Differential impact of CD154 costimulation blockade on alloreactive effector and regulatory T cells in murine renal transplant recipients

BACKGROUND. Although CD154 costimulation blockade prolongs allograft survival in multiple transplantation models, the underlying immunological mechanisms remain to be elucidated. METHODS AND RESULTS. We used a murine orthotopic kidney allograft (KTx) model to analyze the impact of CD154 blockade on trafficking and function of alloreactive T effector versus T regulatory cells. A single dose of MR1 Ab treatment at the time of KTx significantly improved the survival of Balb/c KTx in naïve C57BL/6 recipients (mean survival time >100 days vs. 52 days in controls; P<0.005), and improved graft histology, as evidenced by decreased lymphocyte infiltration and preservation of tissue architecture (days 6-8). In the early posttransplant phase, fluorescence-activated cell sorting analysis revealed preferential depression of T effector (CD8CD25) and relative enrichment of T-regulatory (CD4CD25CD152) cells selectively in KTx. This pattern was further supported by intragraft gene expression analysis, which showed increased FoxP3/Tbet ratio and simultaneously decreased granzyme B/IFN-γ levels in Ab-treated recipients. Additionally, MR1 Ab selectively up-regulated intragraft CCL17, but suppressed CXCL9/CCL5, in parallel with increased CCR4/CCR8 but unaltered CXCR3 expression. CONCLUSION. These results provide evidence, at both cellular and molecular levels, that CD154 blockade in murine KTx recipients differentially targeted T-effector and T-regulatory cell subsets by regulating intragraft induction of chemokines targeting distinct T-cell subsets.