Presence of nonhematopoietic side population cells in the adult human and nonhuman primate pancreas

Abstract

Side population (SP) cells defined by their ability to efflux Hoechst dye 33342 (Hst), demonstrate functional stem cell capabilities in adult murine tissues and may represent organ-specific stem cells. We examined adult human (Hu) and rhesus macaque (Rh) pancreatic tissue for the presence of SP cells. Methods Hu cadaver ( n = 4) and Rh donor ( n = 5) pancreata were dispersed with collagenase and separated by density gradient centrifugation to relatively enrich fractions for islet, ductal, and acinar tissue in human and islet and nonislet tissue in Rh. Single cell suspensions were incubated with varying Hst concentrations to determine optimal conditions for SP cell analysis. Cellular heterogeneity was assessed using a panel of monoclonal antibodies positive for hematopoietic and/or endothelial cells. Results Hu SP cells comprised approximately 0.12%, 0.08%, and 0.45% of the gated populations for Hu islet, ductal, and acinar fractions respectively. In Rh, 5.5% and 3.7% of the islet and nonislet fractions were identified as SP cells. FACS analysis of Hu pancreas-derived SP cells indicated that greater than 95% were CD45 −, and only 6% were CD34 +CD45 −. A similar phenotype was detected in Rh pancreas-derived SP cell populations: greater than 70% were CD45 − and less than 2% were endothelial lineage positive. Conclusions SP cells are found in both islet- and nonislet-enriched fractions of the adult Hu and Rh pancreas. The majority of pancreatic SPs are CD45 − and CD34 −, suggesting nonhematopoietic lineage. Further preclinical study is needed to establish the phenotype and functional role of adult tissue-specific versus tissue-resident stem cells.