The construction and expression of a recombinant immunotoxin consisting of a single chain antibody fused to ricin toxin is being studied. The use of recombinant DNA technology to design and express immunotoxins has numerous advantages over current biochemical methods of preparation. These include formation of a recombinant protein that contains only the sequences required for specific cell recognition and cytotoxic activity. Prokaryotic expression systems can provide high yields of uniformly produced protein. Intact ricin contains nonspecific galactose-binding sites. Currently these must be blocked by chemical means in order to permit the antibody portion of the immunotoxin to selectively target tumors. Expression of recombinant ricin in E. Coli will facilitate the mutagenesis and screening of genetically modified lectin-deficient ricin immunotoxins. If biologically active, a recombinant ricin immunotoxin will permit dissection of the nature of ricin binding and entry into cells, and will serve as a prototype in the molecular restructuring of other carrier protein/ricin hybrids.The potential commercial application as described by the awardee: A recombinant ricin immunotoxin has application in treating diseases of clonogenic origin. These include the treatment of cancer, graft versus host disease, transplant rejection, autoimmune disease and allergies.
