Thy 1.2+ leukemia cells eradicated from in vitro leukemia-bone marrow cell mixtures by antibody-toxin conjugates.

A conjugate constituted by a monoclonal anti-Thy 1.2 antibody chemically coupled to the toxic subunit of ricin was synthesized. The conjugate was specifically cytotoxic for Thy 1.2+ (EL 4) but not for Thy 1.2- (BW5147) thymoma cells. In vitro treatment of bone marrow-leukemia cell mixtures (10:1 and 1:1 bone marrow to EL 4 cell ratios) with anti-Thy 1.2-ricin A chain totally eradicated EL 4 tumor cells, while the number of myeloid colony-forming units and pluripotent colony-forming units developed in vitro and in vivo was unaffected, which suggested that the treatment had no toxic side effects at least on the precursor cells examined.