Long-Term Culture of Human CD34+ Progenitors With FLT3-Ligand, Thrombopoietin, and Stem Cell Factor Induces Extensive Amplification of a CD34−CD14− and a CD34−CD14+ Dendritic Cell Precursor

A method for the generation of large numbers of dendritic cells from CD34+ hematopoietic stem cells from cord blood

Dendritic cells (DCs) play a central role in regulating innate and adaptive immune responses. It is well accepted that their regulatory functions change over the life course. In order to study DCs function during early life it is important to characterize the function of neonatal DCs. However, the availability of neonatal DCs is limited due to ethical reasons or relative small samples of cord blood making it difficult to perform large-scale experiments. Our aim was to establish a robust protocol for the generation of neonatal DCs from cord blood derived CD34+ hematopoietic stem cells. For the expansion of DC precursor cells we used a cytokine cocktail containing Flt-3 L, SCF, TPO, IL-3 and IL-6. The presence of IL-3 and IL-6 in the first 2 weeks of expansion culture was essential for the proliferation of DC precursor cells expressing CD14. After 4 weeks in culture, CD14+ precursor cells were selected and functional DCs were generated in the presence of GM-CSF and IL-4. Neonatal DCs were then stimulated with Poly(I:C) and LPS to mimic viral or bacterial infections, respectively. Poly(I:C) induced a higher expression of the maturation markers CD80, CD86 and CD40 compared to LPS. In line with literature data using cord blood DCs, our Poly(I:C) matured neonatal DCs cells showed a higher release of IL-12p70 compared to LPS matured neonatal DCs. Additionally, we demonstrated a higher release of IFN-γ, TNF-α, IL-1β and IL-6, but lower release of IL-10 in Poly(I:C) matured compared to LPS matured neonatal DCs derived from cord blood CD34+ hematopoietic stem cells. In summary, we established a robust protocol for the generation of large numbers of functional neonatal DCs. In line with previous studies, we showed that neonatal DCs generated form CD34+ cord blood progenitors have a higher inflammatory potential when exposed to viral than bacterial related stimuli.

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A robust protocol for the generation of high numbers of neonatal dendritic cells.

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IL-3 and IL-6 are crucial for the proliferation of cord blood CD34⁺ progenitors.

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Neonatal DCs have a higher inflammatory potential when exposed to viral stimuli.

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LPS induces higher release of IL-10 in neonatal DCs compared to Poly(I:C).

Large-scale production and directed induction of functional dendritic cells ex vivo from serum-free expanded human hematopoietic stem cells

BACKGROUND

Dendritic cells (DCs) that are derived from hematopoietic stem cells (HSCs) are the most potent antigen-presenting cells and play a pivotal role in initiating the immune response. Hence, large-scale production and direct induction of functional DCs ex vivo from HSCs are crucial to HSC research and clinical potential, such as vaccines for cancer and immune therapy.

METHODS

In a previous study, we developed a serum-free HSC expansion system (SF-HSC medium) to expand large numbers of primitive HSCs ex vivo. Herein, a DC induction and expansion medium (DC medium) was proposed to further generate large numbers of functional DCs from serum-free expanded HSCs, which were developed and optimized by factorial design and the steepest ascent method.

RESULTS

The DC medium is composed of effective basal medium (Iscove's modified Dulbecco's medium [IMDM]) and cytokines (2.9 ng/mL stem cell factor [SCF], 2.1 ng/mL Flt-3 ligand, 3.6 ng/mL interleukin [IL]-1β, 19.3 ng/mL granulocyte-macrophage colony-stimulating factor [GM-CSF] and 20.0 ng/mL tumor necrosis factor-α [TNF-α]). After 10-day culture in DC medium, the maximum fold expansion for accumulated CD1a⁺CD11c⁺ DCs was more than 4000-fold, and the induced DCs were characterized and confirmed by analysis of growth kinetics, surface antigen expression, endocytosis ability, mixed lymphocyte reaction, specific cytokine secretion and lipopolysaccharide stimulation.

DISCUSSION

In conclusion, the combination of DC medium and SF-HSC medium can efficiently induce and expand a large amount of functional DCs from a small scale of HSCs and might be a promising source of DCs for vaccine and immune therapy in the near future.

Simultaneous in vitro generation of human CD34+-derived dendritic cells and mast cells from non-mobilized peripheral blood mononuclear cells

Dendritic cells (DCs) and mast cells (MCs) are key players of the immune system, often coming in close proximity in peripheral tissues. The interplay of these cells is, however, still poorly understood, especially with regards to human cells. The reason for that is the absence of a well established in vitro human cell-based study system that would allow a simultaneous preparation of both cell types. In this study, we show a method for simultaneous generation of DCs and MCs from CD34⁺ stem cell progenitors that were isolated from the non-adherent fraction of non-mobilized peripheral blood mononuclear cells of healthy donors. We observed that combining stem cells factor (SCF), IL-3 and GM-CSF in serum-free StemPro-34 medium allowed CD34⁺ cells isolated from an equivalent of 450 ml of peripheral blood to expand to 10-92 × 10⁶ cells after 7 weeks of culturing. These cultures comprised of 6-53% of DCs and 1-21% of MCs as determined by the expression of, respectively, CD11c/HLA-DR or CD117/FcεRI. The DCs were CD1a^-CD14^-, did not express co-stimulatory molecules CD80 and CD83 and chemokine receptor CCR7. However, the DCs expressed co-stimulatory molecule CD86, and had a capacity to uptake dextran, phagocyte latex particles and induce alloreactivity. MCs, on the other hand, degranulated after crosslinking of FcεRI-bound IgE as determined by the externalization of CD107b. Collectively, our data show that CD34⁺-derived human DCs and MCs can be generated in a single culture using CD34⁺ cells isolated from non-mobilized human peripheral blood and that this method may allow ex vivo studies on DC-MC interplay in human system.

Functional characterization and phenotypic monitoring of human hematopoietic stem cell expansion and differentiation of monocytes and macrophages by whole-cell mass spectrometry

The different facets of macrophages allow them to play distinct roles in tissue homeostasis, tissue repair and in response to infections. Individuals displaying dysregulated macrophage functions are proposed to be prone to inflammatory disorders or infections. However, this being a cause or a consequence of the pathology remains often unclear. In this context, we isolated and expanded CD34+ HSCs from healthy blood donors and derived them into CD14+ myeloid progenitors which were further enriched and differentiated into macrophages. Aiming for a comprehensive phenotypic profiling, we generated whole-cell mass spectrometry (WCMS) fingerprints of cell samples collected along the different stages of the differentiation process to build a predictive model using a linear discriminant analysis based on principal components. Through the capacity of the model to accurately predict sample's identity of a validation set, we demonstrate that WCMS profiles obtained from bona fide blood monocytes and respectively derived macrophages mirror profiles obtained from equivalent HSC derivatives. Finally, HSC-derived macrophage functionalities were assessed by quantifying cytokine and chemokine responses to a TLR agonist in a 34-plex luminex assay and by measuring their capacity to phagocytise mycobacteria. These functional read-outs could not discriminate blood monocytes-derived from HSC-derived macrophages. To conclude, we propose that this method opens new avenues to distinguish the impact of human genetics on the dysregulated biological properties of macrophages in pathological conditions.

