Induction of donor-specific tolerance using superagonistic CD28 antibody in rat renal allografts: regulatory T-cell expansion before engraftment may be important.

BACKGROUND: We hypothesized that a superagonistic monoclonal antibody specific for CD28 (CD28SA), which expands regulatory T cells (Tregs) in vivo, would prevent acute rejection and prolong the survival of renal allograft.
METHODS: We examined whether CD28SA treatment induce donor-specific tolerance using our established rat renal allograft model (Wistar-Lewis).
RESULTS: All control rats died within 13 days because of severe azotemia with marked destruction of graft tissue. In contrast, recipients treated with a triple injection of CD28SA (days -3, 0, and 3) showed good preservation of graft histology and function, with considerable infiltration of Tregs into the allografts; 92% of recipients survived for more than 100 days, and 77% survived by the day of harvest at 180 days. These long-surviving recipients received secondary heterotopic bicardiac allografts from both donor-matched Wistar and third-party Brown Norway rats simultaneously 120 days after kidney transplantation, and seven of eight (87.5%) rats exhibited donor-specific tolerance, accepting the Wistar heart, but acutely rejecting the Brown Norway heart. Interestingly, a single injection of CD28SA 3 days before (day -3), but not 3 days after (day 3), transplantation also induced donor-specific tolerance in some recipients. We then performed adoptive transfer of nonspecific CD4+CD25+ Tregs, purified from CD28SA-treated Lewis rats, with simultaneous injection of hepatocyte growth factor (500 μg/kg/day, intravenously). The treatment induced significant prolongation of graft survival (P<0.0001 vs. control group), and five of eight (62.5%) recipients survived until the day of harvest at 180 days with successful induction of donor-specific tolerance.
CONCLUSIONS: We have established a novel therapeutic approach for inducing donor-specific tolerance in rats with renal allografts.