CD34+ cells and CD34+CD38- subset from mobilized blood show different patterns of adhesion molecules compared to those from steady-state blood, bone marrow, and cord blood

Outcomes of stem cell mobilization and engraftment in patients with multiple myeloma according to CD56 expression status

BACKGROUND

The molecular mechanism underlying the mobilization and engraftment of CD34+ cells is poorly understood. The most relevant factors in the regulation of stem cell release and engraftment include chemokines, adhesion molecules, and chemokine receptors. Previously, it was suggested that the absence of CD56 expression could be used as a predictive factor for mobilization failure at the time of diagnosis. Here, we investigated the effect of CD56 expression status on both mobilization and engraftment processes. Additionally, other factors affecting mobilization and engraftment efficacy were investigated.

METHODS

Data from 79 multiple myeloma patients undergoing autologous stem cell transplantation between 2015 and 2020 were analyzed for peripheral stem cell mobilization and posttransplant neutrophil and platelet engraftment according to CD56 expression on myeloma cells.

RESULTS

No difference in either the median number of CD34+ cells collected or time to engraftment was found between the CD56+ and CD56- groups. The age of the patients (p = 0.025) and peak number of circulating CD34+ cells in peripheral blood (p = 0.005) were important predictors for a higher number of collected CD34+ cells. The average time to recovery of leukocytes and platelets after transplantation was markedly correlated with the number of transplanted stem cells and peak number of circulating CD34+ cells in peripheral blood, respectively (p = 0.049 and p = 0.003).

CONCLUSIONS

Our results indicated no effect of CD56 expression status on the mobilization and engraftment of PBSCs. Our results also support the notion that the peak number of circulating CD34+ cells in peripheral blood is clinically important for rapid platelet engraftment following HPC transplantation.

PVR and ICAM-1 on Blast Crisis CML Stem and Progenitor Cells with TKI Resistance Confer Susceptibility to NK Cells

The BCR-ABL1 fusion gene generating an oncogenic tyrosine kinase is a hallmark of chronic myeloid leukemia (CML), which can be successfully targeted by BCR-ABL1 tyrosine kinase inhibitors (TKIs). However, treatment-free remission has been achieved in a minority of patients due to evolving TKI resistance and intolerance. Primary or acquired resistance to the approved TKIs and progression to blast crisis (BC), thus, remain a major clinical challenge that requires alternative therapeutic strategies. Here, we first demonstrate that donor natural killer (NK) cells prepared using a protocol adopted in clinical trials can efficiently eliminate CML-BC blasts, with TKI resistance regardless of BCR-ABL1 mutations, and preferentially target CD34⁺CD38⁻ leukemic stem cells (LSC), a potential source of disease relapse. Mechanistically, the predominant expression of PVR, a ligand for the NK cell-activating DNAM-1 receptor, in concert with ICAM-1, a ligand for NK cell adhesion, confer this susceptibility to NK cells, despite the lack of ligands for NKG2D, a principal NK cell activating receptor, as an immune evasion mechanism. With these mechanistic insights, our findings provide a proof-of-concept that donor NK cell-based therapy is a viable strategy for overcoming TKI resistance in CML, particularly the advanced, multi-TKI-resistant CML with dismal outcome.

The biology of CD44 and HCELL in hematopoiesis: the 'step 2-bypass pathway' and other emerging perspectives

PURPOSE OF REVIEW

The homing and egress of hematopoietic stem and progenitor cells (HSPCs) to and from marrow, respectively, and the proliferation and differentiation of HSPCs within marrow are complex processes critically regulated by the ordered expression and function of adhesion molecules that direct key cell-cell and cell-matrix interactions. The integral membrane molecule CD44, known primarily for its role in binding hyaluronic acid, is characteristically expressed on HSPCs. Conspicuously, human HSPCs uniquely display a specialized glycoform of CD44 known as hematopoietic cell E-/L-selectin ligand (HCELL), which is the most potent ligand for both E-selectin and L-selectin expressed on human cells. This review focuses on recent advances in our understanding of the biology of CD44 and HCELL in hematopoiesis.

