OBJECTIVETo study and compare the biologic activity of two anti-PSA/anti-CD3 bispecific single-chain antibodies.

METHODSFlow cytometry (FCM) was used to detect the binding activity of two antibodies to CD3-positive cell line Jurkat and prostate carcinoma cell line LNCaP. The effect of the two antibodies in mediating tumor cell lysis in vitro was determined by using the 51Cr-release test. For in vivo evaluation of the two antibodies activity, a nude mouse model was used. The mice were inoculated with LNCaP prostate cancer cells.

RESULTSFCM showed that both the antibodies could bind Jurkat and LNCaP cells with high specificity. The percentages of the cells bond by the bispecific single-chain antibodies were 56.3% and 55.4%, and those by the multivalent antibodies were 74.0% and 83.0% respectively. Both the antibodies mediated a specific lysis of LNCaP cells in vitro, with activated CTLs as effector cells, and significantly reduced tumor growth of nude mice in vivo as compared with the untreated controls and the group treated with CTLs only (P <0.05). The experiment also showed that the multivalent antibody had a better activity than the bispecific antibody in binding antigens, mediating lysis of LNCaP cells and reducing tumor growth (P < 0.05).

CONCLUSIONBoth the anti-PSA/anti-CD3 bispecific single-chain antibody and multivalent antibody have good biologic activity, and the formation of the tetramerization of single-chain antibody can improve its biologic activity.