Abstract: Objective To investigate the effect of cell administration route of bone marrow mesenchymal stem cells on regulating immune rejection against heart allograft. Methods Donor hearts from BALB / c mice were heterotopically transplanted into the neck of C57 mice. The recipient animals were randomly divided into 4 groups with 12 animals in each group. In group A, 30 μL cell suspension containing 1×106 eGFP-BMSCs was injected into the animals through heart graft ascending aorta immediately after heart transplant procedure. In group B, the same dose of cell suspension was injected into animals through heart graft right ventricle cavity at the same time point. In group C, the same dose of cell suspension was injected into the heart muscle directly. Group D was control group and no treatment was received. Four mice were sacrificed in each group at post-operative day 7, and the heart grafts were harvested. Green fluorescence cells were detected under microscope and the heart graft histology was evaluated by HE staining. The proportion of macrophages in the heart graft infiltrating leukocytes was measured using flow cytometry. The remaining 8 mice were monitored for heart graft survival.Results At day 7 after transplantation, the eGFP+ cells were only detected in the heart graft of group A. The pathological examination found that the immune rejection was inhibited in group A with less interstitial infiltration and focal heart muscle damage. In group B and C, multifocal lymphocytic infiltration with myocardial cell degeneration and necrosis was observed in the interstitium of transplanted heart. In group D, large number of white blood cells infiltrated in all the graft, and normal myocardial structure disappeared. Flow cytometry analysis showed that highest macrophages cell proportion was found in the graft infiltrating leukocytes in group A compared to those of other groups. Cardiac survival time was significantly longer in group A than that of other groups. Conclusion BMSCs can alleviate cardiac allograft rejection. Intra-arterial injection is the best compared to intravenous and intra-myocardial injection route. The related mechanism may be the longer BMSCs survival and the higher macrophages infiltration in heart graft.

Key words: immune rejection, bone marrow mesenchymal stem cells, organ transplantation, cell administration route