In one aspect, a method of treating a subject having or at risk of having graft-versus-host disease (GvHD) generally includes administering to the subject a plurality of myeloid-derived suppressor cells (MDSCs) effective to ameliorate at least one symptom or clinical sign of graft-versus-host disease compared to a suitable control subject. In another aspect, a method of treating a tumor in a subject generally includes administering to the subject an anti-tumor therapy and co-administering to the subject an inflammasome inciting agent in an amount effective to increase inflammasome activation of MDSCs sufficiently to reduce suppressor function of the MDSCs.