Development of a recombinant hCG-specific single chain immunotoxin cytotoxic to hCG expressing cancer cells

A large number of cancers express human chorionic gonadotropin (hCG) or its subunits ectopically. Patients harboring such cancers have poor prognosis and adverse survival. PiPP is a monoclonal antibody of high affinity and specificity for hCGβ/hCG. Work was carried out to develop a PiPP based recombinant immunotoxin for the immunotherapy of hCG expressing cancers. Recombinant PiPP antibody was constructed in scFv format in which gene encoding the VH and VL domains were joined through a linker. This scFv gene was fused to the gene expressing Pseudomonas exotoxin (PE38), and cloned in a Escherichia coli based expression vector under the control of strong bacteriophage T7 promoter. Immunotoxin conjugating scFv(PiPP) and PE38, was expressed in E. coli as recombinant protein. Recombinant PiPP immunotoxin was purified from the bacterial cell lysate and tested for binding and killing of hCGβ expressing lymphoma, T-lymphoblastic leukemia and lung carcinoma cells in vitro. Immunotoxin showed nearly 90% killing on the cells. This is the first ever report on recombinant immunotoxin for binding and cytotoxicity to hCG expressing cancer cells, and thus can be a potential candidate for the immunotherapy of hCG expressing cells.