Regulation of programmed-death ligand in the human head and neck squamous cell carcinoma microenvironment is mediated through matrix metalloproteinase-mediated proteolytic cleavage

Recurrent and/or metastatic head and neck squamous cell carcinoma (R/M HNSCC) is a devastating malignancy with a poor prognosis. According to recent clinical studies, tumour growth can be effectively reduced and survival can be improved by blocking the programmed death receptor-1 (PD-1)/programmed death-ligand 1 (PD-L1) pathway. PD-L1 expression has been proposed as a potential causative mechanism, as HNSCC is highly immunosuppressive. However, anti-PD-1 treatment is beneficial only for certain patients. Therefore, the mechanisms controlling PD-L1 expression warrant further investigation in order to provide a better understanding of the predicting efficacy of and optimising anti-PD-1 therapy, alone or in combination. In this study, PD-L1 protein extracted from the cell membrane was found to be downregulated in OSC-20 cells compared with OSC-19 cells, despite a higher PD-L1 expression in the total cell lysate of the OSC-20 compared with the OSC-19 cells. Several matrix metalloproteinases (MMPs) were found to be upregulated in HNSCC; in particular, MMP-7 and -13 were upregulated in the OSC-20 compared with the OSC-19 cells. Purified PD-L1 was degraded by recombinant MMP-13 and -7. The expression of PD-L1 was significantly restored by a specific inhibitor of MMP-13 (CL82198), which suggested the involvement of MMP-13 in the shedding/cleavage of PD-L1 in the OSC-20 cells. Among the anticancer drugs conventionally used in the treatment of patients with HNSCC, paclitaxel increased MMP-13 expression in R/M HNSCC cells (HOC313 cells) co-cultured without/with dendritic cells (DCs). These results suggest that the shedding/cleavage of PD-L1 by MMP-13 is one of the mechanisms behind the protective effect against invasion and metastasis. Thus, MMP-13 has potential value as a marker predictive of the decreased efficacy of anti-PD-1 therapy. In addition, paclitaxel is a particularly promising candidate for combination therapy in R/M HNSCC with anti-PD-1 therapy.

Regulation of PD-L1 expression in a high-grade invasive human oral squamous cell carcinoma microenvironment

Blockade of the programmed-death 1 receptor (PD-1)/programmed-death ligand (PD-L1) pathway efficiently reduces tumour growth and improves survival. Durable tumour regression with blockade of the PD-1/PD-L1 checkpoint has been demonstrated in recent clinical studies. Oral squamous cell carcinoma (OSCC) is highly immunosuppressive, and PD-L1 expression has been proposed as a potential mechanism responsible for this phenotype. Despite the fact that anti-PD-1 treatment can produce durable responses, such therapy appears to benefit only a subset of patients. Thus, it is important to understand the mechanisms underlying regulation of PD-L1 expression in the OSCC microenvironment. In this study, we showed that PD-L1 expression in high-grade invasive OSCC cell lines was lower than that in a low-grade invasive OSCC line and found a close correlation between PD-L1 expression and the epithelial-mesenchymal transition (EMT). PD-L1 expression was upregulated in macrophages and dendritic cells (DCs) in high-grade invasive human OSCC tissues or co-cultured with mesenchymal-phenotype OSCC cells in vitro. TLR4-inhibitory peptide successfully suppressed PD-L1 upregulation on macrophages and DCs co-cultured with mesenchymal-phenotype OSCC cells, suggesting that some EMT-induced tumour antigen is critical for PD-L1 induction on tumour-associated macrophages and DCs. Further studies are necessary to explore the impact of EMT on the tumour immune microenvironment and to identify potential biomarkers for selecting patients who might preferentially benefit from PD-1/PD-L1 blockade or immunotherapies more broadly.

Umbilical cord blood-derived CD11c(+) dendritic cells could serve as an alternative allogeneic source of dendritic cells for cancer immunotherapy

Introduction

Allogenic dendritic cells (DCs) generated from healthy donors, who are complete or partially HLA-matched, have been used for clinical trials. One of the sources for allogenic DCs is umbilical cord blood (UCB) cells. However, as far as cord blood cells are concerned, looking at their naïve nature, there is a concern as to whether the DCs generated from them will have enough potential to elicit a proper T cell response. For this, we compared CD11c⁺ UCB-DCs/ Cytotoxic T lymphocytes (CTLs) with the conventional source, i.e. peripheral blood (PBL) monocyte DCs/CTLs, using various parameters.

Methods

CD11c⁺ DCs generated from the two sources were compared morphologically, phenotypically and functionally. Functional assays included antigen uptake, chemotactic migration and MLR (mixed lymphocyte reaction). The CTLs generated were examined for the activation markers, granzyme A & granzyme B, and IFN-γ secretion. MUC1 (STAPPVHNV) peptide-specific CTLs were quantified by Streptamer staining. In vitro CTL activity was assessed by their efficiency in killing MCF-7 cells. For in vivo CTL assay, a xenograft of MCF-7-luc-F5 cells in female NOD/SCID mice was employed. Regression of tumors in mice was monitored using an in vivo imaging system before and after ten days of CTL infusion. Statistical analysis of all the experiments between the two groups was evaluated by one-way ANOVA.

Results

The CD11c⁺ DCs from the two sources were morphologically and phenotypically similar. Their capacity to uptake antigen, migration towards CCL-19 and MLR activity were equivalent. UCB-CTLs had significantly higher levels of activation markers, number of MUC1 specific CTLs, IFN-γ secretion and IL-12p70/IL-10 ratio than that of PBL-CTLs. Hematoxylin and Eosin-stained tumor sections showed T cell infiltration, which was further confirmed by immunofluorescence staining. In vivo CTL activity was found to be similar with the two sources.

Conclusions

Our data demonstrate that CD11c⁺ UCB-DCs/CTLs are as potent as standard CD11c⁺ PBL-DC/CTLs and could therefore be used as an allogenic source for therapeutic purposes. The findings of this study could help in taking us one step closer towards the personalized therapy using DC based cancer vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0160-8) contains supplementary material, which is available to authorized users.

Exogenous addition of arachidonic acid to the culture media enhances the functionality of dendritic cells for their possible use in cancer immunotherapy

The development of dendritic cell based vaccines is a promising approach in cancer immunotherapy. For their successful use in the clinics, the propagation and functionality of DCs is crucial. We earlier established a two-step method for the large scale generation of DCs from umbilical cord blood derived MNCs/CD34+ cells. This work aims at improving their functionality based on the following observations: in vitro generated DCs can be less efficient in migration and other functional activities due to lower eicosanoid levels. The production of eicosanoids from Arachidonic Acid (AA) can be hampered due to suppression of the enzyme phospholipase A2 by IL-4, an essential cytokine required for the differentiation of DCs. We hypothesized that exogenous addition of AA to the culture media during DC generation may result in DCs with improved functionality. DCs were generated with and without AA. The two DC sets were compared by phenotypic analysis, morphology and functional assays like antigen uptake, MLR, CTL assay and in vitro and in vivo migration. Though there were no differences between the two types of DCs in terms of morphology, phenotype and antigen uptake, AA⁺ DCs exhibited an enhanced in vitro and in vivo migration, T cell stimulatory capacity, CTL activity and significantly higher transcript levels of COX-2. AA⁺ DCs also show a favorable Th1 cytokine profile than AA^- DCs. Thus addition of AA to the culture media is skewing the DCs towards the secretion of more IL-12 and less of IL-10 along with the restoration of eicosanoids levels in a COX-2 mediated pathway thereby enhancing the functionality of these cells to be used as a potent cellular vaccine. Taken together, these findings will be helpful in the better contriving of DC based vaccines for cancer immunotherapy.

