Human neonatal blood: stem cell content, kinetics of CD34+ cell decline and ex vivo expansion capacity

Disturbances in the IgG Antibody Profile in HIV-Exposed Uninfected Infants Associated with Maternal Factors

Over the last 20 years, the incidence of vertical HIV transmission has decreased from 25%-42% to less than 1%. Although there are no signs of infection, the health of HIV-exposed uninfected (HEU) infants is notoriously affected during the first months of life, with opportunistic infections being the most common disease. Some studies have reported effects on the vertical transfer of antibodies, but little is known about the subclass distribution of these antibodies. We proposed to evaluate the total IgG concentration and its subclasses in HIV+ mothers and HEU pairs and to determine which maternal factors condition their levels. In this study, plasma from 69 HEU newborns, their mothers, and 71 control pairs was quantified via immunoassays for each IgG isotype. Furthermore, we followed the antibody profile of HEUs throughout the first year of life. We showed that mothers present an antibody profile characterized by high concentrations of IgG1 and IgG3 but reduced IgG2, and HEU infants are born with an IgG subclass profile similar to that of their maternal pair. Interestingly, this passively transferred profile could remain influenced even during their own antibody production in HEU infants, depending on maternal conditions such as CD4+ T-cell counts and maternal antiretroviral treatment. Our findings indicate that HEU infants exhibit an altered IgG subclass profile influenced by maternal factors, potentially contributing to their increased susceptibility to infections.

Impaired T helper cell responses in human immunodeficiency virus-exposed uninfected newborns

Introduction

HIV‐exposed uninfected (HEU) newborns suffer from higher risks of opportunistic infections during the first months of life compared to HIV‐unexposed uninfected (HUU) newborns. Alterations in thymic mass, amounts of T helper (Th) cells, T‐cell receptor diversity, and activation markers have been found in HEU newborns, suggesting alterations in T cell ontogeny and differentiation. However, little is known about the ability of these cells to produce specialized Th responses from CD4⁺ T cells.

Method

To characterize the Th cell profile, we evaluated the frequency of Th₁ (CD183⁺CD194⁻CD196⁻/CXCR3⁺CCR4⁻CCR6⁻), Th₂ (CD183⁻CD194⁺CD196⁻/CXCR3⁻CCR4⁺CCR6⁻), Th₁₇ (CD183⁻CD194⁺CD196⁺/CXCR3⁻CCR4⁺CCR6⁺), and CD4⁺CD25⁺⁺ blood T‐cell phenotypes in 50 HEU and 25 HUU newborns. Early activation markers on CD4⁺ T cells and the Th cytokine profile produced from mononuclear cells under polyclonal T cell stimulation were also studied. Additionally, we probed the ability of CD4⁺ T cells to differentiate into interferon (IFN)‐γ‐producing Th₁ CD4⁺ T cells in vitro.

Results

Lower percentages of differentiated Th₁, Th₂, Th_17, and CD4⁺CD25⁺⁺ T cells were found in blood from HEU newborns than in blood from HUU newborns. However, polyclonally stimulated Th cells showed a similar ability to express CD69 and CD279 but produced less secreted interleukin (IL)‐2 and IL‐4. Interestingly, under Th₁ differentiation conditions, the percentages of CD4⁺IFN‐γ⁺ T cells and soluble IFN‐γ were higher in HEU newborns than in HUU newborns.

Conclusion

HEU neonates are born with reduced proportions of differentiated Th₁/Th₂/Th₁₇ and CD4⁺CD25⁺⁺ T cells, but the intrinsic abilities of CD4⁺ T cells to acquire a Th₁ profile are not affected by the adverse maternal milieu during development.

Autologous cord blood cell therapy for neonatal hypoxic-ischaemic encephalopathy: a pilot study for feasibility and safety

Neonatal hypoxic-ischaemic encephalopathy (HIE) is a serious condition; many survivors develop neurological impairments, including cerebral palsy and intellectual disability. Preclinical studies show that the systemic administration of umbilical cord blood cells (UCBCs) is beneficial for neonatal HIE. We conducted a single-arm clinical study to examine the feasibility and safety of intravenous infusion of autologous UCBCs for newborns with HIE. When a neonate was born with severe asphyxia, the UCB was collected, volume-reduced, and divided into three doses. The processed UCB was infused at 12–24, 36–48, and 60–72 hours after the birth. The designed enrolment was six newborns. All six newborns received UCBC therapy strictly adhering to the study protocol together with therapeutic hypothermia. The physiological parameters and peripheral blood parameters did not change much between pre- and postinfusion. There were no serious adverse events that might be related to cell therapy. At 30 days of age, the six infants survived without circulatory or respiratory support. At 18 months of age, neurofunctional development was normal without any impairment in four infants and delayed with cerebral palsy in two infants. This pilot study shows that autologous UCBC therapy is feasible and safe.

