A recent report has provided additional evidence underpinning a clinical relevance (109); transient DLL1 [anti-human and anti-mouse Dll1 IgG1 (109),] and DLL4 [anti-human and anti-mouse Dll4 IgG1, YW152F (138),] inhibition using specific humanized mAbs was sufficient to provide long-lasting protection against GVHD in mice models. This evidence concerns the gene DLL1 and graft versus host disease.