NGFR and esophageal squamous cell carcinoma: Next, flow cytometry was applied to analysis of p75NTR positive cells, and the results showed that HPV16 E6-E7 induced the stemness in ESCC cells because of the increased ratio of p75NTR positive cells in Eca109-psb, TE-1-psb cells and spheres derived from them (Figure 2C–2F).