To investigate the differences of the number and migration ability of endothelial progenitor cell (EPC) isolated from umbilical cord blood among preterm infants with different gestational ages.

From October 2014 to July 2015, a total of 47 cases of umbilical cord blood of neonates in West China Second University Hospital, Sichuan University, Sichuan Academy of Medical Sciences & Sichuan Provincial People′s Hospital, and Chengdu First People′s Hospital were chosen into this study. According to the gestational age of newborns whose umbilical cord blood was collected, they were divided into very preterm group (the gestational ages were 28 to 32 weeks, n=12), preterm group (the gestational ages were 32 to 36 weeks, n=20), and full-term group (the gestational ages were > 37 weeks, n=15). Before the induced differentiation of umbilical cord blood in the three groups, flow cytometry was used to detect the level of EPC. After the induced differentiation of umbilical cord blood in the three groups, the mononuclear cells were incubated and stained by fluorescent probes labeled Dil-acetylated low-density lipoprotein (Dil-Ac-LDL) and fluorescein isothiocyanate-labeled ulex europaeus agglutinin-1 (FITC-UEA-1). The stainings of mononuclear cells in the three groups were observed under fluorescence microscope to detect whether the EPC was successfully induced or not. Transwell migration assay was used to detect the migration ability of EPC in the three groups. The levels of EPC before the induced differentiation of umbilical cord blood in three groups and the migration numbers of EPC after the induced differentiation of umbilical cord blood in three groups were compared by statistical methods. The study protocol was approved by the Ethical Review Boards of three hospitals from which the umbilical cord blood was collected. Informed consent was obtained from each pregnant woman before obtaining umbilical cord blood. There were no significant differences in gender ratio, delivery method, Apgar scores and other basic data among the newborns from which the umbilical cord blood was collected in the three groups (P>0.05).

①Flow cytometry results showed that, there was no statistical difference in the level of EPC before the induced differentiation of umbilical cord blood in the three groups (F=0.302, P=0.654). ②Dil-Ac-LDL and FITC-UEA-1 double fluorescent staining results showed that, EPC in the three groups all were successfully induced to differentiate from the umbilical cord blood, and with the increase of gestational age, the number of EPC induced from mononuclear cells increased gradually at the same time. ③Transwell migration experimental results show that, the migration number of EPC in very preterm group, preterm group and full-term group was (13.8±21.7) cells/field, (18.8±12.4) cells/field, (39.9±23.8) cells/field, respectively, and the difference was statistically significant (F=3.826, P=0.027). The migration number of EPC in very preterm group and preterm group were both significantly lower than that in full-term group, and both the differences were statistically significant (P=0.016, 0.035). The migration number of EPC in very preterm group was significantly lower than that in preterm group, and the difference was statistically significant (P=0.042).

With the increasing of gestational age, the level of EPC in preterm infants′ umbilical cord blood does not increase obviously, but the migration ability of EPC improves gradually as the gestational age increases.