Circulating regulatory (CD4+CD25+FOXP3+) T cells decrease in breast cancer patients after vaccination with an Ii-Key-modified class II HER2/ neu peptide (AE37)

Abstract #3134 Background: CD4+CD25+FOXP3+ regulatory T cells (Tregs) have been implicated in the suppression of immune responses against various tumors. To monitor the potential induction of Tregs in breast cancer (BrCa) patients receiving a modified HLA Class II HER2/neu peptide (AE37) vaccine in a clinical trial, we have analyzed peripheral blood lymphocytes (PBL) from vaccinated patients for the presence of Tregs and correlated our findings with ex vivo immune assays and in vivo delayed type hypersensitivity (DTH) responses to the vaccine. Methods: Fifteen BrCa patients have completed 6 monthly injections of the AE37+GM-CSF vaccine in a dose escalation safety study. The AE37 peptide consists of a HER2/neu peptide (776-790) linked to the Ii-Key moiety of the HLA Class II-associated invariant chain, which enhances epitope interaction with the Class II molecule. PBL obtained pre- and post-vaccination were stained with anti-CD4/CD25 (n=15) and FOXP3 (n=9) antibodies (PCH101 and 236A/E7) and analyzed by flow cytometry. Cells were also stimulated ex vivo with AE37 peptide to measure IFN-γ ELISPOT, proliferation (3H-thymidine-cpm) and cytokine secretion (TGF-β). DTH responses to the AE37 peptide pre- and post-vaccination were also recorded. Results: The mean CD4+ and CD4+CD25+ T cell populations for all patients (n=15) did not change from pre- to post-vaccination (CD4+ = 52.3+3.3% vs. 50.5+3.9%, p=0.6; CD4+CD25+ = 1.9+0.2% vs. 2.4+0.5%, p=0.2). Tregs (CD4+CD25+FOXP3+) were reduced in all 9 patients tested pre- to post-vaccination for both FOXP3 antibodies (Ab) (FOXP3 Ab1 = 2.1+0.2% vs. 1.1+0.1%, p=0.002; FOXP3 Ab2 = 2.0+0.2% vs. 1.0+0.2%, p=0.0009). There was no difference in pre- to post-vaccination levels of TGF-β (2720+582 pg/ml vs. 3387+848 pg/ml; p=0.9). AE37-specific proliferative responses increased from pre- to post-vaccination (34+23cpm vs. 6427+1431 cpm; p