Inhibition of tumor cell growth by antibodies induced after vaccination with peptides derived from the extracellular domain of Her-2/neu.

Abstract

The anti Her-2/neu monoclonal antibody Trastuzumab has strong inhibiting effects on tumor growth in vitro and in vivo and is therefore used for immunotherapy in breast cancer patients. Due to necessity of frequent applications, however, cost intensiveness of Trastuzumab treatment and its limited duration of affectivity, an active immunization inducing a perhaps preventive and long-term immunity to Her-2/neu remains a desirable goal. We attempted to induce anti Her-2/neu antibodies by peptide vaccination and to test their efficacy in inhibiting tumor cell growth in vitro. By computer aided analyses, 7 putative B cell epitopes of Her-2/neu were defined and synthesized. These peptide epitopes were coupled to tetanus toxoid and used for immunization in BALB/c mice. Among these peptides, immunizations with 2 single peptides or a combination of 2 peptides induced anti-peptide antibody levels, primarily of the IgG1 isotype. These antibodies were also directed against the native Her-2/neu antigen, as shown in precipitation assays and ELISA with cell lysates of the Her-2/neu overexpressing breast cancer cell line SK-BR-3. Isolated IgG fractions from immune sera incubated with SK-BR-3 cells led to a moderate inhibition of the tumor cell growth in vitro, as well as to complement dependent cell lyses comparable to that achieved by incubation with Trastuzumab. Moreover, peptide immunization in rabbits generated anti-Her 2-neu IgG that, in contrast to mouse sera, were able to mediate a 31-46% lysis of SK-BR-3 cells in ADCC experiments. We conclude from our data that immunization with Her-2/neu peptides successfully induced humoral immune response with anti-tumor activity in an animal model.