Anti–IL-7Rα antibody treatment can successfully prevent GVHD-related mortality and morbidity following allogeneic BM transplantation. Following 1300 cGy total body irradiation (TBI), B6 recipient mice received transplants of 1 × 10⁶ TCD BM and 4 × 10⁶ LN cells from allogeneic BALB/c donor mice and were injected with either PBS or anti–IL-7Rα antibody (100 μg per mouse once a week) subcutaneously for 4 weeks. As controls, 1 × 10⁶ TCD BM cells from either congenic B6.SJL (CD45.1) or allogenic BALB/c (H2K^d) donors were transplanted into lethally irradiated B6 recipients. (A) Survival of anti-IL-7Rα antibody-treated allogeneic BMT-plus-LN recipients is significantly greater than that of the PBS-treated allogeneic BMT-plus-LN recipients (P < .005). Survival over the 150 days after BMT is shown. (B) The severity of GVHD was evaluated by using a GVHD clinical grading system with scoring for 5 clinical criteria: percentage of weight loss, skin integrity, posture, mobility, and fur texture.²⁹  Clinical signs were graded on a scale of 0 to 2, where 0 was absent, 1 was moderate, and 2 was severe, and the individual signs summed. Shown are GVHD clinical index scores at day 30 following BMT. The difference between anti–IL-7Rα antibody- and PBS-treated allogeneic BMT-plus-LN recipients is P < .001*(asterisk).