Construction and in vivo evaluation of an anti-PSA x anti-CD3 bispecific antibody for the immunotherapy of prostate cancer

Background: Cross-linking of tumor antigens with the T-cell associated CD3 antigen can be effectively achieved by bispecific monoclonal antibodies and lead to an increase in antigen-specific cytotoxicity in T cells. Because o f the high organ specificity of the prostate specific antigen (PSA) a bispe cific antibody (BiAb) directed against this antigen and CD3 may be a tool f or a highly specific immune therapy of prostate cancer. Methods: For genera ting BiAb, the quadroma technique was used. Binding properties both to CD3 and PSA were shown by flow cytometry with the CD3 expressing Jurkat cell li ne and fluorescein-labeled PSA. Specific tumor cell lysis was tested with t he PSA expressing prostate carcinoma cell line LNCaP as target and interleu kin-2 activated human peripheral blood lymphocytes as effector cells in a c hromium-51-release assay. For in vivo evaluation of the BiAb, a nude mouse model was used. The mice were inoculated with LNCaP prostate carcinoma cell s. Animals with growing tumors were treated with 100 mu g BiAb and 5x10(6) effector cells. Results: Three stable quadromas producing anti-CD3 x anti-P SA BiAb were established From the culture supernatant of one quadroma, BiAb was separated by affinity chromatography and rested in vitro and in vivo f or its ability to target effector T lymphocytes against appropriate tumor c ells. In vitro, a specific lysis of PSA expressing prostate carcinoma cells was demonstrated In vivo a significant reduction in tumor growth (p < 0.05 ) could be shown in nude mice treated with BiAb and effector cells as compa red to a group treated only with effector cells and an untreated control gr oup. Conclusion: In the present study, an anti-CD3 x anti-PSA-BiAb was demo nstrated to be effective against prostate carcinoma cells in vitro and in v ivo. Therefore this BiAb may be a tool for the immunotherapy of prostate ca ncer.