A sensitive quantitative single-platform flow cytometry protocol to measure human platelets in mouse peripheral blood

AA2P-mediated DNA demethylation synergizes with stem cell agonists to promote expansion of hematopoietic stem cells

Small molecules have enabled expansion of hematopoietic stem and progenitor cells (HSPCs), but limited knowledge is available on whether these agonists can act synergistically. In this work, we identify a stem cell agonist in AA2P and optimize a series of stem cell agonist cocktails (SCACs) to help promote robust expansion of human HSPCs. We find that SCACs provide strong growth-promoting activities while promoting retention and function of immature HSPC. We show that AA2P-mediated HSPC expansion is driven through DNA demethylation leading to enhanced expression of AXL and GAS6. Further, we demonstrate that GAS6 enhances the serial engraftment activity of HSPCs and show that the GAS6/AXL pathway is critical for robust HSPC expansion.

Dimethyl sulfoxide-free cryopreservation solutions for hematopoietic stem cell grafts

BACKGROUND AIMS

The use of effective methods for the cryopreservation of hematopoietic stem cells (HSCs) is vital to retain the maximum engraftment activity of cord blood units (CBUs). Current protocols entail the use of dimethyl sulfoxide (DMSO) as intracellular cryoprotective agent (CPA) and dextran and plasma proteins as extracellular CPAs, but DMSO is known to be cytotoxic, and its infusion in patients is associated with mild to moderate side effects. However, new, commercially available, DMSO-free cryopreservation solutions have been developed, but their capacity to protect HSCs remains poorly investigated.

METHODS

Herein the authors compared the capacity of four DMSO-free freezing media to cryopreserve cord blood (CB) HSCs: CryoProtectPureSTEM (CPP-STEM), CryoScarless (CSL), CryoNovo P24 (CN) and Pentaisomaltose (PIM). Clinical-grade DMSO/dextran solution was used as control.

RESULTS

Of the four cryopreservation solutions tested, the best post-thaw cell viability, recovery of viable CD45+ and CD34+ cells and potency were achieved with CPP-STEM, which was equal or superior to that seen with the control DMSO. CSL provided the second best post-thaw results followed by PIM, whereas CN was associated with modest viability and potency. Further work with CPP-STEM revealed that CB CD34-enriched HSCs and progenitors cryopreserved with CPP-STEM maintained high viability and growth expansion activity. In line with this, a pilot transplantation assay confirmed that CPP-STEM-protected CB grafts supported normal short- and long-term engraftment kinetics.

CONCLUSIONS

The authors' results suggest that new, valuable alternatives to DMSO are now available for the cryopreservation of HSCs and grafts, including CBUs.

Preclinical evaluation of eltrombopag in a PDX model of myelodysplastic syndromes

Preclinical research of myelodysplastic syndromes (MDSs) is hampered by a lack of feasible disease models. Previously, we have established a robust patient-derived xenograft (PDX) model for MDS. Here we demonstrate for the first time that this model is applicable as a preclinical platform to address pending clinical questions by interrogating the efficacy and safety of the thrombopoietin receptor agonist eltrombopag. Our preclinical study included n = 49 xenografts generated from n = 9 MDS patient samples. Substance efficacy was evidenced by FACS-based human platelet quantification and clonal bone marrow evolution was reconstructed by serial whole-exome sequencing of the PDX samples. In contrast to clinical trials in humans, this experimental setup allowed vehicle- and replicate-controlled analyses on a patient–individual level deciphering substance-specific effects from natural disease progression. We found that eltrombopag effectively stimulated thrombopoiesis in MDS PDX without adversely affecting the patients’ clonal composition. In conclusion, our MDS PDX model is a useful tool for testing new therapeutic concepts in MDS preceding clinical trials.

Flow cytometric analysis from fish samples stored at low, ultra-low and cryogenic temperatures

Flow cytometry is a valuable tool in biomedical and animal sciences. However, equipment used for such analysis presents limitations at field conditions, suggesting then preservation procedures for future analysis at laboratory conditions. In this study, freezing at low (-20 °C), ultra-low (-80 °C) and cryogenic temperatures (-196 °C, i.e. liquid nitrogen) were used as preservation procedures of fish tissue. Samples were maintained in 0.9% NaCl or lysing solution, and stored at the temperatures above for 0 (fresh control), 60, 120 and 180 days of storage. After storage, the samples were thawed and proceeded to flow cytometric analysis. Storage at low temperatures (-20 °C), both in lysing and 0.9% NaCl, exhibited poor results when analyzed after 60, 120 and 180 days, showing noisy peaks, deviation in the DNA content and absence of peaks. Ultralow (-80 °C) and cryogenic (-196 °C) temperatures, both in lysing solution and 0.9% NaCl, showed good results and high quality of histograms. Both storage procedures gave similar histograms and DNA content in comparison with control group (fresh) even after 60, 120 and 180 days of storage, exhibiting the main peak at 2C content from diploid cells and a secondary peak at 4C derived from dividing cells. In conclusion, samples may be stored for 180 days at -80 °C and -196 °C in both, 0.9% NaCl or lysing solution. As cryogenic temperatures in liquid nitrogen permits indefinite storage, this procedure should be used for long-term preservation.

