title: Persistent chimerism despite antidonor MHC in vitro responses in miniature swine following allogeneic hematopoietic cell transplantation.
abstract: BACKGROUND
  T-cell chimerism predominates in miniature swine receiving hematopoietic-cell transplantation without myelosuppressive conditioning. Several chimeric recipients have become hyporesponsive to donor-major histocompatibility complex (MHC) in vitro and accepted donor-matched renal transplants without immunosuppression. However, some retained antidonor in vitro responses and subsequently rejected donor renal allografts despite the persistence of peripheral blood chimerism. In this study, we characterize the donor cells in both "tolerant" and "nontolerant" chimeric miniature swine.
  
  
  METHODS
  Peripheral blood chimerism was determined by flow cytometry. In vitro antidonor responsiveness was determined by mixed lymphocyte reaction (MLR) and cell-mediated lymphocytotoxicity (CML). Donor cells were separated from chimeras by immunomagnetic bead separation and used as stimulators or targets in CML assays. Phenotypic analysis of donor cells in chimeras was performed using flow cytometry.
  
  
  RESULTS
  Peripheral blood chimerism stabilized beyond 100 days and was made up almost entirely of T cells. PBMC from nontolerant chimeras could be stimulated in vitro to kill donor cells isolated from the mixed chimera itself. In contrast, PBMC from tolerant chimeras hyporesponsive to donor-type cells could not be stimulated in vitro to kill their own sorted donor cells.
  
  
  CONCLUSIONS
  The in vivo persistence of donor T cells in mixed chimeric animals with in vitro antidonor responsiveness is not caused by an inability of these cells to be killed but rather by the poor stimulating capacity of these donor T cells. The nature of donor T cells that persist in the face of in vitro antidonor responses, has important implications for the induction of transplant tolerance by way of the generation of mixed chimerism.
authors.affiliation: Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02129, USA.
authors.forename: Zachary L
authors.initials: ZL
authors.lastname: Gleit
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Cameron
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Fuchimoto
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Melendy
authors.forename: Leila
authors.initials: L
authors.lastname: Monajati
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Coburn
authors.forename: David H
authors.initials: DH
authors.lastname: Sachs
authors.forename: Christene A
authors.initials: CA
authors.lastname: Huang
mesh_terms: D000818:Animals; D018380:Hematopoietic Stem Cell Transplantation; D066298:In Vitro Techniques; D007959:Lymphocyte Culture Test, Mixed; D008285:Major Histocompatibility Complex / Q000276:immunology*; D009000:Monocytes / Q000502:physiology; D013552:Swine; D013556:Swine, Miniature; D013601:T-Lymphocytes / Q000502:physiology; D013602:T-Lymphocytes, Cytotoxic / Q000502:physiology; D014019:Tissue Donors; D018183:Transplantation Chimera; D023001:Transplantation Tolerance