Anti-CD3 × Anti-HER2 Bispecific Antibody Effectively Redirects Armed T Cells to Inhibit Tumor Development and Growth in Hormone-Refractory Prostate Cancer–Bearing Severe Combined Immunodeficient Beige Mice

The bispecific antibody (BiAb) anti-CD3 × anti-Her2/neu (Her2Bi), combines Her2/neu targeting with nonmajor histocompatibility complex–restricted cytotoxicity mediated by activated T cells (ATCs). To evaluate this adaptive immunotherapeutic strategy for augmenting antitumor immune response toward hormone-refractory prostate cancer (HRPC), normal donor or patient T cells were activated with anti- CD3, expanded ex vivo in interleukin-2, and then armed with Her2Bi (5-500 ng per million ATCs). In vitro, arming ATCs with Her2Bi increased the percent specific cytotoxicity toward PC-3 prostate adenocarcinoma cells 2-3 fold and increased the secretion of Th₁ cytokines granulocyte-macrophage colony-stimulating factor, tumor necrosis factor–α, and interferon-γ when compared with unarmed ATCs or ATCs armed with an irrelevant BiAb. Her2Bi-armed ATCs administered with PC-3 (Winn Assay) or injected intratumorally prevented development or induced remissions, respectively, of PC-3 tumors in severe combined immunodeficient beige mice. Intravenously administered Her2Bi-armed ATCs localized to PC-3 xenografts mediated cytotoxicity toward tumor cells and produced significant tumor growth delay of PC-3 tumors, but not Her2/neu–negative LS174T colon adenocarcinoma xenografts. By flow cytometry analyses, Her2Biarmed ATCs had a proliferative advantage over unarmed ATCs and persisted in the circulation and tumor tissues longer than unarmed ATCs. These findings suggest that Her2Bi-armed ATC therapy may be an effective, nontoxic, tumor-specific treatment for Her2-positive HRPC.