Regulation of Circulating Hematopoietic Stem/Progenitor Cells in Preterm Infants with Septicemia

Preterm infants are at high risk of developing severe sepsis. Circulating hematopoietic stem and progenitor cells (HSPCs; CD45⁺CD34⁺) have been suggested to play a vital role in the host immunological defense against invading pathogens. The objectives were to investigate the regulation of circulating HSPCs in preterm infants during infection episodes, and to assess the relationship of CD45⁺CD34⁺ cells with immunological mediators and differential leukocyte populations. First, we conducted a cross-sectional case-control study comparing these parameters among infected infants (n = 23), gestational and postnatal age-matched noninfected infants (n = 46), and "healthy" control (CTL) infants (n = 12). Second, we investigated the longitudinal change of CD45⁺CD34⁺ cell concentrations in infected infants before, during, and after an infection episode, and compared them with the other two groups. Our cross-sectional results showed that CD45⁺CD34⁺ cell count and percentage were significantly reduced in infected infants during systemic infection, compared with the noninfected or CTL infants. There were significant positive correlation between levels of CD45⁺CD34⁺ cells and lymphocytes or monocytes, and significant negative correlation between CD45⁺CD34⁺ cells and neutrophils or interleukin (IL)-6 in infected infants. Longitudinal analysis showed that changes of CD45⁺CD34⁺ cells at the onset of sepsis relative to levels 1 week prior and 1 week postsepsis in infected infants were significantly different from those changes in the corresponding time points for the other two groups. Our findings suggested that circulating HSPCs were dynamically regulated during septicemia and could play an important role in the defense mechanism, plausibly contributing to replenishment of leukocytes during sepsis in preterm infants.

Cord blood mononuclear cells prevent neuronal apoptosis in response to perinatal asphyxia in the newborn lamb

Perinatal asphyxia is a significant cause of death or long-term neurodevelopmental impairment. Hypothermia, currently the only effective treatment, leads to modest improvements, but new therapeutic strategies are required. Umbilical cord blood (UCB) mononuclear cells have potent anti-inflammatory properties and may reduce neuropathology. This study examined whether autologous UCB mononuclear cells were neuroprotective when administered to newborn lambs at 12 h after birth asphyxia. At caesarean section, birth asphyxia was induced by clamping the umbilical cord until mean arterial blood pressure decreased to 18-20 mmHg. Asphyxia (n = 20) or control (n = 11) lambs were resuscitated and maintained, with magnetic resonance spectroscropy (MRS) performed at 12 and 72 h, and were then killed at 72 h. Cord blood was collected once the cord was clamped, and mononuclear cells were isolated and labelled fluorescently and administered to control (n = 3) or asphyxia (n = 8) lambs. Asphyxia induced a significant increase in cellular apoptosis (caspase-3 immunopositive) within all brain regions examined, including cortex, hippocampus, thalamus, striatum and subcortical white matter (P < 0.01 vs. control). Additionally, asphyxia induced significant and widespread astrogliosis and increased inflammatory cells (activated microglia and macrophages). The administration of UCB mononuclear cells (asphyxia+UCB) significantly decreased neuronal apoptosis, astrogliosis and inflammation (P < 0.05 vs. asphyxia alone). Asphyxia+UCB lambs also demonstrated decreased brain metabolites lactate:choline (P = 0.01) and lactate:N-acetylaspartate (P < 0.01) from 12 to 72 h, detected using MRS. Autologous UCB mononuclear cell treatment restores normal brain metabolism following perinatal asphyxia, and reduces brain inflammation, astrogliosis and neuronal apoptosis, supporting its use as a neuroprotective therapy following asphyxia.

