Background:Vascular endothelial growth factor action in tumour angiogenesis is well characterised; nevertheless, it functions as a key element in the promotion of the immune system's evasion by tumours. We sought to investigate the possible direct effect of VEGF on T-cell activation and through which type of VEGF receptor it exerts this effect on cells isolated from ovarian cancer patients' ascites.Methods:T cells isolated from the ascites of ovarian cancer patients were cultured with anti-CD3 and IL-2, with or without VEGF for 14 days and the number of viable T cells was counted. Cytotoxic activity of cultured T cells and expression of VEGF receptor-2 (VEGFR-2), was assayed.Results:The addition of VEGF in cultures significantly reduced the number and proliferation rate of T cells in a dose-dependent manner and CD3+ T cells expressed VEGFR-2 on their surface upon activation. Experiments with specific anti-VEGFR-2 antibodies revealed that the direct suppressive effect of VEGF on T-cell proliferation is mediated by VEGFR-2. We also showed that VEGF significantly reduced the cytotoxic activity of T cells.Conclusion:Our study showed that ascites-derived T cells secrete VEGF and express VEGFR-2 upon activation. Vascular endothelial growth factor directly suppresses T-cell activation via VEGFR-2.

The role of vascular endothelial growth factor (VEGF) in tumor angiogenesis is well characterized; nevertheless, it is also a key element in promoting tumor evasion of the immune system by downregulating dendritic cell maturation and thus T cell activation. We sought to investigate the possible direct effect of VEGF on T cell activation and through which type of VEGF receptor (VEGFR) it exerts this effect. Circulating T cells from healthy donors and ovarian cancer patients were expanded in cultures with anti‐CD3 and IL‐2 with or without VEGF for 14 days, and the number of T cells was assessed. Cultured T cells were also tested for their cytotoxic activity in a standard 4‐hr 51Cr‐release assay, and the expression of VEGFRs 1, 2 and 3 was assayed by flow cytometry, immunocytochemistry and Western blotting. To assess the ability of activated T cells to secrete VEGF, levels in culture supernatants were measured by enzyme linked immunosorbent assay. The addition of VEGF in cultures significantly reduced T cell proliferation in a dose‐dependent manner. Protein expression studies demonstrated that CD3+ T cells express VEGFR‐2 on their surface upon activation. Experiments with anti‐VEGFR‐2 antibodies showed that the direct suppressive effect of VEGF on T cell proliferation is mediated by VEGFR‐2. We also showed that VEGF significantly reduced the cytotoxic activity of T cells and that activated T cells secrete VEGF in the culture environment. Overall, our study shows that T cells secret VEGF and expresses VEGFR‐2 upon activation. VEGF directly suppresses T cell activation via VEGF receptor type 2.

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