Polychromatic flow cytometry analysis of CD34+ hematopoietic stem cells in cryopreserved early preterm human cord blood samples

During the last decades, extended characterizations were performed of human full-term cord blood (hTCB) cells, but little information is available on human early preterm cord blood (hEPCB) hematopoietic stem cells (HSCs). In our study, we analyzed by flow cytometry 19 hEPCB and 17 hTCB samples. First, we observed that the percentage of CD34 ^PosCD45 ^Dim cells was higher in hEPCB compared with hTCB and that it decreased during 16th-20th week of pregnancy. Within the CD34 ^PosCD45 ^Dim population, we examined the expression of CD29, CD31, CD38, CD90, CD117, CD133, CD135, CD200, CD243, and CD338. We found that CD135 intensity and CD243 ^Pos cells percentage were lower in hEPCB compared with hTCB. As to CD38, we observed that hEPCB samples were richer in undifferentiated CD34 ^PosCD45 ^DimCD38 ^Neg HSCs compared with hTCB counterparts. We also compared the expression of the above-mentioned molecules in undifferentiated and committed HSCs residing in hEPCB and hTCB. In particular, although CD34 ^PosCD45 ^DimCD38 ^Pos HSCs from both hEPCB and hTCB expressed relatively higher amounts of CD29, CD71, and CD135 compared with CD34 ^PosCD45 ^DimCD38 ^Neg cells, a higher expression of CD31 was restricted to CD34 ^PosCD45 ^DimCD38 ^Pos cells from hEPCB samples, and a higher expression of CD117 was demonstrated in CD34 ^PosCD45 ^DimCD38 ^Pos cells from hTCB samples. Moreover, our data showed that CD34 ^PosCD45 ^Dim cell population from hEPCB displayed higher percent of undifferentiated CD38 ^NegCD133 ^Pos cells compared with hTCB samples. Finally, analyzing monocytes and lymphocytes within the two samples, we observed that T-cell percentages were higher in hTCB, whereas B-cell percentages were higher in hEPCB. We, therefore, studied the B-cell lineage maturation and found a higher percent of pro-B and pre-B cells in hEPCB compared with hTCB samples. Taken together, these results evidence the hematopoietic peculiarity of hEPCB, potentially useful for highlighting early steps of human hematolymphopoiesis as well as for developing novel strategies of stem cell-based therapy.