish MHC-I as a predictive biomarker for immunotherapy response and underscore the need for APM-enhancing strategies in antigen-poor tumours. By bridging murine models to human APM heterogeneity, this work provides a framework for optimising preclinical immunotherapy evaluation and patient stratification, advancing tailored therapeutic approaches for HGSC.