Background. Combined treatment of allograft recipients with anti-CD40 ligand and CTLA-4Ig (costimulation blockade) is a powerful promising albeit not consistently tolerizing therapy. It would be desirable to use an effective conventional immunosuppressive regimen in low doses or for a short course as an adjunct; however, cyclosporine treatment drastically blunts the ability of costimulation blockade to produce long-term engraftment. Methods. Short courses of cyclosporine or rapamycin were compared as adjuncts to costimulation blockade in the murine BALB/c to C3H/He heterotopic cardiac allograft model. Results. Although cyclosporine therapy blocked the capacity of costimulation blockade to produce permanent engraftment, combined rapamycin and costimulation blockade treatment produced permanent engraftment. Conclusion. A theoretical basis for the differing effects of cyclosporine and rapamycin upon the outcome of costimulation blockade is forwarded. Combined use of costimulation blockade and rapamycin may provide a means to bring costimulation blockade into the clinic.
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