Selective killing of target cells by antibody-ricin A chain or antibody-gelonin hybrid molecules: comparison of cytotoxic potency and use in immunoselection procedures

Ricin A chain and gelonin, two plant proteins that can powerfully reduce the protein synthetic capacity of ribosome preparations, were covalently coupled to a monoclonal anti-Thy-1.2 antibody. Two conjugates were prepared by using N-succinimidyl-3-2(-pyridyldithio)propionate, which generates a disulfide linkage between the component molecules. Both conjugates specifically killed Thy-1.2 antigen-bearing EL-4 cells, but had no effect on Thy-1.2- BW5147 cells. The cytotoxic potency of both reagents was determined by comparing the cloning efficiency of E1-4 target cells after treatment with the conjugate. The frequency of cells surviving treatment with 45 micrograms/10(6) cells of the gelonin conjugate was 1/72, whereas this frequency was 1/836 after exposure to 7 micrograms of the Ricin A chain conjugate. Both reagents could be successfully used to select Thy-1.2- cells from cell mixtures consisting of Thy-1.2+ and Thy-1.2- cells.