Ghale, Romina

Abstract Introduction Immunotherapy has achieved remarkable success in hematologic malignancies, but its efficacy in solid tumors remains limited due to tumor heterogeneity, immune suppression within the tumor microenvironment, and inefficient T cell infiltration. I hypothesize that enhancing tumor cell sensitivity to cytokine-mediated killing can potentiate paracrine killing, in which T cell—derived cytokines induce tumor cell death even without direct cell—cell contact. This mechanism can overcome antigen heterogeneity and limited T cell penetration, broadening the therapeutic reach of immunotherapy. Methods I propose targeting ADAR1, an RNA-editing enzyme that suppresses innate immune activation, to enhance paracrine killing. Loss of ADAR1 leads to dsRNA accumulation and activation of PKR, MDA5, and RIG-I, sensitizing tumor cells to T cell—derived cytokines such as IFNγ and TNF. To test this, I performed in vitro paracrine killing co-culture assays using T cells from healthy donor PBMCs, antigen-positive tumor targets, and GFP-labeled antigen-negative ADAR1KO tumor targets. GFP signal loss in ADAR1KO cells will indicate enhanced paracrine killing independent of antigen recognition. Results My data show that ADAR1 inhibition sensitizes tumor cells to cytokine-mediated cytotoxicity, though how dsRNA sensor and cytokine receptor signaling intersect remains unclear. Supernatant from antigen-positive T cell—tumor co-cultures induced cell death in ADAR1KO but not WT tumor targets, indicating selective cytokine sensitivity. Consistently, Western blot analysis revealed increased cleaved Caspase-3 and PARP in ADAR1KO cells. The paracrine killing assay is ongoing. Conclusion This study aims to elucidate the interplay between dsRNA sensing and cytokine signaling in the absence of ADAR1 and to define how this crosstalk shapes the efficacy of paracrine killing in solid tumors. These insights could inform new therapeutic strategies to enhance the potency of immunotherapy against resistant and heterogeneous solid tumors. Funding Source n/a Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)

ABSTRACT Cytotoxic T lymphocytes (CTLs) are known to eliminate target cells through perforin-mediated, contact-dependent killing - a process limited by the number of effector T cells despite its serial nature. CTLs likely also possess a mass killing mechanism that can eliminate target cells more efficiently. Using CAR-T cells against B7H3 present on B16 tumor targets, we demonstrate that activated T cells can also kill targets in a perforin-independent manner by releasing diffusible TNF and IFNγ capable of killing nearby targets in a paracrine fashion even if they bear no antigen. Against an unperturbed target, paracrine killing is inefficient but is enhanced by the deletion of TNFR1 signaling molecules such as TAK1, HOIP, or TBK1/IKKε. Notably, these molecules are inhibited naturally by pathogen-encoded antagonists. Expression of a microbial-encoded antagonist, such as the Yersinia -encoded YopJ that antagonizes TAK1 or Ebola-encoded VP35 that antagonizes TBK1/IKKε, alters the target cell response to these cytokines from non-lethal to lethal. We propose that target cells are inherently resistant to killing by TNF and IFNγ, but the presence of a microbial factor alters this sensitivity, providing for the selective elimination of the infected cell while minimizing harm to uninfected bystander cells. We propose the term ‘pathogen-restriction’ to describe this discriminatory mechanism. Potentially, any microbial-derived factor that crosstalks with the TNF and IFNγ signaling pathways can function as a pathogen-restriction element. GRAPHICAL ABSTRACT Short Summary T cells use TNF and IFNγ to kill target cells in a paracrine manner where target elimination is restricted by the presence of pathogen-derived factors.