Mammaglobin-A cDNA vaccination of breast cancer patients induces antigen-specific cytotoxic CD4+ICOShi T cells

Abstract

Mammaglobin-A (Mam-A) is a 10 kDa secretory protein that is overexpressed in 80% of primary and metastatic human breast cancers. Previous studies from our laboratory demonstrated that Mam-A cDNA vaccine can induce Mam-A-specific CD8 T cell responses and mediate regression of human breast cancer xenografts in NOD/SCID mice. In this article, we present our results on a phase I clinical trial of a Mam-A cDNA vaccination in breast cancer patients with stage-IV metastatic disease, including the impact of vaccination on the expression of the inducible co-stimulator molecule (ICOS) on CD4 T cells. Specimens from seven patients with stage-IV metastatic cancer were available for these analyses. Patients were vaccinated with a Mam-A cDNA vaccine on days 0, 28, and 56, and immune responses were assessed at serial time points following vaccination. At 6 months following the first vaccination, flow cytometric analysis demonstrated a significant increase in the frequency of CD4+ICOS(hi) T cells from 5±2% pre-vaccination to 23±4% (p<0.001), with a concomitant decrease in the frequency of CD4+FoxP3+ T cells (regulatory T cells [Treg]) from 19±6 to 10±5% (p<0.05). ELISpot analysis of CD4+ICOS(hi) sorted T cells demonstrated that following vaccination the cytokines produced by Mam-A-specific T cells switched from IL-10 (78±21 spm pre-vaccination to 32±14 spm 5months post-vaccine p<0.001) to IFN-γ (12±6 spm pre-vaccination to 124±31 spm 5months post-vaccine p<0.001). The ratio of CD4+ICOS(hi) T cells to CD4+FoxP3+ T cells increased from 0.37±0.12 before vaccination to 2.3±0.72 (p=0.021) following vaccination. Further, these activated CD4+ICOS(hi) T cells induced preferential lysis of human breast cancer cells expressing Mam-A protein. We conclude that Mam-A cDNA vaccination is associated with specific expansion and activation of CD4+ICOS(hi) T cells, with a concomitant decrease in Treg frequency. These encouraging results strongly suggest that Mam-A cDNA vaccination can induce antitumor immunity in breast cancer patients.