P-07.03 A20 as a novel immune checkpoint in KRAS-driven lung adenocarcinoma

<h3>Background</h3> Lung cancer is the second most commonly diagnosed cancer worldwide and remains the leading cause of cancer-related mortality. Although immune checkpoint blockade therapy has become the first-line treatment for KRAS-mutated lung adenocarcinoma, resistance remains a significant challenge, highlighting the need for improved immunotherapy strategies. The anti-inflammatory protein A20, a key negative regulator of the NF-κB pathway, has emerged as a promising candidate for modulating the tumor microenvironment. Consequently, this study investigates how A20 modulation reshapes the tumor microenvironment, with the ultimate goal of enhancing the efficacy of immune-based therapies in KRAS-driven lung adenocarcinoma. <h3>Materials and Methods</h3> We used KRAS-driven lung adenocarcinoma mouse models to study how partial systemic downregulation of A20 affects the tumor immune microenvironment and immune response. Through adoptive transfer of A20 wild-type and A20-heterozygous antigen-specific T cells and by using A20 wild-type and A20 heterozygous recipients, we assessed their impact on cell therapy effectiveness. <i>Ex vivo</i>, we further analyzed how A20 downregulation influences CD8⁺ T cell cytotoxic activity and proliferation. <h3>Results</h3> Our study revealed that systemic reduction of A20, as observed in A20-heterozygous mice, induces an anti-tumorigenic tumor microenvironment. This microenvironment is characterized by enhanced infiltration of CD4⁺ and CD8⁺ T lymphocytes, as well as dendritic cells, in lung tumor-bearing mice. <i>Ex vivo</i> experiments showed that A20 downregulation in CD8⁺ T cells increases their proliferation and anti-tumor activity in cytotoxicity assays. Additionally, adoptive transfer of antigen-specific A20-heterozygous CD8⁺ T cells led to greater tumor growth reduction in Rag2^-/- recipient mice. Similarly, tumor-bearing A20-heterozygous recipients showed improved tumor control after receiving wild-type CD8⁺ T cells compared to wild-type recipients. These findings indicate that A20 downregulation enhances the anti-tumor activity of CD8⁺ T cells. Furthermore, systemic A20 reduction amplifies the efficacy of adoptive cell transfer by fostering a strongly anti-tumorigenic microenvironment in A20-heterozygous mice. <h3>Conclusions</h3> This study serves as proof of principle, demonstrating that systemic downregulation of A20 can shape a tumor-suppressive microenvironment and enhance CD8⁺ T cell effector functions, leading to better tumor control in KRAS-driven lung adenocarcinoma. These findings highlight the translational potential of A20 as a promising therapeutic target to optimize cellular and immunotherapies. By selectively modulating A20 expression in immune cells, this approach could significantly boost anti-tumor immunity. Moreover, combining controlled A20 knockdown with immune checkpoint blockade holds great promise for improving treatment efficacy. This work lays the foundation for further exploration of A20-targeted strategies in cancer therapy. M. Homolya: None. M. Schwab: None. M. Machtinger: None. E. Casanova: None. H.P. Moll: None.