Tolerance associated with cord blood transplantation may depend on the state of host dendritic cells

Immunology of cord blood T-cells favors augmented disease response during clinical pediatric stem cell transplantation for acute leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) has been an important and efficacious treatment for acute leukemia in children for over 60 years. It works primarily through the graft-vs.-leukemia (GVL) effect, in which donor T-cells and other immune cells act to eliminate residual leukemia. Cord blood is an alternative source of stem cells for transplantation, with distinct biological and immunological characteristics. Retrospective clinical studies report superior relapse rates with cord blood transplantation (CBT), when compared to other stem cell sources, particularly for patients with high-risk leukemia. Xenograft models also support the superiority of cord blood T-cells in eradicating malignancy, when compared to those derived from peripheral blood. Conversely, CBT has historically been associated with an increased risk of transplant-related mortality (TRM) and morbidity, particularly from infection. Here we discuss clinical aspects of CBT, the unique immunology of cord blood T-cells, their role in the GVL effect and future methods to maximize their utility in cellular therapies for leukemia, honing and harnessing their antitumor properties whilst managing the risks of TRM.

Decreased phosphorylation of PDGFR-β impairs the angiogenic potential of expanded endothelial progenitor cells via the inhibition of PI3K/Akt signaling

Human umbilical cord blood-derived endothelial progenitor cells (EPCs) have been proven to contribute to post-natal angiogenesis, and have been applied in various models of ischemia. However, to date, to the best of our knowledge, there is no available data on the angiogenic properties of EPCs during the process of in vitro expansion. In this study, we expanded EPCs to obtain cells at different passages, and analyzed their cellular properties and angiogenic ability. In the process of expansion, no changes were observed in cell cobblestone-like morphology, apoptotic rate and telomere length. However, the cell proliferative ability was significantly decreased. Additionally, the expression of CD144, CD90 and KDR was significantly downregulated in the later-passage cells. Vascular formation assay in vitro revealed that EPCs at passage 4 and 6 formed more integrated and organized capillary-like networks. In a murine model of hind limb ischemia, the transplantation of EPCs at passage 4 and 6 more effectively promoted perfusion recovery in the limbs on days 7 and 14, and promoted limb salvage and histological recovery. Furthermore, the phosphorylation levels of platelet‑derived growth factor receptor-β (PDGFR-β) were found to be significantly decreased with the in vitro expansion process, accompanied by the decreased activation of the PI3K/Akt signaling pathway. When PDGFR inhibitor was used to treat the EPCs, the differences in the angiogenic potential and migratory ability among the EPCs at different passages were no longer observed; no significant differences were also observed in the levels of phosphorylated PI3K/Akt between the EPCs at different passages following treatment with the inhibitor. On the whole, our findings indicate that the levels of phosphorylated PDGFR-β are decreased in EPCs with the in vitro expansion process, which impairs their angiogenic potential by inhibiting PI3K/Akt signaling. Our findings may aid in the more effective selection of EPCs of different passages for the clinical therapy of ischemic disease.

Cord blood endothelial progenitor cells as therapeutic and imaging probes

Numerous studies demonstrated that neovascularization processes associated with severe tissue ischemia commonly found in conditions such as cardiovascular disorders and tumor growth occur via angiogenic and vasculogenic mechanisms. Over the past decade, it has been demonstrated that endothelial progenitor cells (EPCs) play a significant role in neo-angiogenic and neovasculogenic processes. Due to their ability to self-renew, circulate, home to the ischemic sites and differentiate into mature endothelial cells, EPCs derived from various sources hold enormous potential to be used as therapeutic agents in pro- or anti-angiogenic strategies for the treatment of ischemic and tumor conditions, respectively. However, the development of EPC-based therapies requires accompanying, noninvasive imaging protocol for in vivo tracking of transplanted cells. Hence, this review focuses on cord blood-derived EPCs and their role in neovascularization with emphasis on the potential use of EPCs as a therapeutic and imaging probe.

Umbilical cord blood immunology: relevance to stem cell transplantation

Because of its easier accessibility and less severe graft-versus-host disease, umbilical cord blood (UCB) has been increasingly used as an alternative to bone marrow for hematopoietic stem cell transplantation. Naiveté of UCB lymphocytes, however, results in delayed immune reconstitution and infection-related mortality in transplant recipients. This review updates the phenotypic and functional deficiencies of various immune cell populations in UCB compared with their adult counterparts and discusses clinical implications and possible therapeutic strategies to improve the outcome of stem cell transplantation.