Procedures for the expansion of CD14(+) precursors from acute myeloid leukemic cells to facilitate dendritic cell-based immunotherapy

AIMS

Vaccination with acute myeloid leukemia (AML)-derived dendritic cells (DCs) is a promising immunotherapeutic approach to prevent relapse of AML. However, in clinical practice AML-derived DC culture is unfeasible in 40% of cases. Here, we demonstrate that AML cells can be expanded in vitro prior to differentiation with cocktails of cytokines with known myeloid growth-promoting effects.

RESULTS

Nine out of 13 initially CD14(-) samples gain de novo CD14 (>10%) expression (69% increment; p = 0.01) after in vitro expansion. These expanded CD14(+) leukemic cells displayed a high probability (six out of six initially CD14(-) samples tested) to differentiate into DCs upon culture with GM-CSF, TNF-α and IL-4.

CONCLUSION

Induction of CD14 on initially CD14(-) AML cells potentially increases the number of patients eligible for DC-based immunotherapy.

Cord blood stem-cell-derived dendritic cells generate potent antigen-specific immune responses and anti-tumour effects

The aim of the present study was to investigate whether CBSCs [(umbilical) cord blood stem cells] can be a new source of DCs (dendritic cells), which can generate more potent antigen-specific immune responses and anti-tumour effects. CBSCs and PBMCs (peripheral blood mononuclear cells) were collected, cultured and differentiated into DCs. Surface markers, secreting cytokines, antigen-presentation activity, antigen-specific cell-mediated immunity and cytotoxic killing effects induced by these two DC origins were evaluated and compared. CBSCs were expanded ~17-fold by ex vivo culture. The expression of surface markers in CBSC-derived DCs were higher than those in PBMC-derived DCs treated with LPS (lipopolysaccharide). The CBSC-derived DCs mainly secreted IL (interleukin)-6, IL-10 and TNF (tumour necrosis factor)-α, whereas PBMC-derived DCs mainly secreted IL-5 and IFN (interferon)-γ. The CBSC-derived DCs had better antigen-presentation abilities when stimulated with LPS or TNF-α, induced higher numbers of IFN-γ-secreting antigen-specific CD8+ T-cells, as assessed using an ELISpot (enzyme-linked immunosorbent spot) assay, and stimulated more potent antigen-specific CTL (cytotoxic T-cell) activities (P<0.01, one-way ANOVA). CBSC-derived DCs had quicker and greater ERK (extracellular-signal-regulated kinase) and Akt phosphorylation, and weaker p38 phosphorylation, than PBMC-derived DCs when stimulated with LPS. In conclusion, CBSC-derived DCs have the ability to induce stronger antigen-specific immunity and more potent anti-tumour effects and therefore could be a good source of DCs for use in DC-based cancer vaccines and immunotherapy.

Production of large numbers of plasmacytoid dendritic cells with functional activities from CD34(+) hematopoietic progenitor cells: use of interleukin-3

Plasmacytoid dendritic cells (pDC), a subset of dendritic cells characterized by a rapid and massive type-I interferon secretion through the Toll-like receptor pathway in response to viral infection, play important roles in the pathogenesis of several diseases, such as chronic viral infections (e.g., hepatitis C virus, human immunodeficiency virus), autoimmunity (e.g., psoriasis, systemic lupus erythematosus), and cancer. As pDC represent a rare cell type in the peripheral blood, the goal of this study was to develop a new method to efficiently generate large numbers of cells from a limited number of CD34(+) cord blood progenitors to provide a tool to resolve important questions about how pDC mediate tolerance, autoimmunity, and cancer. Human CD34(+) hematopoietic progenitor cells isolated from cord blood were cultured with a combination of Flt3-ligand (Flt3L), thrombopoietin (TPO), and one of the following cytokine: interleukin (IL)-3, interferon-β(IFN-β), or prostaglandin E2(PGE(2)). Cells obtained in the different culture conditions were analyzed for their phenotype and functional characteristics. The addition of IL-3 cooperates with Flt3L and TPO in the induction of pDC from CD34(+) hematopoietic progenitor cells. Indeed, Flt3L/TPO alone or supplemented with prostaglandin E2 or interferon-β produced smaller amounts of pDC from hematopoietic progenitor cells. In addition, pDC generated in Flt3L/TPO/IL-3 cultures exhibited morphological, immunohistochemical, and functional features of peripheral blood pDC. We showed that IL-3, in association with Flt3L and TPO, provides an advantageous tool for large-scale generation of pDC. This culture condition generated, starting from 2 × 10(5) CD34(+) cells, up to 2.6 × 10(6) pDC presenting features of blood pDC.

Non-human primate dendritic cells

Non-human primates (NHP) are essential translational models for biomedical research. Dendritic cells (DC) are a group of antigen presenting cells (APC) that play pivotal roles in the immunobiology of health and disease and are attractive cells for adoptive immunotherapy to stimulate and suppress immunity. DC have been studied extensively in humans and mice but until recently, have not been well characterized in NHP. This review considers the available data about DC across a range of NHP species and summarizes the understanding of in vitro-propagated DC and in vivo-isolated DC, which is now established. It is clear that although NHP DC exist within the paradigm of human DC, there are important functional and phenotypic differences when compared with human DC subsets. These differences need to be taken into account when designing preclinical, translational studies of DC therapy using NHP models.

A large number of mature and functional dendritic cells can be efficiently generated from umbilical cord blood-derived mononuclear cells by a simple two-step culture method

BACKGROUND

Advances in the past two decades in dendritic cell (DC) biology paved the way to exploit them as a promising tool in cancer immunotherapy. The prerequisite for DC vaccine preparations is large-scale in vitro generations of homogeneous, mature, and functional DCs. Frequent improvements are being made in the existing in vitro DC production protocols to achieve this goal. In our previous study we reported a large-scale generation of mature, functional DCs from umbilical cord blood (UCB) CD34+ cells. Here we report that this method can be used for the efficient generation of DCs from UCB mononuclear cells (MNCs) and thus the hematopoietic stem cell isolation step is not essential.

STUDY DESIGN AND METHODS

MNCs or CD34+ cells isolated from the same cord blood (CB) samples were used for the generation of DCs. DCs were characterized for morphology, phenotype, and functional assays including antigen uptake, chemotaxis, and mixed leukocyte reaction. Similarly DCs generated from the MNCs of same fresh and frozen CB units were compared.

