For GVHD models, mice were irradiated with 12 Gy (BDF1) or 10 Gy (B6) twelve hours prior to adoptive transfer of MACS isolated splenic and LN pan T cells (Miltenyi Biotec) and TCD-BM (MACS thy1.2-microbeads as previously described (22 (link)). For the B6 to BDF1 GVHD/CTL mice were not irradiated and 2.5 × 107 total splenocytes/mouse were adoptively transferred. For CD25 depletion, pan T cells were isolated with CD25-biotin (BD biosciences) and anti-biotin microbeads (Miltenyi), and passed over LD depletion columns (Miltenyi). 200 ug/mouse of MH5A or control Ab was injected via tail vein, and mice were monitored daily for all experiments.