RECENT FINDINGS

New data indicate that CD44-mediated events in hematopoiesis are more complex than previously imagined. Ex-vivo glycan engineering has established that HCELL serves as a 'bone marrow homing receptor'. Moreover, biochemical studies now show that CD44 forms bimolecular complexes with a variety of membrane proteins, one of which is VLA-4. Engagement of CD44 or of HCELL directly induces VLA-4 activation via G-protein-dependent signaling, triggering a 'step 2-bypass pathway' of cell migration, and extravascular lodgment, in absence of chemokine receptor engagement.

SUMMARY

Recent studies have further clarified the roles of CD44 and its glycoform HCELL in hematopoietic processes, providing key insights on how targeting these molecules may be beneficial in promoting hematopoiesis and in treating hematologic malignancies.

Changes of cytokine levels during granulocyte-colony-stimulating factor stem cell mobilization in healthy donors: association with mobilization efficiency and potential predictive significance

BACKGROUND

Peripheral blood stem cells are an important source of hematopoietic stem cells (HSCs) for allogeneic transplantations. Some allogeneic donors mobilize HSCs poorly in response to the granulocyte--colony-stimulating factor (G-CSF). The estimation of the mobilization result in an individual donor is difficult due to the absence of suitable predictive factors.

STUDY DESIGN AND METHODS

We analyzed the concentrations and kinetics of certain cytokines induced by G-CSF in 76 healthy donors and compared them with the mobilization efficiency.

RESULTS

The levels of the most cytokines increased after the G-CSF application: sICAM, sVCAM, MMP-9, interleukin (IL)-6, TNF-α, sE-selectin, and fibronectin. The concentrations of SDF-1α and IL-8 decreased and VEGF and fractalkine remained unchanged. The premobilization concentrations of IL-6 (p = 0.0093) and TNF-a (p = 0.0006) correlated with preapheresis CD34+ cell count. The comparison of premobilization cytokine levels between better and worse mobilizers showed a difference for TNF-α (p = 0.0006) and IL-6 (p = 0.0682). The TNF-α level below cutoff of 3.6 pg/mL implied approximately 20 times higher risk of poor mobilization (odds ratio, 19.9; p = 0.0002). The immunophenotyping of CD34+ cells suggested a negative correlation between Day +5 CD34+ count and expression of CD11a (p = 0.0319) and a positive correlation with CD44 antigen expression (p = 0.0096).

CONCLUSION

The concentrations of certain cytokines corresponded to the quality of HSC mobilization in healthy donors. Their levels measured before mobilization could probably serve as predictive factors for mobilization efficacy and prospectively detect donors who might profit from new mobilization molecules.

MT1-MMP and RECK are involved in human CD34+ progenitor cell retention, egress, and mobilization

The mechanisms governing hematopoietic progenitor cell mobilization are not fully understood. We report higher membrane type 1-MMP (MT1-MMP) and lower expression of the MT1-MMP inhibitor, reversion-inducing cysteine-rich protein with Kazal motifs (RECK), on isolated circulating human CD34+ progenitor cells compared with immature BM cells. The expression of MT1-MMP correlated with clinical mobilization of CD34+ cells in healthy donors and patients with lymphoid malignancies. Treatment with G-CSF further increased MT1-MMP and decreased RECK expression in human and murine hematopoietic cells in a PI3K/Akt-dependent manner, resulting in elevated MT1-MMP activity. Blocking MT1-MMP function by Abs or siRNAs impaired chemotaxis and homing of G-CSF-mobilized human CD34+ progenitors. The mobilization of immature and maturing human progenitors in chimeric NOD/SCID mice by G-CSF was inhibited by anti-MT1-MMP treatment, while RECK neutralization promoted motility and egress of BM CD34+ cells. BM c-kit+ cells from MT1-MMP-deficient mice also exhibited inferior chemotaxis, reduced homing and engraftment capacities, and impaired G-CSF-induced mobilization in murine chimeras. Membranal CD44 cleavage by MT1-MMP was enhanced following G-CSF treatment, reducing CD34+ cell adhesion. Accordingly, CD44-deficient mice had a higher frequency of circulating progenitors. Our results reveal that the motility, adhesion, homing, and mobilization of human hematopoietic progenitor cells are regulated in a cell-autonomous manner by dynamic and opposite changes in MT1-MMP and RECK expression.

