Pig-to-human heart xenotransplantation in two recently deceased human recipients.

Genetically modified xenografts are one of the most promising solutions to the discrepancy between the numbers of available human organs for transplantation and potential recipients. To date, a porcine heart has been implanted into only one human recipient. Here, using 10-gene-edited pigs, we transplanted porcine hearts into two brain-dead human recipients and monitored xenograft function, hemodynamics and systemic responses over the course of 66 hours. Although both xenografts demonstrated excellent cardiac function immediately after transplantation and continued to function for the duration of the study, cardiac function declined postoperatively in one case, attributed to a size mismatch between the donor pig and the recipient. For both hearts, we confirmed transgene expression and found no evidence of cellular or antibody-mediated rejection, as assessed using histology, flow cytometry and a cytotoxic crossmatch assay. Moreover, we found no evidence of zoonotic transmission from the donor pigs to the human recipients. While substantial additional work will be needed to advance this technology to human trials, these results indicate that pig-to-human heart xenotransplantation can be performed successfully without hyperacute rejection or zoonosis.

Production and characterization of transgenic pigs expressing porcine CTLA4-Ig.

BACKGROUND: Inhibition of the T-cell-mediated immune response is a necessary component of preventing rejection following xenotransplantation with pig alpha1,3-galactosyltransferase gene-knockout (GTKO) organs. Cytotoxic T lymphocyte-associated antigen (CTLA4) is a co-stimulatory molecule that inhibits T-cell activity and may be useful in prolonging graft rejection. METHODS: An expression vector was built containing the extracellular coding region of porcine (p) CTLA4 fused to the hinge and CH2/CH3 regions of human IgG1 (pCTLA4-Ig). Pigs transgenic for pCTLA4-Ig, on either a GTKO or wild-type (WT) genetic background, were produced by nuclear transfer and characterized using Western blot analysis, immunofluorescence, ELISA, and necropsy. RESULTS: Fifteen pCTLA4-Ig-transgenic piglets resulted from five pregnancies produced by nuclear transfer. All transgenic pigs exhibited robust expression of the pCTLA4-Ig protein and most expressed the transgene in all organs analyzed, with significant levels in the blood as well. Despite initial good health, these pigs exhibited diminished humoral immunity, and were susceptible to infection, which could be managed for a limited time with antibiotics. CONCLUSIONS: Viable pigs exhibiting robust and ubiquitous expression of pCTLA4-Ig were produced on both a WT and GTKO background. Expression of pCTLA4-Ig resulted in acute susceptibility to opportunistic pathogens due at least in part to a significantly compromised humoral immune status. As this molecule is known to have immunosuppressive activity, high levels of pCTLA4-Ig expression in the blood, as well as defective development related to exposure to pCTLA4-Ig in utero, may contribute to this reduced immune status. Prophylactic treatment with antibiotics may promote survival of disease-free transgenic pigs to a size optimal for organ procurement for transplantation. Additional genetic modifications and/or tightly regulated expression of pCTLA4Ig may reduce the impact of this transgene on the humoral immune system.