CD34+CD38- is a good predictive marker of cloning ability and expansion potential of CD34+ cord blood cells

Wharton's jelly mesenchymal stem cell-based or umbilical vein endothelial cell-based serum-free coculture with cytokines supports the ex vivo expansion/maintenance of cord blood hematopoietic stem/progenitor cells

Background

The umbilical cord blood (UCB) has been widely accepted as an alternative source of hematopoietic stem/progenitor cells (HSPCs) for transplantation, and its use in adults is still restricted because of low absolute numbers. To overcome this obstacle, expansion of UCB-HSPCs under feeder cell-based coculture is a promising possibility. In this study, we explored UCB-CD34+ cells ex vivo expansion using Wharton’s jelly mesenchymal stem cells (WJ-MSCs) or umbilical vein endothelial cells (UVECs) as feeder layer-based serum-free coculture system with a cocktail of cytokines.

Methods

UCB-CD34+ cells were cultured in five different coculture conditions composed of umbilical cord stromal cells (WJ-MSCs or UVECs) with or without a cocktail of cytokines (SCF, FLT3L, and TPO). The cultured cells were harvested at day 10 and analyzed for phenotypes and functionalities, including total nuclear cells (TNCs), CD34+ cells, CD34+CD38− cells, colony-forming unit (CFU) for committed progenitors, and long-term culture initiating cells (LTC-ICs) for HSPCs.

Results

Our work showed the numbers of TNC cells, CD34+ cells, and CD34+CD38− cells were expanded under five coculture conditions, and the feeder layer-based cocultures further promoted the expansion. The numbers of colonies of CFU-GM, CFU-E/BFU-E, and CFU-GEMM in the cocultures with cytokines were significantly higher than their counterparts at day 0 (p < 0.05), while no significant difference (p > 0.05) in those without the addition of cytokines. The numbers of LTC-ICs were increased both under the WJ-MSCs and UVECs with cytokine cocultures, but only in the UVECs group showed a significant difference (p < 0.05), and were decreased under conditions without cytokine (p < 0.05).

Conclusion

Our data demonstrate that both WJ-MSCs and UVECs as feeder layer could efficiently support the expansion of UCB-CD34+ cells in synergy with SCF, FLT3L, and TPO under serum-free culture condition. The UVECs combined with the 3GF cytokine cocktail could maintain the growth of LTC-ICs derived from UCB-CD34+ cells and even expand to some extent.

Protocols for hematopoietic stem cell expansion from umbilical cord blood

The reconstitution of adult stem cells may be a promising source for the regeneration of damaged tissues and for the reconstitution of organ dysfunction. However, there are two major limitations to the use of such cells: they are rare, and only a few types exist that can easily be isolated without harming the patient. The best studied and most widely used stem cells are of the hematopoietic lineage. Pioneering work on hematopoietic stem cell (HSC) transplantation was done in the early 1970s by ED. Thomas and colleagues. Since then HSCs have been used in allogenic and autologous transplantation settings to reconstitute blood formation after high-dose chemotherapy for various blood disorders. The cells can be easily harvested from donors, but the cell number is limited, especially when the HSCs originate from umbilical cord blood (UCB). It would be desirable to set up an ex vivo strategy to expand HSCs in order to overcome the cell dose limit, whereby the expansion would favor cell proliferation over cell differentiation. This review provides an overview of the various existing HSC expansion strategies-focusing particularly on stem cells derived from UCB-of the parameters that might affect the outcome, and of the difficulties that may occur when trying to expand such cells.

Pre-clinical development of cord blood-derived progenitor cell graft expanded ex vivo with cytokines and the polyamine copper chelator tetraethylenepentamine

BACKGROUND

We have previously demonstrated that the copper chelator tetraethylenepentamine (TEPA) enables preferential expansion of early hematopoietic progenitor cells (CD34+CD38-, CD34+CD38-Lin-) in human umbilical cord blood (CB)-derived CD34+ cell cultures. This study extends our previous findings that copper chelation can modulate the balance between self-renewal and differentiation of hematopoietic progenitor cells.

METHODS

In the present study we established a clinically applicative protocol for large-scale ex vivo expansion of CB-derived progenitors. Briefly, CD133+ cells, purified from CB using Miltenyi Biotec's (Bergisch Gladbach, Germany) CliniMACS separation device and the anti-CD133 reagent, were cultured for 3 weeks in a clinical-grade closed culture bag system, using the chelator-based technology in combination with early-acting cytokines (SCF, thrombopoietin, IL-6 and FLT-3 ligand). This protocol was evaluated using frozen units derived from accredited cord blood banks.

