Pancreatic tissues were fixed in 10% formaldehyde, 5-μm paraffin sections were made, and stained with hematoxylin and eosin (H&E) to assess insulitis. Stained sections were analyzed using a 0-4 insulitis severity grading system as described in our earlier studies[45 (link),49 (link),50 ]. In some experiments, paraffin sections of pancreatic tissues were stained using anti-insulin (mouse monoclonal, sc-8033 Santa Cruz Biotechnology) and/or anti-glucagon (rabbit polyclonal; Santa Cruz Biotechnology antibodies, followed by Alexa fluor 488- and 568- linked secondary antibodies and DAPI, and scored for insulitis based on DAPI-positive cells in islet areas and insulin positivity. In some experiments, insulin positive islets among total islet structures in different groups were compared. In some experiments, control (GFP expressing)-MSCs were injected into pre-diabetic and early hyperglycemic mice as described above and euthanized after 48h along with non-injected control mice, pancreatic tissues were subjected to cryo-sectioning. Intermittent sections were stained using aforementioned anti-insulin antibody followed by Alexa-flour 568 linked anti-mouse IgG secondary antibody, or with the secondary antibody alone, and DAPI. Stained sectioned were examined for the presence of GFP+ cells in islet area with and without immune cell infiltration based on insulin and DAPI staining.