Inhibition of ice recrystallization during cryopreservation of cord blood grafts improves platelet engraftment

BACKGROUND

Platelet engraftment following cord blood (CB) transplantation remains a significant hurdle to this day. The uncontrolled growth of ice, a process referred to as ice recrystallization, is one of several mechanisms that lead to cell loss and decreased potency during freezing and thawing. We hypothesized that reducing cell damage induced by ice recrystallization in CB units (CBUs) would reduce losses of stem and progenitor cells and therefore improve engraftment. We previously demonstrated that the ice recrystallization inhibitor (IRI) N-(2-fluorophenyl)-D-gluconamide (IRI 2) increases the postthaw recovery of CB progenitors. Herein, we set out to ascertain whether IRI 2 can enhance platelet and bone marrow engraftment activity of hematopoietic stem cells (HSCs) in cryopreserved CBUs using a serial transplantation model.

STUDY DESIGN AND METHODS

CBUs were processed following standard volume/red blood cell reduction procedure and portions frozen with dimethyl sulfoxide (DMSO) supplemented or not with IRI 2. Thawed CB samples were serially transplanted into immunodeficient mice.

RESULTS

Our results show that supplementation of DMSO with IRI 2 had several beneficial effects. Specifically, higher levels of human platelets were observed in the peripheral blood (p < 0.05; n = 4) upon transplant of CBUs preserved with the IRIs. In addition, human BM chimerism and the number of human CFU progenitors in the bone marrow were superior in IRI 2 recipients compared to DMSO recipients. Moreover, IRI 2 had no negative impact on the multilineage differentiation and self-renewal activities of HSCs.

DISCUSSION

Taken together, these results demonstrate that supplementation of a hematopoietic graft with IRI can improve the postthaw engraftment activities of HSCs.

Thrombopoietin treatment of one graft in a double cord blood transplant provides early platelet recovery while contributing to long-term engraftment in NSG mice

Human cord blood (CB) hematopoietic stem cell (HSC) transplants demonstrate delayed early neutrophil and platelet recovery and delayed longer term immune reconstitution compared to bone marrow and mobilized peripheral blood transplants. Despite advances in enhancing early neutrophil engraftment, platelet recovery after CB transplantation is not significantly altered when compared to contemporaneous controls. Recent studies have identified a platelet-biased murine HSC subset, maintained by thrombopoietin (TPO), which has enhanced capacity for short- and long-term platelet reconstitution, can self-renew, and can give rise to myeloid- and lymphoid-biased HSCs. In previous studies, we have shown that transplantation of human CB CD34(+) cells precultured in TPO as a single graft accelerates early platelet recovery as well as yielding long-term repopulation in immune-deficient mice. In this study, using a double CB murine transplant model, we investigated whether TPO cultured human CB CD34(+) cells have a competitive advantage or disadvantage over untreated human CB CD34(+) cells in terms of (1) short-term and longer term platelet recovery and (2) longer term hematological recovery. Our studies demonstrate that the TPO treated graft shows accelerated early platelet recovery without impairing the platelet engraftment of untreated CD34(+) cells. Notably, this was followed by a dominant contribution to platelet production through the untreated CD34(+) cell graft over the intermediate to longer term. Furthermore, although the contribution of the TPO treated graft to long-term hematological engraftment was reduced, the TPO treated and untreated grafts both contributed significantly to long-term chimerism in vivo.

