Soluble CD146 cooperates with VEGF-A to generate an immunosuppressive microenvironment in CD146-positive tumors: interest of a combined antibody-based therapy.

Tumor development necessitates immune escape through different mechanisms. To counteract these effects, the development of therapies targeting Immune Checkpoints (ICP) has generated interest as they have produced lasting objective responses in patients with advanced metastatic tumors. However, many tumors do not respond to inhibitors of ICP, necessitating to further study the underlying mechanisms of exhaustion. Vascular Endothelial Growth Factor a (VEGFa), a pro-angiogenic molecule secreted by tumors, was described to participate to tumor immune exhaustion by increasing ICP, justifying in part the use of an anti-VEGFa monoclonal antibody (mAb), bevacizumab, in patients. However, recent studies from our group have demonstrated that tumors can escape anti-VEGFa therapy through the secretion of soluble CD146 (sCD146). In this study, we show that both VEGFa and sCD146 cooperate to create an immunosuppressive microenvironment by increasing the expression of ICP. In addition, sCD146 favors pro-tumoral M2-type macrophages and induces the secretion of pro-inflammatory cytokines. An anti-sCD146 mAb reverses these effects and displays additive effects with anti-VEGFa antibody to eliminate tumors in a syngeneic murine model grafted with melanoma cells. Combining bevacizumab with mucizumab could thus be of major therapeutic interest to prevent immune escape in malignant melanoma and other CD146-positive tumors.