Therefore, in haploidentical KIR-ligand mismatch settings, 2B4-mediated CD56dim NK killing of CD48 positive hematopoietic cells could be not only involved in driving CD56dim against host hematopoietic cells and thus (sparing other tissues) limiting GVHD, but particularly against host (and donor) hematopoietic cells undergoing CD48 upregulation due to viral reactivation. This evidence concerns the gene KIR3DL1 and graft versus host disease.