Sorted PSGL1loCD4+ T cells from GVHD target tissues (liver and lung) of murine and humanized murine recipients augmented in vitro differentiation of syngeneic or autologous memory B cells but not naïve B cells into IgG-producing plasma cells in a manner that depended on PD-1/PD-L2 interaction and IL-21 (47). The gene discussed is PDCD1LG2; the disease is graft versus host disease.