While the T-allele of rs5742909 had a higher odd of survival and relapse in haplo-HSCT and C-allele was a risk allele for chronic GVHD in ALL patients [11], it is speculated that the presence of C-allele in rs5742909 leads to a higher expression of CTLA4, causing donor T cells to attack host cells and cause GVHD. Here, CTLA4 is linked to chronic graft versus host disease.