Abstract P09: Functional Dissection of NK Cell Evasion Mechanisms in <i>TP53</i> -Inactivated Acute Myeloid Leukemia

Abstract Introduction: TP53 mutations occur in 30% of relapsed/refractory AML patients and are associated with poor prognosis, therapy resistance, and immune dysfunction. While TP53 mutations have been shown to induce T cell exhaustion and impair adaptive immunity, their impact on innate immune mechanisms, particularly NK cell-mediated cytotoxicity, remains poorly understood. Given the critical role of NK cells in immune surveillance against malignant cells, we investigated how TP53 loss alters AML susceptibility to NK cell killing and explored therapeutic strategies to overcome this resistance. Methods: We established co-culture systems using TP53-wildtype and TP53-inactivated AML cells with NK-92 cells, with validation using primary human NK cells. TP53-inactivated AML cells exhibited significantly reduced susceptibility to NK-92-mediated cytotoxicity, a phenotype confirmed with primary NK cells. To assess whether resistance was mediated by secreted factors, we compared killing in direct co-culture versus conditioned media experiments, revealing that resistance required direct cell-cell contact as conditioned media alone did not impair NK cell killing, suggesting membrane-bound or contact-dependent mechanisms. Results: A genome-wide CRISPR KO screen in TP53-inactivated AML cells was performed to identify genes regulating sensitivity to NK cell-mediated cytotoxicity, revealing several modulators of NK sensitivity, including cIAP1. Functional validation using genetic and pharmacological approaches demonstrated that targeting inhibitor of apoptosis proteins (IAPs) with small-molecule antagonists including birinapant, tolinapant, or PROTAC-based degrader (CST-626) at sublethal doses effectively sensitized TP53-inactivated AML cells to NK cell cytotoxicity. Analysis of NK-activating and inhibiting ligand expression profiles revealed that while TP53 loss altered the expression of multiple NK-interacting ligands, no single ligand was solely responsible for the resistance phenotype, suggesting a broader immune evasion program induced by p53 deficiency that parallels the T cell dysfunction observed in TP53-mutant AML patients. Conclusion: Overall, these results provide a rationale for combination strategies targeting both immune evasion mechanisms and apoptotic resistance in this patient population. Citation Format: Jordan Yong Ming Tan, Chuqi Wang, Wen Kang Soh, Yash Manish Agrawal, En Tong Lim, Fang Qi Lim, Yuhan Wang, Nishtha Chitkara, Xiao Xian Lin, Ahmed M. Mamdouh, Gloryn Chia, Nicholas R.J. Gascoigne, Shruti Bhatt. Functional Dissection of NK Cell Evasion Mechanisms in TP53-Inactivated Acute Myeloid Leukemia [abstract]. In: Proceedings of Frontiers in Cancer Science 2025; 2025 Nov 5-7; Singapore. Philadelphia (PA): AACR; Cancer Res 2026;86(13_Suppl):Abstract nr P09.