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 endothelia engenders potent antitumor effects without significant pathology. Recently, the first human tumor endothelial antigen vascular endothelial 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 CD4(+) T cells.
Experimental design: To identify HLA-DR-restricted antigenic peptides on VEGFR-2 recognized by CD4(+) T cells of healthy donors and cancer patients.
Results: Nine candidate VEGFR-2 peptides with high binding probability to six common HLA-DRB1 alleles were synthesized using the SYFPEITHI algorithm. One 15-mer peptide (EKRFVPDGNRISWDS), mapping to the 167-181 region of VEGFR-2, stimulated CD4(+) T cells in association with several HLA-DR alleles, including DR4 and DR7. Importantly, the epitope could be naturally processed and presented both by HLA-DR-matched antigen-expressing proliferating endothelial cells and by dendritic cells loaded with the native antigen. Furthermore, circulating VEGFR-2-specific CD4(+) T cells were detected in 4 of 10 healthy donors and 12 of 40 cancer patients even after single-round peptide stimulation in short-term culture. Patient's T cells could recognize antigen-expressing proliferating endothelial 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.