Trifunctional Bispecific Antibodies Induce Tumor-Specific T Cells and Elicit a Vaccination Effect

A major goal of tumor immunotherapy is the induction of long-lasting systemic T-cell immunity. Bispecific antibodies (bsAbs) that lack the immunoglobulin Fc region confer T-cell-mediated killing of tumor cells but do not induce long-term memory. In contrast, trifunctional bsAbs comprise an appropriate Fc region and, therefore, not only recruit T cells but also accessory cells that bear activating Fc gamma receptors (Fc gamma R), providing additional T-cell-activating signals and securing presentation of tumor-derived antigens to T cells. In this study, we show that trifunctional bsAbs induce a polyvalent T-cell response and, therefore, a vaccination effect. Mice were treated with melanoma cells and with a trifunctional bsAb directed against the melanoma target antigen ganglioside GD2 in addition to murine CD3. The trifunctional bsAb activated dendritic cells and induced a systemic immune response that was not replicated by treatment with the F(ab')(2)-counterpart lacking the Fc region. Restimulation of spleen and lymph node cells in vitro yielded T-cell lines that specifically produced interferon-gamma in response to tumor. In addition, trifunctional bsAb-induced T cells recognized various specific peptides derived from melanoma-associated antigens. Moreover, these polyvalent responses proved to be tumor-suppressive and could not be induced by the corresponding bsF(ab')(2)-fragment. Taken together, our findings provide preclinical proof of concept that trifunctional bsAbs can induce tumor-specific T cells with defined antigen specificity. Cancer Res; 72(16); 3958-66. (C) 2012 AACR.