Recombinant S100A9 proteins or upregulation of S100A9 by treatment of anti-IFNGRα antibodies reduce GVHD by altering donor cell trafficking. (A) Survival rate of mice treated with recombinant murine S100A9 with or without S100A8 proteins (1 μg/injection starting on day 0, 5 times per week for 2 weeks), after allo-HSCT.