Interplay of telomerase non-canonical functions in NK cell resistance to iCasp9-mediated apoptosis

NK cells are promising candidates for adoptive cell therapy; however, their proliferative capacity and functional persistence may be limited. Genetic modification with hTERT enhances their proliferative potential, while co-expression of the iCASP9 suicide gene provides a safety mechanism based on late-stage apoptosis induction by chemical dimerizer (CID). Whether hTERT overexpression interferes with iCasp9-mediated cell death remains unclear, and the non-canonical functions of telomerase in this context are poorly understood. This study served a dual purpose: to assess the efficacy of the iCasp9 "suicide switch" in NK cells, and to investigate a non-canonical role of telomerase in NK cell-mediated evasion from cell death. Here, we demonstrate that hTERT-modified NK cells exhibit significant resistance to CID-induced apoptosis, an effect independent of telomerase catalytic activity, as confirmed using a dominant-negative hTERT (DN-hTERT) mutant. Transcriptomic profiling revealed that both CID-resistant iCasp9-NK cells and hTERT-iCasp9-NK cells share common gene expression signatures: upregulation of cell cycle-associated genes and downregulation of splicing-related factors, including HNRNPH1 and SNRPD3, accompanied by shared patterns of alternative splicing. Among apoptosis-related transcripts, BIRC3, which encodes c-IAP-2, a direct inhibitor of caspase 9, was consistently elevated in both "resistant" and "survived" NK cells. However, shRNA-mediated knockdown of BIRC3 failed to restore sensitivity to CID, indicating that BIRC3 upregulation is not the unique determinant of resistance and suggesting involvement of additional compensatory pathways. Overall, our findings define specific transcriptional signatures associated with evasion of NK cells from iCasp9-mediated apoptosis, implying the contribution of cell cycle progression, enhanced anti-apoptotic signaling, and alterations in splicing regulation, and highlighting the complex role of non-canonical hTERT functions in these adaptations. In the rational design of next-generation gene-modified NK cell therapies with improved safety and persistence, the uncovered insights should be considered.