Levels of circulating regulatory CD4+CD25+ T cells are decreased in breast cancer patients after vaccination with a HER2/neu peptide (E75) and GM-CSF vaccine

SummaryPurpose We are conducting clinical trials in breast cancer (BrCa) patients to test the HER2/neu peptide vaccine (E75). We have investigated the impact of this vaccine on circulating levels of regulatory T cells (T_reg) and the resulting effects on antitumor responses.Experimental design Twenty-two blood samples from healthy individuals and from 22 BrCa patients including pre- and post-vaccination samples from seven vaccinated HLA-A2⁺ patients were stained for CD4, CD25, and CD69 as well as CD8 and E75:HLA-A2 Ig dimer and quantified by flow cytometry. Cytotoxic activity against HER2/neu ⁺ tumors was measured by ⁵¹Cr-release. Serum from BrCa patients and normal subjects were analyzed for TGF-β levels.Results BrCa patients have a greater percentage of circulating T_reg (CD4⁺CD25⁺, 4.45% versus 2.96%; p = 0.007) than normal subjects. HLA-A2⁺ BrCa patients had more T_reg compared to the HLA-A2^– BrCa patients (CD4⁺CD25⁺, 5.63% versus 3.28%; p = 0.001). E75 vaccination increased circulating activated CD4⁺ T cells post-vaccination (CD4⁺CD69⁺, 1.23 versus 3.81%; p = 0.03). However, T_reg were significantly reduced after vaccination (CD4⁺CD25⁺, 5.31–1.81%; p < 0.0001). Furthermore, activated T_reg also decreased (CD4⁺CD25⁺CD69⁺, 0.23% versus 0.08%; p = 0.06). Importantly, post-vaccination decreases in T_reg were temporally associated with increased E75 vaccine-specific CD8⁺ T cells and corresponding HER2/neu ⁺ tumor cytotoxicity. Serum TGF-β levels were significantly elevated in BrCa patients compared to normals (3548 pg/ml versus 1007 pg/ml; p = 0.007). Four of seven vaccinated patients showed decreased serum TGF-β levels post-vaccination.Conclusions T_reg, are increased in BrCa patients along with serum levels of TGF-β. E75 vaccination resulted in CD4⁺ recruitment but was associated with a significant decrease in circulating T_reg and TGF-β levels in the majority of the vaccinated patients. Successful cancer vaccination strategies may require the alteration of complex immune interactions.The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of the Army or the Department of Defense