Modulation of beta1-integrins on hemopoietic progenitor cells after allergen challenge in asthmatic subjects

BACKGROUND

Mobilization of hemopoietic progenitor cells from the bone marrow (BM) is a feature of inflammatory asthmatic responses. Understanding the mechanisms regulating progenitor cell mobilization and trafficking to the peripheral circulation might be important for the development of effective asthma therapies.

OBJECTIVE

We investigated the role of adhesion molecules in the mobilization of hemopoietic progenitor cells from the BM during an allergen-induced asthmatic response.

METHODS

BM and peripheral blood samples were obtained from dual-responders with mild asthma before and at several time points after allergen challenge. Fluctuations in expression and adhesive properties of beta1- and beta2-integrins on CD34(+)CD45(+) progenitor cells were assessed by using flow cytometry and adhesion to protein-coated wells, respectively.

RESULTS

On BM-derived CD34(+)CD45(+) cells, expression of very late antigen (VLA) 4, but not VLA-5 or Mac-1, decreased significantly 24 hours after allergen challenge and had begun to recover by 48 hours after challenge. In peripheral blood allergen challenge induced a significant decrease in VLA-4 levels after 6 hours, which had not recovered by 96 hours after challenge. Similarly, VLA-5 expression decreased, most prominently at 72 to 96 hours after allergen challenge. In contrast, Mac-1 levels did not change. Chemokine-stimulated adhesion of BM-derived CD34(+)CD45(+) cells to fibronectin was significantly attenuated 24 hours after challenge. Furthermore, adhesion to fibronectin and vascular cell adhesion molecule 1 was greatly reduced by anti-VLA-4 or anti-VLA-5 antibodies.

CONCLUSIONS

Preferential downregulation of beta1-integrin expression on progenitor cells can reduce the tethering forces to BM components, thus facilitating their egress to the peripheral circulation during an allergic inflammatory response.

Hematopoietic progenitor cells (HPC) from mobilized peripheral blood display enhanced migration and marrow homing compared to steady-state bone marrow HPC

OBJECTIVE

Faster engraftment of G-CSF-mobilized peripheral blood (MPB) transplants compared to steady-state bone marrow (ssBM) is well documented and clinically relevant. A number of different factors likely contribute to this outcome. In the present study we explored whether independent of cell number there are intrinsic differences in the efficiency of progenitor cell homing to marrow between MPB and ssBM.

METHODS

Mobilization was achieved by continuous infusion of G-CSF alone or in combination with other mobilizing agents. In vivo homing assays, in vitro migration assays, gene expression analysis, and flow cytometry were utilized to compare homing-related in vivo and in vitro properties of MPB and ssBM HPC.

RESULTS

Marrow homing of murine MPB HPC, generated by different mobilizing schemes, was reproducibly significantly superior to that of ssBM, in lethally irradiated as well as in nonirradiated hosts. This phenotype was independent of MMP9, selectins, and beta2- and alpha4-integrins. Superior homing was also observed for human MPB HPC transplanted into NOD/SCIDbeta2microglobulin(-/-) recipients. Inhibition of HPC migration abrogated the homing advantage of MPB but did not affect homing of ssBM HPC, whereas enhancement of motility by CD26 inhibition improved marrow homing only of ssBM HPC. Enhanced SDF-1-dependent chemotaxis and low CD26 expression on MPB HPC were identified as potential contributing factors. Significant contributions of the putative alternative SDF-1 receptor, RDC1, were unlikely based on gene expression data.

CONCLUSION

The data suggest increased motility as a converging endpoint of complex changes seen in MPB HPC which is likely responsible for their favorable homing.

