In addition, in a study on xenogeneic graft-versus-host disease (X-GVHD) (168), the authors found that in mice treated with IL-21 monoclonal antibody after receiving human PBMCs, the number of CD8 T cells in peripheral blood and spleen decreased, while the number and proportion of Treg cells in the spleen increased. Here, IL21 is linked to graft versus host disease.