A recombinant bispecific single-chain antibody, CD19 x CD3, induces rapid and high lymphoma-directed cytotoxicity by unstimulated T lymphocytes

Although bispecific antibodies directed against malignant lymphoma have bee n shown to be effective in vitro and in vivo, extended clinical trials so f ar have been hampered by the fact that conventional approaches to produce t hese antibodies suffer from low yields, ill-defined byproducts, or laboriou s purification procedures. To overcome this problem, we have generated a sm all, recombinant, lymphoma-directed, bispecific single-chain (bsc) antibody according to a novel technique recently described. The antibody consists o f 2 different single-chain Fv fragments joined by a glycine-serine linker. One specificity is directed against the CD3 antigen of human T cells, and t he other antigen-binding site engages the pan-B-cell marker CD19, uniformly expressed on the vast majority of B-cell malignancies. The construct was e xpressed in Chinese hamster ovary cells and purified by its C-terminal hist ioline tag. Specific binding to CD19 and CD3 was demonstrated by fluorescen ce-activated cell sorter analysis. By redirecting unstimulated primary huma n T cells derived from the peripheral blood against CD19-positive lymphoma cells, the bscCD19 x CD3 antibody showed significant cytotoxic activity at very low concentrations of 10 to 100 pg/mL and at effector to target cell r atios as low as 2:1, Moreover, strong lymphoma-directed cytotoxicity at low antibody concentrations was rapidly induced during 4 hours even in experim ents without any T-cell prestimulation. Thus, this particular antibody prov es to be much more efficacious than the bispecific antibodies described unt il now. Therefore, the described bscCD19 x CD3 molecule should be a suitabl e candidate to prove the therapeutic benefit of bispecific antibodies in th e treatment of non-Hodgkin lymphoma. (C) 2000 by me American Society of Hem atology.