Intra-graft injection of tacrolimus promotes survival of vascularized composite allotransplantation.

BACKGROUND: Immunosuppressive therapies derived from solid organ transplantation are effective in promoting survival of vascularized composite allotransplantation (VCA), but they cause serious side effects that are difficult to justify for this non-life-saving procedure. Unlike solid organ transplantation, hand and face transplants offer the possibility of site-specific immunosuppression for reducing systemic exposure while increasing intra-graft concentrations of the drug. Therefore, in this study, we tested whether a single intra-graft injection tacrolimus could promote VCA survival.

METHODS: Brown Norway-to-Lewis hind limb transplantations were performed, and animals were left untreated (group I), treated with a daily injection of 1-mg/kg tacrolimus for 21 days (group 2) or injected with 7-mg tacrolimus directly into the transplanted limb on day 1 (group III). Graft rejection was monitored, and animals were sacrificed at grade 3 rejection or 200 days after transplantation.

RESULTS: Intra-graft injection of tacrolimus significantly prolonged allograft survival as compared to untreated animals or animals treated with systemic tacrolimus. Half of the intra-graft-treated rats rejected their graft on average at day 70.5. Interestingly, the other half remained rejection-free for more than 200 days without signs of kidney or liver toxicity. In these animals, tacrolimus was detected in the VCA skin but not in the blood until day 200. Long-term survival was not linked to induction of donor-specific tolerance but to a higher level of lymphocyte chimerism.

CONCLUSIONS: Intra-graft delivery of tacrolimus may promote VCA survival by increasing tissue drug availability and promoting the establishment of transient chimerism and thus long-term graft acceptance.