Abstract 4409: A bispecific T-cell engager effectively eradicates EGFRvIII-expressing glioblastoma multiforme

Abstract

Abstract Glioblastoma multiforme (GBM) is the most common primary brain tumor and remains uniformly lethal despite the progress of conventional therapies, which lack specificity and thus result in high toxicity to normal cells. Immunotherapy promises to induce robust tumor-specific immune responses that eliminate neoplastic cells with unparalleled specificity and with no additional toxicity to multimodality therapy. Recently, an approach using recombinant bispecific T-cell engagers (BiTEs), which consist of a tumor-targeting, single-chain antibody conjugated to a single-chain antibody directed against a T-cell activation ligand such as CD3, has arisen as a promising means for treating tumors. Human trials using a CD19XaCD3 BiTE confirmed the potency of these constructs by producing tumor regression in 7/7 patients with non-Hodgkin's lymphoma. The most significant limitation of these promising constructs, however, is the lack of tumor-specific targets that are frequently and homogeneously expressed. The epidermal growth factor receptor mutation EGFRvIII is a consistent 801-base-pair in-frame deletion in the extracellular domain of EGFR, not expressed in normal tissues but widely expressed in GBM and other common neoplasms. EGFRvIII also produces a constitutively active tyrosine kinase that enhances neoplastic cell growth and migration and confers radiation and chemotherapeutic resistance. Thus EGFRvIII appears to be a perfect anti-tumor target for these novel constructs. Here, we hypothesize that by targeting EGFRvIII through the T-cell engager MR1-1XaCD3, GBM will be efficiently eradicated. To test our hypothesis, we constructed the molecule MR1-1XaCD3, which consists of MR1-1, the murine anti-human EGFRvIII single-chain Fv, and aCD3, the murine anti-human CD3 single-chain Fv. MR1-1XaCD3 was expressed in and purified from bacteria BL21 (DE3), and the activity of this double function molecule was confirmed by FACS showing its specific binding to EGFRvIII-expressing cell lines, as well as human T cells. The cytotoxicity of MR1-1XaCD3 on EGFRvIII-expressing GBM D54MG. EGFRvIII cell lines was measured in vitro by standard chromium release assay. Preliminary results show that the MR1-1 construct is highly cytotoxic and antigen-specific, with an 8-fold increase in specific lysis for D54MG. EGFRvIII over the wild-type control. Currently, the efficacy of MR1-1XaCD3 is being evaluated in NOD/SCID gamma mice where human EGFRvIII-expressing xenografts have been implanted. In summary, our experiments showed that a human EGFRvIII-specific T-cell engager, MR1-1XaCD3, is effective on EGFRvIII-expressing tumor cells and provide new insights into GBM treatments. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4409.