Abnormal surface markers expression on bone marrow CD34+ cells and correlation with disease activity in patients with systemic lupus erythematosus

Defects of hematopoietic stem cells (HSCs) have been suggested to contribute to the development of systemic lupus erythematosus (SLE). The aim of this study was to investigate the phenotypic characteristics of bone marrow (BM) CD34(+) cells in patients with SLE and its relationship with SLE disease activity. Ten SLE patients and 10 healthy subjects were recruited and their BM CD34(+) cells were analyzed by flow cytometric analysis with CD45/SSC gating for the expression of CD90, CD95, CD117, CD123, CD164, CD166, FAS-L, and HLA-DR. The percentage of BM CD34(+) cells was significantly decreased in active SLE patients (1.48 +/- 0.41%, n = 7) compared to the healthy controls (2.31 +/- 0.75%, n = 10, p < 0.01), but no significant difference was found between the inactive patients (2.04 +/- 0.44%, n = 3) and the controls. The expression of CD95, CD123, and CD166 on BM CD34(+) cells were significantly increased in SLE patients (48.31 +/- 10.59%, 44.9 +/- 21.5%, 30.9 +/- 19.54%, respectively, n = 10) when compared with the control subjects (24.33 +/- 11.1%, 19.5 +/- 4.4%, 10.7 +/- 5.5%, respectively, n = 10, p < 0.05). The increased CD123 expression was negatively correlated with the number of peripheral white blood cells (r = -0.700, p < 0.05, n = 10). The percentage of CD166 expression was found significantly correlated with the index of SLE disease activity (r = 0.472, p < 0.05, n = 10) and 24 h proteinuria (r = 0.558, p < 0.05, n = 10), but negatively correlated with serum C3 level (r = -0.712, p < 0.01, n = 10). Our study found that the surface marker expression of CD95, CD123, and CD166 on BM CD34(+) cells were significantly increased in patients. This supports the hypothesis that there are abnormalities of the HSC in SLE. Since CD166 and CD123 correlated with the overall lupus activity, their role as a biomarker of inflammatory disease activity also requires further study.

Kinetics of CXCR-4 and adhesion molecule expression during autologous stem cell mobilisation with G-CSF plus AMD3100 in patients with multiple myeloma

AMD3100, a competitive antagonist of CXCR-4, disrupts the binding of its ligand, stromal cell-derived factor-1 (SDF-1), and facilitates stem cell mobilisation in patients with haematological malignancies. This study investigated the differential kinetics of CXCR-4 and adhesion molecule expression and their impact on stem cell yield during mobilisation with granulocyte-colony stimulating factor (G-CSF) (days 1-4) followed by AMD3100 in 10 patients with multiple myeloma. A four-colour flow cytometry-based determination of CXCR-4, VLA-4, L-selectin, PECAM, LFA-1 and CD44 expression on CD34+ cells and measurement of SDF-1 concentration were performed at different time points. After G-CSF alone, CXCR-4 expression on patients' blood and marrow CD34+ cells was significantly lower than in the healthy controls (p < 0.001), but allowed no prediction of stem cell yield. Except in the single poorly mobilising patient, AMD3100 led to a further significant decrease of CXCR4 (p = 0.001), which inversely correlated with the CD34+ counts in the blood (p = 0.005). SDF-1 level in patients' marrow was positively correlated with CXCR-4 expression on CD34+ cells (p = 0.011). It is interesting to note that the expression of adhesion molecules remained unaffected by AMD3100 administration. Further studies will define the possible prognostic role of AMD3100 mediated changes in CXCR-4 expression for the prediction of stem cell yield attainable with this new mobilisation regimen.

Adhesion of hematopoietic progenitor cells to human mesenchymal stem cells as a model for cell−cell interaction

OBJECTIVE

The significant role of direct contact between hematopoietic progenitor cells (HPC) and the cellular microenvironment for maintaining "stemness" has been demonstrated. Human mesenchymal stem cell (MSC) feeder layers represent a surrogate model for this interaction. Specific adhesion molecules are responsible for this cell-cell contact.

METHODS

To define cell-cell contact between HPC and MSC, we have studied adhesive interaction of various fractions of HPC by using a novel assay based on gravitational force upon inversion. Adherent and nonadherent cells were separated and further analyzed with regard to gene expression and long-term hematopoietic culture initiating cell (LTC-IC) frequency.

RESULTS

HPC subsets with higher self-renewing capacity demonstrated significantly higher adherence to human MSC (CD34(+) vs CD34(-), CD34(+)/CD38(-) vs CD34(+)/CD38(+), slow dividing fraction vs fast dividing fraction). LTC-IC frequency was significantly higher in the adherent fraction than in the nonadherent fraction. Furthermore, genes coding for adhesion proteins and extracellular matrix were higher expressed in the adherent subsets of CD34(+) cells (fibronectin 1, cadherin 11, vascular cell adhesion molecule-1, connexin 43, integrin beta-like 1, and TGFBI).

