Tumor-suppressive activity of sTRAIL on circulating CD44+ cells in patients with non-small cell lung cancer

Circulating CD44+ cells have been identified as a prognostic marker for patients with non-small cell lung cancer (NSCLC). Serum tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) is involved in the pathophysiology of many cancers. However, no previous studies have shown the roles of sTRAIL in circulating CD44+ cells in the blood of NSCLC patients. We detected circulating CD44+ cells and sTRAIL levels in blood samples from NSCLC patients using flow cytometry and an enzyme-linked immunosorbent assay (ELISA). Anti-tumor roles of TRAIL in CD44+ cells were confirmed using a CCK-8 assay and mouse models. A higher number of circulating CD44+ cells were identified in NSCLC patients compared with healthy control individuals. In addition, we confirmed the anti-tumor roles and mechanisms of TRAIL in CD44+ cells both in vitro and in vivo. Our results indicate that (1) there is a negative correlation between sTRAIL and circulating CD44+ cells in NSCLC patients and (2) CD44+ cells have cancer stem cell properties and are more sensitive than CD44- cells to TRAIL.