Vascular endothelial growth factor blockade reduces intratumoral regulatory T cells and enhances the efficacy of a GM-CSF - Secreting cancer immunotherapy

Purpose: The purpose of the present study was to evaluate granulocyte macrophage colony-stimulating factor (GM-CSF) -secreting tumor cell immunotherapy in combination with vascular endothelial growth factor (VEGF) blockage in preclinical models. Experimental Design: Survival and immune response were monitored in the B16 melanoma and the CT26 colon carcinoma models. VEGF blockade was achieved by using a recombinant adeno-associated virus vector expressing a soluble VEGF receptor consisting of selected domains of the VEGF receptors 1 and 2 (termed sVEGFR1/R2). Dendritic cell and tumor infiltrating lymphocyte activation status and numbers were evaluated by fluorescence-activated cell sorting analysis. Regulatory T cells were quantified by their CD4(+)CD25(hi) and CD4(+)FoxP3(+) phenotype. Results: The present study established that GM-CSF - secreting tumor cell immunotherapy with VEGF blockade significantly prolonged the survival of tumor-bearing mice. Enhanced anti-tumor protection correlated with an increased number of activated CD4(+) and CD8(+) tumor-infiltrating T cells and a pronounced decrease in the number of suppressive regulatory T cells residing in the tumor. Conversely, overexpression of VEGF from tumors resulted in elevated numbers of regulatory T cells in the tumor, suggesting a novel mechanism of VEGF-mediated immune suppression at the tumor site. Conclusion: GM-CSF -secreting cancer immunotherapy and VEGF blockade increases the i.t. ratio of effector to regulatory T cells to provide enhanced antitumor responses. This therapeutic combination may prove to be an effective strategy for the treatment of patients with cancer.