Intrathymic deletion of alloreactive T cells in mixed bone marrow chimeras prepared with a nonmyeloablative conditioning regimen.
BACKGROUND
Mixed hematopoietic chimerism induced with a nonmyeloablative conditioning regimen leads to donor-specific transplantation tolerance. Analyses of specific Vbeta-bearing T-cell families that recognize endogenous superantigens demonstrated that donor-specific tolerance is due mainly to an intrathymic deletional mechanism in these mixed chimeras. However, superantigens are not known to behave as classical transplantation antigens. We therefore used T-cell receptor (TCR) transgenic (Tg) recipients expressing a clonotypic TCR specific for an allogeneic major histocompatibility complex antigen to further assess deletional tolerance.


METHODS
2C TCR Tg mice (H2b), whose Tg TCR recognizes major histocompatibility complex class I Ld, were used as recipients of Ld+ bone marrow cells after conditioning with depleting anti-CD4 and CD8 monoclonal antibodies, 3 Gy whole-body irradiation, and 7 Gy thymic irradiation. Chimerism and deletion of CD8+ 2C recipient T cells was evaluated by flow cytometry and by immunohistochemical staining. Tolerance was tested with in vitro cell-mediated lympholysis assays and in vivo by grafting with donor skin.


RESULTS
Intrathymic and peripheral deletion of 2C+ CD8-single-positive T cells was evident in mixed chimeras, and deletion correlated with the presence of donor-type cells with dendritic morphology in the thymus, and with chimerism in lymphohematopoietic tissues. Chimeras showed tolerance to the donor in cell-mediated lympholysis assays and specifically accepted donor skin grafts.


CONCLUSIONS
Tolerance to transplantation antigens is achieved through intrathymic deletion of donor-reactive T cells in mixed chimeras prepared with a nonmyeloablative conditioning regimen and allogeneic bone marrow transplantation.
Bone Marrow Transplantation Section, Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston 02129, USA.
J O
JO
Manilay
D A
DA
Pearson
J J
JJ
Sergio
K G
KG
Swenson
M
M
Sykes
D000818:Animals; D001854:Bone Marrow Cells / Q000276:immunology; D016026:Bone Marrow Transplantation; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology; D002678:Chimera / Q000276:immunology; D005260:Female; D005821:Genetic Techniques; D005856:Germ-Free Life; D007108:Immune Tolerance / Q000502:physiology; D007519:Isoantigens / Q000276:immunology*; D008212:Lymphocyte Depletion; D008221:Lymphoid Tissue / Q000166:cytology; D051379:Mice; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic / Q000235:genetics; D011948:Receptors, Antigen, T-Cell / Q000235:genetics; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology*; D014184:Transplantation, Homologous
D007519:Isoantigens; D011948:Receptors, Antigen, T-Cell