ImmunostainingSections from formalin-fixed paraffin-embedded donor-derived pancreata were obtained from the Network for Pancreatic Organ Donors With Diabetes (nPOD) repository, the Diabetes Virus Detection (DiViD) study, and the tissue bank of A.C.P. at Vanderbilt University (including age-matched control subjects without diabetes). Full details on all donors are listed in Supplementary Table 1. Paraffin sections were rehydrated, and antigen retrieval was performed in a decloaking chamber (Biocare Medical) in 50 mmol/L citrate buffer (pH 6). The following primary antibodies were used: guinea pig anti-insulin (1:400; DAKO), mouse antiglucagon (1:200; Abcam), rabbit anti-53BP1 (1:200; Bethyl), mouse anti-γ−H2AX Ser139 (1:3,000; Millipore), mouse anti-CD45 (1:100; DAKO), rabbit antiphosphorylated (phospho)-Kap1 (1:100; Bethyl), rabbit anti-p53 (1:400; Novocastra), rat anti-CD3 (1:300; Millipore), and rabbit anti–human growth hormone (hGH) (1:200; Abcam). Fluorophore-conjugated secondary antibodies used were donkey anti–guinea pig Alexa Fluor 488, donkey anti-rabbit Cy3/Cy5, and donkey anti-mouse Alexa Fluor 488/Cy3 (The Jackson Laboratory). DAPI (Invitrogen) was used as a nuclei marker. Horseradish peroxidase­–conjugated secondary antibody was donkey anti-rabbit (Histofine; Nichirei Biosciences). Diaminobenzidine (Lab Vision) was used as chromogen. Fluorescent images were taken with a Nikon C1 confocal microscope at 400× magnification. Bright-field images were taken with an Olympus BX53 at 400× magnification. Image quantification was performed using the ImageJ software.