Promoting Immune Response of Human Vascular Endothelial Cells by Bevacizumab: Insights into the Immune Supportive Role of Anti-VEGF Therapy.

Compelling clinical evidence strongly indicates that anti-angiogenesis therapeutics including Bevacizumab, a humanised anti-VEGF mAb, can alleviate the resistance to immunotherapy. We explored the direct modulation of Bevacizumab on endothelial cell (EC) immune response including surface expression of adhesion and MHC molecules and EC-elicited proliferation of immune cells under inflammatory conditions. Flow cytometry showed that addition of VEGF inhibited TNF-α stimulation of expression of ICAM-1 and VCAM-1 on HUVECs, whereas Bevacizumab enhanced this TNF-α-stimulated expression. The presence of MHC Class I on HUVECs was decreased by VEGF and increased by TNF-α, respectively. Bevacizumab reversed VEGF downregulation and promoted TNF-α upregulation of MHC class I expression, suggesting that anti-VEGF treatment can boost the endothelial immunological reaction, a prerequisite for immune cell trafficking. Functionally, real-time monitoring of the proliferation of human PBMCs co-cultured on HUVEC monolayers over 3 days showed opposing effects on the proliferation of PBMCs between VEGF and TNF-α. Consistently, Bevacizumab antagonised VEGF suppression and sensitized TNF-α activation of PBMC growth over the time course. In line with these findings, Bevacizumab increased the surface expression of CD69 on VEGF-treated T cells collected from PBMCs after 3-day co-cultures with HUVECs. Furthermore, the proliferation of CD3+, CD8+ and CD4+ T cells was promoted via Bevacizumab. Collectively, this study demonstrates that targeting VEGF can enhance the immune response of ECs required for T cell recruitment. Our findings provide insights to a deeper understanding of increased vascular inflammatory response conferred by anti-VEGF treatment in addition to inhibiting angiogenesis, which supports its favourable dual role in the positive immunological synergism with immunotherapy.