T-cell homing to the pancreas in autoimmune mouse models of diabetes: in vivo MR imaging

PURPOSE: To evaluate the efficiency of T-cell labeling with anionic magnetic nanoparticles (AMNPs) and in vivo magnetic resonance (MR) imaging monitoring of T-cell homing to the pancreas. MATERIALS AND METHODS: In vivo MR images of pancreas were obtained with a 7-T MR system in 12 NOD (nonobese diabetic) mice at 11 and 20 days after injection of AMNP-loaded or unloaded T cells. Homing of loaded T cells in pancreatic lymph nodes was detected by the presence of a focal dark spot with T2* effect in a caudal area of the pancreas. Detection of loaded T cells in pancreatic islets was evaluated by comparison of histograms of MR signal intensity generated in whole pancreas in mice injected with loaded and unloaded T cells. Homing of loaded T cells was confirmed at transmission electronic microscopy (TEM). Fifty-six mice underwent all experiments. RESULTS: Focal dark spots with T2* effect were observed at 11 days in all three mice injected with loaded T cells and in none of the three mice injected with unloaded T cells. At 20 days, a more diffuse negative enhancement of the whole pancreas was noticed in one mouse injected with loaded T cells than in three mice injected with unloaded T cells. Presence of loaded T cells was confirmed with TEM. In vitro and in vivo tests confirmed that survival and function were not altered by loading. CONCLUSION: The ability of MR imaging to depict cell homing in living organisms at least 20 days after cell labeling was demonstrated, opening the way of follow-up in autoimmune diseases and cell therapy.