We describe here that a humanized anti-LT-α mAb depleted activated T and B cells and increased survival in xenogeneic human T cell-dependent peripheral blood mononuclear cell (PBMC) transplanted SCID (Hu-SCID) mouse model of GVHD, whereas an Fc-effectorless mutant version of the antibody did not. Here, LTA is linked to graft versus host disease.