Experimental limb transplantation, part II: excellent return of function and indefinite survival after withdrawal of...

In this study the three components of an immunosuppressive combination therapy were gradually withdrawn in a rat limb transplantation model to evaluate the effects on long-term survival of the grafted limbs, rejection rate, and functional recovery. The procedure was performed in 16 rats across a strong Brown Norway to Fischer 344 histocompatibility barrier. Eight animals served as a control group that was not given any antirejection therapy and rejected their limb within a few days. The remaining eight animals were administered a 2-week course of immunosuppressive therapy including tacrolimus (TRL; 2 mg/kg/d), mycophenolate mofetil (MMF; 15 mg/kg/d), and prednisolone (Pred; 0.5 mg/kg/d). At 2 weeks, Pred and MMF were simultaneously tapered by 20% of the dosage every week; by week 7 the animals were on TRL only. TRL was then tapered at the same rate (20% every week) to a maintenance dose of 0.6 mg/kg/d at week 12. After 6 months the immunosuppression was stopped. Four of 8 animals did not reject throughout the study up, to the 1-year endpoint. At this stage they show excellent functional outcomes, evaluated by clinical tests and walking tract analysis. The remaining four rats developed a rejection at an average of 267 days postoperatively (range 224 to 302 days), corresponding to an average of 87 days (range 44 to 122 days) without any immunosuppression. They were sacrificed as soon as rejection was confirmed for histological examination of the various tissues. This study showed that a triple combination therapy provides excellent long-term functional outcomes of the transplanted limbs, with no rejection episodes, no side effects, or complications, even 6 months after withdrawal of all immunosuppressive components, suggesting the possible emergence of tolerance.