Circulating hematopoietic and endothelial progenitor cells in newborn infants: effects of gestational age, postnatal age and clinical stress in the first 3 weeks of life

INTRODUCTION

Circulating endothelial progenitor cells (EPC) are bone marrow derived progenitors that can be mobilized by erythropoietin or in response to tissue injury, and participate in vascular repair. EPC are understudied in human neonates. Whether EPC frequency in newborn infants may be influenced by gestational age or postnatal stress is unknown.

METHODS

Blood samples were collected on day 1 of life and weekly for 3 weeks from hospitalized neonates for plasma erythropoietin and flow cytometry analysis for CD34+, CD34+CD45-, CD34+VEGFR2+ and CD34+CD45-VEGFR2+ cells (EPC). Associations between CD34+ cell subsets and clinical parameters were studied.

RESULTS

Forty five patients were enrolled. An inverse correlation with gestational age was observed for CD34+ and CD34+ VEGFR2+ cell frequencies in whole blood (WB) on day 1 (p<0.05). In preterm infants, CD34+ cell frequency decreased with increased postnatal age (p=0.0001) and CD34+VEGFR2+ cell frequency was higher at week 3 than on day 1 in WB (p=0.0002). On day one, CD34+ and CD34+CD45- cell frequencies in the mononuclear cell fraction (MNC) were higher in preterm than term infants (p=0.035 and p=0.049, respectively) but CD34+CD45-VEGFR2+ cell frequency (median 2.2/million MNC versus 3.8/million MNC) and erythropoietin levels were not significantly different. Transient increases in EPC were observed in five infants with infection. Four preterm infants who developed bronchopulmonary dysplasia had undetectable or low EPC through the first 3 weeks of life.

CONCLUSIONS

Gestational age and postnatal age influenced circulating CD34+ and CD34+VEGFR2+ but not CD34+CD45-VEGFR2+ (EPC) cell frequencies. Circulating EPC in neonates may be influenced by clinical stress.

Factors modulating circulation of hematopoietic progenitor cells in cord blood and neonates

BACKGROUND

Hematopoietic progenitor cells (HPC) circulate at high levels at birth and disappear rapidly afterwards, but the underlying mechanism it is not known. The aim of this study was to assess circulating HPC in cord blood at different gestational ages and shortly after birth and concomitantly study the biologic markers involved in this phenomenon.

METHODS

All samples were analyzed for CD34(+) cells, colony-forming units (CFU) and cytokines.

RESULTS

The results obtained confirmed a slight decrease in HPC concentration during the late stage of fetal life (R(2)=0.41). After birth, CD34(+) cells showed a rapid decline from circulation: 25+/-29% at 3 h, 51+/-42% at 12 h and 80+/-48% at 60 h. CFU cleared following a similar pattern. Cord plasma showed higher concentrations of stem cell factor (SCF), fetal liver tyrosine kinase 3-ligand (FLT3l), erythrpoietin (EPO), granulocyte colony-stimulating factor (G-CSF) and interleukin-11 (IL-11) compared with an adult control. Interestingly, the EPO concentration in newborn plasma correlated with the kinetics of HPC decline after birth. Moreover, we observed an up-regulation of l-selectin and a down-regulation of CXCR4 expression in CD34(+) cells 3 h after birth.

DISCUSSION

These data combined suggest that an active homing process results in the clearance of HPC from the circulation immediately after birth.

Circulating stem cells in extremely preterm neonates

AIM

To measure circulating CD34+ cell levels in premature neonates and to correlate the initial CD34+ counts with measures of pulmonary function and neonatal morbidity.

METHODS

CD34+ cell counts were measured in the peripheral blood of preterm neonates (gestational ages 24-32 weeks) ventilated for respiratory disease at <48 h of life, and at the start of the 2nd, 3rd and 4th weeks of life. Data pertaining to neonatal demographics and short-term outcomes were collected. Pulmonary function tests were performed to coincide with CD34+ sampling.

RESULTS

Thirty preterm neonates with median gestational age of 24 weeks and birth weight of 641 g were analysed. A mean of 99.4 CD34+ cells per microliter was observed in the 1st week of life with a decline to 54.4 cells per microliter by the 4th week. An inverse correlation between initial CD34+ count and gestational age (p=0.01) was observed. No significant correlations were observed with measures of pulmonary function or neonatal morbidities.

