Feedback loop between fatty acid transport protein 2 and receptor interacting protein 3 pathways promotes polymorphonuclear neutrophil myeloid-derived suppressor cells-potentiated suppressive immunity in bladder cancer

Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) promote tumor immune tolerance and cause tumor immunotherapy failure. In this study, we found that high PMN-MDSCs infiltration, overexpressed fatty acid transporter protein 2 (FATP2) and underexpressed receptor-interacting protein kinase 3 (RIPK3) existed in the mouse and human bladder cancer tissues. However, the related mechanisms remain largely unknown.

Both FATP2 and RIPK3 expressions were associated with clinical stage. FATP2 knockout or up-regulating RIPK3 reduced the synthesis of prostaglandin E2 (PGE2) in PMN-MDSCs, attenuated the suppressive activity of PMN-MDSCs on CD8⁺ T cells functions and inhibited the tumor growth. There was a PGE2-mediated feedback loop between FATP2 and RIPK3 pathways, which markedly promoted the immunosuppressive activity of PMN-MDSCs. Combination therapy with inhibition of FATP2 and activation of RIPK3 can effectively inhibit tumor growth.

This study demonstrated that a feedback loop between FATP2 and RIPK3 pathways in PMN-MDSCs significantly promoted the synthesis of PGE2, which severely impaired the CD8⁺ T cell functions. This study may provide new ideas for immunotherapy of human bladder cancer.