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.

KEYWORDS:

• Antigen-specific memory CD4⁺ T-cells
• cancer vaccines
• MHC Class II tetramer
• prostate cancer
• Tregs

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank Panagiotis Tzonis, MD for the clinical support and Joanne Kalogeropoulou for excellent technical assistance.