ULBP2 and neuroblastoma: In the search for molecular strategies leading to increased expression of ligands for NK-cell-activating receptors in NB cells, the restoration of p53 function led to the upregulation of the ligands ULBP1 and ULBP2 for NKG2D [9] and, as we previously reported, of the ligand PVR (CD155) for DNAM-1 [10].