Introduction: The International Xenotransplantation Association has recommended clinical xenotransplantation trials based on preclinical studies performed under Good Laboratory Practice (GLP), in which consistent life-supporting xenograft survival of >6 months has been achieved. Here, we present the first preclinical GLP study of pig-to-baboon thymokidney (TK) xenotransplantation using single knock-out (GalT-KO) swine as donors.
Methods: Recipient baboons (n=5) with low natural non-Gal antibodies underwent total thymectomy and induction therapy with rATG and rituximab. On day 0, they underwent bilateral nephrectomy and splenectomy and received transplants of TK grafts from inbred GalT-KO miniature swine. Immunosuppression (IS) included MMF, rapamycin, anti-CD40 mAb, and Belatacept. Kidney function was assessed through biochemical analyses and biopsies. Donor-specific antibodies (DSA) and absolute T-cell, B-cell, and recent thymic emigrant (RTE) counts were monitored. Mixed lymphocyte reaction (MLR) assays were performed monthly.
Results: Two animals were followed until POD 180, and 3 animals were continued through POD 365. Mean creatinine was 1.88±0.53 and 2.8±0.29 mg/dl on days 180 and 370, respectively for the two groups. Kidney biopsies indicated mild transplant glomerulopathy and mild interstitial fibrosis without any signs of rejection or immunoglobulin deposition. After the post-transplant decrease, DSA remained stable. RTEs defined as CD45RA+CCR7+CD28+CD95-CD31+ cells, were detected in the circulation within two months after transplantation. In all animals except Animal 5, at least one MLR indicated pig-specific hyporesponsiveness.
Conclusion: In a GLP setting, we achieved 1 year life-supporting TK xenograft survival in baboons utilizing single GalT-KO miniature swine as donors. TK grafts maintained good function with no signs of rejection prior to termination. Post-transplant detection of RTE suggests that functioning pig thymus grafts may contribute to pig-specific hyporesponsiveness. Our results suggest that single GalT-KO inbred miniature swine donors may be appropriate for use in clinical trials. Future studies will focus on enhancing thymus-dependent tolerance to achieve IS-free survival.