CONCLUSIONS

Extremely premature neonates have remarkably high levels of CD34+ cells in their peripheral blood at birth. Umbilical cord blood from this population may potentially provide an abundant source of hematopoietic stem and progenitor cells for therapeutic purposes.

A comparison of the kinetics of nucleated cells and CD34+ cells in neonatal peripheral blood and cord blood

We investigated the kinetics of nucleated cells and CD34+ cells to determine the differences between cord blood (CB) and neonatal peripheral blood (NB). The correlation coefficient between white blood cell (WBC) counts and neutrophil counts was statistically significant for CB and NB at 0, 24, and 48 hours postnatally. There were no differences in the absolute counts of lymphocytes, CD3+ cells, and CD19+ cells; however, the CD16/56+ cell counts for CB were significantly decreased 48 hours postnatally (P = .011). The number of GM-CFU counts (P = .02) and CD34(+) cells (P = .049) as well as CD34+CXCR4+ cells (P = .002), CD34+CD49d+ cells (P = .001), and CD34+CD44+ cells (P = .001) in CB were significantly increased over those of NB at delivery, and the numbers decreased gradually until 48 hours after delivery. In conclusion, the change in WBC count several days after delivery were closely associated with a temporary increase in neutrophils, and NK cells significantly decreased over time postdelivery. In addition, CD34+ cells were more prevalent in CB than in NB, and gradually decreased after birth. Such a change might be directly related to the kinetic changes of CXCR4 or CD49d and CD44 expression on CD34+ cells in CB and NB.

Stress-induced cholinergic signaling promotes inflammation-associated thrombopoiesis

To study the role of the stress-induced “readthrough” acetylcholinesterase splice variant, AChE-R, in thrombopoiesis, we used transgenic mice overexpressing human AChE-R (TgR). Increased AChE hydrolytic activity in the peripheral blood of TgR mice was associated with increased thrombopoietin levels and platelet counts. Bone marrow (BM) progenitor cells from TgR mice presented an elevated capacity to produce mixed (GEMM) and megakaryocyte (Mk) colonies, which showed intensified labeling of AChE-R and its interacting proteins RACK1 and PKC. When injected with bacterial lipopolysaccharide (LPS), parent strain FVB/N mice, but not TgR mice, showed reduced platelet counts. Therefore, we primed human CD34+ cells with the synthetic ARP26 peptide, derived from the cleavable C-terminus of AChE-R prior to transplantation, into sublethally irradiated NOD/SCID mice. Engraftment of human cells (both CD45+ and CD41+ Mk) was significantly increased in mice that received ARP26-primed CD34+ human cells versus mice that received fresh nonprimed CD34+ human cells. Moreover, ARP26 induced polyploidization and proplatelet shedding in human MEG-01 promegakaryotic cells, and human platelet engraftment increased following ex vivo expansion of ARP26-treated CD34+ cells as compared to cells expanded with thrombopoietin and stem cell factor. Our findings implicate AChE-R in thrombopoietic recovery, suggesting new therapeutic modalities for supporting platelet production.

Rapid isolation, expansion, and differentiation of osteoprogenitors from full-term umbilical cord blood

There is an urgent clinical requirement for appropriate bone substitutes that can be used for the repair and regeneration of diseased or damaged skeletal tissues. Cell-sourcing limitations in particular have affected progress, largely because of the shortage of accessible tissues capable of yielding sufficient numbers of viable osteoprogenitor cells. Previous work has suggested that umbilical cord blood (UCB) contains circulating progenitor cells (mesenchymal stem cells) capable of osteogenic differentiation, although a comparable number of reports refute this claim. From a screen of more than 20 different culture conditions, we have identified an optimal, simple, and reliable technique to generate, from full-term human UCB, stromal cells with the ability to undergo rapid osteogenic differentiation. By comparing different sorting and culture strategies, we demonstrated that early exposure of mononuclear UCB cells to medium conditioned by osteoblastic cells in the presence of osteogenic supplements and human plasma, markedly increased the frequency of stromal cell growth, the rate of osteogenic differentiation, and their attachment to and spreading on calcium phosphate scaffolds. These findings suggest that full-term UCB may act as an appropriate source of osteoprogenitor cells, which will impact significantly on the development of autologous tissue- engineered bone constructs.

