Blocking CD40 signaling on diabetogenic clone BDC-5.2.9 abrogates disease transfer capacity. BDC-5.2.9 , BDC-5.2.9 MIGR, BDC-5.2.9 CD40hi, or BDC-5.2.9 CD40DN T cells (1 × 107) were injected i.p. into 6-14 day-old NOD.scid recipients and mice were monitored for hyperglycemia. Results from disease transfer: all mice receiving the parent clone BDC-5.2.9, BDC-5.2.9 CD40hi, or the BDC-5.2.9 MIGR (empty vector) became diabetic within 3 weeks of being injected, whereas none of the mice receiving the CD40DN variant became diabetic (p < 0.001). Data summarizes at least three independent experiments for the CD40DN and BDC-5.2.9 and two experiments for BDC-5.2.9 MIGR.