Background: Accumulated evidence from clinical transplantation has suggested that tacrolimus-based treatment can reverse ongoing allograft rejection in patients treated with cyclosporine (CsA)-based immunosuppression, even when a high dose of antirejection rescue therapy has failed. This evidence prompted us to investigate whether these two compounds, which share an in vitro mechanism, would differ in their abilities to regulate in situ cellular and molecular events during ongoing allograft rejection.
Methods: The equivalent effective doses of tacrolimus (3.2 mg/kg/day) and CsA (10 mg/kg/day), when administered orally to Lewis rats for 10 days (day 0-9), were predetermined and defined as the ability of the drug to induce a similar survival of Brown Norway rat heart allografts with an equal suppression of intragraft interleukin (IL)-2 mRNA expression. To investigate the ability of each drug to rescue ongoing allograft rejection, Lewis recipients of Brown Norway rat heart grafts were left untreated for the first 5 days after transplantation. Tacrolimus or CsA was then administered at the equivalent effective dose for 10 days (days 5-14). Heart grafts and blood samples, harvested on days 3, 5, 7, and 10, were analyzed by reverse transcriptase-polymerase chain reaction, real-time quantitative polymerase chain reaction, ELISA, and immunohistology.
Results: Ongoing allograft rejection was found to be rescued by tacrolimus but not by CsA at the equivalent dose (median survival time: untreated, 6 days; tacrolimus, 18 days; and CsA, 7 days). A significant suppression of local intragraft IL-10 mRNA expression and serum protein production along with a dramatic down-regulation of functional CD8+ T and NKR-P1a+ natural killer cell local infiltration by means of decreased of cytotoxic factor release, including granzyme B and perforin 1, was found to be associated with tacrolimus but not CsA treatment. However, both drugs inhibited other immune cells (CD4+ T cell, ED2+ macrophage) and cytokines (IL-1beta, IL-2, IL-4, IL-6, IL-12, interferon-gamma, transforming growth factor-beta, and tumor necrosis factor-alpha) at almost the same levels. The inability of CsA to overcome ongoing allograft rejection could be rescued by cotreating recipients with neutralizing anti-IL-10 antibody on day 5 and day 6 after transplantation: anti-IL-10 antibody alone did not show such an effect.
Conclusions: Inhibition of IL-10 production is a critical factor in the ability of tacrolimus to reverse ongoing allograft rejection.