Aging and T cell development: interplay between progenitors and their environment

Thymic involution is the hallmark of hematopoietic aging. Because T cell differentiation is a multistep process that occurs non-cell autonomously, aging defects can occur at multiple points along the developmental pathway, both in the T progenitors themselves and in the thymic stromal cells that support their development. Here we review the evidence for age-related thymopoiesis defects at key steps in the production of naïve mature T cells, highlighting the importance of the interaction between stromal aging and progenitor aging.

Intestinal αβ T Cells Differentiate and Rearrange Antigen Receptor Genes In Situ in the Human Infant

Intestinal Ag exposure during neonatal life influences appropriate adult immune responses. To define the mechanisms shaping the T cell repertoire during this period, we examined T cell differentiation and receptor diversity in the intestine of human infants. Developmental phenotypes of intraepithelial and lamina propria intestinal T cells from infants aged 1 day to 2 years were assessed ex vivo by flow cytometry and in situ by triple-fluorescent immunohistochemistry. Gene recombination-specific enzymes were assessed by PCR. TCR beta-chain V region gene diversity was determined by sequencing. Several different early lineage T cell populations were present neonatally: CD3(+)4(-)8(-) T cells were present at birth and numbers decreased during the neonatal period; CD3(+)4(+)8(+) T cells were present in low numbers throughout infancy; and CD3(+)4(+)8(-) or CD3(+)4(-)8(+) T cells increased with age. Very early lineage T cells, CD3(-)2(-)7(+) and CD3(-)2(+)7(+), were present neonatally, but were essentially absent at 1 year. Most lamina propria T cells differentiated rapidly after birth, but maturation of intraepithelial T cells took place over 1 year. Intestinal samples from infants less than 6 mo old contained transcripts of T early alpha and TdT, and 15 of 19 infant samples contained mRNA for RAG-1, some coexpressing RAG-2. TCR beta-chain repertoires were polyclonal in infants. Immature T cells, pre-T cells, and genes involved in T cell recombination were found in the intestine during infancy. T cell differentiation occurs within the neonatal human intestine, and the TCR repertoire of these developing immature T cells is likely to be influenced by luminal Ags. Thus, mucosal T cell responsiveness to environmental Ag is shaped in situ during early life.

Platelet characteristic antigens of CD34+ cells in cryopreserved cord blood: a study of platelet-derived microparticles in transplant processing

BACKGROUND AND OBJECTIVES

In previous studies, we found that platelet microparticles (PMPs) bind to cord blood (CB) CD34+ cells and transfer adhesion molecules to them, which enhances their engraftment. Before applying this phenomenon in actual transplants, we investigated the effect of PMPs on cryopreserved CD34+ cells in CB.

MATERIALS AND METHODS

We cryopreserved 18 CB units, then evaluated the binding of PMPs to CD34+ cells after thawing, by varying the expression of platelet characteristic antigens (CD41a, CD61, CD62P and CXCR4) on these cells. Adherence of the CD34+ cells, coated with freeze/thaw-induced PMPs, to endothelium and fibronectin was also studied, as were the effects of thrombin-induced PMPs from both fresh and preserved CB platelets.

RESULTS

PMPs induced by freezing and thawing adhered less well to CD34+ cells than did those from fresh CB, and cells coated with these PMPs had poor adherence. However, thrombin-induced PMPs from both fresh and preserved CB platelets bound equally well to cryopreserved CD34+ cells and improved their adhesion properties.

CONCLUSIONS

PMPs could be a useful tool for enhancing engraftment after CB transplantation.

The concentration of circulating megakaryocyte progenitors in preterm neonates is a function of post-conceptional age

Circulating megakaryocyte (Mk) progenitors have been used as a measure of megakaryocytopoiesis in neonates. Prior studies have shown a gestational age-dependent decrease in their concentration, but it is unclear how this process continues after birth in preterm neonates. To answer this question, we quantified the Mk progenitors in the blood of 42 neonates of varying post-conceptional ages (gestational age+days of life). We found an inverse relationship between concentration of circulating Mk progenitors and post-conceptional age (r=-0.54, p=0.0002).

