Elimination of IL-10-Inducing T-Helper Epitopes from an IGFBP-2 Vaccine Ensures Potent Antitumor Activity

Immunization against self-tumor antigens can induce T-regulatory cells, which inhibit proliferation of type I CD4(+) T-helper (T(H)1) and CD8(+) cytotoxic T cells. Type I T cells are required for potent antitumor immunity. We questioned whether immunosuppressive epitopes could be identified and deleted from a cancer vaccine targeting insulin-like growth factor-binding protein (IGFBP-2) and enhance vaccine efficacy. Screening breast cancer patient lymphocytes with IFN-gamma and interleukin (IL)-10 ELISPOT, we found epitopes in the N-terminus of IGFBP-2 that elicited predominantly T(H)1 whereas the C-terminus stimulated T(H)2 and mixed T(H)1/T(H)2 responses. Epitope-specific T(H)2 demonstrated a higher functional avidity for antigen than epitopes, which induced IFN-gamma (P = 0.014). We immunized TgMMTV-neu mice with DNA constructs encoding IGFBP-2 N-and C-termini. T cell lines expanded from the C-terminus vaccinated animals secreted significantly more type II cytokines than those vaccinated with the N-terminus and could not control tumor growth when infused into tumor-bearing animals. In contrast, N-terminus epitope-specific T cells secreted T(H)1 cytokines and significantly inhibited tumor growth, as compared with naive T cells, when adoptively transferred (P = 0.005). To determine whether removal of T(H)2-inducing epitopes had any effect on the vaccinated antitumor response, we immunized mice with the N-terminus, C-terminus, and a mix of equivalent concentrations of both vaccines. The N-terminus vaccine significantly inhibited tumor growth (P < 0.001) as compared with the C-terminus vaccine, which had no antitumor effect. Mixing the C-terminus with the N-terminus vaccine abrogated the antitumor response of the N-terminus vaccine alone. The clinical efficacy of cancer vaccines targeting self-tumor antigens may be greatly improved by identification and removal of immunosuppressive epitopes. (C)2014 AACR.