XENOTRANSPLANTATION 1,3-Galactosyltransferase Gene-Knockout Pig Heart Transplantation in Baboons with Survival Approaching 6 Months Yau-Lin Tseng, 1 Kenji Kuwaki, 1 Frank J. M. F. Dor, 5 Akira Shimizu, 2,3 Stuart Houser, 2 Yosuke Hisashi, 1 Kazuhiko Yamada, 1 Simon C. Robson, 4 Michel Awwad, 3 Henk-Jan Schuurman, 3 David H. Sachs, 3 and David K. C. Cooper 1,6 Background. The recent generation of 1,3-galactosyltransferase gene-knockout (GalT-KO) pigs has allowed investi- gation of the survival of GalT-KO pig organs in nonhuman primates. Methods. Heterotopic heart transplantation from GalT-KO pigs was carried out in baboons (n=8) using a human antihuman CD154 monoclonal antibody-based immunosuppressive regimen. Results. In six of the eight cases, graft survival extended to between approximately 2 and 6 months. All grafts developed thrombotic microangiopathy (TM). In particular, the clinical course of one baboon in which the graft functioned for 179 days is summarized. This baboon received aspirin (40 mg on alternate days) from day 4 in addition to heparin, which may have been a factor in the delay of onset and progression of TM and in prolonged graft survival. Maintenance therapy with anti-CD154 mAb, mycophenolate mofetil, and methylprednisolone was associated with persistently low numbers of CD3 + CD4 + and CD3 + CD8 + cells. Despite persisting depletion of these cells, no infectious complications occurred. Conclusions. It remains to be established whether TM is related to a very low level of natural preformed or T-cell- induced antibody deposition on the graft, inducing endothelial activation and injury, or to molecular incompatibilities in the coagulation mechanisms between pig and baboon, or to both. However, function of a pig organ in a baboon for a period approaching six months, which has not been reported previously, lends encouragement that the barriers to xenotransplantation will eventually be overcome. Keywords: 1,3-galactosyltransferase gene-knockout, Anti-CD154 monoclonal antibody, Baboon, Costimulatory blockade, Heart transplantation, Pig , Xenotransplantation. (Transplantation 2005;80: 1493–1500) T here has been significant recent progress in pig organ transplantation in nonhuman primates. McGregor and his colleagues have reported a median survival of pig heart grafts in baboons of 76 days, with survival of one graft for 113 days, using organs from pigs transgenic for human mem- brane cofactor protein (1). We here report survival of a heart from a homozygous 1,3-galactosyltransferase gene-knock- out (GalT-KO) pig, where graft survival was a few days short of 6 months. We previously reported a median survival of 22 days (mean 23) of hearts (n=4) from pigs transgenic for human decay-accelerating factor, where the recipient baboons were treated with an immunosuppressive regimen consisting of induction therapy with antithymocyte globulin and an anti- baboon T cell monoclonal antibody (mAb), with mainte- nance therapy with a human-anti-human CD154 mAb, my- cophenolate mofetil, and tapering methylprednisolone (2). This regimen also involved an initial short course of cobra venom factor or soluble complement receptor-1 to deplete complement, and the continuous intravenous infusion of a synthetic Gal1,3Gal (Gal)-conjugate to adsorb anti-Gal an- tibody. Earlier initiation and an increased level of anticoagu- lation with heparin prolonged graft survival (n=5) to a me- dian of 53 days (mean 55), with one graft functioning for 139 days (2). Using the same regimen, but without the need for Gal- This study was supported by National Institutes of Health Program Project 1PO1 A145897, a sponsored research agreement between the Massachu- setts General Hospital and Immerge Biotherapeutics, and grants from the National Cheng Kung University Hospital, Taiwan (Y.-L.T.), the Ter Meulen Fund from the Royal Netherlands Academy of Arts and Sciences (F.J.M.F.D.), the Prof. Michae ¨l-van Vloten Fund (F.J.M.F.D.), and the Netherland-America Foundation (F.J.M.F.D.). Y.-L. Tseng and K. Kuwaki contributed equally to this study. 1 Transplantation Biology Research Center, Massachusetts General Hospi- tal/Harvard Medical School, Boston, MA. 2 Department of Pathology, Massachusetts General Hospital/Harvard Med- ical School, Boston, MA. 3 Immerge BioTherapeutics, Inc., Cambridge, MA. 4 Center for Immunobiology, Beth Israel Deaconess Medical Center/Har- vard Medical School, Boston, MA. 5 Department of Surgery, Erasmus MC, Rotterdam, The Netherlands. 6 Address correspondence to: D.K.C. Cooper, M.D., Ph.D., FRCS, Thomas E. Starzl Transplantation Institute, University of Pittsburgh Medical Cen- ter, Biomedical Science Tower East 1550A, 200 Lothrop Street, Pitts- burgh, PA 15261. E-mail: cooperdk@upmc.edu Received 6 June 2005. Revision requested 28 June 2005. Accepted 28 July 2005. Copyright © 2005 by Lippincott Williams & Wilkins ISSN 0041-1337/05/8010-1493 DOI: 10.1097/01.tp.0000181397.41143.fa Transplantation • Volume 80, Number 10, November 27, 2005 1493