Ex vivo expansion of human umbilical cord blood CD34+ cells in a collagen bead-containing 3-dimensional culture system

Self-renewal of stem cells depends on several critical factors, including the hematopoietic microenvironment, interactions with supporting stromal cells, features of the extracellular matrix, hematopoietic growth factors, and cytokines. Our study investigated the role of artificial 3-dimensional microenvironments as a means of replicating a more physiologic milieu in expansion of cord blood CD34+ cells. In the 3-dimensional model, hematopoietic cells inside collagen beads are exposed to cytokines added to a culture medium. We found that amplification of CD34+ cells with a clonogenic assay, fluorescence-activated cell sorter analysis, and bone marrow repopulation of NOD/SCID mice showed greater clonogenic ability of cells cultured by the 3-dimensional method compared with the 2-dimensional method. The present study demonstrated that 3-dimensional matrix support may be useful for extended periods in expansion and preservation of stem cells or progenitor cells in vitro.

Ultrastructural and phenotypic analysis of in vitro erythropoiesis from human cord blood CD34+ cells

Erythropoietin (EPO) induces erythropoiesis in vitro as well as in vivo, and the process of erythroid differentiation has been explored phenotypically and morphologically. However, morphological analysis of in vitro erythropoiesis of human hematopoietic progenitor cells at the ultrastructural level has not been reported before. In the present study, we have traced the ultrastructural changes of erythroid differentiation during ex vivo expansion of human cord blood (CB) CD34(+) cells in the presence of EPO by electron microscopy (EM), along with concurrent phenotypic analysis. CD34(+) cells purified from ten CBs by immunomagnetic selection were cultured in serum-free essential media in the presence of a combination of the several cytokines including EPO, thrombopoietin, flt3-ligand (FL), stem cell factor (SCF), granulocyte colony-stimulating factor, interleukin (IL)-3 and/or IL-11. Phenotypic analysis was performed by flow cytometric analysis for erythroid markers, including glycophorin C (GPC), Kell-related, glycophorin A (GPA), band 3, Lu(b), and RhD. Ultrastructural analysis was performed by electron-microscopic examination of the cultured cells stained with uranyl acetate and lead citrate. Phenotypic analysis revealed that in the absence of EPO, genuine erythroid fraction expressing the typical pattern of erythroid markers did not appear. The order of the above markers expressed in the cultured cells in the presence of EPO was GPC, Kell-related, GPA, band 3, Lu(b), and RhD, irrespective of the type of cytokine added. Of the cytokines used in combination with EPO, FL + IL-3 was the most efficient in inducing erythroid differentiation, which was followed by SCF + IL-3. EM examination demonstrated complete process of erythroid development from pronormoblasts to reticulocytes with nuclei having been extruded and mature erythrocytes. These results suggest that morphologically intact erythrocytes could be produced by ex vivo expansion of CB CD34(+) cells using EPO.

Cobblestone area-forming cells, long-term culture-initiating cells and NOD/SCID repopulating cells in human neonatal blood: a comparison with umbilical cord blood

Our prior study demonstrated that neonatal blood (NB) contained hematopoietic stem and progenitor cells that declined rapidly after birth. To validate that NB is a source of functional stem cells, we characterized this population in terms of cobblestone area-forming cells (CAFC), long-term culture-initiating cells (LTC-IC) and NOD/SCID mouse repopulating cells (SRC) in NB and umbilical cord blood (CB). Our data demonstrated that the frequencies of CAFC (30.2 vs 37.1, P = 0.14) and LTC-IC (28.6 vs 31.0, P = 0.49) in 1 x 10(5) mononuclear cells (MNC) of NB and CB were similar, suggesting that these cells were preserved in the circulation of the neonates shortly after birth. Sublethally irradiated NOD/SCID mice were transplanted with CD34(+) cells enriched from thawed NB and CB. At 6 weeks post transplant, human (hu)CD45(+) cells were detected in the bone marrow (BM), spleen and peripheral blood (PB) of the mice as demonstrated by flow cytometric and DNA analysis. Levels of huCD45(+)cells and colony forming units (CFU) appeared to be dependent on the infusion cell dose and were higher in animals receiving CB cells when compared with those of the NB group. The transplanted cells were capable of differentiation into multi-lineage progenitor cells (CD34(+) cells and differential CFU), as well as mature myeloid (CD14(+), CD33(+)), B lymphoid (CD19(+)) and megakaryocytic (CD61(+)) cells in the recipients. NB cells, subjected to ex vivo culture in an optimized preclinical condition, were significantly expanded to early and committed progenitor cells. Expanded NB contained SRC at a reduced quantity but with high proportions of CD14(+) cells and CD33(+) cells. Our study confirms that NB contains pluripotent hematopoietic stem and progenitor cells capable of homing and engrafting the NOD/SCID mice.

