While an apparent association between inactive AAT and poor HSCT outcomes was observed by Mullins RE et al. in as early as the year 1987 [30], it has yet to be determined whether insufficient AAT functionality predisposes allogeneic HSCT patients to acute GVHD, and in which time point relative to HSCT, at that. This evidence concerns the gene SERPINA1 and acute graft versus host disease.