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In the present study, the efficacy of a new drug, i.e. the bispecific single-chain antibody MT110 targeting the epithelial antigen EpCAM and the T-cell antigen CD3 was tested ex vivo in malignant pleural effusions (MPEs). EpCAM ? epithelial cells were found in 78% of the MPEs (n = 18). Ex vivo treatment of seven MPEs resulted in a dose-dependent specific lysis of 37 ± 27% (±SD) EpCAM ? cells with 10 ng/ml (P = 0.03) and 57 ± 29.5% EpCAM ? cells with 1,000 ng/ml MT110 (P = 0.016) after 72 h. As a prerequisite for redirected lysis, stimulation of he autologous CD4 ? and CD8 ? cells in MPE by 1,000 ng/ml MT110 resulted in 21 ± 17% CD4 ? /CD25 ? and 29.4 ± 22% CD8 ? /CD25 ? cells (P = 0.016, respectively) after 72 h. This was confirmed by a 22-fold release of TNF-a and 230-fold release of IFN-c (1,000 ng/ml, 48 h, P = 0.03, respectively). Thus, relapsed breast cancer patients resistant to standard treatment might benefit from targeted therapy using MT110.Keywords Malignant pleural effusion Á Breast cancer Á Bispecific antibody Á EpCAM Á CD3 Á MT110 Á Ex vivo therapy

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Rationale: Despite therapy, most patients with advanced breast cancer develop malignant pleural effusion (MPE) associated with short survival. Strikingly, the metastatic cancer cells are frequently hormon receptor negative and show a reduced Her2/neu expression compared to the corresponding primary tumors. Thus, new treatment strategies are urgently needed.Objectives: In the present study, the efficacy of the bispecific single-chain antibody MT110 targeting both the epithelial antigen EpCAM (CD326) and the T cell antigen CD3 was investigated ex vivo with MPE samples of breast cancer patients.Methods: Target antigen expression of MPE cells was analyzed by immunohistochemistry. Percentage of redirected target cell lysis by MT110 was determined by double staining of cells with 7-amino actinomycin and an anti-EpCAM antibody using FACS analysis. Activation of autologous CD4+ and CD8+ cells in response to MT110 was studied by expression of CD25 and granzyme B using FACS staining and different cytokines (IL-2, IL-4, IL-6, IL-10, TNF-α and IFN-γ) using ELISA analysis.Results: EpCAM+ cells were found in 14 out of 18 (78%) MPE samples from metastatic breast cancer patients. The fraction of EpCAM+ pleural carcinoma cells varied between 30% and 100% (mean 78%). CD3-positive cells were detected in all MPE samples ranging from 60% to 93% (mean 80%). Seven effusion samples were analyzed for MT110 treatment and revealed a dose-dependent and specific redirected lysis of EpCAM+ cells after 48h and 72h with 10 ng/ml (48h, 72h: p=0.03, respectively) and 1000 ng/ml (48h, p=0.03; 72h, p=0.016). After 72 h, 57% ± 29.5% (mean ± SD) of EpCAM+ cells were killed using 1000 ng/ml MT110. The ratio between effector (E) and target (T) cells revealed no influence on the extent of the redircted specific lysis. Antibody treatment increased the fraction of CD25/CD4 cells after 48h (p=0.03) and 72h (p=0.016). Similar, CD25 expression on CD8 cells was stimulated after 48h (p=0.03) and 72h (p=0.016) using 1000 ng/ml MT110. Cytokine analysis revealed a strong TH1 immune response detecting an increased TNFα (p=0.016) and IFNγ (p=0.03) secretion. Conclusion: Single-agent therapy with MT110 is capable of activating unstimulated autologous T cells for efficient and specific redirected lysis of EpCAM+ tumor cells in MPE from breast cancer patients. MPE revealed interindividual differences regarding the extent of specific lysis and the stimulation of the microenvironmental T cells. Thus, treatment with the bispecific antibody MT110 might by an option in the management of a subcohort of metastatic breast cancer patients. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4133.