Abstract 5284: Immune surveillance of chemotherapy-induced mutant subclones in CRC

Abstract Molecular alterations generated by DNA repair deficiencies and DNA damaging agents can be detected by the host immune system and this can restrict cancer growth. We have previously reported that temozolomide (TMZ) is able to induce MMR defects and hypermutability leading to immunotherapy clinical benefit in the subset of CRCs characterized by inactivation of O6-methylguanine methyltransferase (MGMT). We reasoned that combination of chemotherapeutic agents could similarly impair DNA repair function, increase mutational burden and trigger cancer immunogenicity in the larger group of MMR proficient (MMRp) /MGMT wild type (MGMTwt) CRCs. For this reason, we investigated the impact of treatment with TMZ and cisplatin (CDDP), as well as other commonly used cytotoxic agents in CRC such as 5-fluorouracil, irinotecan and oxaliplatin, on the immunogenomic features of murine CRC cells. We performed a two-step experiment: first, murine CRC models were exposed in vitro to chemotherapy agents used alone or in combination in a pulsatile schedule in order to mimic drug exposure in the clinical setting (priming phase) ; second, the cells were challenged in vivo with subcutaneous injection in immune-deficient and -proficient syngeneic mice (editing phase). Whole exome sequencing (WES) was performed at baseline and after both the priming and the editing phases to identify mutational signatures, predict neoantigens and assess immunoediting. We found that combinatorial treatment of MMRp/MGMTwt CRC cells with CDDP and TMZ causes clonal and subclonal hypermutability, eventually leading to tumor rejection in syngeneic mice. By following the fate of chemotherapy-induced mutations and predicted neoantigens in primed tumors grown in immunocompromised or immunocompetent mice we found that the majority of chemo-induced mutant clones were immunologically deleted in the CDDP-TMZ combination arm. The same effect was not observed when CDDP and TMZ were administered as monotherapy or when CRC cells were primed with the 5-fluorouracil-oxaliplatin-irinotecan (FOLFOXIRI) triplet. Mutational signature profiling of the immunologically deleted mutations was consistent with the previous exposure to chemotherapy in the priming phase. Moreover, the extent of the immunoediting was related to the clonality of the chemo-induced mutations, underlining the relevance of clonal abundance of immunogenic mutations in immune recognition and surveillance. These results indicate that rational combinations of commonly used cytotoxic agents can be exploited to promote cancer cell subclonal and clonal hypermutability. This approach can be used to promote cancer immunogenicity with implications for the design of new chemo-immunotherapy strategies in CRC. Citation Format: Pietro Paolo Vitiello, Paolo Battuello, Rosaria Chilá, Vittorio Battaglieri, Vito Amodio, Gaia Grasso, Federica Di Nicolantonio, Giovanni Crisafulli, Giovanni Germano, Alberto Bardelli. Immune surveillance of chemotherapy-induced mutant subclones in CRC abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5284.