CONCLUSION

In this study we have demonstrated that primitive subsets of HPC have higher affinity to human MSC. The essential role of specific junction proteins for stabilization of cell-cell contact is indicated by their significant higher expression.

CD34+ cell adhesion molecule profiles differ between patients mobilized with granulocyte-colony-stimulating factor alone and chemotherapy followed by granulocyte-colony-stimulating factor

BACKGROUND

High-dose therapy with autologous peripheral blood progenitor cell support is widely utilized but requires successful CD34+ cell mobilization and collection. Chemotherapy plus growth factors appear to mobilize more CD34+ cells than growth factors alone. Because alterations in expression of adhesion molecules are important in the trafficking of hematopoietic progenitors, the possibility was explored that the mechanism of this superior mobilization may be greater down regulation of adhesion molecules.

STUDY DESIGN AND METHODS

The expression of eight adhesion molecules (CD11a, b, and c; 15s; 49d and e; 54; and 62L) on the collected CD34+ cells from 15 patients undergoing mobilization with chemotherapy plus granulocyte-colony-stimulating factor (G-CSF) was compared with those of 14 concomitant patients receiving G-CSF alone.

RESULTS

Patients receiving chemotherapy plus G-CSF mobilized more CD34+ cells and did not differ in prior chemotherapy or radiation. There were no significant differences in the percentage of CD34+ cells expressing any of the adhesion molecules examined between the two groups. The chemotherapy plus G-CSF-mobilized cells consistently showed higher expression intensity, and this showed significance or a strong trend for CD11a and c, CD15s, and CD54. Despite these higher expression levels, there were no differences in engraftment kinetics.

CONCLUSIONS

CD34+ cells mobilized by chemotherapy plus growth factors appear to have higher intensities of expression of several adhesion molecules. The significance of this observation will require further study.

The thrombopoietin receptor, c-Mpl, is a selective surface marker for human hematopoietic stem cells

Background

Thrombopoietin (TPO), the primary cytokine regulating megakaryocyte proliferation and differentiation, exerts significant influence on other hematopoietic lineages as well, including erythroid, granulocytic and lymphoid lineages. We previously demonstrated that the receptor for TPO, c-mpl, is expressed by a subset of human adult bone marrow hematopoietic stem/progenitor cells (HSC/PC) that are enriched for long-term multilineage repopulating ability in the SCID-hu Bone in vivo model of human hematopoiesis.

Methods

Here, we employ flow cytometry and an anti-c-mpl monoclonal antibody to comprehensively define the surface expression pattern of c-mpl in four differentiation stages of human CD34⁺ HSC/PC (I: CD34⁺38^--, II: CD34⁺38^dim, III: CD34⁺38⁺, IV: CD34^dim38⁺) for the major sources of human HSC: fetal liver (FL), umbilical cord blood (UCB), adult bone marrow (ABM), and cytokine-mobilized peripheral blood stem cells (mPBSC). We use a surrogate in vivo model of human thymopoiesis, SCID-hu Thy/Liv, to compare the capacity of c-mpl⁺ vs. c-mpl^-- CD34⁺38^--/dim HSC/PC for thymocyte reconstitution.

Results

For all tissue sources, the percentage of c-mpl⁺ cells was significantly highest in stage I HSC/PC (FL 72 ± 10%, UCB 67 ± 19%, ABM 82 ± 16%, mPBSC 71 ± 15%), and decreased significantly through stages II, III, and IV ((FL 3 ± 3%, UCB 8 ± 13%, ABM 0.6 ± 0.6%, mPBSC 0.2 ± 0.1%) [ANOVA: P < 0.0001]. The relative median fluorescence intensity of c-mpl expression was similarly highest in stage I, decreasing through stage IV [ANOVA: P < 0.0001]. No significant differences between tissue sources were observed for either % c-mpl⁺ cells [P = 0.89] or intensity of c-mpl expression [P = 0.21]. Primary Thy/Liv grafts injected with CD34⁺38^--/dimc-mpl⁺ cells showed slightly higher levels of donor HLA⁺ thymocyte reconstitution vs. CD34⁺38^--/dimc-mpl^---injected grafts and non-injected controls (c-mpl⁺ vs. c-mpl^--: CD2⁺ 6.8 ± 4.5% vs. 2.8 ± 3.3%, CD4⁺8^-- 54 ± 35% vs. 31 ± 29%, CD4^--8⁺ 29 ± 19% vs. 18 ± 14%).

