A LONG-TERM STUDY OF ALLOGENEIC RAT HINDLIMB TRANSPLANTS IMMUNOSUPPRESSED WITH RS-61443

Although technically possible, limb allotransplantation has not been applied clinically. The skin component is especially antigenic, requiring high immunosuppressant doses with an unacceptable toxicity profile. RS-61443, an experimental mycophenolic acid ester that inhibits lymphocyte proliferation without major systemic toxicity, was tested as an immunosuppressant to prevent rejection of rat hindlimb allotransplants. Utilizing Brown-Norway donors and F344 recipients to provide a major mismatch at the MHC, midfemur orthotopic limb transfer was performed with microsurgical repair of femoral vessels and sciatic nerve. Four primary groups were studied: autografts (n=4); untreated allografts (n=6); allograft receiving CsA 10 mg/kg for 20 days, then twice per week (n=6); and allografts receiving RS-61443 30 mg/kg/day (n=6). Skin and soft tissues were biopsied to assess rejection. Autografts had indefinite limb survival, while untreated allografts had complete acute rejection within 10-12 days. Five of the six CsA rate developed delayed mild-moderate acute rejection within 6 months. In contrast, 5 of the 6 RS-61443 rats had no rejection after at least 32 weeks, while the sixth rat developed only slight rejection on skin biopsy. All animals regained full sensation and partial functional return. RS-61443 is highly effective as a primary immunosuppressant for hindlimb allotransplantation. The disturbing moderate rejection observed in CsA animals, which was absent with RS-61443, may significantly hamper function of transplanted limbs.