PTPRC and neuroblastoma: Both the disialoganglioside GD2 and the adhesion molecule CD56 have been shown to be widely and brightly expressed on neuroblastoma tumors (33, 34), however, given that CD56 is also expressed at varying cell surface density on subsets of natural killer cells (35), all experiments were carried out using GD2 for positive selection, and CD45 for negative selection of cells of hematopoietic origin.