SOX2 and neuroblastoma: SK-N-BE (2) neuroblastoma cells were shown to form CD133+ tumorspheres, unlike SH-SY5Y cells, hence we have first sorted CD133− and CD133+ SK-N-BE (2) cells and showed that expression of CD133, ELK-1, SOX2, NANOG, and POU5F1 were all significantly more in CD133+ cells than in CD133− cells (Figure 4A).