Characterization and clinical relevance of circulating and biopsy-derived endothelial progenitor cells in lymphoma patients.

BACKGROUND AND OBJECTIVES Endothelial progenitor cells (EPC) have been proven to be essential for tumor angiogenesis and growth in animal tumor models. However, the involvement and relevance of EPC in human cancers remain poorly studied. We, therefore, investigated the presence, differentiation potential and molecular characteristics of EPC in lymphoma patients. DESIGN AND METHODS EPC (CD133+CD34+KDR+ cells) were detected in peripheral blood (PB) and lymph node (LN) biopsy samples of 70 lymphoma patients by reverse transcription-polymerase chain reaction (RT-PCR) and flow cytometry. Magnetically isolated EPC (PB and LN-derived) were tested, in vitro, for endothelial differentiation potential and RNA was collected to study their gene expression profiles by Affymetrix oligonucleotide arrays. Lymphoma patients were classified according to disease aggressiveness (indolent vs aggressive lymphoma) and their data (tumor angiogenesis, tumor stage and clinical treatment) were related to the presence or absence of EPC in the circulation or in tumor samples. RESULTS Circulating EPC (CEPC) were more frequent in patients than in healthy controls and more frequent in younger patients than in older patients and in those with aggressive lymphomas. The levels of CEPC decreased in patients with complete response to treatment, but were sustained or increased in the non- or partial- responders to lymphoma therapy. Notably, EPC in the LN (LN-EPC) were more frequently detected than CEPC; LN-EPC were detected in vascular structures and also in the stroma, and after isolation differentiated into endothelial cells in vitro. The presence of LN-EPC correlated with lesion size and with increased angiogenesis in indolent lymphomas. CEPC and LN-EPC share endothelial markers but can be identified and quantified separately, since they express different CD133 isoforms. Gene expression profiling of isolated LN-EPC revealed the expression of pro-angiogenic and tumor growth factors that may influence lymphoma growth. INTERPRETATION AND CONCLUSIONS EPC are present in the circulation and in tumor samples from patients with non-Hodgkin's lymphoma. Since there are relationships between EPC and various characteristics of lymphoma, our research has demonstrated the clinical and biological relevance of studying CEPC and LN-EPC in lymphoma patients.