FOXP3 and graft versus host disease: Since Treg cryopreservation, an intricate part of banking, has proven very challenging (38, 61, 213), with varying recoveries, effects on Foxp3 expression, and in vitro suppressive functions, cryopreservation and thawing parameters that maintain a Treg phenotype and in vivo suppressive function after thawing is key to fully unlocking Treg ACT for GVHD and other indications such as graft rejection and autoimmune disease.