Targeting of glioblastoma with activated T cells armed with anti-CD3xanti-HER2/neu (HER2Bi) and anti-CD3xanti-EGFR (EGFRBi) bispecific antibodies

Abstract

3038 Background: Malignant gliomas are the most common primary brain tumors in adults. The prognosis for patients with glioblastoma remains poor despite aggressive multimodality treatment including surgery and chemoradiotherapy. The receptor tyrosine kinases EGFR, mutant EGFR (EGFRvIII), and HER2/neu are expressed on the majority of glioblastomas and are potential targets for activated T cells (ATCs) armed with bispecific antibodies (BiAbs). Methods: ATCs were generated from human peripheral blood mononuclear cells (PBMC) by culture for 14 days with monoclonal anti-CD3 and interleukin-2 and armed with HER2Bi and/or EGFRBi. HER2Bi- and/or EGFRBi-armed ATCs were examined for in vitro cytotoxicity (MTT and 51Cr release assays) against long-term malignant glioma lines (U87MG, U118MG, and U251MG) as well as primary glioblastoma lines derived from surgical specimens. Expression of EGFR and HER2/neu were evaluated by FACS. Anti-CD133 coated magnetic microbeads were used to separate CD133-positive and CD133-negative cell populations. Results: EGFRBi-armed ATCs killed up to 85% of U87, U118, and U251 targets. HER2Bi-armed ATCs exhibited comparable cytotoxicity against U118 and U251, but did not kill HER2-negative glioma U87. Cytotoxicity exhibited by either HER2Bi- or EGFRBi-armed ATCs against four primary glioblastoma cell lines was 50–80%. We found that both CD133-negative and CD133-positive cell populations were susceptible to killing by armed ATCs. When we armed ATCs simultaneously with HER2Bi and EGFRBi, killing by doubly armed ATCs was equal to or greater than that by EGFRBi-armed ATCs against the tested cell lines. Conclusions: BiAbs efficiently target ATCs to kill EGFR and/or HER2/neu expressing glioblastomas. Long-term malignant glioma cell lines and primary lines derived from surgical specimens are equally susceptible. Both CD133-negative and CD133-positive (the putative glioma stem cells) are killed. ATCs armed with BiAbs represent a potentially valuable adjuvant to current treatment. No significant financial relationships to disclose.