RESULTS

Following 3 weeks of expansion under large-scale culture conditions that were suitable for clinical manufacturing, the median output value of CD34+ cells increase by 89-fold, CD34+CD38- increase by 30-fold and CFU cells (CFUc) by 172-fold over the input value. Transplantation into sublethally irradiated non-obese diabetic (NOD/SCID) mice indicated that the engraftment potential of the ex vivo expanded CD133+ cells was significantly superior to that of unexpanded cells: 60+/-5.5% vs. 21+/-3.5% CD45+ cells, P=0.001, and 11+/-1.8% vs. 4+/-0.68% CD45+CD34+ cells, P=0.012, n=32, respectively.

DISCUSSION

Based on these large-scale experiments, the chelator-based ex vivo expansion technology is currently being tested in a phase 1 clinical trial in patients undergoing CB transplantation for hematological malignancies.

Immunophenotype of hematopoietic stem cells from placental/umbilical cord blood after culture

Identification and enumeration of human hematopoietic stem cells remain problematic, since in vitro and in vivo stem cell assays have different outcomes. We determined if the altered expression of adhesion molecules during stem cell expansion could be a reason for the discrepancy. CD34+CD38- and CD34+CD38+ cells from umbilical cord blood were analyzed before and after culture with thrombopoietin (TPO), FLT-3 ligand (FL) and kit ligand (KL; or stem cell factor) in different combinations: TPO + FL + KL, TPO + FL and TPO, at concentrations of 50 ng/mL each. Cells were immunophenotyped by four-color fluorescence using antibodies against CD11c, CD31, CD49e, CD61, CD62L, CD117, and HLA-DR. Low-density cord blood contained 1.4 +/- 0.9% CD34+ cells, 2.6 +/- 2.1% of which were CD38-negative. CD34+ cells were isolated using immuno-magnetic beads and cultured for up to 7 days. The TPO + FL + KL combination presented the best condition for maintenance of stem cells. The total cell number increased 4.3 +/- 1.8-fold, but the number of viable CD34+ cells decreased by 46 +/- 25%. On the other hand, the fraction of CD34+CD38- cells became 52.0 +/- 29% of all CD34+ cells. The absolute number of CD34+CD38- cells was expanded on average 15 +/- 12-fold when CD34+ cells were cultured with TPO + FL + KL for 7 days. The expression of CD62L, HLA-DR and CD117 was modulated after culture, particularly with TPO + FL + KL, explaining differences between the adhesion and engraftment of primary and cultured candidate stem cells. We conclude that culture of CD34+ cells with TPO + FL + KL results in a significant increase in the number of candidate stem cells with the CD34+CD38- phenotype.

Histone Deacetylase Inhibitor Valproic Acid Enhances the Cytokine-Induced Expansion of Human Hematopoietic Stem Cells

Ex vivo amplification of human hematopoietic stem cells (HSC) without loss of their self-renewing potential represents an important target for transplantation, gene and cellular therapies. Valproic acid is a safe and widely used neurologic agent that acts as a potent inhibitor of histone deacetylase activities. Here, we show that valproic acid addition to liquid cultures of human CD34+ cells isolated from cord blood, mobilized peripheral blood, and bone marrow strongly enhances the ex vivo expansion potential of different cytokine cocktails as shown by morphologic, cytochemical, immunophenotypical, clonogenic, and gene expression analyses. Notably, valproic acid highly preserves the CD34 positivity after 1 week (range, 40-89%) or 3 weeks (range, 21-52%) amplification cultures with two (Flt3L + thrombopoietin) or four cytokines (Flt3L + thrombopoietin + stem cell factor + interleukin 3). Moreover, valproic acid treatment increases histone H4 acetylation levels at specific regulatory sites on HOXB4, a transcription factor gene with a key role in the regulation of HSC self-renewal and AC133, a recognized marker gene for stem cell populations. Overall, our results relate the changes induced by valproic acid on chromatin accessibility with the enhancement of the cytokine effect on the maintenance and expansion of a primitive hematopoietic stem cell population. These findings underscore the potentiality of novel epigenetic approaches to modify HSC fate in vitro.