Haematopoietic stem and progenitor cells in human term and preterm neonatal blood

BACKGROUND AND OBJECTIVES

Whilst cord blood (CB) contains a significant number of haematopoietic stem and progenitor cells suitable for bone marrow transplantation, levels of these cells are very low in the adult circulation. In previous studies, we demonstrated that stem and progenitor cells are present in neonatal blood (NB) and reported the first sibling transplant using a combination of CB and NB for a patient with beta-thalassaemia major. However, our preliminary data showed that the number of CD34+ cells decreased rapidly in the peripheral blood of neonates soon after birth. To further investigate the mechanism of the change of stem and progenitor cells in NB, we measured the steady-state levels of CD34+ cells, early progenitor subsets and the expression of adhesion molecules, in term and preterm neonates.

MATERIALS AND METHODS

NB was collected serially from infants at 2, 4, 6, 8, 24 and 48 h after birth and was analysed by three-colour flow cytometry.

RESULTS

Our results demonstrated that the number of CD34+ cells rapidly decreased in term NB, particularly during the first 2-6 h of life, by 29.2 +/- 5.55% (P = 0.0003) in absolute counts/ml. A decrease was observed in all subsets of CD34+ cells studied, including the CD33+, CD71+, CD62L+ and CD49d+ populations. In contrast, the CD34+ cell number increased in preterm infants in the first 8 h of life, before starting to decrease. Significant inverse correlations were observed between gestational age and levels of CD34+ cells (P = 0.0065, 4-h collection time-point).

CONCLUSION

Our study suggests that changes in the levels of CD34+ stem and progenitor cells in NB might be triggered by parturition and affected by the gestational age. Our findings confirmed that if targeted as a supplementary source of stem and progenitor cells to CB for transplantation, NB should be collected as soon as possible after birth.

Granulocyte colony-stimulating factor-mobilized peripheral blood CD34+ cells from children contain the same levels of long-term culture-initiating cells producing the same numbers of colony-forming cells as those from adults, but display greater in vitro monocyte/macrophage potential

Autologous peripheral blood progenitor cell (PBPC) transplantation is now commonly used in children. The ontogenic differences in haematopoiesis published in recent years suggest differences in the categories of mobilized PBPCs between children and adults. We investigated the frequency and distribution of mature progenitor cells (colony-forming cells, CFCs) and primitive progenitor cells [CD34+ CD38- and CD34+ Thy-1+ cells, long-term culture-initiating cells (LTC-ICs)] in children and adults mobilized using granulocyte colony-stimulating factor alone. We found similar proportions of granulocyte colony-forming units (CFU-G) and/or macrophage CFUs (CFU-M), mixed lineage CFUs (CFU-Mix) and megakarocyte CFUs (CFU-Mk), CD34+ CD38- and CD34+ Thy-1+ cells, and LTC-ICs (16.5 +/- 3.5 vs. 10.65 +/- 5 per 104 CD34+ cells), which produced the same number of CFCs (5 +/- 1 vs. 6 +/- 1 CFCs/LTC-ICs) in PB CD34+ cells from children and adults. However, we noted a higher proportion of erythroid blast-forming units (BFU-E) in PB CD34+ cells from adults (x 1.5, P = 0.003). Using cord blood as a third ageing point, we observed an inverse age-related propensity for commitment to the monocyte/macrophage lineage that was still found after normalizing the data per body weight and processed blood mass. This ontogeny-related programming was detected from the LTC-IC level, which produced 1.7 times more CFU-M in children than in adults (P = 0.048). These subtle differences in commitment between children and adults, shown here for the first time, are of interest for the in vitro manipulation of PBPCs and, in particular, for application in adoptive immunotherapy in children.