No Synergistic Effect of Cotransplantation of MSC and Ex Vivo TPO-Expanded CD34(+) Cord Blood Cells on Platelet Recovery and Bone Marrow Engraftment in NOD SCID Mice

After cord blood (CB) transplantation, early platelet recovery in immune-deficient mice is obtained by expansion of CB CD34(+) cells with thrombopoietin (TPO) as single growth factor. Moreover, improvement of hematopoietic engraftment has been shown by cotransplantation of mesenchymal stem cells (MSC). We investigated whether a combination of both approaches would further enhance the outcome of CB transplantation in NOD SCID mice. NOD SCID mice were transplanted with either CB CD34(+) cells, CD34(+) cells with MSC, TPO-expanded CD34(+) cells or TPO-expanded CD34(+) cells with MSC. We analyzed human platelet recovery in the peripheral blood (PB) from day 4 after transplantation onward and human bone marrow (BM) engraftment at week 6. The different transplants were assessed in vitro for their migration capacity and expression of CXCR4. TPO expansion improved the early platelet recovery in the PB of the mice. Cotransplantation of MSC with CD34(+) cells improved BM engraftment and platelet levels in the PB 6 weeks after transplantation. Combining TPO expansion and MSC cotransplantation, however, neither resulted in a more efficient early platelet recovery, nor in a better BM engraftment, nor even very low or absent BM engraftment occurred. In vitro, MSC boosted the migration of CD34(+) cells, suggesting a possible mechanism for the increase in engraftment. Our results show that cotransplantation of MSC with TPO-expanded CD34(+) cells at most combines, but does not increase the separate advantages of these different strategies. A combination of both strategies even adds a risk of non engraftment.

Introducing a dexamethasone mouse model for monitoring in vivo viability of stored human platelets

OBJECTIVES

The aim of this study is to establish an available animal model which can evaluate in vivo viability of stored human platelets (HuPLTs).

BACKGROUND

The viability in vivo of HuPLTs was usually evaluated by transfusing HuPLTs into animals before clinical trials. It is necessary to develop a method which may slow down rapid clearance of HuPLTs from circulation of the animal.

METHODS

Carbon clearance tests were performed by treating mice with dexamethasone (DEX) to determine the phagocytic ability of the mice macrophages. HuPLTs in mice whole blood were detected by flow cytometric analysis with mouse anti-human CD41-fluorescein isothiocyanate monoclonal antibody. Recovery and survival of the HuPLTs stored at 22 °C for 1 day were evaluated after transfusing these HuPLTs into DEX-treated mice, and compared with those either stored at 22 °C for 5 days or at 4 °C for 1 day.

RESULTS

Corrected phagocytic indexes of DEX-treated mice decreased significantly compared with those of control mice (P < 0.05). The recovery after 24 h and survival time of fresh HuPLTs in DEX-treated mice were much higher than those in control mice (P < 0.01). After transfused into the DEX-treated mice, HuPLTs stored either at 22 °C for 5 days or at 4 °C for 1 day showed decrease in recovery and survival compared with those stored at 22 °C for 1 day (P < 0.05).

CONCLUSION

Dexamethasone slows down the rate of HuPLTs clearance efficiently in mouse circulation. And the DEX-treated mouse model was able to evaluate the in vivo viability of stored HuPLTs.

Functional characterization of TPO-expanded CD34+ cord blood cells identifies CD34- CD61- cells as platelet-producing cells early after transplantation in NOD/SCID mice and rCD34+ cells as CAFC colony-forming cells

Transplantation of thrombopoietin (TPO)-expanded cord blood CD34(+) cells accelerates human platelet recovery in NOD/SCID mice. It is unknown which subpopulations of the TPO-expanded cells mediate accelerated platelet recovery and bone marrow (BM) engraftment. In this study, the contribution of these subpopulations to human platelet appearance in the blood and BM engraftment was studied in NOD/SCID mice. Following transplantation of CD34(-) /CD61(-)/lineage(-) cells (Lin(-)), human platelets were detected in the blood of recipient mice from day 4. Both time to platelet recovery and blood platelet counts at 6 weeks after transplantation showed Lin(-) dose dependence. The Lin(-) population was virtually negative for lineage marker expression and lacked CD42b expression but was heterogeneous with regard to CD36 and CD38 expression, reflecting a population in transit but not fully committed toward the megakaryocyte (MK) lineage. Although no definitive phenotype could be established of the cells generating prompt platelet production and cells generating platelets 6 weeks after transplantation, this relatively heterogeneous Lin(-) population is prerequisite to accelerate platelet recovery in vivo. The interval to platelet recovery after transplantation of the CD34(+) cells remaining after expansion (rCD34(+)) was similar to mice transplanted with nonexpanded CD34(+) cells, although the total platelet counts and the engraftment levels in the BM were lower. Cobblestone area-forming cell colony-forming cells resided mostly in the rCD34(+) population. The pro-MK CD61(+) cells did not contribute to human platelet recovery or engraftment in the BM. Our study shows that not all expanded cells appear critical for transplantation. These data support that functional characterization of the expanded cell populations is warranted to make future expansion protocols suitable for clinical application.

