Abstract 2395: A bispecific T- cell engager antibody (BiTE) against TAG-72/ CD3 for targeted cancer immunotherapy

Abstract Background: Immunotherapies involving cytotoxic T lymphocytes (CTL’s) have been central to cancer immunotherapy. Bi-specific T cell engager antibody (BiTE) therapy has emerged as an effective immunotherapy by redirecting cytotoxic T cells against cell surface protein on tumor cells. Our BiTE antibody targets human tumor associated glycoprotein 72 (TAG-72). TAG-72 is a pan-carcinoma marker expressed on the surfaces of many cancer tissues including breast, prostate, ovary, endometrium, stomach, esophagus, and pancreas. It is not expressed in normal tissues making it an ideal target therapy for cancer. Our BiTE antibody can bind CD3 to activate the T-cell’s while simultaneously binding TAG-72 on the surface of the cancer cell leading to perforin induced cancer cell death. The in vitro and in vivo effects of TAG-72/ CD3 BiTE antibody on different cancer cells are presented here. Methods: We studied in vitro and in vivo effects of TAG-72/ CD3 BiTE antibody on different cancer cells; breast (DOX resistant MCF-7, SKBR3, MDA-MB-175 VII), ovarian (OVCAR-3), endometrium (KLE) and colon (Ls174T). In vitro cytotoxicity assay was performed by flow cytometry and immunofluorescence staining using live/ dead cell labelling fluorescent dyes. The cells were co-cultured with naïve human CD8 T cells with/ without BiTE antibody (1 µg, 5 µg and 10 µg) for different time intervals and assayed. In vivo study was carried out in NSG mice implanted with MCF-7 breast cancer cells + naïve human CD8 T cells and treated with a total of 4 doses of BiTE antibody (200µg/ dose). Results: Different tumor cells showed varying (%) of TAG-72 expression determined by flow cytometry, viz; DOX (55%), SKBR3 (16%), MDA 175 VII (8%), OVCAR-3 (27%), KLE (27%), Ls174T (30%). The BiTE antibody also showed dose dependent binding to these cells. Flow cytometry analysis showed that addition of the BiTE antibody to naïve CD8 T-cells and incubation for 4 days significantly increases tumor cell death as indicated by the Annexin V/ PI+ve signal from DOX (52.4% vs. 41.4% CD8 alone), SKBR-3 (47.9% vs. 30% CD8 alone), MDA 175 VII (23% vs 11% CD8 alone), OVCAR-3 (31.1% vs. 23.8% CD8 alone), KLE (27% vs 13% CD8 alone) and Ls174T (54% vs 29% CD8 alone) respectively (p<0.05). Further, a significant level of IFN-γ secreted by activated T-cells was only detected in the bispecific T-cell engager Ab + CD8 conditions. In vivo data showed good tumor regression at day 45 with tumors measuring (8 mm2) in group treated with BiTE antibody as compared to untreated group (31 mm2) (p<0.01). Conclusion: Our in vitro and in vivo data indicates that the TAG-72/ CD3 BiTE antibody can effectively redirect cytotoxic T cells against different cancer cells expressing TAG-72 glycoprotein and may be effective in the treatment of breast, ovarian, endometrium and colon cancers. Citation Format: Fatema Khambati, Hatem Soliman. A bispecific T- cell engager antibody (BiTE) against TAG-72/ CD3 for targeted cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2395.