HUMAN GENE THERAPY 9:235-248 (January 20, 1998) Mary Ann Liebert, Inc. Targeting Strategy for Gene Delivery to Carcinoembryonic Antigen-Producing Cancer Cells by Retrovirus Displaying a Single-Chain Variable Fragment Antibody HIROYASU K0NISHI,i'2 TAKAHIRO OCHIYA,' KERRY A. CHESTER,^ RICHARD H.J. BE(^ENT,3 TETSUICHIRO MUTO,^ TAKASHI SUGIMURA,' and MASAAKI TERADA' ABSTRACT Cancer-specific antigens are promising targets for the specific delivery of certain drugs or genes to cancer cells in cancer therapy. Carcinoembryonic antigen (CEA) is one of the cancer-associated antigens predomi- nantly detected in the gastrointestinal cancer of the colon and stomach. Targeting strategies for CEA-pro- ducing cancer cells have been thoroughly developed mainly by the production of monoclonal antibodies to C E A and further single-chain variable fragment (scFv) antibodies. Here, we have generated Moloney murine leukemia virus-derived retroviral vectors co-displaying an anti-CEA scFv-envelope chimeric protein and an unmodified envelope protein to deliver a gene for hepres simplex virus thymidine kinase (HSV-tk) or Esch- erichia coli /3-galactosidase. The harvested viruses successfully incorporated the chimeric envelope protein as well as the unmodified envelope into the viral particles, and specifically bound to and infected human CEA- producing cancer cells via recognition of CEA, depending on the CEA-producing phenotype of the target cells. These results may have significant implications for the use of scFv directed against tumor-specific antigens for targeting specific antigen-producing cancer cells, a potential step toward in vivo cancer therapy. OVERVIEW SUMMARY antibodies should then be selected; and appropriate scFv in- sertion sites in the envelope protein, an appropriate linker Targeting to tumor-specific antigens is a powerful approach size between the scFv and the envelope, and an appropri- to obtain safe and efficient therapeutic effects in cancer gene ate expression ratio of the chimeric envelope to the un- therapy. The present study showed that a murine leukemia modified envelope should be determined. virus-derived virus co-displaying an anti-CEA scFv-enve- lope protein and an unmodified envelope could infect hu- man CEA-producing cancer cells and deliver a suicide gene INTRODUCTION to human CEA-producing cancer cells specifically through the recognition of CEA, depending on the CEA-producing r • iargeting to human tumor-specihc antigens has a great phenotype of the target cells. This strategy may possibly M. potential in cancer therapy for selective delivery of thera- lead to a specific killing of the antigen-producing cancer peutic agents or genes to cancer cells. Carcinoembryonic anti- cells by specific suicide gene delivery, and may also be ap- gen (CEA) is one oftiiemost extensively characterized tumor- plied to other tumor-specific cell-surface antigens or recep- associated antigens detected on the surface of cancer of tiie tors expressed solely on cancer cells. However, further im- colon, stomach, pancreas, lung, and breast as well as fetal in- provement is required to achieve more efTicient and specific testine (Gold and Freedman, 1965a,b). CEA is a glycosylphos- retroviral gene transfer. For this purpose, the following is- phatidylinositol (GPI)-anchored glycoprotein (Hefta ef al, sues should be addressed: Appropriate target antigens or 1988) belonging to the immunoglobulin superfamily (Oikawa receptors on target cells should be selected to facilitate more et al, 1987; Zknmermann et al, 1987; Sato et al, 1988). The efficient viral infection of the target cells; high-affinity scFv normal counterparts of C E A such as NCA-2 (Burtin etal, 1973) 'Genetics Division, National Cancer Center Research bistitute, Tokyo 104, Japan. ^First Department of Surgery, Faculty of Medicine, University of Tokyo, Tokyo 113, Japan. ^Department of Clinical Oncology, Royal Free Hospital School of Medicine, London NWl 4JL, UK. 235