Conclusion

These findings support the hypothesis that the TPO receptor, c-mpl, participates in the regulation of primitive human HSC from mid-fetal through adult life. This study extends our previous work documenting human B-lineage, myeloid and CD34⁺ cell repopulation by c-mpl⁺ progenitors to show that c-mpl⁺ HSC/PC are also capable of significant T-lineage reconstitution in vivo. These results suggest that c-mpl merits consideration as a selective surface marker for the identification and isolation of human HSC in both basic research and clinical settings.

Phenotypic and functional characteristics of CD34+cells are related to their anatomical environment: is their versatility a prerequisite for their bio-availability"

Human CD34+ hematopoietic progenitors (HP) are mainly resident in adult bone marrow (BM). However, their recent revelation in nonhematopoietic tissues implies their circulation through peripheral blood (PB). The intimate mechanisms of this physiological process are not yet understood. Our results showed that steady-state CD34+ HP exhibit a differential phenotypic profile according to their BM versus PB localization. We demonstrated that this phenotype could be modulated by incubation in the presence of their counterpart mononuclear cells (MNC) through cell interactions and cytokine production. Such a modulation mainly concerns migration-mediated cytokine and chemokine receptors as well as some adhesion molecules and partly results from MNC specificity. These phenotypic profiles are associated with distinct cell-cycle position, cloning efficiency, and migration capacity of CD34+ cells from the different anatomical sources. We therefore propose a definition for a circulating versus resident CD34+ cell profile, which mostly depends on their cellular environment. We suggest that blood would represent a supply of cells for which phenotypic and functional characteristics would be a prerequisite for their bio-availability.

Peripheral blood and BM CD34+ CD38− cells show better resistance to cryopreservation than CD34+ CD38+ cells in autologous stem cell transplantation

BACKGROUND

We and others have shown a critical role for CD34+ CD38- cells in hematopoietic recovery after autologous stem cell transplantation (ASCT), in particular for platelet reconstitution. Thus a routine assessment of CD34+ CD38- cells in freezing-thawing procedures for autografting could represent an important tool for predicting poor engraftment.

METHODS

To compare the impact of cryopreservation on CD34+ CD38+ and CD34+ CD38- hematopoietic stem cell subsets, 193 autograft products collected in 84 patients with malignancies were assessed before controlled-rate cryopreservation in 10% DMSO and after thawing for autografting.

RESULTS

Cell counts after thawing were significantly different from the pre-freezing counts for total CD34+ (P<0.0001) and CD34+ CD38+ (P<0.0001) cells, but not for CD34+ CD38- cells (P=0.252). Median losses for CD34+, CD34+ CD38+ and CD34+ CD38- cells were, respectively, 11.8%, 11.4% and 0.0%. The magnitude of fresh/post-thawing percentage cell variation was significantly different when comparing between the CD34+ CD38+ and CD34+ CD38- cell subsets (P<0.001). Moreover, CD34+ CD38- cells exhibited recovery values > or =100% in 85/160 graft products, compared with 51/193 in CD34+ CD38+ cells (P<0.0001). Also, recovery values > or =90% were significantly better in the CD34+ CD38- (98/160 grafts) than in the CD34+ CD38+ subsets (89/193 grafts) (P<0.01).

DISCUSSION

In this work we have demonstrated that CD34+ cells that do not express the CD38 Ag show a significantly better resistance to cryopreservation. This could represent another example of the particular ability of less committed progenitor cells to overcome environmental injuries. Moreover, we consider routine assessment of CD34+ CD38- cells before freezing as clinically relevant, but post-thawing controls may be avoided because of their good resistance to freezing.