Transplant Immunology 1996; 4: 257-264 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Gene theram in transdantation Stuart J Knechtle, Yuan Zhai and John Fechner Division of Transplantation, Department of Surgery, Madison, Wisconsin Received 15 April 1996; accepted for publication 7 May 1996 Introduction The field of gene therapy has received considerable attention in recent years as a promising new approach to the treatment of genetically determined diseases, as well as a host of other appli- cations, including cancer, AIDS, cardiovascular disease and neurologic disease. Because of exuberant early enthusiasm, and perhaps the promise of early returns, the field of gene therapy has been criticized as being slow to yield clinical applications. Regardless of expectations, the field has continued to move for- ward at the experimental level and progress has been directly linked to new developments in molecular biology, principally the advent of new and better ways of transferring genes in vitro and in vim, a better understanding of the molecular genetics of the immune response, and a growing understanding of strategies to genetically manipulate the host. This review will discuss the current techniques of gene transfer in general and then focus on strategies being con- sidered at the experimental level for application to transplan- tation. Strategies of gene transfer to specific transplanted organs are reviewed. In view of the high success rate of human organ transplants using non-specific immunosuppressive stra- tegies, gene therapy approaches are not currently justified for clinical application. However, since the ultimate goal of trans- plant immunology is the development of tolerance, gene ther- apy strategies may play an important role in achieving this elusive goal in the future. The role of DNA in transplantation immunity was first con- sidered by Haskova and Hrubesova in 1958 when they reported that donor type DNA transferred intraperitoneally to recipient strain mice did not immunize recipients.’ In actuality, a low level of immunity was produced in some recipients, but this was attributed by Peter Medawar in an editorial response to be due to antigenic contamination with polysaccharides. A role for DNA transfer in immune tolerance was considered by Florsheim, who devised a method of replacing murine hemato- poietic cells damaged by treatment with alkalinizing agent.* Florsheim attempted to replace murine hematopoietic cells with allogeneic hematopoietic cells following incubation of the donor cells with DNA or DNA/RNA complex derived from recipient strain spleen and thymus. Unfortunately, the allog- Address for correspondence: Stuart J Knechtle, Department of Surgery, University of Wisconsin Hospital, 600 Highland Avenue, Madison, WI 53792, USA. 0 Arnold 1996 eneic donor cells did not increase the survival of recipient mice treated with dimethyhnyleran. Both of these early experiments, if repeated today using slightly different approaches, might have led to different conclusions had current gene transfer technology been understood at the time. For instance, if Has- kova and Hrubesova had injected their DNA intramuscularly instead of intraperitoneally, they may well have immunized their recipients effectively, as was later reported by Geissler et aL3 If Florsheim had been able to accomplish efficient gene transfer to hematopoietic cells, he might have produced stable allogenic bone marrow graft survival. Gene therapy offers several theoretical and practical advan- tages in the field of transplantation. From the perspective of transplant immunology, transfer of a single allogeneic gene to a recipient permits the study of the immune response to a sin- gle allogeneic antigen rather than a host of allogeneic or foreign antigens. Although this goal can be achieved using congenic inbred strains of laboratory animals, gene therapy approaches give considerably more flexibility in this area. Another advantage is that gene therapy can be targeted to a specific organ or tissue. This feature lends itself to the concept of local immunosuppression confined to the transplanted organ. In contrast to protein administration, in vivo gene ther- apy also offers the possibility of continuous long-term expression of a gene product under biological control. In the same way that DNA vaccines are being considered for gene therapy approaches to infectious disease, gene therapy approaches in transplantation might include the strategy of tolerizing to either a specific or a broad range of MHC anti- gens. Clearly, gene therapy offers many potential advantages for mechanistic studies in the field of transplant immunology as well as therapeutic strategies. Gene therapy can be divided into somatic cell gene therapy, which is considered in this review, and germ line gene therapy. Genetic manipulation of germ line cells results in transgenic animals which have become a useful tool for studying mech- anisms of transplant tolerance. This approach is also being developed as a therapeutic strategy for xenotransplantation. Namely, transgenic pigs are being developed as potential sources of organs for human transplantation.4-6 While germ line gene therapy and transgenic animals have exciting poten- tial, this is another large field of its own and will not be con- sidered. This review will be limited to somatic cell gene ther- apy applications in transplantation.