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 of the high organ specificity of the prostate specific antigen (PSA), a bispecific antibody (BiAb) directed against this antigen and CD3 may be a tool for a highly specific immune therapy of prostate cancer.

METHODS

For generating BiAb, the quadroma technique was used. Binding properties both to CD3 and PSA were shown by flow cytometry with the CD3 expressing Jurkat cell line and fluorescein-labeled PSA. Specific tumor cell lysis was tested with the PSA expressing prostate carcinoma cell line LNCaP as target and interleukin-2 activated human peripheral blood lymphocytes as effector cells in a chromium-51-release assay. For in vivo evaluation of the BiAb, a nude mouse model was used. The mice were inoculated with LNCaP prostate carcinoma cells. Animals with growing tumors were treated with 100 micrograms BiAb and 5 x 10(6) effector cells.

RESULTS

Three stable quadromas producing anti-CD3 x anti-PSA BiAb were established. From the culture supernatant of one quadroma, BiAb was separated by affinity chromatography and tested in vitro and in vivo for its ability to target effector T lymphocytes against appropriate tumor cells. 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 compared to a group treated only with effector cells and an untreated control group.

CONCLUSION

In the present study, an anti-CD3 x anti-PSA-BiAb was demonstrated to be effective against prostate carcinoma cells in vitro and in vivo. Therefore this BiAb may be a tool for the immunotherapy of prostate cancer.