In previous studies, the authors found that doxorubicin-conjugated anti-CD137 mAb selectively killed CD137-expressing T cells in vitro. Therefore, in this work, the authors tried to test the ability of this conjugate in vivo. C571b/6 mice were induced with acute GVHD for further examination. The kinetic of CD137 (CD137) expression was checked on CD4 and CD8 T cells to choose a suitable time of treatment. The authors found that the T cells in spleen and lymph nodes of aGVHD mice expressed highest CD137 at the 7th day after transplantation. The mice were completely prevented from aGVHD if they were treated by doxorubicin-conjugeted-anti-CD137 antibody at the 7th day after transplantation. This finding encourages applying the toxin-antibody conjugate to treat humans GVHD.