Evolutionary-developmental perspectives on immune system interactions among the pregnant woman, placenta, and fetus, and responses to sexually transmitted infectious agents

A balance has evolved over deep time between the various immune systems of the "triad" that is linked together for a short period: the pregnant woman, the fetus, and the placenta. This balance is affected by, and helps to determine, the immune responses to maternal infectious agents that may be transmitted to the fetus/infant transplacentally, intrapartum, or via breast milk. This review identifies newer evolutionary concepts and processes related particularly to the human placenta, innate and adaptive immune systems involved in tolerance, and in responses to sexually transmitted infectious (STI) agents that may be pathogenic to the fetus/infant at different gestational periods and in the first year of life. An evolutionary-developmental (EVO-DEVO) perspective has been applied to the complexities within, and among, the different actors and their beneficial or deleterious outcomes. Such a phylogenetic and ontogenic approach has helped to stimulate several basic questions and suggested possible explanations and novel practical interventions.

Mycobacterium bovis bacillus Calmette-Guerin treated human cord blood monocyte-derived dendritic cells polarize naïve T cells into a tolerogenic phenotype in newborns

BACKGROUND

As one of the first infectious challenges of life, the impact of neonatal Mycobacterium bovis bacillus Calmette-Guerin (BCG) vaccination on the polarization of neonatal T helper subset has not been well defined.

METHODS

We investigated the effect of BCG-treated cord blood (CB) dendritic cells (DCs) on naïve CD4+ T cells polarization compared with that of adult blood DCs.

RESULTS

BCG-treated CB DCs had significantly lower expression of CD83 and a higher ratio of CD47/Fas than BCG-treated adult blood DCs. BCG induced significantly lower IL-12 but relatively higher IL-10 production from CB DCs than adult blood DCs. Moreover, in comparison with BCG-treated adult blood DCs, BCG-treated CB DCs induced higher IL-10 production and cytotoxic T-lymphocyte antigen 4 (CTLA-4) expression, and lower interferon-gamma (IFN-gamma) production from naïve CD4+ T cells. On the other hand, lipopolysaccharide-treated CB DCs had similar capacity as prime naïve CD4+ T cells did to produce higher IFN-gamma, lower IL-10 production, and CTLA-4 expression compared with their adult counterparts.

CONCLUSION

These results suggested that BCG-treated CB DCs might be semi-mature DCs which polarize naïve T cells into a tolerogenic T cell phenotype in newborns.

Differential gene expression in umbilical cord blood and maternal peripheral blood

OBJECTIVES

Umbilical cord blood (UCB) has become a useful alternative source of hematopoietic stem cells for clinical and research applications. UCB represents neonatal blood and differs from adult blood in many aspects, displaying different cell composition and various features of cellular immaturity. To understand molecular basis of phenotypic differences between neonatal and adult blood, we studied variations in transcriptome of UCB and maternal peripheral blood (PB).

METHODS

Using Illumina microarrays, we determined gene expression profiles of UCB and PB samples obtained from 30 mothers giving birth to living baby.

RESULTS

Out of 20,589 tested genes, 424 genes were down-regulated and 417 genes were up-regulated in UCB compared with PB. Reduced expression of many immunity-related pathways (e.g. TLR pathway, Jak-STAT pathway, cytokine-cytokine receptor interaction) in neonatal blood cells may contribute to the poor response to antigens, increasing susceptibility to infections at the time of disappearance of protective maternal antibodies. On the other hand, overexpression of erythropoiesis-related genes (glycophorins, fetal hemoglobins, enzymes catalysing heme synthesis and erythrocyte differentiation) in UCB probably enforces red cell production in newborns.

CONCLUSIONS

Our study demonstrates that neonatal and maternal bloods show specific gene expression profiles, likely reflecting differences in phenotypes of immunologically immature and fully evolved hematopoietic cells.

Critical issues for engineering cord blood stem cells to produce insulin

BACKGROUND/OBJECTIVES

The objectives of using cord blood stem cells for treating type 1 diabetes are simple in principle yet complex in biological and molecular mechanisms. These are defined by the complexity of the insulin-producing unit of the pancreas, the islet. Islets are composed of various cell types that arise from diverse lineages and communicate by hormones, growth factors and small-molecule mediators. These processes are regulated by integration of signal transduction pathways. While advances have been made to engineer umbilical cord blood stem cells to produce insulin, these studies only illuminate the potential of such cells to fulfil a necessary, but not sufficient, requirement for transplantation.

