However, clinical studies exploring TLR9 polymorphisms in allo-HCT hosts suggested that those with homozygous CC gene variant of TLR9 (which correlates with lower expression of TLR9 mRNA) showed significantly improved overall survival (OS) and reduced relapse rate with no difference in acute GVHD when compared with patients having TC/TT gene variants (42, 43). The gene discussed is TLR9; the disease is acute graft versus host disease.