Because of its requirement for signaling by multiple cytokines, Janus kinase 3 (JAK3) is an excellent target for clinical immunosuppression. We report the development of a specific, orally active inhibitor of JAK3, CP-690,550, that significantly prolonged survival in a murine model of heart transplantation and in cynomolgus monkeys receiving kidney transplants. CP-690,550 treatment was not associated with hypertension, hyperlipidemia, or lymphoproliferative disease. On the basis of these preclinical results, we believe JAK3 blockade by CP-690,550 has potential for therapeutically desirable immunosuppression in human organ transplantation and in other clinical settings.

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In human chronic renal allograft rejection, CD40 is expressed on graft-infiltrating cells of the T cell and macrophage compartments. CD154 expression is induced on glomerular and tubular epithelial cells during CR, demonstrating another novel source of CD154 expression. The data substantiate the potential contributory role of an interaction between CD40+ graft-destructive effector T cells and macrophages with CD154+ renal allograft parenchymal cells in the development of chronic renal allograft rejection.

The CD40-CD40L (CD154) interaction plays a pivotal role in the effector mechanisms of allograft rejection. Blockade of the CD40/CD40L costimulatory pathway prevents the development of chronic allograft rejection in several animal transplant models. The relevance of in situ CD40 and CD40L expression in human liver allografts was assessed by immunohistochemistry during ductopenic chronic rejection (CR). In CR allograft specimens (n ‫؍‬ 8), marked CD40L expression was detected on Kupffer cells (KCs) and sinusoidal macrophages with a unique centrilobular distribution (P F .001). The CD40L؉ KCs and macrophages were shown to be CD68؉ after immunohistochemical analysis of serial sections with anti-CD68 monoclonal antibody. Moderate staining of vascular and sinusoidal endothelial cells and mononuclear infiltrates was observed in some CR cases. These findings were in contrast to the absence of CD40L expression in controls (n ‫؍‬ 11) consisting of stable liver allograft and normal liver tissue specimens. Only occasional CD40 expression in some cases of CR and controls was observed. In CR, CD40L (CD154) expression is manifested on KCs and macrophages. The present novel data show another important cellular source of CD40L expression and suggest a potential role of KCs/macrophages and CD40/CD40L costimulatory interactions in the pathogenesis of chronic rejection ductopenic liver allograft.