CD4 and graft versus host disease: Sorted donor CD4+ T cells can cause severe GVHD by expressing FASL and producing proinflammatory cytokines (e.g., IFN-γ and TNF-α) (159, 160), while sorted donor CD8+ T cells prevent graft rejection and mediate GVL effects by expressing perforin/granzyme, without causing aGVHD in animal models (161, 162).