Combined treatment with CD40 costimulation blockade, T-cell depletion, low-dose irradiation, and donor bone marrow transfusion in limb allograft survival

To determine the efficacy of a regimen based on CD40 costimulation blockade and donor bone marrow in the limb allograft model, C57B1/6 mice received limb allografts from Balb/c mice and either no treatment or a combination of MR1 (anti-CD40 ligand monoclonal antibody), CD4⁺ and CD8⁺ T-cell-depleting antibodies, low-dose irradiation, and bone marrow transfusion from Balb/c donors for 1 or 2 weeks. Recipients treated for 1 week showed rejection at 38.2 ± 5.4 (mean ± SEM) days, while those treated for 2 weeks had allograft survival of 56.5 ± 9.9, with a range up to 91 days. Histology demonstrated rejection which was less cell-mediated and suggestive of transplant vasculopathy. Differential rejection of skin occurred first. Thus, a combined regimen based on CD40 costimulatory blockade and donor marrow significantly prolonged allograft survival. However, tolerance was not achieved, and histology suggests chronic rejection as a possible cause of allograft loss.