ANTI-CD28 ANTIBODIES-MEDIATED SUPPRESSION OF ACUTE AND CHRONIC ALLOGRAFT REJECTION IS ASSOCIATED WITH THE PRESENCE OF REGULATORY CELLS AND WITH ANTI-DONOR CLASS II ANTIBODIES

Abstract

P913 Aims: B7/CD28 interactions participate in the initiation of T cell activation and B7/CTLA-4 in the termination. CTLA-4 interaction on B7 molecules on APC also results in the production of indoleamine deoxygenase (IDO), an enzyme that catabolizes tryptophan which, in turn, inhibits T cell proliferation. The activation of IDO has been associated with tolerance induction in rodents. Therefore, our hypothesis is that selectively inhibiting the B7/CD28 pathway without blocking that of B7/CTLA-4 may facilitate tolerance induction. Methods: We monitored the immune responses in a model of acute kidney graft rejection (LEW 1W -RT1Au- to fully mismatched LEW 1A -RT1Aa-), after the selective inhibition of CD28/B7 interaction using the modulating anti-rat monoclonal antibody JJ319. This antibody was previously shown to prevent rejection in the F344 to LEW model of chronic rat kidney graft rejection. Results: A short term treatment with 8 doses of 4mg/kg of JJ319 (day 0 to 7) resulted in 55% of grafts surviving long term (>150 days). Three to four months after transplantation, kidney graft function was normal and stable (Urea: 10 mmol/L, Creatinine: 39μmol/L) and no histological evidence of chronic rejection. Nonetheless, recipients presented an alloantibody response skewed towards a Th-2 type (IgG1 and IgG2a isotypes) and specifically directed against donor MHC II molecules. Alloantibodies were occasionally found deposited onto the graft endothelium but not into the glomeruli. This contrasted with the antibody response of the Th1-type (IgG2b) directed against both MHC I and II molecules deposited onto the endothelium and the glomeruli found in untreated rejecting recipients and in recipients treated on the short term with cyclosporine A, a treatment which prevents acute but not chronic rejection in this combination. In anti-CD28 treated functionally tolerant animals, PBMC and spleen cells were unable to proliferate against donor cells in mixed lymphocyte reactions but proliferated against third party cells. The blockade of IDO (using 1D methyl tryptophan) and NO generation (using N-Methyl-L-Arginin) fully restored the anti-donor reactivity. Moreover, whereas T cells purified from the same PBMC and splenocytes were fully reactive, depletion of either OX42+ (CD11b/c), OX62+, IgM+, HIS24+, or CD8+ cell subsets did not restore proliferation. Conclusions: The selective blockade of CD28 does not generates classical regulatory T cells but regulatory APCs as well as an anti-class II antibody response of the Th2-type. These regulatory mechanisms are associated with a normal kidney graft function in the long term without histological signs of chronic rejection.