VEGFA-VEGFR Pathway Blockade Inhibits Tumor-Induced Regulatory T-cell Proliferation in Colorectal Cancer

Multitarget antiangiogenic tyrosine kinase inhibitors (TKI) have been shown to reduce regulatory T cells (Treg) in tumor-bearing animals and patients with metastatic renal carcinomas. However, a direct role of the VEGF-A/VEGFR pathway inhibition in this phenomenon is a matter of debate and molecular mechanisms leading to Treg modulation in this setting have not been explored to date. Treg proportion, number, and proliferation were analyzed by flow cytometry in peripheral blood of patients with metastatic colorectal cancer (mCRC) treated with bevacizumab, a monoclonal antibody targeting specifically VEGF-A, and in colon cancer-bearing mice (CT26) treated with drugs targeting the VEGF/VEGFR axis. The direct impact of VEGF-A on Treg induction was assessed together with specific blockade of different isoforms of VEGFRs that may be involved. In CT26-bearing mice, anti-VEGF antibody and sunitinib treatments reduced Treg but masitinib, a TKI not targeting VEGFR, did not. Targeting VEGF-A/VEGFR axis seems sufficient to affect Treg percentages, without any changes in their function. Similarly, bevacizumab inhibited Treg accumulation in peripheral blood of patients with mCRCs. In vitro, Treg expressing VEGFR from tumor-bearing mice directly proliferated in response to VEGF-A. Anti-VEGF-A treatment decreased Treg proliferation in mice as well as in patients with mCRCs. VEGFR-2- but not VEGFR-1-specific blockade led to the same results. We identified a novel mechanism of tumor escape by which VEGF-A directly triggers Treg proliferation. This proliferation is inhibited by VEGF-A/VEGFR-2 blockade. Anti-VEGF-A therapies also have immunologic effects that may be used with a therapeutic goal in the future. Cancer Res; 73(2); 539-49. (c) 2012 AACR.