Developmental changes in adhesion molecule expressions in umbilical cord blood CD34 hematopoietic progenitor and stem cells

OBJECTIVE

The purpose of this study was to determine whether expressions of the cell adhesion molecules LFA-1 (CD11a), VLA-4 (CD49d), and L -selectin (CD62L ) on CD34(+) stem and progenitor cells in umbilical cord blood change during gestation.

STUDY DESIGN

In a prospective observational study 3-color fluorescence-activated cell sorting was used to assess the levels of expression of CD11a, CD49d, and CD62L on CD34(+) cells in fresh cord blood samples collected at delivery between 22 and 42 weeks' gestation.

RESULTS

The relative number of CD34(+) cells decreased as gestational age increased (r = -0.71; P<.001). Conversely, we found significant increases in cell adhesion molecule expression by CD34(+) cells during gestation (LFA-1, r = 0.47; P =.001; VLA-4, r = 0.33, P =.031; L -selectin, r = 0.61; P<.001). Comparisons between grouped samples from early preterm (22-32 weeks' gestation), late preterm (33-37 weeks' gestation), and term (38-42 weeks' gestation) infants confirmed this correlation and revealed that the major increases occurred between early and late preterm gestation.

CONCLUSION

These results suggest a role for cell adhesion molecule expression in the process of migration and homing of circulating stem cells to the fetal bone marrow toward the end of pregnancy. The findings may have implications for the use of preterm cord blood for hematopoietic stem cell transplantation and also for prenatal gene therapy.

Cocultivation of umbilical cord blood cells with endothelial cells leads to extensive amplification of competent CD34+CD38- cells

OBJECTIVE

In this report, methods to expand the number of human cord blood hematopoietic stem cells were explored.

MATERIALS AND METHODS

CD34+ cord blood cells were expanded in the presence of various cytokine combinations in either a stroma-free cell culture system or a preformed porcine microvascular endothelial cell layer. After 7 to 21 days, stem cell number and function were monitored. In addition, the replicative history of stem cells was tracked using the fluorescent dye, PKH26.

RESULTS

With the addition of various cytokine combinations, total cellular expansion was equivalent for both culture systems, although the endothelial cell-based system contained statistically greater numbers of CD34+ cells. By day 21, the endothelial-based system receiving the FLT3L, SCF, IL-6, and GM-CSF cytokine combination contained five-fold greater numbers of CD34+ than the stroma cell-free culture cell system. Endothelial-based cultures receiving these four cytokines plus megakaryocyte growth and development factor produced a 640-fold expansion of CD34+CD38- cells as compared to a four-fold expansion in the stroma-free system. The number of progenitor cells generated was similar with both systems, yet the greatest degree of expansion of cobblestone area-forming cells was observed in the endothelial based cultures (11-fold vs four-fold). Virtually all CD34+ and CD34+CD38+ cells expanded in the presence of endothelial cells had undergone self replication by day 10, yet stromal cell-free cultures contained a significant number (4.8%) of quiescent cells. Identical numbers of re-isolated cord blood CD34+ cells expanded in both systems exhibited a similar ability to engraft and generate cells belonging to multiple hematopoietic lineages in human fetal bones implanted in immunodeficient mice.

CONCLUSIONS

These results suggest that the use of preformed endothelial cell monolayers might permit the ex vivo generation of sufficient numbers of cord stem cells to serve as successful grafts for adult transplant recipients.

Role of thrombopoietin in hematopoietic stem cell and progenitor regulation

Thrombopoietin performs an essential role during hematopoiesis by regulating the expansion and maturation of megakaryocytes. In keeping with this function, megakaryocytes, platelets, and their precursors all express the thrombopoietin receptor, Mpl, on their cell surface. However, Mpl is also expressed on primitive, pluripotent hematopoietic progenitors and plays an important role in the regulation of lineages other than megakaryocytes as well as primitive progenitors. Recently, the ability of thrombopoietin to maintain and expand repopulating stem cells has been demonstrated. Thus, thrombopoietin is unique among the hematopoietic cytokines because it is necessary both for terminal maturation and regulation of lineage-specific megakaryocytes and also for maintenance of the most primitive hematopoietic stem cells. Many new strategies are evolving to exploit the activity of thrombopoietin on primitive progenitors. This may lead to faster hematopoietic recovery from marrow-suppressive therapy, effective methods of ex vivo expansion of hematopoietic stem cells, and retroviral transduction of stem cells to facilitate gene therapy.