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★

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Abstract
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 (Treg) and the resulting effects on antitumor responses. 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. BrCa patients have a greater percentage of circulating Treg (CD4+CD25+, 4.45% versus 2.96%; p = 0.007) than normal subjects. HLA-A2+ BrCa patients had more Treg 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, Treg were significantly reduced after vaccination (CD4+CD25+, 5.31–1.81%; p < 0.0001). Furthermore, activated Treg also decreased (CD4+CD25+CD69+, 0.23% versus 0.08%; p = 0.06). Importantly, post-vaccination decreases in Treg 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. Treg, 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 Treg and TGF-β levels in the majority of the vaccinated patients. Successful cancer vaccination strategies may require the alteration of complex immune interactions.

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