T-cell based cancer immunotherapy with a bispecific antibody directed at CD3 and EGFR

2552 Background: Epidermal growth factor receptor (EGFR) is expressed on various normal and malignant human tissues. Overexpression of EGFR and its role in proliferation of some malignant tumor cells make it a therapeutic target. Unfortunately, results from clinical trials suggest limited anti-tumor activity mediated by anti-EGFR (cetuximab) despite high affinity (HA) binding to the receptor. Exploiting this HA for for cytotoxic T cell therapy, we developed a bispecific antibody, EGFRBi, produced by chemical heteroconjugation of anti-CD3 and anti-EGFR, with which we then arm activated T cells (ATC). Methods: ATC from normal and patient donors were expanded ex vivo. Specific cytolytic activity of ATC armed with EGFRBi (50 ng/106 ATC; dose-titration optimized) against EGFR-expressing cell lines derived from lung (A549, Calu-6, IMR-90); pancreas (MIA PaCa-2, COLO 356/FG); colon (LS174T, HCT-8); brain (U-373 MG, U-87 MG; SK-N-MC); and skin (SCC-25, A431) or an EGFR-negative breast carcinoma (MDA-MB-453) was evaluated in Cr51 release assays. Results: At effector:target ratios (E:T) ranging from 3.125:1 to 50:1, EGFRBi-armed ATC induced significant cytotoxicity (23 to 79%, respectively) against all the EGFR+ cell lines compared to unarmed ATC, unconjugated mAbs, or ATC armed with an irrelevant BiAb (OKT3 x Rituximab, CD20Bi). No enhanced EGFRBi-armed ATC killing was noted against the EGFR- cells, and cytotoxicity was competitively blocked in the presence of cetuximab. After binding to EGFR+ tumor cells, EGFRBi-armed ATC secreted significantly higher levels of anti-tumor associated cytokines, IL2, RANTES, IFNγ and TNFα, compared to unarmed or CD20Bi-armed ATC. Conclusions: Our studies show significantly enhanced, specific cytotoxicity mediated by EGFRBi-armed ATC directed at multiple tumor cell lines expressing EGFR compared to treatment with unarmed ATC or cetuximab alone. Combining anti-EGFR antibody targeting with non-MHC restricted cytotoxicity of ATC into a single biologic drug may bypass limitations of receptor functional status when using cetuximab alone. These data and in vivo observations in an animal model provide the basis for phase I/II clinical trials using EGFRBi-armed ATC to target various tumor types. No significant financial relationships to disclose.