Jo. Manilay et al., INTRATHYMIC DELETION OF ALLOREACTIVE T-CELLS IN MIXED BONE-MARROW CHIMERAS PREPARED WITH A NONMYELOABLATIVE CONDITIONING - REGIMEN, Transplantation, 66(1), 1998, pp. 96-102
Background. Mixed hematopoietic chimerism induced with a nonmyeloablat
ive conditioning regimen leads to donor-specific transplantation toler
ance. Analyses of specific Vp bearing T-cell families that recognize e
ndogenous superantigens demonstrated that donor-specific tolerance is
due mainly to an intrathymic deletional mechanism in these mixed chime
ras. However, superantigens are not known to behave as classical trans
plantation antigens, We therefore used T-cell receptor (TCR) transgeni
c (Tg) recipients expressing a clonotypic TCR specific for an allogene
ic major histocompatibility complex antigen to further assess deletion
al tolerance. Methods. 2C TCR Tg mice (H2(b)), 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 an
d CD8 monoclonal antibodies, 3 Gy whole-body irradiation, and 7 Gy thy
mic 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 an
d in vivo by grafting with donor skin. Results. Intrathymic and periph
eral deletion of 2C(+) CD8-single-positive T cells was evident in mixe
d chimeras, and deletion correlated with the presence of donor-type ce
lls with dendritic morphology in the thymus, and with chimerism in lym
phohematopoietic tissues. Chimeras showed tolerance to the donor in ce
ll-mediated lympholysis assays and specifically accepted donor skin gr
afts, Conclusions, Tolerance to transplantation antigens is achieved t
hrough intrathymic deletion of donor-reactive T cells in mixed chimera
s prepared with a nonmyeloablative conditioning regimen and allogeneic
bone marrow transplantation.