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_H1) 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-g and interleukin (IL)-10 ELISPOT, we found epitopes in the N-terminus of IGFBP-2 that elicited predominantly T_H1 whereas the C-terminus stimulated T_H2 and mixed T _H1/T_H2 responses. Epitopespecific T_H2 demonstrated a higher functional avidity for antigen than epitopes, which induced IFN-γ (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 TH1 cytokines and significantly inhibited tumor growth, as compared with naεve T cells, when adoptively transferred (P = 0.005). To determine whether removal of T_H2- 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.