Abstract
Immune recognition of tumor targets by specific cytotoxic lymphocytes is essential for the effective rejection of tumors. A phase I clinical trial of ipilimumab (an antibody that blocks CTLA-4 function) in combination with bevacizumab (an antibody that inhibits angiogenesis) in patients with metastatic melanoma found favorable clinical outcomes were associated with increased tumor endothelial activation and lymphocyte infiltration. To better understand the underlying mechanisms, we sought features and factors that changed as a function of treatment in patients. Ipilimumab plus bevacizumab (Ipi-Bev) increased tumor vascular expression of ICAM1 and VCAM1. Treatment also altered concentrations of many circulating cytokines and chemokines, including increases of CXCL10, IL1α, TNFα, CXCL1, IFNα2, and IL8, with decreases in VEGF-A in most patients. IL1α and TNFα induced expression of E-selectin, CXCL1, and VCAM1 on melanoma tumor-associated endothelial cells (TEC) in vitro and promoted adhesion of activated T cells onto TEC. VEGFA inhibited TNFα-induced expression of ICAM1 and VCAM1 and T-cell adhesion, which was blocked by bevacizumab. CXCL10 promoted T-cell migration across TEC in vitro, was frequently expressed by melanoma cells, and was upregulated in a subset of tumors in treated patients. Robust upregulation of CXCL10 in tumors was accompanied by increased T-cell infiltration. Ipi-Bev also augmented humoral immune responses recognizing targets in melanoma, tumor endothelial, and tumor mesenchymal stem cells. Our findings suggest that Ipi-Bev therapy augments immune recognition in the tumor microenvironment through enhancing lymphocyte infiltration and antibody responses. IL1α, TNFα, and CXCL10, together with VEGF neutralization, contribute to Ipi-Bev-induced melanoma immune recognition. Cancer Immunol Res; 4(10); 858-68. ©2016 AACR.