Flow Cytometric Aldehyde Dehydrogenase Assay Enables a Fast and Accurate Human Umbilical Cord Blood Hematopoietic Stem Cell Assessment

In vivo and in vitro effects of cord blood hematopoietic stem and progenitor cell (HSPC) expansion using valproic acid and/or nicotinamide

BACKGROUND

High self-renewal capacity and most permissive nature of umbilical cord blood (CB) results with successful transplant outcomes but low hematopoietic stem and progenitor cell (HSPC) counts limits wider use. In order to overcome this problem ex vivo expansion with small molecules such as Valproic acid (VPA) or Nicotinamide (NAM) have been shown to be effective. To the best of our knowledge, the combinatory effects of VPA and NAM on HSPC expansion has not been studied earlier. The aim of this study was to analyze ex vivo and in vivo efficacy of VPA and NAM either alone or in combination in terms of expansion and engraftment.

METHODS

A total of 44 CB units were included in this study. To determine the ex vivo and in vivo efficacy, human CB CD34+ cells were expanded with VPA and/or NAM and colony forming unit (CFU) assay was performed on expanded HSPC. Xenotransplantation was performed simultaneously by intravenous injection of expanded HSPC to NOD-SCID gamma (NSG) mice (n = 22). Significance of the difference between the expansion groups or xenotransplantation models was analyzed using t-test, Mann-Whitney, ANOVA or Kruskal-Wallis tests as appropriate considering the normality of distributions and the number of groups analyzed.

RESULTS

In vitro CD34+ HSPC expansion fold relative to cytokines-only was significantly higher with VPA compared to NAM [2.23 (1.07-5.59) vs 1.48 (1.00-4.40); p < 0.05]. Synergistic effect of VPA+NAM has achieved a maximum relative expansion fold at 21 days (D21) of incubation [2.95 (1.00-11.94)]. There was no significant difference between VPA and VPA+NAM D21 (p = 0.44). Fold number of colony-forming unit granulocyte-macrophage (CFU-GM) colonies relative to the cytokine-only group was in favor of NAM compared to VPA [1.87 (1.00-3.59) vs 1.00 (1.00-1.81); p < 0.01]. VPA+NAM D21 [1.62 (1.00-2.77)] was also superior against VPA (p < 0.05). There was no significant difference between NAM and VPA+NAM D21. Following human CB34+ CB transplantation (CBT) in the mouse model, fastest in vivo leukocyte recovery was observed with VPA+NAM expanded cells (6 ± 2 days) and the highest levels of human CD45 chimerism was detectable with VPA-expanded CBT (VPA: 5.42 % at day 28; NAM: 2.45 % at day 31; VPA+NAM 1.8 % at day 31).

CONCLUSION

Our study results suggest using VPA alone, rather than in combination with NAM or NAM alone, to achieve better and faster expansion and engraftment of CB HSPC.

Update of ALDH as a Potential Biomarker and Therapeutic Target for AML

Studies employing mouse transplantation have illustrated the role of aldehyde dehydrogenase (ALDH) defining hematopoietic stem cells (HSCs) and leukemia stem cells (LSCs). Besides being a molecular marker, ALDH mediates drug resistance in AML, which induces poor prognosis of the patients. In AML patients, either CD34⁺ALDH^br population or CD34⁺CD38^-ALDH^int population was found to denote LSCs and minimal residual disease (MRD). A bunch of reagents targeting ALDH directly or indirectly have been evaluated. ATRA, disulfiram, and dimethyl ampal thiolester (DIMATE) are all shown to be potential candidates to open new perspective for AML treatment. However, inconsistent results have been shown for markers of LSCs, which makes it even more difficult to differentiate LSCs and HSCs. In this review, we elevated the role of ALDH to be a potential marker to define and distinguish HSCs and LSCs and its importance in prognosis and target therapy in AML patients. In addition to immunophenotypical markers, ALDH is also functionally active in defining and distinguishing HSCs and LSCs and offers intracellular protections against cytotoxic drugs. Targeting ALDH may be a potential strategy to improve AML treatment. Additional studies concerning specific targeting ALDH and mechanisms of its roles in LSCs are warranted.