To test a new approach of donor conditioning with recipient bone marrow cells (BMC) to induce tolerance in vascularized composite allograft (VCA) transplantation.

Lewis rats' (recipients) BMC were stained with PKH‐26. The ACI rats (donors) were conditioned with 80 × 10⁶ Lewis BMC, 24 or 72 hours before VCA (groin flap) transplantation. Forty‐eight VCA were performed between ACI donors and Lewis recipients. In groups I and II, donors were preconditioned (24 and 72 hours before transplantation, respectively), and recipients received 7‐day anti‐αβ‐TCR/cyclosporine‐A post‐transplantation. In groups III and IV, donors were preconditioned (24 and 72 hours before transplantation, respectively), and recipients received no systemic immunosuppression. In group V, recipients received 7‐day anti‐αβ‐TCR/cyclosporine‐A post‐transplantation. In group VI, recipients received no systemic immunosuppression. Assessment included evaluation of transplant viability and induction of donor‐specific chimerism via flow cytometry, immunofluorescence, and PCR.

Groups III, IV, and VI rejected allografts, at an average of 14 ± 5.2, 10 ± 2.7, and 8 ± 0.7 days. In groups I, II, and V, the mean survival was 80 ± 18.2 (p = 0.0002), 64 ± 27.4 (p = 0.001), and 30 ± 4.7 (p = 0.02) days. In groups I and II, donor‐specific chimerism in the blood decreased from 8.8 ± 3.4% and 8.6 ± 3.4% on day 7 to 3.7 ± 1.32% (p = 0.02) and 4.7 ± 2.7% when the flaps manifested grade 3 rejection. The presence of PKH‐26⁺ Lewis BMC was confirmed in the donor's blood, bone marrow, lymphoid organs, and liver (preconditioned at 24 and 72 hours).

Donor preconditioning is a novel approach modifying recipient's responsiveness to donor allograft and prolonging the allograft survival under short‐term immunosuppression. © 2015 Wiley Periodicals, Inc. Microsurgery 36:676–683, 2016.