PIG TO MONKEY BONE-MARROW AND KIDNEY XENOTRANSPLANTATION

Background. The intensity of discordant xenograft cellular rejection m akes it unlikely that safe doses of immunosuppressive drugs will alone be sufficient to permit long-term survival. We have therefore concent rated our efforts on establishing tolerance to xenogeneic organs throu gh lymphohematopoietic chimerism and the elimination of performed natu ral antibodies (nAbs). Methods. Here we report the most recent series of II technically successful porcine to nonhuman primate transplantati on procedures. In eight experimental animals induction therapy consist ed of (1) 3 x 100 cGy nonlethal whole body irradiation (day -6 and day -5) to all animals, (2) horse anti-human thymocyte globulin (day -5 d ay -1, and day 0) to seven of the animals, (3) 700 cGy thymic irradiat ion (day -1) to five of the animals, and (4) pig bone marrow infused o n day 0 (2-9 x 10(8)/cells/kg). On day 0, just before the renal xenogr aft, the recipient was splenectomized, and antipig nAbs were removed b y means of perfusion of the monkey's blood through either a pig liver (n = 6) or a Gal-alpha(1,3)-Gal adsorption column (n = 5). Three contr ol animals did not receive this pretransplantation induction therapy b ut did undergo hemoperfusion and posttransplantation immunosuppression identical to the experimental animals. All II recipients were treated after transplantation with cyclosporin A and 15-deoxyspergualin. Reco mbinant pig-specific growth factors (interleukin-3 and stem cell facto r) were given to six experimental animal from day 0 until the terminat ion of the experiment. Results. Analysis of recipients' sera by means of flow cytometry indicated the effective removal of immunoglobulin M and immunoglobulin G nAbs by either liver perfusion or column adsorpti on. In the eight experimental animal nAb titers remained low until dea th (up to IT days), but in the three control animals nAb titers increa sed substantially with time. The longest surviving recipient maintaine d excellent Kidney function with creatinine levels at 0.8 to 1.3 mg/dl throughout its course. Death occurred at day 15 from complications ca used by a urinary leak and pancytopenia. Histologic examination of the xenograft revealed only focal tubular necrosis and cytoplasmic vacuol ization, with trace amounts of fibrin and C3 in peritubular capillarie s. In this animal a fraction of the peripheral blood cells (3%) at day 7 were of pig origin as detected by pig-specific monoclonal antibodie s. In addition, colony-forming assays performed on a bone marrow biops y specimen taken at day 14 indicated that approximately 30% of the rel atively few myeloid progenitors detected were of swine origin. Conclus ions. We have demonstrated that our protocol is effective in the preve ntion of hyperacute rejection and in the maintenance of excellent func tion of the renal xenograft for up to 15 days. These results also indi cate that at least short-term engraftment of the xenogeneic donor bone marrow cells is possible to achieve in this discordant large animal c ombination. Longer survivals will be required to assess the possible e ffect of this engraftment on induction of tolerance.