COMPARATIVE-STUDIES OF SPECIFIC ACQUIRED SYSTEMIC TOLERANCE INDUCED BY INTRATHYMIC INOCULATION OF A SINGLE SYNTHETIC WISTAR-FURTH (RT1(U)) ALLO-MHC CLASS-I (RT1.A(U)) PEPTIDE OR WAG (RT1(U))-DERIVED CLASS-I PEPTIDE
Nc. Chowdhury et al., COMPARATIVE-STUDIES OF SPECIFIC ACQUIRED SYSTEMIC TOLERANCE INDUCED BY INTRATHYMIC INOCULATION OF A SINGLE SYNTHETIC WISTAR-FURTH (RT1(U)) ALLO-MHC CLASS-I (RT1.A(U)) PEPTIDE OR WAG (RT1(U))-DERIVED CLASS-I PEPTIDE, Transplantation, 66(8), 1998, pp. 1059-1066
Background. Because T cell receptor-MHC class I/self-peptide interacti
ons regulate T-cell development, the presence of MHC allopeptides in t
he thymus may influence T-cell tolerance to alloantigens. This hypothe
sis is supported by our most recent finding that intrathymic (IT) inoc
ulation of nonimmunogenic synthetic peptides derived from ''WAG'' RT1.
A induces tolerance to cardiac allografts in the Wistar-Furth (WF)-to-
ACI model. To evaluate whether in vivo immunogenicity of MHC peptides
is relevant to tolerance induction and to examine the effect of peptid
e specificity, we compared the effects on graft survival of well-defin
ed, strain-specific immunogenic WF MHC class I peptides (RT1.A(U)) wit
h closely related but non-strain-specific class I peptides derived fro
m WAG (RT1(U)). Methods. In vivo immunization of seven MHC class I pep
tides synthesized from RT1.A(U) sequences showed that two (u-5 and u-7
) were immunogenic, whereas five others were not immunogenic in ACI re
cipients. We then examined the effects on cardiac allograft survival i
n the WF-to-ACI model of the two immunogenic RT1.A(U) peptides (u-5 an
d u-7) and three immunogenic WAG-derived peptides (peptides 1, 2, and
5). Results. A combination of equal amounts (150 mu g or 300 mu g) of
u-5 or u-7 each with 0.5 ml of antilmyphocyte serum (ALS) on day -7 le
d to 60% and 100% permanent graft survival (>150 days), respectively.
IT injection of the individual peptides on day -7 showed that only 300
Erg of u-5 significantly prolonged graft survival to a median surviva
l time of 17.3 days from 10.5 days in naive recipients. IT injection o
f 150, 300, and 600 mu g of u-5 combined with 0.5 mi of ALS on day -7
led to permanent graft survival (> 150 days) in four of six, nine of n
ine, and six of six ACI recipients, respectively compared with a media
n survival time of 15.4: days in ALS alone-treated controls. In contra
st, similar treatments with peptide u-7 with or without 0.5 mi of ALS
did not prolong graft survival, thus demonstrating that peptide u-5 al
one mediates the observed effects on graft prolongation. A total of 30
0 mu g of u-5 injected IT combined with ALS led to acute rejection of
third-party (Lewis) grafts. Intravenous injection of 300 mu g of u-5 w
ith ALS also did not prolong WP graft survival in ACI recipients. The
long-term unresponsive ACI recipients accepted permanently donor-type
(WF) but not third-party (Lewis) second-set cardiac and islet allograf
ts. Similarly, we showed that although IT injection of 600 and 1200 mu
g of a mixture of immunogenic WAG-derived peptides 1, 2, and 5 combin
ed with 0.5 mi of ALS on day -7 led to permanent WF graft survival in
ACI, only IT injection of 300 mu g of peptide 2 combined with BLS led
to permanent graft survival (>150 days) in four of five animals. To de
fine the underlying mechanisms of tolerance, we examined in vitro the
mixed lymphocyte reaction (MLR), cell-mediated lymphocytotoxicity, and
cytokine profile of unresponsive recipients. Although the results sho
wed nonspecific T-cell suppression in the MLR at 25 days after transpl
antation, which correlated with the persistence of ALS immunosuppressi
on, long-term unresponsive animals showed normal MLR to donor and thir
d-party antigens. In contrast, the donor-specific reactive cytotoxic T
lymphocytes remained suppressed in short-term and long-term unrespons
ive rats. Conclusion. Of interest is our finding that IT injection of
a short segment of WAG-derived MHC class I peptide induces active acqu
ired tolerance similar to results obtained with the use of pure WE-der
ived peptide u-5 in the WF-to-ACI rat combination. It is noteworthy th
at we could not confirm the T helper (Th)1/Th2 paradigm in this model
by initial cytokine analysis. Whether induction of tolerance by IT inj
ection of allo-MHC peptides will have clinical usefulness must await r
esults of similar studies in large animals. However, of major interest
is the finding that a short segment of RT1.A(U) represents the tolero
genic epitope that induces tolerance.