Purpose: Induction of antitumor immune responses requires adequate function of dendritic cells. Dendritic cell defects in cancer patients have been implicated in tumor escape and the limited efficacy of cancer vaccines. Previous studies have shown that vascular endothelial growth factor (VEGF) plays a major role in abnormal dendritic cell differentiation and function in cancer. It has been proposed that inhibition of VEGF may result in improved immune responses. The goal of this study was to test this hypothesis.

Experimental Design: Fifteen patients with refractory solid tumors were enrolled into a phase I clinical trial of VEGF-Trap. Phenotype and function of different subsets of mononuclear cells were measured before and at different time points after the start of treatment.

Results: VEGF-Trap treatment did not affect the total population of dendritic cells, their myeloid or plasmacytoid subsets, myeloid-derived suppressor cells (MDSC), or regulatory T cells. It significantly increased the proportion of mature dendritic cells. However, that improvement was not associated with an overall increase in immune responses to various antigens and mitogens. A subset analysis revealed significant improvement in immune responses in patients who had no increase in the proportion of MDSC. An improvement in immune responses was absent in patients with an increase in the proportion of MDSC.

Conclusions: Inhibition of VEGF signaling may improve differentiation of dendritic cells in cancer patients. However, it was not sufficient to improve immune responses. This shows multifaceted nature of immune deficiency and points out to the need for complex approach to modulation of immune reactivity in cancer.