RESULTS/CONCLUSIONS

The challenges ahead demand detailed understanding of molecular mechanisms to move from an opportunistic, phenotypic approach to transplantation and amelioration of blood glucose, to an orderly and logical approach to a biologically and medically meaningful solution. The issues include expansion to generate large numbers of cells, self-renewal to regulate the destiny of cord blood stem cells to repopulate the hematopoietic system, and multipotency of stem cells to generate the distinct cell types of an islet.

Umbilical cord blood transplantation: basic biology and clinical challenges to immune reconstitution

Allogeneic stem cell transplantation has continued to evolve as a common procedure for the treatment of hematological malignancies and bone marrow failure. Donor bone marrow and mobilized peripheral stem cells are routinely employed for the reconstitution of immune function in leukemia and lymphoma patients following radiation and/or chemotherapy. Unfortunately, only 30% of patients have an HLA-identical sibling donor and the identification of matched unrelated donors, particularly for minorities, can present an exceptional challenge. The transplantation of umbilical cord blood (UCB) represents the most recent strategy to expand the potential donor pool while maintaining an acceptable level of treatment-related complications. First utilized in children, UCB transplantation permits a higher degree of HLA disparity while demonstrating a reduction in the incidence and severity of graft-versus-host disease (GvHD) compared to previous transplantation modalities. Despite the apparent decrease in GvHD, relapse rates remain comparable to transplantation with bone marrow or mobilized peripheral blood suggesting a strong graft-versus-leukemia/lymphoma (GvL) effect. However, several issues complicate the use of UCB transplantation and its extension to the treatment of adults. Many infections that afflict transplant patients are particularly frequent and more severe in the context of UCB transplantation. UCB T-cells are naive and therefore display less proliferation and IFN-gamma production in response to cognate antigen and also appear to demonstrate defects in signal transduction mechanisms. In addition, UCB contains T regulatory cells (Treg) with more potent suppressor function than adult Treg. Furthermore, adult patients often require more total cells and CD34+ progenitors for transplantation than a single UCB unit can provide. Thus, strategies to expand selected subpopulations from UCB and the use of multi-unit transplantation are areas of active research. This review will provide a condensed summary of the clinical history of UCB transplantation and emphasize the advantages and disadvantages of this approach to hematological malignancies in comparison to other methods of hematopoietic stem cell transplantation. Subsequently, it will mainly focus on the current challenges to immune reconstitution presented by UCB transplantation, recent research into their cellular and molecular mechanisms, and experimental approaches to overcome them.

Potential for access to embryonic-like cells from human umbilical cord blood

All too often media attention clouds the reality that there are many types of stem cell. The embryos, bone marrow and umbilical cord blood (UCB) are the three most used sources. However, despite what it would appear, embryonic stem cells have not been the first to yield life-saving cures at present. Faster routes to clinical intervention have been using adult stem cells that can be sourced from bone marrow and from cord blood, and that are readily accessible and are more ethically acceptable to the general public. Both these non-embryonic sources have been able to provide sufficient numbers of cells to allow development of clinical translational protocols. Bone marrow-derived cells have been used successfully in myocardial infarct therapy where relining by endothelial tissue has allowed limited reperfusion to damaged cardiac tissue. UCB have also demonstrated significant success for around 20 years in haematotransplantation. With a global human population in excess of 6 billion, births thus UCB, remain the largest untouched source of stem cells available every year. UCB also provide a distinct advantage over other adult stem cells due to the length of the telomere and also due protected immunological status of the developing neonatal environment. The total mutation load in the UCB populations is clearly likely to be significant less than in adult tissues.

Reduced IL-10 production and -receptor expression in neonatal T lymphocytes

AIM

To further evaluate the underlying mechanism of a formerly demonstrated immature anti-inflammatory response in neonates (1).

METHODS

Interleukin (IL)-10 production was measured by enzyme-linked immunosorbent-assay (ELISA) after anti-CD3/anti-CD28 costimulation of neonatal and adult T cells. IL-10 receptor expression on T lymphocytes, B lymphocytes and monocytes were analysed by flow cytometry in neonates and adult controls.

RESULTS

After anti-CD3/anti-CD28 costimulation, IL-10 production of neonatal T lymphocytes was profoundly reduced (median 247 pg/mL vs. 1062 pg/mL, p < 0.0001). IL-10 receptor expression was diminished on neonatal T lymphocytes compared to adults (3% vs. 39.5% IL-10 receptor positive lymphocytes; p < 0.0001). On neonatal B lymphocytes and monocytes the IL-10 receptor expression was comparable to adult controls.

