Transgenic expression of CTLA4-Ig by fetal pig neurons for xenotransplantation

Cellular xenotransplantation

PURPOSE OF REVIEW

Expectations are high on cellular therapy. Being fundamental to elucidate organogenesis, it is unlikely that embryonic stem cells will be used for clinical purposes. Postembryonic stage, developing cells are, therefore, the front-runner for regenerative medicine. In addition to autologous cells, both allogeneic and xenogeneic cells are hypothetical candidates to treat specific diseases. This review summarizes the current knowledge on immunological and functional aspects of xeno(allo)-cellular transplantation for cardiomyopathy, diabetes, liver failure, neural diseases, and bone regeneration.

RECENT FINDINGS

Xenocellular transplantation is promising for tissue repair in immunologically privileged sites such as the central nervous system or nonvascularized tissues in which no or moderate immunosuppression is required. In vascularized organs, major immune responses are present when cells are transplanted without additional conditioning. Positive results from encapsulation methods that protect cells from the immune system should further stimulate preclinical research. Also, conditioning immunosuppression could be used to circumvent the initial immune response. Transgenic pigs cells are probably the best xenogeneic substitute for human application, although basic research on innate and noninnate immunity toward pig cells is still required.

SUMMARY

In several fields of medicine, cellular xenotransplantation is slowly emerging as a potential therapeutic tool.

Genetic manipulation in pigs

PURPOSE OF REVIEW

Recent developments in the field of genetic engineering have made it possible to add, delete or exchange genes from one species to another. This technology has special relevance to the field of xenotransplantation, in which the elimination of a species-specific disparity could make the difference between success and failure of an organ transplant. This review focuses on developments in both the techniques and applications of genetically modified animals.

RECENT FINDINGS

Advances have been made using existing techniques for genetic modifications of swine and in the development of new, emerging technologies, including enzymatic engineering and the use of small interfering RNA. Applications of the modified animals have provided evidence that genetically modified swine have the potential to overcome both physiologic and immunologic barriers that have previously impeded this field. The use of alpha-1,3-galactosyltransferase gene-knockout animals as donors have shown marked improvements in xenograft survivals.

SUMMARY

Techniques for genetic engineering of swine have been directed toward avoiding naturally existing cellular and antibody responses to species-specific antigens. Organs from genetically engineered animals have enjoyed markedly improved survivals in nonhuman primates, especially in protocols directed toward the induction of tolerance, presumably by avoiding immunization to new antigens.

Xenotransplantation as a model of integrated, multidisciplinary research

Xenotransplantation was proposed a long time ago as a possible solution to the world-wide shortage of human organs. For years, researchers in this field have almost exclusively directed their efforts towards combating the immunological barrier that precluded long-term xenograft survival. Studies have been conducted in both small and large animal models and the most relevant results have been obtained in pre-clincal studies, specifically those utilising the pig-to-nonhuman primate combination. In this context, a better understanding of the immunological mechanisms underlying the rejection of a xenograft have allowed the identification of specific targets of intervention that have resulted in considerable improvements in survival of porcine organs or cells in nonhuman primates. However it has also become apparent that if xenotransplantation has to enter the clinical arena, a multidisciplinary approach will be needed to comprehensively tackle the different issues related to the use of a xenograft to cure human disease.In this regard, the safety, ethics and regulatory aspects of xenotransplantation are currently being aggressively addressed to enable the initiation of xenotransplantation with a favourable risk/benefit ratio.

Pig islet xenotransplantation into non-human primate model

Allogeneic islet transplantation faces difficulties because (1) organ shortage is recurrent; (2) several pancreas donors are often needed to treat one diabetic recipient; and (3) the intrahepatic site of islet implantation may not be the most appropriate site. Another source of insulin-producing cells, therefore, would be of major interest, and pigs represent a possible and serious source for obtaining such cells. Pig islet grafts may seem difficult because of the species barrier, but recent reports demonstrate that pig islets may function in primates for at least 6 months. Pig islet xenotransplantation, however, must still overcome several hurdles before becoming clinically applicable. The actual consensus is to produce more preclinical data in the pig-to-primate model as a necessary requirement to envisage any pig-to-human transplantation of islets; therefore, a summary of the actual acquired knowledge of pig islet transplantation in primates seemed useful and is summarized in this overview.

Transgenic expression of cytotoxic T-lymphocyte-associated antigen 4-immunoglobulin prolongs xenogeneic skin graft survival without extensive immunosuppression in rat burn wounds

BACKGROUND

We sought to establish a transgenic animal line skin-specifically overexpressing cytotoxic T-lymphocyte-associated antigen 4-immunoglobulin (CTLA4Ig) as a reproducible source of xenogeneic skin grafts with extended survival for wound coverage. We tested this strategy in mice based on a previously established transgenic mouse line that stably and skin-specifically expresses CTLA4Ig for lifetimes and generations.

METHODS

CTLA4Ig expression was examined by immunohistochemical assay, and its bio-activity was tested by mixed lymphocyte reaction. The survival of transgenic mouse skin grafted onto rat burn wounds was observed. The impact of transgenic skin grafting on recipient immunity was evaluated by inspecting the survival of the wild-type skin grafted along with transgenic skin onto a separate wound on the same rat. The circulatory CTLA4Ig protein in recipient was detected by sandwich enzyme-linked immunosorbent assay, and its impact on recipient lymphocyte response against donor antigen was tested by mixed lymphocyte reaction.

RESULTS

The transgenic CTLA4Ig protein suppressed lymphocyte proliferation in vitro, and the transgenic skin graft survival was remarkably prolonged compared with the wild-type skin derived from the same mouse strain. The survival of the wild-type skin grafted along with transgenic skin exhibited no significant difference from that grafted alone. Circulatory CTLA4Ig protein was detected in recipients, however, no significantly reduced recipient lymphocyte response against donor antigen was observed.

CONCLUSION

transgenic expression of CTLA4Ig may be a potential and safe method to prolong xenogenic skin graft survival in burn wounds, and transgenic animal lines can be established as a reproducible source of skin grafts with extended survival for wound coverage.

Pigs taking wing with transposons and recombinases

Swine production has been an important part of our lives since the late Mesolithic or early Neolithic periods, and ranks number one in world meat production. Pig production also contributes to high-value-added medical markets in the form of pharmaceuticals, heart valves, and surgical materials. Genetic engineering, including the addition of exogenous genetic material or manipulation of the endogenous genome, holds great promise for changing pig phenotypes for agricultural and medical applications. Although the first transgenic pigs were described in 1985, poor survival of manipulated embryos; inefficiencies in the integration, transmission, and expression of transgenes; and expensive husbandry costs have impeded the widespread application of pig genetic engineering. Sequencing of the pig genome and advances in reproductive technologies have rejuvenated efforts to apply transgenesis to swine. Pigs provide a compelling new resource for the directed production of pharmaceutical proteins and the provision of cells, vascular grafts, and organs for xenotransplantation. Additionally, given remarkable similarities in the physiology and size of people and pigs, swine will increasingly provide large animal models of human disease where rodent models are insufficient. We review the challenges facing pig transgenesis and discuss the utility of transposases and recombinases for enhancing the success and sophistication of pig genetic engineering. 'The paradise of my fancy is one where pigs have wings.' (GK Chesterton).