Regulation Of CD8~+T Cells Infiltration And Immunotherapy By CircMGA/HNRNPL Complex In Bladder Cancer

Objective:Immunotherapies targeting the PD-1/PD-L1 are expected to revolutionize the treatment paradigm of bladder cancer.However,only a small number of patients respond to the current immunotherapy treatment.Accumulating evidence indicates that circular RNAs(circRNAs)are not simply a by-product of splicing but are functional.Nevertheless,how to improve immunotherapy response and the role of circRNAs in immunotherapy are yet to be well revealed.Methods:Through analyzing the expression profile of circRNAs in bladder cancer tissues,RNase R treatment and Actinomycin D assay,RNA FISH,RIP,circRNA pull down assay and mass spectrometry analysis,circMGA was identified and its interaction with HNRNPL was also confirmed.The effects of circMGA/HNRNPL complexes on CCL5 mRNA stability was examined by RNA stability assay.Chemotaxis assay and CCK-8 assay were used to investigate the functions of circMGA and HNRNPL in recruiting CD8+T cells into tumors and subsequently the killing effect on tumor cells.Biological implications of circMGA and HNRNPL in bladder cancer were implemented in the humanized immune mice models.Results:CircMGA was downregulated in bladder cancer and expression was positively correlated with favorable prognosis.Moreover,circMGA interacted with HNRNPL protein,which increased the expression of CCL5 and recruited CD8+T cells into tumor tissues to further enhance the immunotherapeutic effect of anti-PD-1 antibodies in vitro and in vivo.Mechanistically,circMGA augmented the interaction between HNRNPL and CCL5,ultimately contributing to stabilize mRNA of CCL5,which mediated recruitment of CD8+T cells.Importantly,circMGA potentiated response to PD-1 checkpoint blockade in the humanized immune mice models.Conclusions:We provide the first line of comprehensive evidence that circMGA is an important tumor suppressor as well as a prognostic biomarker for bladder cancer.CircMGA exerts a critical role in stabilizing CCL5 mRNA by forming a circMGA/HNRNPL complex to suppress bladder cancer progression.Importantly,our findings implies that circMGA,as a potent co-treatment strategy with anti-PD-1,may have attractive potential for future combination immunotherapy of bladder cancer.