RESULTS

The morphologic, phenotypic, and functional characterization of the DCs generated from various sets show that they were comparable in nature irrespective of the starting population used.

CONCLUSION

We conclude that the CD34+ isolation step is not essential for the generation of mature, functional DCs and thus can be eliminated. More importantly, we show that DCs can be generated with equal efficiency from the MNCs of frozen CB units. Our culture method will be useful for exploiting the potential of UCB as an additional source for allogeneic DCs in the clinical settings.

Revised map of the human progenitor hierarchy shows the origin of macrophages and dendritic cells in early lymphoid development

The classical model of hematopoiesis posits the segregation of lymphoid and myeloid lineages as the earliest fate decision. The validity of this model in the mouse has been questioned; however, little is known about the lineage potential of human progenitors. Here we provide a comprehensive analysis of the human hematopoietic hierarchy by clonally mapping the developmental potential of seven progenitor classes from neonatal cord blood and adult bone marrow. Human multilymphoid progenitors, identified as a distinct population of Thy-1(neg-lo)CD45RA(+) cells in the CD34(+)CD38(-) stem cell compartment, gave rise to all lymphoid cell types, as well as monocytes, macrophages and dendritic cells, which indicated that these myeloid lineages arise in early lymphoid lineage specification. Thus, as in the mouse, human hematopoiesis does not follow a rigid model of myeloid-lymphoid segregation.

Propagation and characterisation of dendritic cells from G-CSF mobilised peripheral blood monocytes and stem cells in common marmoset monkeys

The common marmoset is a small New World Primate that has been used as an immunological model for a number of human diseases. Dendritic cells (DC) have not been extensively characterised in this species and in particular protocols to derive DC from living donors without the need for animal sacrifice are presently lacking. This study establishes new protocols to generate substantial numbers of marmoset DC for use in cell therapy studies. Recombinant human G-CSF was used to mobilise peripheral blood monocytes and CD34(+) stem cells in sufficient numbers for large scale in-vitro DC propagation using cytokine conditioning including IL-4, GM-CSF, FLT3-L, stem cell factor and thrombopoietin. Marmoset DC exhibited morphology similar to human DC, were capable of antigen uptake and presentation and had moderate allo-stimulatory ability. Monocyte-derived DC had a maturation-resistant immature phenotype, whereas haematopoietic precursor-derived DC were semi-mature in phenotype and function. This study confirms the feasibility of the marmoset as a unique small primate model in which to pursue DC-based immunotherapy strategies.

Cord blood CD34+ cells cultured with FLT3L, stem cell factor, interleukin-6, and IL-3 produce CD11c+CD1a-/c- myeloid dendritic cells

Methods that allow expansion of myeloid dendritic cells (MDCs) from CD34(+) cells are potentially important for boosting anti-leukemic responses after cord blood (CB) hematopoietic stem cell transplantation (HSCT). We showed that the combination of early-acting cytokines FLT3-ligand (FL), stem cell factor (SCF), interleukin (IL)-3, and IL-6 supported the generation of CD11c(+)CD16() CD1a()/c() MDCs from CB CD34(+) cells or CB myeloid precursors. Early-acting cytokine-derived MDCs were maintained within the myeloid CD33(+)CD14()CD15() precursors with a mean of 4 x 10(6) cells generated from 1-4 x 10(4) CB CD34(+) cells or myeloid precursors after 2 weeks. After 8-12 days of culture the MDCs expressed higher levels of HLA-DR antigen but lower levels of CD40 and CD86 antigen, compared to adult blood MDCs. At this stage of differentiation, the early-acting cytokine-derived MDCs had acquired the ability to induce greater allogeneic T cell proliferation than monocytes or granulocytes derived from same culture. Early-acting cytokine-derived MDCs exposed to the cytokine cocktail (CC) comprising IL-1beta, IL-6, tumor necrosis factor (TNF)-alpha, and prostaglandin E (PGE)-2, upregulated the surface co-stimulatory molecules CD40 and CD86 and enhanced allogeneic T cell proliferation, as is characteristic of MDCs maturation. The reliable production of MDCs from CB CD34(+) cells provides a novel way to study their lineage commitment pathway(s) and also a potential means of enriching CB with MDCs to improve prospects for DC immunotherapy following CB HSCT.

The isolation and identification of murine dendritic cell populations from lymphoid tissues and their production in culture

Dendritic cells (DC) are widely regarded as the most potent cellular inducers of the adaptive immune response; so, immunotherapy through DC manipulation is a promising option in the future fight against many human ailments. We have developed a method of isolating DC from the mouse that involves efficient extraction from tissues, followed by the selection of the lightest density cells, then depletion of non-DC through a cocktail of monoclonal antibodies and anti-immunoglobulin magnetic beads. Finally, purification and segregation into DC subtypes is achieved by immunofluorescent labeling and sorting. This has demonstrated a network of DC populations differing in surface phenotype and function. We can now produce larger numbers of many of these DC subpopulations from their precursors using bone marrow cultures supplemented with fms-like tyrosine kinase 3 ligand (Flt3L). The culture-generated DC can be aligned with the populations directly isolated from tissues. Combining the in vivo and in vitro systems will make study of murine DC and their alignment to their human counterparts an easier break process.

Human CD34+ CD11b- cord blood stem cells generate in vitro a CD34- CD11b+ subset that is enriched in langerin+ Langerhans dendritic cell precursors

OBJECTIVE

We investigated whether the expression of CD11b on precursors derived in vitro from CD34+ hematopoietic stem cells was related to their ability to generate CD11b- and CD11b+ Langerhans dendritic cells (LC).

METHODS

Human CD34+ cells purified from cord blood were cultured with FLT3 ligand, thrombopoietin, and stem cell factor (FTS) for 2 weeks, analyzed, and sorted by FACS. Sorted fractions were cultured as above, or differentiated into LC with GM-CSF, IL-4, and TGF-beta1 (G4-TGF) for 6 days. The capacity of LC to internalize langerin and dextran was assessed.

RESULTS

Ex vivo, human CD34+ cells were CD11b- and mostly CLA+. After 2 weeks of culture with FTS, CD34- CLA- CD11b- and CD34- CLA- CD11b+ cells emerged. CD11b- cells were the most ancestral because they were the only ones to proliferate with FTS, and constantly generated CD11b+ cells. Both CD11b- and CD11b+ sorted cells generated E-cadherin+ langerin+ LC after incubation with G4-TGF. The former fraction contained 46% +/- 15% of E-cadherin+ and 10% +/- 5% of langerin+ cells, whereas in the latter fraction these values reached respectively 66% +/- 23% and 30% +/- 16% (mean +/- SD, n = 7, p < 0.056). Looking at functional properties, CD11b- and CD11b+ LC were similar in terms of langerin and dextran endocytosis. By contrast, only CD11b+ LC internalized fluorescent LPS.

CONCLUSION

Human CD34+ CD11b- cells differentiate in FTS culture into a CD34- CD11b- precursor that in turn generates CD34- CD11b+ cells. These cells are enriched in LC precursors compared to CD34- CD11b- cells. Both CD11b- and CD11b+ LC are generated in vitro, and each fraction may assume different functions in inflammatory situations.