CONCLUSION

The strongly reduced IL-10 receptor expression on the main immune regulative T lymphocytes in conjunction with a significantly impaired synthesis of IL-10 may play a crucial role in the formerly demonstrated deficient anti-inflammatory immune response in neonates.

Impaired allogeneic activation and T-helper 1 differentiation of human cord blood naive CD4 T cells

CD4 T cells, particularly those of the T-helper 1 (Th1) subset, are important effectors in alloimmune diseases, such as graft-versus-host disease, and in controlling infections with intracellular pathogens. Thus, it is plausible that impaired neonatal CD4 T-cell immunity might contribute to the low incidence of acute graft-versus-host disease after allogeneic transplantation of hematopoietic stem cells using cord blood (CB) compared with adult sources of hematopoietic stem cells. In support of this hypothesis, we found that CB naive CD4 T cells had reduced activation and impaired early Th1 differentiation compared with adult peripheral blood naive CD4 T cells after stimulation by allogeneic dendritic cells derived from adult monocytes. Early Th1 polarization was dependent on interleukin-12 and CD154, and CB CD4 T cell/dendritic cell co-cultures had impaired expression of both proteins. CB naive CD4 T cells had low basal levels of signal transduction and activation of transcription 4 messenger RNA and protein, and, after alloantigen stimulation, reduced interleukin-12-induced signal transduction and activation of transcription 4 tyrosine phosphorylation, compared with adult peripheral blood naive T cells. Lastly, FoxP3 protein expression, a marker for regulatory CD25(high) CD4 T cells, was lower for naive CD4 T cells of CB compared with those of adult peripheral blood, which argued against increased T-regulatory activity as a mechanism for the decreased Th1 differentiation of CB CD4 T cells. Together, these intrinsic limitations in T-cell activation and Th1 differentiation may impair the ability of T cells in CB and the neonate to respond to allogeneic or infectious challenges.

Defective antigen-presenting cell function in human neonates

Immaturity of the immune system has been suggested as an underlying factor for the high rate of morbidity and mortality from infections in newborns. Functional impairment of neonatal T cells is frequently quoted as the main underlying mechanism for such immaturity. However, recent studies suggest that neonatal antigen-presenting cells (APCs) also exhibit functional alterations, which could lead to secondary defects of adaptive T-cell responses. In this review, we summarize what is known on the functionality of APC at birth and during early childhood. Compared to adults, neonatal APCs display markers of immaturity and produce low levels of cytokines. Multiple factors could be involved in neonatal APC alteration, such as intrinsic immaturity, defective interaction between APCs and T cells and regulatory T-cell-mediated inhibition. Characterization of the relative contribution of each mechanism is clearly needed to better understand the functional capability of the neonatal immune system.

Effect of interleukin-15 on alloreactivity in umbilical cord blood

Interleukin(IL)-15 is a promising immunotherapeutic agent for immune reconstitution following stem cell transplantation. To investigate whether IL-15 would aggravate graft-versus-host disease (GVHD) in the setting of unrelated umbilical cord blood (CB) transplantation, we examined the effect of IL-15 on activation marker expression, proliferation and cytokine production of CB in a one-way mixed lymphocyte culture (MLC) assay. We found that IL-15 differentially enhanced CD69 and CD25 expression on CB T cells following allo-stimulation. The maximum degree of allo-specific CB proliferation was achieved on Day 6. IL-15 down-regulated the CB alloreactive proliferative response on Days 4, 6, and 8, with preferentially enhanced autologous proliferation. Exogenous IL-15 further enhanced CB TNF-alpha and IL-10 production in both autologous and allogeneic MLC 6 days after allopriming. Thus, IL-15 was effective in enhancing activation marker expression and cytokine production during CB alloreactivity, but failed to enhance allospecific proliferation. Further studies would be needed to study the role of IL-15 on GVHD in the setting of CB transplantation.

Differential expression of chemokines and their receptors in adult and neonatal macrophages infected with human or avian influenza viruses

In 1997, avian influenza virus H5N1 was transmitted directly from chicken to human and resulted in a severe disease that had a higher mortality rate in adults than in children. The characteristic mononuclear leukocyte infiltration in the lung and the high inflammatory response in H5N1 infection prompted us to compare the chemokine responses between influenza virus–infected adult and neonatal monocyte-derived macrophages (MDMs). The effects of avian influenza virus A/Hong Kong/483/97 (H5N1) (H5N1/97), its precursor A/Quail/Hong Kong/G1/97 (H9N2) (H9N2/G1), and human influenza virus A/Hong Kong/54/98 (H1N1) (H1N1/98) were compared. Significantly higher expression of CCL2, CCL3, CCL5, and CXCL10 was induced by avian influenza viruses than by human influenza virus. Moreover, the increase in CCL3 expression in H5N1/97-infected adult MDMs was significantly higher than that in neonatal MDMs. Enhanced expression of CCR1 and CCR5 was found in avian virus–infected adult MDMs. The strong induction of chemokines and their receptors by avian influenza viruses, particularly in adult MDMs, may account for the severity of H5N1 disease

