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Background Genetically-engineered pigs could provide a source of kidneys for clinical transplantation. The two longest kidney graft survivals reported to date have been 136 days and 310 days, but graft survival >30 days has been unusual until recently. Methods Donor pigs (n=4) were on an α1,3-galactosyltransferase gene-knockout (GTKO)/human complement-regulatory protein (CD46) background (GTKO/CD46). In addition, the pigs were transgenic for at least one human coagulation-regulatory protein. Two baboons received a kidney from a 6-gene pig (Group A) and two from a 3-gene pig (Group B). Immunosuppressive therapy was identical in all 4 cases, and consisted of anti-thymoglobulin (ATG) + anti-CD20mAb (induction) and anti-CD40mAb + rapamycin + corticosteroids (maintenance). Anti-TNF-α and anti-IL-6R mAbs were administered to reduce the inflammatory response. Baboons were followed by clinical/laboratory monitoring of immune/coagulation/inflammatory/physiological parameters. At biopsy or euthanasia, the grafts were examined by microscopy. Results The two Group A baboons remained healthy with normal renal function >7 and >8 months, respectively, but then developed infectious complications. However, no features of a consumptive coagulopathy, e.g., thrombocytopenia, reduction of fibrinogen, or of a protein-losing nephropathy were observed. There was no evidence of an elicited anti-pig antibody response, and histology of biopsies taken at approximately 4, 6, and 7 months and at necropsy showed no significant abnormalities. In contrast, both Group B baboons developed features of a consumptive coagulopathy and required euthanasia on day 12. Conclusions The combination of (i) a graft from a specific 6-gene genetically-modified pig, (ii) an effective immunosuppressive regimen, and (iii) anti-inflammatory therapy prevented immune injury, a protein-losing nephropathy, and coagulation dysfunction for >7 months. Although the number of experiments is very limited, our impression is that expression of human endothelial protein C receptor (+/− CD55) in the graft is important if coagulation dysregulation is to be avoided.

Summary Spermatogonial stem cells (SSCs) maintain spermatogenesis throughout a man’s life and may have application for treating some cases of male infertility, including those caused by chemotherapy before puberty. We performed autologous and allogeneic SSC transplantations into the testes of 18 adult and 5 prepubertal recipient macaques that were rendered infertile with alkylating chemotherapy. After autologous transplant, the donor genotype from lentivirus-marked SSCs was evident in the ejaculated sperm of 9/12 adult and 3/5 prepubertal recipients after they reached maturity. Allogeneic transplant led to donor-recipient chimerism in sperm from 2/6 adult recipients. Ejaculated sperm from one recipient transplanted with allogeneic donor SSCs were injected into 85 rhesus oocytes via intracytoplasmic sperm injection. Eighty-one oocytes were fertilized, producing embryos ranging from 4-cell to blastocyst with donor paternal origin confirmed in 7/81 embryos. This demonstration of functional donor spermatogenesis following SSC transplantation in primates is an important milestone for informed clinical translation.

The survival rates after intestinal transplantation have cumulatively improved during the past decade. With the management strategies currently under evaluation, intestinal transplant procedures have the potential to become the standard of care for patients with end-stage intestinal failure.

The longest survival of a nonhuman primate with a life-supporting kidney graft to date has been 90 days, though graft survival >30 days has been unusual. A baboon received a kidney graft from an α1,3-galactosyltransferase gene-knockout pig transgenic for two human complement- and three human coagulation- regulatory proteins (though only one was expressed in the kidney). Immunosuppressive therapy was with ATG+anti-CD20mAb (induction) and anti-CD40mAb+rapamycin+corticosteroids (maintenance). Anti-TNF-α and anti-IL-6R were administered. The baboon survived 136 days with a generally stable serum creatinine (0.6–1.6mg/dL) until terminally. No features of a consumptive coagulopathy (e.g., thrombocytopenia, decreased fibrinogen) or of a protein-losing nephropathy were observed. There was no evidence of an elicited anti-pig antibody response. Death was from septic shock (Myroides spp). Histology of a biopsy on day 103 was normal, but by day 136 the kidney showed features of glomerular enlargement, thrombi, and mesangial expansion. The combination of (i) a graft from a specific genetically-engineered pig, (ii) an effective immunosuppressive regimen, and (iii) anti-inflammatory agents prevented immune injury and a protein-losing nephropathy, and delayed coagulation dysfunction. This outcome encourages us that clinical renal xenotransplantation may become a reality.