Expansion and differentiation of CD14+CD16(-) and CD14+ +CD16+ human monocyte subsets from cord blood CD34+ hematopoietic progenitors

To determine whether monocytes can be generated from CD34+ hematopoietic progenitors in large numbers, cord blood CD34+ cells were first expanded for 3-10 days in X-VIVO 10 medium supplemented with FCS, stem cell factor (SCF), thrombopoietin (TPO), and Flt-3 Ligand (Flt-3L), and then differentiated in IMDM medium supplemented with FCS, SCF, Flt-3L, IL-3 and M-CSF for 7-14 days. These two step cultures resulted in up to a 600-fold mean increase of total CD14+ cells. Using this approach, two subpopulations of monocytes were obtained: CD14+CD16(-) and CD14++CD16+ occurring at 2:1 ratio. 1.25(OH)2 Vitamin D3 added to the differentiation medium altered this ratio by decreasing proportion of CD14++CD16+ monocytes. In comparison to CD14+CD16(-), the CD14++CD16+ cells showed different morphology and an enhanced expression of CD11b, CD33, CD40, CD64, CD86, CD163, HLA-DR, and CCR5. Both subpopulations secreted TNF and IL-12p40 but little or no IL-10. CD14++CD16+ monocytes released significantly more IL-12p40, were better stimulators of MLR but showed less S. aureus phagocytosis. These subpopulations are clearly different from those present in the blood and may be novel monocyte subsets that represent different stages in monocyte differentiation with distinct biological function.

A CD34(+) human cell line model of myeloid dendritic cell differentiation: evidence for a CD14(+)CD11b(+) Langerhans cell precursor

The study of early events in dendritic cell (DC) differentiation is hampered by the lack of homogeneous primary cell systems that allow the study of cytokine-driven, transitional DC differentiation steps. The CD34(+) acute myeloid leukemia cell line MUTZ-3 displays a unique ability to differentiate into interstitial DC (IDC) and Langerhans cells (LC) in a cytokine-dependent manner. Phenotypic characterization revealed MUTZ-3 to consist of three distinct subpopulations. Small CD34(+)CD14(-)CD11b(-) progenitors constitute the proliferative compartment of the cell line with the ability to differentiate through a CD34(-)CD14(-)CD11b(+) stage to ultimately give rise to a morphologically large, nonproliferating CD14(+)CD11b(hi) progeny. These CD14(+)CD11b(hi) cells were identified as common, immediate myeloid DC precursors with the ability to differentiate into LC and IDC, exhibiting characteristic and mutually exclusive expression of Langerin and DC-specific ICAM-grabbing nonintegrin, respectively. The identity of the MUTZ-3-derived LC subset was confirmed further by the presence of Birbeck granules. We conclude that the MUTZ-3 cell line provides a ready and continuous supply of common myeloid precursors, which should facilitate further study of the ontogeny of myeloid DC lineages.

Ex Vivo Expansion Does Not Alter the Capacity of Umbilical Cord Blood CD34+Cells to Generate Functional T Lymphocytes and Dendritic Cells

We examined whether ex vivo expansion of umbilical cord blood progenitor cells affected their capacity to generate immune cells such as T lymphocytes (TLs) and dendritic cells (DCs). The capacity to generate TLs from cord blood CD34(+) cells expanded for 14 days (d14) was compared with that of nonexpanded CD34(+) cells (d0) using fetal thymus organ cultures or transfer into nonobese diabetic/severe combined immunodeficient mice. The cell preparations yielded comparable percentages of immature (CD4(+)CD8(-), CD4(+)CD8(+)) TLs and functional mature (CD3(+)CD4(+), CD3(+)CD8(+)) TLs with an analogous TCR (T-cell receptor)-Vbeta repertoire pattern. As regards DCs, d0 and d14 CD34(+) cells also yielded similar percentages of CD1a(+) DCs with the same expression levels of HLA-DR, costimulatory and adhesion molecules, and chemokine receptors. DCs derived from either d14 or d0 CD34(+) stimulated allogeneic TLs to the same extent, and the cytokine pattern production of these allogeneic TLs was similar with no shift toward a predominant Th1 or Th2 response. Even though the intrinsic capacity of d14 CD34(+) cells to generate DCs was 13-fold lower than that of d0 CD34(+) cells, this reduction was offset by the prior amplification of the CD34(+) cells, resulting in the overall production of 15-fold more DCs. These data indicate that ex vivo expansion of CD34(+) cells does not impair T lymphopoiesis nor DC differentiation capacity.

Differences in the transmigration of different dendritic cells

OBJECTIVE

Although several methods for the generation of dendritic cells (DCs) exist, little is known about the transmigration capacities of the cells developed. Their ability to migrate to the adjacent lymphatic system is relevant since their efficacy does also rely on their potential to interact with lymphocytes.

METHODS

We studied the transmigration of DCs derived from hematopoietic progenitor cells (HPC), from peripheral blood monocytes, and from leukemic cells. DCs from monocytes and leukemic cells could be generated within 1 week, whereas DCs from HPC needed 2 weeks for maturation.

RESULTS

While DCs from all sources showed similar morphologic features and allostimulatory capacities, their transmigration capacities varied: HPC-derived DCs showed the highest migratory response to macrophage inflammatory protein (MIP)-3alpha and beta. Monocyte-derived DCs were equally attracted to MIP-3beta and stroma-derived factor (SDF)-1alpha. Only few leukemic DCs migrated in response to SDF-1. Other chemoattractants tested included MIP-1alpha and RANTES. Replacement of fetal bovine by human serum did not change the DC's overall migratory capacities. It did, however, influence the responsiveness to certain chemokines.

CONCLUSION

Although DCs from all three sources are immunocompetent antigen-presenting cells, our findings suggest that HPC and monocyte-derived DCs can be administered subcutaneously and intravenously, but that leukemic DCs should be injected into the lymph node.

Phagocytosis of codeveloping megakaryocytic progenitors by dendritic cells in culture with thrombopoietin and tumor necrosis factor-α and its possible role in hemophagocytic syndrome

Tumor necrosis factor-α (TNF-α) and thrombopoietin (TPO) have been shown to induce the differentiation and proliferation of CD34+ cells toward dendritic cells (DCs) in the presence of multiacting cytokines. We hypothesized that the costimulation of TPO and TNF-α generates megakaryocytic progenitors and DCs together from human CD34+ cells and that the interaction of these cells may indicate a physiologic and/or a pathologic role of DCs in megakaryopoiesis. When highly purified human CD34+ cells were cultured for 7 days with TPO alone, the generated cells expressed megakaryocytic markers, such as CD41, CD42b, and CD61. The addition of TNF-α with TPO remarkably decreased the number of megakaryocytic progenitor cells without affecting the cell yield. Almost half of the cells thus generated expressed CD11c, and most of them were positive for CD4 and CD123. Furthermore, CD11c+ cells were found to capture damaged CD61+ cells and to induce autologous T-cell proliferation, although the cytokine productions were low. We also confirmed an engulfment of CD61+ cells and their fragment by CD11c+ cells in bone marrow cells from patients with hemophagocytic syndrome. These findings suggest that DCs generated under megakaryocytic and inflammatory stimuli are involved in megakaryopoiesis and the subsequent immune responses to self-antigens.