Macrophage colony-stimulating factor drives cord blood monocyte differentiation into IL-10(high)IL-12absent dendritic cells with tolerogenic potential

Immature dendritic cells (DCs) induce tolerance and mature DCs induce inflammatory immune responses. However, the likelihood of maturation of immature DCs in vivo limits its potential application for suppression of unwanted immune reactions in vivo. The aim of this study was to generate DCs with anti-inflammatory properties in both the immature and mature states. GM-CSF combined with IL-4 drives monocyte differentiation into DCs. As M-CSF is a critical cytokine in development of the monocytic lineage and its level is dramatically elevated in immunosuppressive conditions, we investigated whether M-CSF could replace GM-CSF and generate DCs with distinct functions from umbilical cord blood monocytes. Highly purified umbilical cord blood monocytes cultured with M-CSF and IL-4, in a GM-CSF-independent fashion, differentiated into IL-10(high)IL-12absent cells with a DC phenotype (termed M-DC). Single time stimulation with immature DCs (both M-DCs and DCs) derived from cord blood induced hyporesponsive and regulatory CD4+ T cells. In contrast to mature DCs, mature M-DCs induced decreased Th1 differentiation and proliferation of naive CD4+ T cells in both primary and secondary allogeneic MLR and showed tolerogenic potential. These results demonstrate an unrecognized role for M-CSF in alternative differentiation of monocytes into anti-inflammatory M-DCs and suggest that M-CSF-induced DCs may be of use for suppressing unwanted immune responses.

Chemokine up-regulation in SARS-coronavirus-infected, monocyte-derived human dendritic cells

Lymphopenia and increasing viral load in the first 10 days of severe acute respiratory syndrome (SARS) suggested immune evasion by SARS-coronavirus (CoV). In this study, we focused on dendritic cells (DCs) which play important roles in linking the innate and adaptive immunity. SARS-CoV was shown to infect both immature and mature human monocyte-derived DCs by electron microscopy and immunofluorescence. The detection of negative strands of SARS-CoV RNA in DCs suggested viral replication. However, no increase in viral RNA was observed. Using cytopathic assays, no increase in virus titer was detected in infected DCs and cell-culture supernatant, confirming that virus replication was incomplete. No induction of apoptosis or maturation was detected in SARS-CoV–infected DCs. The SARS-CoV–infected DCs showed low expression of antiviral cytokines (interferon α [IFN-α], IFN-β, IFN-γ, and interleukin 12p40 [IL-12p40]), moderate up-regulation of proinflammatory cytokines (tumor necrosis factor α [TNF-α] and IL-6) but significant up-regulation of inflammatory chemokines (macrophage inflammatory protein 1α [MIP-1α], regulated on activation normal T cell expressed and secreted [RANTES]), interferon-inducible protein of 10 kDa [IP-10], and monocyte chemoattractant protein 1 [MCP-1]). The lack of antiviral cytokine response against a background of intense chemokine up-regulation could represent a mechanism of immune evasion by SARS-CoV.

Umbilical Cord Blood Transplantation: A New Alternative Option

Allogeneic hematopoietic stem cell transplantation is a life-saving procedure for hematopoietic malignancies, marrow failure syndromes, and hereditary immunodeficiency disorders. However, wide application of this procedure is limited by availability of suitably HLA-matched adult donors. Umbilical cord blood (UCB) has being increasingly used as an alternative hematopoietic stem cell source for these patients. To date, over 6000 UCB transplant procedures in children and adults have been performed worldwide using UCB donors. Broader use of UCB for adult patients is however limited by the available infused cell dose. This has prompted intensive research on ex vivo expansion of UCB stem cells and UCB graft-engineering including accessory cells able to improve UCB engraftment and reconstitution and for tissue regenerative potential. Recently, two large European and North American retrospective studies demonstrated that UCB is an acceptable alternative source of hematopoietic stem cells for adult recipients who lack HLA-matched adult donors. UCB is anticipated to address needs in both transplantation and regenerative medicine fields. It has advantages of easy procurement, no risk to donors, low risk of transmitting infections, immediate availability and immune tolerance allowing successful transplantation despite HLA disparity.