Purified immunotoxins that are reactive with human lymphoid cells. Monoclonal antibodies conjugated to the ribosome-inactivating proteins gelonin and the pokeweed antiviral proteins.

Seven different monoclonal antibodies of the IgG class that are reactive with four different antigens on human lymphoid cells were utilized to form immunotoxins with the ribosome-inactivating proteins gelonin and the three known pokeweed antiviral proteins. Thirteen different immunotoxin combinations were prepared. The ribosome-inactivating proteins were modified with 2-iminothiolane. The sulfhydryl groups so introduced were reacted with maleimido groups or with dithiopyridyl groups that had been introduced into the antibodies. The toxin-antibody conjugates so formed were purified by affinity chromatography on protein A-Sepharose CL-4B, ion exchange chromatography, and by gel filtration and were characterized by polyacrylamide-dodecyl sulfate gel electrophoresis. The purified immunotoxins were free of nonconjugated monomeric proteins and aggregates of very high molecular weight. All the immunotoxins showed the specific binding of the component antibody as measured by indirect immunofluorescence binding assays. The activities of the ribosome-inactivating proteins were unaffected by conjugation where the cross-link to the antibody contained a disulfide bond and when assayed after reductive cleavage of the linker. Disulfide-linked immunotoxins with six of the antibodies were highly cytotoxic for the target cells. However, immunotoxins containing an anti-B1 antibody showed no cytotoxicity.