A comparison of anti‐lymphocyte immunotoxins containing different ribosome‐inactivating proteins and antibodies
Immunotoxins were prepared with several single‐chain ribosome‐inactivating proteins (RIPs type 1) and with the A‐chain of ricin linked to the F(ab′)2 fragment of sheep anti‐mouse IgG. The cytotoxic activity of these conjugates was tested on human lymphocytes pretreated with an anti‐CD3 murine MoAb. The immunotoxins inhibited DNA synthesis in phytohaemagglutinin (PHA)‐stimulated lymphocytes with IC50S (concentrations causing 50% inhibition) ranging from 8.9 × 10−13 to 5.7 × 10−11m (immunotoxins containing dianthin 32, saporin, pokeweed antiviral protein from seeds (PAP‐S), bryodin, momordin, momorcochin, and trichokirin), 1 × 10−8m (immunotoxin containing gelonin) and 5 × 10−9m (immunotoxin containing ricin A‐chain). The immunotoxin containing saporin linked to the anti‐mouse IgG F(ab′)2 fragment was also highly toxic to human lymphocytes pretreated with anti‐CD2, ‐CD3, ‐CD5 and ‐CD45 MoAbs, with IC50s × 10−11m. Immunotoxins were prepared also with saporin linked to MoAbs against various CD antigens. The immunotoxin prepared with the anti‐CD3 antibody had the highest specific cytotoxicity to human lymphocytes.