B7-homolog 1 expression by human glioma: a new mechanism of immune evasion

Immunosuppressive soluble factors such as transforming growth factor beta and cell surface molecules such as FasL may contribute to the immune evasion of malignant glioma. B7 homolog 1 is a member of the B7 family of costimulatory molecules implicated in the negative regulation of T cell immune responses. Here, we show that human glioma cell lines express B7 homolog 1 protein that reduces interferon-gamma production by activated T cells. The expression of B7 homolog 1 in vivo was demonstrated in a large series of human glioma samples, with a significant correlation between the level of B7 homolog 1 expression and the tumor grade. Overall, our data suggest that B7 homolog 1 may be involved in the immune evasion of glioma and encourage the blockade of this pathway in future immunotherapies.

Efficient maturation and cytokine production of neonatal DCs requires combined proinflammatory signals

Specific functional properties of dendritic cells (DCs) have been suspected as being responsible for the impaired specific immune responses observed in human neonates. To analyze stimulatory requirements for the critical transition from immature, antigen-processing DCs to mature, antigen-presenting DCs, we investigated the effect of different proinflammatory mediators and antigens on phenotype and cytokine secretion of human neonatal DCs derived from hematopoietic progenitor cells (HPCs). Whereas single proinflammatory mediators were unable to induce the maturation of neonatal DCs, various combinations of IFNγ, CD40L, TNFα, LPS and antigens, induced the maturation of neonatal DCs documented by up-regulation of HLA-DR, CD83 and CD86. Combinations of proinflammatory mediators also increased cytokine secretion by neonatal DCs. Especially combined stimulation with LPS and IFNγ proved to be very efficient in inducing maturation and cytokine synthesis of neonatal DCs. In conclusion, neonatal DCs can be stimulated to express maturation as well as costimulatory surface molecules. However, induction of maturation requires combined stimulation with multiple proinflammatory signals.

Unilineage monocytopoiesis in hematopoietic progenitor culture: switching cytokine treatment at all Mo developmental stages induces differentiation into dendritic cells

We have developed a new culture system whereby human hematopoietic progenitors purified from adult peripheral blood extensively proliferate and gradually differentiate into >95% pure monocytic (Mo) cells. At all developmental stages treatment with interleukin (IL)-4+granulocyte-macrophage colony-stimulating factor or IL-4+c-Kit-ligand+FLT-3 ligand switched the Mo precursors into dendritic cells (DCs). The switching capacity decreased only at the end of the culture, when most Mo cells matured to macrophages. Moreover, the Mo precursors were highly susceptible to transduction with lentiviral vectors: once switched to DCs, they maintained the transgene expression, as well as the phenotype and function of the DC lineage. Our results provide new insight into the potential role of the Mo lineage as a reservoir of DCs in vivo. Furthermore, the methodology for transduction of Mo precursors provides a tool to generate genetically modified, normally functioning DCs potentially useful for immunotherapy.

Production of large numbers of Langerhans' cells with intraepithelial migration ability in vitro

Langerhans' cells (LCs) are a subset of immature dendritic cells (DCs) and play a key role in the initiation and regulation of immune responses. Functional studies of these cells have been hampered by difficulties in generating a large number of LCs in vitro. We describe a new method to efficiently generate immature DCs exhibiting morphological, immunohistochemical, and ultrastructural features of LCs (CD1a+, Birbeck Granules+, CD207+, E-cadherin+, cutaneous lymphocyte-associated antigen+, and CCR6+) from a limited number of CD34+ cord blood progenitors. This method is based on a two-step procedure consisting of an amplification phase followed by a terminal differentiation induction. The amplification step is initiated with a combination of hematopoietic growth factors (thrombopoietin/stem cell factor/fetal liver tyrosine kinase-3 ligand), cytokines (granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interleukin-4), and 5 ng/ml of transforming growth factor (TGF)-beta1. The differentiation is induced by increasing the concentration of TGF-beta1 to 12.5 ng/ml. These culture conditions were efficient for generating a large number of immature LCs (8.74 x 10(6) +/- 3.2) from 15 x 10(4) CD34+ progenitor cells. In addition, these LCs were shown to be able to infiltrate an in vitro reconstructed epithelium. Because LCs play an important role in the mucosal immunity, this technique could be useful to study their interactions with epithelial pathogenic agents and to perform pharmacological, toxicological, and clinical research.

Progressive and Controlled Development of Mouse Dendritic Cells from Flt3+CD11b+Progenitors In Vitro

Dendritic cells (DC) represent key regulators of the immune system, yet their development from hemopoietic precursors is poorly defined. In this study, we describe an in vitro system for amplification of a Flt3(+)CD11b(+) progenitor from mouse bone marrow with specific cytokines. Such progenitor cells develop into both CD11b(+) and CD11b(-) DC, and CD8alpha(+) and CD8alpha(-) DC in vivo. Furthermore, with GM-CSF, these progenitors synchronously differentiated into fully functional DC in vitro. This two-step culture system yields homogeneous populations of Flt3(+)CD11b(+) progenitor cells in high numbers and allows monitoring the consecutive steps of DC development in vitro under well-defined conditions. We used phenotypic and functional markers and transcriptional profiling by DNA microarrays to study the Flt3(+)CD11b(+) progenitor and differentiated DC. We report here on an extensive analysis of the surface Ag expression of Flt3(+)CD11b(+) progenitor cells and relate that to surface Ag expression of hemopoietic stem cells. Flt3(+)CD11b(+) progenitors studied exhibit a broad overlap of surface Ags with stem cells and express several stem cell Ags such as Flt3, IL-6R, c-kit/SCF receptor, and CD93/AA4.1, CD133/AC133, and CD49f/integrin alpha(6). Thus, Flt3(+)CD11b(+) progenitors express several stem cell surface Ags and develop into both CD11b(+) and CD11b(-) DC, and CD8alpha(+) and CD8alpha(-) DC in vivo, and thus into both of the main conventional DC subtypes.

DC-SIGN-mediated infectious synapse formation enhances X4 HIV-1 transmission from dendritic cells to T cells

Dendritic cells (DCs) are essential for the early events of human immunodeficiency virus (HIV) infection. Model systems of HIV sexual transmission have shown that DCs expressing the DC-specific C-type lectin DC-SIGN capture and internalize HIV at mucosal surfaces and efficiently transfer HIV to CD4⁺ T cells in lymph nodes, where viral replication occurs. Upon DC–T cell clustering, internalized HIV accumulates on the DC side at the contact zone (infectious synapse), between DCs and T cells, whereas HIV receptors and coreceptors are enriched on the T cell side. Viral concentration at the infectious synapse may explain, at least in part, why DC transmission of HIV to T cells is so efficient.

