MHC class II tetramer analyses in AE37-vaccinated prostate cancer patients reveal vaccine-specific polyfunctional and long-lasting CD4+ T-cells

Abstract

Realizing the basis for generating long-lasting clinical responses in cancer patients after therapeutic vaccinations provides the means to further ameliorate clinical efficacy. Peptide cancer vaccines stimulating CD4+ T helper cells are often promising for inducing immunological memory and persistent CD8+ cytotoxic T cell responses. Recent reports from our clinical trial with the AE37 vaccine, which is a HER2 hybrid polypeptide, documented its efficacy to induce CD4+ T cell immunity, which was associated with clinical improvements preferentially among HLA-DRB1*11+ prostate cancer patients. Here, we performed in-depth investigation of the CD4+ T cell response against the AE37 vaccine. We used the DR11/AE37 tetramer in combination with multicolor flow cytometry to identify and characterize AE37-specific CD4+ T cells regarding memory and Tregs phenotype in HLA-DRB1*11+ vaccinated patients. To verify vaccine-specific immunological memory in vivo, we also assessed AE37-specific CD4+ T cells in defined CD4+ memory subsets by cell sorting. Finally, vaccine-induced AE37-specific CD4+ T cells were assessed regarding their functional profile. AE37-specific memory CD4+ T cells could be detected in peptide-stimulated cultures from prostate cancer patients following vaccination even 4 y post-vaccination. The vast majority of vaccine-induced AE37-specific CD4+ T cells exhibited a multifunctional, mostly Th1 cytokine signature, with the potential of granzyme B production. In contrast, we found relatively low frequencies of Tregs among AE37-specific CD4+ T cells. This is the first report on the identification of vaccine-induced HER2-specific multifunctional long-lasting CD4+ T cells in vaccinated prostate cancer patients.