Objective To evaluate the feasibility of the diagnosis of the early immunologic rejection after xeno-islet transplantation by MR imaging enhanced with superparamagnetic iron oxide(SPIO)marking CD4+T cell antibody.Methods Two thousand neonatal porcine islets(NPI)were transplanted under the left renal capsule of BALB/C nude mice.When the grafts could be observed bv MRI.107 human PBMC was intraperitoneal injected to nude mouse models to reconstitute the human immunologic system,20 mice were reconstituted.Before and 3,7,14 days after reconstitution of human immunologic system on BALB/C nude mice,MRI imaging Was performed half an hour after intravenous injection of nano-immunomagnetic beads via vena caudalis to observe the grafts'MRI signal.BALB/C nude mice were sacrificed after MRI scanning immediately,the histopathologic examination was assessed on grafts,the results were compared with MRI results.And calculate the sensitivity,specificity,Youden index number and coincidence of the MRI for immunologic rejection.Results Grafts can be observed bv MRI 3 weeks after islet cell transplantation (before immunologic rejection modeling),there is no abnormal MRI signal detected in nude mice'graft region after mierobeads injected.Seven days after building of immunologic rejection model,MRI hypo-signal in graft site is shown in the T2 WI sequence after nano-bioprober injected.Histopathologic assessments were employed on grafts in nude mice immediately(HE and immunohistochemistry staining),the results shown that there are a lot of T lymphocyts infiltrated in graft region.implying the occurrence of immunologic rejection.And the sensitivity,specificity,Youden index number and coincidence is:(72.96±0.24)%,100%,0.73±0.24,(88.46±0.13)%respectively.The correct Kappa between the MRI and the imunohistochemistry staining was 0.76.Conclusion The cellular immunological rejection to xeno-islet grarts can be assessed with nano-bioprobe with anti-CD4+ antibody MR imaging,real time,and noninvasively.