Here, we have investigated the role of DC-SIGN on primary DCs in X4 HIV-1 capture and transmission using small interfering RNA–expressing lentiviral vectors to specifically knockdown DC-SIGN. We demonstrate that DC-SIGN⁻ DCs internalize X4 HIV-1 as well as DC-SIGN⁺ DCs, although binding of virions is reduced. Strikingly, DC-SIGN knockdown in DCs selectively impairs infectious synapse formation between DCs and resting CD4⁺ T cells, but does not prevent the formation of DC–T cells conjugates.

Our results demonstrate that DC-SIGN is required downstream from viral capture for the formation of the infectious synapse between DCs and T cells. These findings provide a novel explanation for the role of DC-SIGN in the transfer and enhancement of HIV infection from DCs to T cells, a crucial step for HIV transmission and pathogenesis.

Impaired CD40L signaling is a cause of defective IL-12 and TNF-α production in Sézary syndrome: circumvention by hexameric soluble CD40L

Sézary syndrome (SzS) is an advanced form of cutaneous T-cell lymphoma characterized by peripheral blood involvement, impaired cell-mediated immunity, and T-helper 1 (TH1) cytokine production. To understand the mechanism of these defects, we studied the expression and function of CD40L in peripheral blood mononuclear cells (PBMCs) of patients with SzS. We found that PBMCs of patients with SzS have a defect in interleukin-12 (IL-12) and tumor necrosis factor-α (TNF-α) production upon anti-CD3 stimulation and that tumor CD4+ T lymphocytes have a specific defect in CD40L induction after anti-CD3 ligation in vitro. This defect may explain the poor IL-12 production, because IL-12 production by anti-CD3-stimulated PBMCs was dependent on CD40L in healthy donors. The observed defect in tumor cell CD40L expression appears to be due to inappropriate T-cell signaling upon CD3 ligation, because expression of other T-cell activation antigens such as CD25, and to a lesser extent CD69, are also impaired on tumor cells. Importantly however, the inability of SzS PBMCs to appropriately produce IL-12 and TNF-α could be restored by recombinant hexameric CD40L. Taken together, our results demonstrate that impaired IL-12 and TNF-α production in SzS is associated with defective CD4+ T lymphocyte CD40L induction and indicate that CD40L may have therapeutic potential in SzS. (Blood. 2005;105:219-225)

Human ribonuclease A superfamily members, eosinophil-derived neurotoxin and pancreatic ribonuclease, induce dendritic cell maturation and activation

A number of mammalian antimicrobial proteins produced by neutrophils and cells of epithelial origin have chemotactic and activating effects on host cells, including cells of the immune system. Eosinophil granules contain an antimicrobial protein known as eosinophil-derived neurotoxin (EDN), which belongs to the RNase A superfamily. EDN has antiviral and chemotactic activities in vitro. In this study, we show that EDN, and to a lesser extent human pancreatic RNase (hPR), another RNase A superfamily member, activates human dendritic cells (DCs), leading to the production of a variety of inflammatory cytokines, chemokines, growth factors, and soluble receptors. Human angiogenin, a RNase evolutionarily more distant to EDN and hPR, did not display such activating effects. Additionally, EDN and hPR also induced phenotypic and functional maturation DCs. These RNases were as efficacious as TNF-alpha, but induced a different set of cytokine mediators. Furthermore, EDN production by human macrophages could be induced by proinflammatory stimuli. The results reveal the DC-activating activity of EDN and hPR and suggest that they are likely participants of inflammatory and immune responses. A number of endogenous mediators in addition to EDN have been reported to have both chemotactic and activating effects on APCs, and can thus amplify innate and Ag-specific immune responses to danger signals. We therefore propose these mediators be considered as endogenous multifunctional immune alarmins.

Are interleukin-16 and thrombopoietin new tools for the in vitro generation of dendritic cells?

The effects of interleukin 16 (IL-16) on dendritic cell (DC) generation from human CD34+ progenitor cells are not known. Here, we show that IL-16 added to a basal cocktail comprised of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-4, Flt-3 ligand (Flt3L), and tumor necrosis factor α (TNF-α) does induce the CD34+ hematopoietic cells to proliferate in vitro and to differentiate into phenotypically and functionally mature DCs. IL-16 exerts this function more efficiently than stem cell factor (SCF) as a control, thrombopoietin (TPO), or IL-16 plus TPO. Moreover, we show that the combination of IL-16 plus TPO induces the generation of tolerogenic DCs, able to induce an anergic state in T cells that persists when T cells are rechallenged with immunogenic DCs. An altered pattern of cytokine production, a reduced expression of the C-type lectin DC-SIGN, and an increased surface expression of the inhibitory molecules immunoglobulin-like transcript 2 (ILT-2), ILT-3, and ILT-4 may all contribute to confer the tolerogenic properties of these DCs. Generation of tolerogenic DCs may aid the exploration of new therapeutic strategies to promote tolerance to autoantigens and prevent disease development. (Blood. 2004;104:4020-4028)

Lentivirus-mediated RNA interference of DC-SIGN expression inhibits human immunodeficiency virus transmission from dendritic cells to T cells

In the early events of human immunodeficiency virus type 1 (HIV-1) infection, immature dendritic cells (DCs) expressing the DC-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) receptor capture small amounts of HIV-1 on mucosal surfaces and spread viral infection to CD4(+) T cells in lymph nodes (22, 34, 45). RNA interference has emerged as a powerful tool to gain insight into gene function. For this purpose, lentiviral vectors that express short hairpin RNA (shRNA) for the delivery of small interfering RNA (siRNA) into mammalian cells represent a powerful tool to achieve stable gene silencing. In order to interfere with DC-SIGN function, we developed shRNA-expressing lentiviral vectors capable of conditionally suppressing DC-SIGN expression. Selectivity of inhibition of human DC-SIGN and L-SIGN and chimpanzee and rhesus macaque DC-SIGN was obtained by using distinct siRNAs. Suppression of DC-SIGN expression inhibited the attachment of the gp120 envelope glycoprotein of HIV-1 to DC-SIGN transfectants, as well as transfer of HIV-1 to target cells in trans. Furthermore, shRNA-expressing lentiviral vectors were capable of efficiently suppressing DC-SIGN expression in primary human DCs. DC-SIGN-negative DCs were unable to enhance transfer of HIV-1 infectivity to T cells in trans, demonstrating an essential role for the DC-SIGN receptor in transferring infectious viral particles from DCs to T cells. The present system should have broad applications for studying the function of DC-SIGN in the pathogenesis of HIV as well as other pathogens also recognized by this receptor.

Dexamethasone selectively inhibits differentiation of cord blood stem cell derived-dendritic cell (DC) precursors into immature DCs

Perinatal dexamethasone (Dx) alters the immune system leading to increased infections and developmental abnormalities. Dendritic cells (DCs) derived from cord-blood monocytes are especially Dx sensitive and we sought to determine the effects of Dx on cord-blood CD34+-DCs. Distinct stages of cord-blood CD34+-DC development were delineated: pre-DC, immature, and mature DCs. Dx added during development of pre-DCs did not suppress precursor number, or translocate the glucocorticoid receptor (GcR) from the cytoplasm to the nucleus. However, Dx added during pre-DCs differentiation into immature DCs, prompted GcR translocation to the nucleus, enhanced DC apoptosis, suppressed differentiation to CD1a+ cells, inhibited expression of CD86, reduced subsequent CD83 expression, maintained DC endocytic activity, suppressed IL-6 secretion, enhanced IL-10 secretion, and reduced DC-mediated T cell stimulation. Dx added during the maturation stage caused less dramatic effects. Thus, Dx stalled maturation, selectively induced apoptosis of developing DCs and the sensitivity peaked during pre-DCs differentiation into immature DCs.

