Lysis of Prostate Carcinoma Cells by Trifunctional Bispecific Antibodies (αEpCAM × αCD3)

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Abstract
Bispecific monoclonal antibodies (bsAbs) are a promising immunotherapeutic option for treatment of cancer, especially in situations of minimal residual disease. The combination of an anti-CD3 and anti-tumor-associated antigen antibody redirects cytotoxic T-lymphocytes towards malignant cells. Using a trifunctional bispecific antibody against Ep-CAM × CD3, that additionally activates FcγR+ accessory cells via its Fc region, we investigated the interaction between three EpCAM+ prostate carcinoma cell lines and peripheral blood mononuclear cells (PBMCs) of healthy donors and patients with prostate carcinoma (PC). Visualization was performed by double immunocytochemical methods and computerized sequential video microscopy. Tumor cells and PBMCs supplemented with αEpCAM × αCD3 in 16-well chamber slides resulted in lysis of tumor cells within 1–3 days without any differences between patient and healthy donor PBMCs. The characteristic necrotic way of tumor cell killing (rounding, swelling, disrupting) could be observed in computerized sequences of video frames. Simultaneously, we could not reveal any form of apoptotic signal using three different apoptotic markers (TUNEL, M30 cyto death, anti-active caspase 3). Within the first 48 hr we observed typical PBMC cluster formation with increasing cell proliferation. PBMCs surrounding the tumor cells were not dominated by CD4+, CD8+, or CD14+ cells. Lymphocytes with pore-forming perforin proteins concentrated towards the tumor target cells. Our combination of double immunocytochemical and computerized video microscopic techniques may serve as an important improvement of validity of cell–cell interaction experiments using in vitro models.