Abstract 2561: Immune mediated expansion of p53 mutant clonal hematopoiesis following carboplatin treatment

Abstract Therapy-related myeloid neoplasms (t-MNs) are devastating complications arising from cancer chemotherapy, particularly affecting patients treated with agents like alkylating agents and platinum compounds. TP53 mutations are the most frequent genetic alterations in t-MNs, present in 25-40% of cases. While the selective expansion of p53-mutant HSCs under chemotherapeutic pressure, known as clonal hematopoiesis (CH), has been implicated in t-MN development, the transition from clonal expansion to malignant transformation remains poorly understood. To elucidate the mechanisms driving the transformation of p53 mutant HSCs following chemotherapy, we established a mouse model of p53-mutated CH. Using a chimeric bone marrow transplantation approach, we co-transplanted GFP-labeled Trp53R172H mutant BM cells and RFP-labeled wild-type BM cells into irradiated recipients. Six weeks post-transplantation, mice were treated with weekly intraperitoneal injections of carboplatin or no treatment for four weeks. Flow cytometry revealed a significant expansion of p53 mutant cells in the carboplatin-treated group compared to both baseline and controls. All carboplatin-treated mice developed t-MNs within four months, while none of the control group did. Bone marrow analysis using CyTOF identified a distinct population of proliferative erythroid progenitors expressing c-Kit, Ki-67, mutant p53, and CD71 exclusively in the carboplatin group. Whole exome sequencing of sorted GFP-positive p53 mutant cells revealed recurrent deletions in chromosomal regions 1q, 4q, and chromosome 10. Frequent mutations in RAS pathway genes were also identified, with Ptpn11 mutations in six out of eight mice and Kras and Nf1 mutations in the remaining two. Single-cell RNA sequencing of GFP+c-Kit+ cells from t-MN mice uncovered proliferative progenitor clusters with upregulated DNA damage response and repair pathways. Importantly, a recurrent deletion on chromosome 4 included genes encoding the interferon alpha (Ifn-α) family was identified. In NSG mice lacking functional immune cells, p53 mutant clones did not expand or progress to AML following carboplatin, suggesting a non-cell-autonomous immune role in clonal expansion. Our findings reveal a critical role of immune-mediated mechanisms, particularly through IFN-α signaling, in driving the expansion and transformation of p53 mutant HSCs. Modulating immune interactions may offer a strategy to prevent t-MNs. Future studies should explore combining chemotherapy with immunosuppressive therapies to mitigate the risk of t-MNs and improve patient outcomes. Citation Format: Priyanka Khanna, Dexin Yang, Muharrem Muftuoglu, Lauren Ostermann, Shayaun Khazaei, Ran Zhao, Mahesh Basyal, Michael Andreeff, Mihai Gagea, Ruoyan Li, Koichi Takahashi, Rasoul Pourebrahim. Immune mediated expansion of p53 mutant clonal hematopoiesis following carboplatin treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2561.