Validation of human monoclonal HLA Class I antibodies to evaluate the kinetics of donor chimerism in different cell subsets after double-cord-blood transplantation in the NOD/SCID model

BACKGROUND

Double-cord-blood transplantation (DCBT) in patients is typically accompanied by predominance of a single unit. The causative mechanism, however, is unknown. Identifying the dynamics of mixed donor chimerism in general and in specific subpopulations may help to resolve this question. We conducted studies in a mouse model to develop a new analytic method using anti-human HLA Class I allele-specific monoclonal antibodies (HLA-MoAbs) in flow cytometry.

STUDY DESIGN AND METHODS

Single-cord-blood transplantation or DCBT from HLA-mismatched donors was performed in NOD/SCID mice. Bone marrow (BM) and peripheral blood were collected from 3 to 20 weeks after transplantation. Donor chimerism was determined quantitatively within human platelets (hPLTs), human CD45+ (hCD45+) cells, and human myeloid and lymphocyte subsets by flow cytometry.

RESULTS

Both cord donors stably engrafted in NOD/SCID. The sensitivity to detect chimerism measured with all HLA-MoAbs was 1% (>10 cells/µL). In mouse BM, the percentage of human cells measured with hCD45+ versus HLA-MoAbs correlated excellently (r = 0.999). Donor origin could be defined with HLA-MoAbs for nearly all (>93.6%) human cells in mouse peripheral blood and BM in all lineages. Chimerism of hPLTs in peripheral blood correlated well with hCD45+ cells in BM enabling frequent measurement of chimerism from early after transplantation onward.

CONCLUSION

This approach using HLA-MoAbs enables longitudinal analysis of double-mixed human chimeric populations despite low absolute concentrations of human hematopoietic cell subsets in peripheral blood and BM in mice. Lacking reactivity with mouse cells, the HLA-MoAbs are suitable for use in other mouse models and in humans to identify the mechanisms involved in DCBT.

Drug-induced thrombocytopenia: development of a novel NOD/SCID mouse model to evaluate clearance of circulating platelets by drug-dependent antibodies and the efficacy of IVIG

Drug-induced immune thrombocytopenia (DITP) is an adverse drug effect mediated by drug-dependent antibodies. Intravenous immunoglobulin (IVIG) is frequently used to treat DITP and primary immune thrombocytopenia (ITP). Despite IVIG's proven beneficial effects in ITP, its efficacy in DITP is unclear. We have established a nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse model of DITP in which human platelets survive for more than 24 hours, allowing platelet clearance by DITP/ITP antibodies to be studied. Rapid human platelet clearance was uniformly observed with all quinine-induced thrombocytopenia (QITP) patient sera studied (mean platelet lifespans: QITP 1.5 ± 0.3 hours vs controls 16.5 ± 4.3 hours), consistent with the clinical presentation of DITP. In contrast, clearance rates with ITP antibodies were more variable. IVIG treatment partially prevented platelet clearance by DITP and ITP antibodies. Our results suggest that the NOD/SCID mouse model is useful for investigating the efficacy of current and future DITP therapies, an area in which there is little experimental evidence to guide treatment.

Human platelets produced in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice upon transplantation of human cord blood CD34(+) cells are functionally active in an ex vivo flow model of thrombosis

Xenotransplantation systems have been used with increasing success to better understand human hematopoiesis and thrombopoiesis. In this study, we demonstrate that production of human platelets in nonobese diabetic/severe combined immunodeficient mice after transplantation of unexpanded cord-blood CD34(+) cells was detected within 10 days after transplantation, with the number of circulating human platelets peaking at 2 weeks (up to 87 x 10(3)/microL). This rapid human platelet production was followed by a second wave of platelet formation 5 weeks after transplantation, with a population of 5% still detected after 8 weeks, attesting for long-term engraftment. Platelets issued from human hematopoietic stem cell progenitors are functional, as assessed by increased CD62P expression and PAC1 binding in response to collagen-related peptide and thrombin receptor-activating peptide activation and their ability to incorporate into thrombi formed on a collagen-coated surface in an ex vivo flow model of thrombosis. This interaction was abrogated by addition of inhibitory monoclonal antibodies against human glycoprotein Ibalpha (GPIbalpha) and GPIIb/IIIa. Thus, our mouse model with production of human platelets may be further explored to study the function of genetically modified platelets, but also to investigate the effect of stimulators or inhibitors of human thrombopoiesis in vivo.