Increased numbers of endothelial progenitor cells in peripheral blood and tumor specimens in non-small cell lung cancer: a methodological challenge and an ongoing debate on the clinical relevance.

Bone marrow-derived endothelial progenitor cells (EPC) play an important role in neovascularisation and tumor growth. However, the clinical relevance of EPCs on blood vessel formation in non-small cell lung cancer (NSCLC) is unclear. EPC numbers in circulation are very low and therefore their detection is technically challenging. In the present study, 10 NSCLC patients and 5 healthy controls were included. Patients underwent blood analyses before and after surgery. EPCs were isolated from whole blood by magnetic cell sorting to CD34 (MACS). Afterwards, FACS analyses using antibodies against CD133, CD34, VEGFR2 and CD45 and and immunocytological staining to CD133 on cytospins (MCA) were performed. Cryostat sections of tumor samples were stained for CD133, CD31 and cytokeratin A7. Serum levels of the vascular endothelial growth factor (VEGF) were quantified by sandwich ELISA. Compared to the control group NSCLC patients showed significantly elevated EPC counts and VEGF levels in peripheral blood before and after surgery. From a methodological point of view, the tested procedure (MCA) was validated as compared to the standard FACS analyses (CD34+/VEGFR2+). MCA proved to have a very high sensitivity and even allowed the identification of singular positive EPCs.