IDDF2024-ABS-0175 Ribonucleases 1 promotes the polarization of tumor-associated macrophages into anti-inflammatory phenotypes by targeting ALK in hepatocellular carcinoma

<h3>Background</h3> Ribonucleases (RNases) are secreted in the circulatory system and are reported to mediate physiologically and pathologically relevant cellular events, including cancer cell growth, cancer cell stemness, and regenerative capabilities. However, little is known about the regulation and function of RNases in the tumor microenvironment (TME) of hepatocellular carcinoma (HCC). <h3>Methods</h3> Transcriptome analyses were performed to compare the secreted proteins in responders and non-responders among patients receiving Nivolumab. Cytometry by time-of-flight analyses and flow cytometry analyses were performed to evaluate the immunosuppressive role of ribonucleases 1 (RNase1) in an HCC orthotopic mouse model. The ligand-receptor relationship between RNase1 and ALK was validated by Duolink and immunoprecipitation assays. Clinical relevance between RNase1 and immune status in 174 HCC patients was established by retrospective analysis. <h3>Results</h3> We observed that secreted RNase1 was abundant in non-responders and associated with poor prognosis in HCC. Mechanisms, RNase1 polarized macrophages to a tumor growth-promoting (M2) phenotype by activating anaplastic lymphoma kinase (ALK) signaling and prevented from CD8+ T cell tumor-infiltration, contributing to anti-PD-1 resistance. Targeting the RNase1/ALK axis reprogrammed the macrophage polarization, with increased CD8+ T- and Th1- cell recruitment. In addition, combined treatment of ALK inhibitor and anti-PD-1 results in enhanced tumor regression and long-term immunity in HCC. <h3>Conclusions</h3> This work reveals a previously undescribed mechanism whereby secretion of human RNase1 drives HCC resistance to immunotherapy, promotes an immunosuppressive TME and points to avenues for improving the efficacy of immunotherapy.