Human CD4+ T lymphocytes recognize a vascular endothelial growth factor receptor-2-derived epitope in association with HLA-DR

Purpose: Given the multiple escape mechanisms of tumor cells, immunotherapy targeting tumor-dependent stroma may be an effective cancer treatment strategy. Animal models indicate that inducing immunity to tumor enclothelia engenders potent antitumor effects without significant pathology. Recently, the first human tumor enclothelial antigen vascular enclothelial growth factor receptor-2 (VEGFR-2) recognized by HLA class I-restricted CD8(+) T cells has been characterized. In this study, we sought to investigate specific recognition of this molecule by human CDC+ Tcells. Experimental Design: To identify HLA-DR-restricted antigenic pepticles on VEGFR-2 recognized by CDC Tcells of healthy donors and cancer patients. Results: Nine candidate VEGFR-2 pepticles with high binding probability to six common HLA-DRB1 alleles were synthesized using the SYFPEITHI algorithm. One 15-mer pepticle (EKRFVPDGNRISWDS), mapping to the 167-181 region of VEGFR-2, stimulated CDC Tcells in association with several HLA-DR alleles, including DR4 and DR7. Importantly, the epitope could be naturally processed and presented both by HILA-DR-matched antigen-expressing proliferating endothelial cells and by dendritic cells loaded with the native antigen. Furthermore, circulating VEGFR-2- specific CDC T cells were detected in 4 of 10 healthy donors and 12 of 40 cancer patients even after single-round pepticle stimulation in short-term culture. Patient's T cells could recognize a ntigen-expressing proliferating enclothelial cells in a HLA-DR-restricted fashion. Conclusion: These findings indicate an important role for the 167-181 region of VEGFR-2 in the stimulation of CD4(+) T cell responses to VEGFR-2 protein, and may be instrumental both for the development and monitoring of upcoming antitumor vessel vaccines against different cancers based on VEGFR-2 immunogens.