To experimentally dissect the link between TMB level, TLS development and sensitivity to ICIs, we harnessed two mouse models of ovarian cancer that are syngeneic to C57BL/6J mice and exhibit significantly different level of somatic mutations and TMB, namely, ID8 cells and Brca1−/−Trp53−/−/Myc/Hras SO1 cells59 (Fig. 6A, B) to generate tumors in immunocompetent female C56BL/6 mice for TLS analyses (Fig. 6C). Here, HRAS is linked to ovarian cancer.