We found that the patients most well-situated to benefit from MSC therapy have these characteristics: (1) younger patients, especially those younger than 10 years old; (2) GVHD with skin but not liver involvement; (3) the degree of tissue damage is mild, manifested as lower levels of TNFRI, IL-2Rα, elafin, CK18 and ST2; (4) a higher proportion of naïve T, B cells and imDCs, better thymic function and lower levels of pro-inflammatory chemokines. Here, PI3 is linked to graft versus host disease.