In Vitro Generation of Functional Dendritic Cells from Human Umbilical Cord Blood CD34 + Cells by a 2-Step Culture Method

Dendritic cells (DCs) are the most potent antigen-presenting cells in terms of initiating primary T-cell-dependent immune responses. We devised a 2-step culture method for obtaining sufficient numbers of functional DCs from umbilical cord blood (CB) CD34+ cells. In the first step, CB CD34+ cells were expanded by stimulation with early-acting cytokines such as stem cell factor (SCF), flt3 ligand (FL), and thrombopoietin (TPO) to amplify the hematopoietic progenitor cells. In the second step, granulocyte-macrophage colony-stimulating factor and interleukin 4 were added, and incubation was continued for another 5 days to induce differentiation of the expanded cells into DCs. During the first step of culturing with TPO, SCF, and FL, the total numbers of nucleated cells gradually increased, peaking at 4 weeks (245.3-fold). During the second step, expression of CD1a, CD83, and CD86 increased. Electron microscopic findings showed that these cells had cytosolic expansion to form dendrites and major histocompatibility complex class II compartments, which are characteristic of DCs. Functional analyses revealed that these cells had phagocytic activity and were capable of stimulating allogeneic T-cells in vitro.

Selective Generation of Different Dendritic Cell Precursors from CD34+ Cells by Interleukin-6 and Interleukin-3

There is a growing interest in generating dendritic cells (DCs) for using as vaccines. Several cytokines, especially stem cell factor (SCF) and FLT3-ligand (FL), have been identified as essential to produce large numbers of myeloid precursors and even to increase DC yield obtained by the action of granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor alpha (TNF-alpha). However, there are few studies on the effect of the early-acting cytokines, commonly used to expand CD34+ progenitor cells, on DC generation. We report here that in the absence of serum, SCF, FL, and thrombopoietin (TPO) plus interleukin-6 (IL-6) and SCF, FL, and TPO plus IL-3 were able to generate CD14+CD1a- and CD14- CD1a+ myeloid DC precursors from CD34+ cells, but IL-6 had an inhibitory effect on the generation of CD14- CD1a+ cells. Both DC precursors differentiated into mature DCs by GM-CSF, IL-4, and TNF-alpha, and DCs obtained from both types of culture exhibited equal allostimulatory capacity. CD1a+ DCs generated could be identified on the basis of DC-specific intracellular adhesion molecule-grabbing nonintegrin (DC-SIGN) expression, a novel C-type lectin receptor expressed on dermal DCs but not on Langerhans cells. In addition, the inclusion of IL-3 to the culture medium induced the appearance of CD13- cells that differentiated into plasmacytoid DC (DC2) on the addition of TNF-alpha, allowing the identification of developmental stages of DC2. Like true plasmacytoid DCs, these cells secreted interferon-alpha after TLR9-specific stimulation with a specific CpG nucleotide.

Non-hematopoietic human bone marrow contains long-lasting, pluripotential mesenchymal stem cells

Mesenchymal stem cells (MSC) are considered as potential agents for reconstructive and gene-targeting therapies since they differentiate into various cell-lineages, exhibit an extended survival once injected into a host, and can easily be transfected with engineered DNA. MSC are essentially isolated from hematopoietic bone marrow (BM), a process that is rather invasive and may raise ethical concerns. In an attempt to find an alternative source, we evaluated whether non-hematopoietic (nh)BM recovered from femoral heads of patients undergoing hip arthroplasty contained MSC. Ex vivo, 99% of nhBM cells were CD45(+) leukocytes. After culture, leukocytes were replaced by a homogeneous layer of adherent CD45(-) CD14(-) CD34(-) CD11b(-) CD90(+) HLA-ABC(+) cells. Culture doubling time (mean = 4 days, range 1.6-6.7 days) was not correlated with patient age (27-81 years, n = 16). Amplified cultures supported long-term hematopoiesis, and could be differentiated in vitro into adipocytes and chondrocytes. Moreover, a small fraction of nhBM cells spontaneously expressed MyoD1 and formed myotubes, suggesting that myogenic differentiation also occurred. nhBM contained clonogenic cells whose frequency (1/13,000), doubling time (2.1 days), and maximal amplification (up to 10(6)-fold) were not age-related. All 14 clones analyzed (from five patients, ages 27-78 years) differentiated into at least one mesenchymal lineage, and 66% were bipotential (n = 8/12), or tripotential (n = 2/3). In conclusion, nhBM contains pluripotential mesenchymal progenitors which are similar to hematopoietic BM-derived MSC, and whose biological functions are not altered by aging. Furthermore, if MSC-based therapies hold their promises, nhBM may become the source of choice for responding to the increasing demand for MSC.

Exploiting dendritic cells for cancer immunotherapy: genetic modification of dendritic cells

Dendritic cells (DCs) are pivotal regulators of immune reactivity and immune tolerance. The observation that DCs can recruit naive T cells has invigorated cancer immunology and led to the proposal of DCs as the basis for vaccines designed for the treatment of cancer. Designing effective strategies to load DCs with antigens is a challenging field of research. The successful realization of gene transfer to DCs will be highly dependent on the employed vector system. Here, we review various viral and non-viral gene transfer systems, and discuss their distinct characteristics and possible advantages and disadvantages in respect to their use in DC-based immunotherapy.

Thrombopoietin cooperates with FLT3-ligand in the generation of plasmacytoid dendritic cell precursors from human hematopoietic progenitors

Type 1 interferon-producing cells (IPCs), also known as plasmacytoid dendritic cell (DC) precursors, represent the key effectors in antiviral innate immunity and triggers for adaptive immune responses. IPCs play important roles in the pathogenesis of systemic lupus erythematosus (SLE) and in modulating immune responses after hematopoietic stem cell transplantation. Understanding IPC development from hematopoietic progenitor cells (HPCs) may provide critical information in controlling viral infection, autoimmune SLE, and graft-versus-host disease. FLT3-ligand (FLT3-L) represents a key IPC differentiation factor from HPCs. Although hematopoietic cytokines such as interleukin-3 (IL-3), IL-7, stem cell factor (SCF), macrophage-colony-stimulating factor (M-CSF), and granulocyte M-CSF (GM-CSF) promote the expansion of CD34+ HPCs in FLT3-L culture, they strongly inhibit HPC differentiation into IPCs. Here we show that thrombopoietin (TPO) cooperates with FLT3-L, inducing CD34+ HPCs to undergo a 400-fold expansion in cell numbers and to generate more than 6 x 10(6) IPCs per 10(6) CD34+ HPCs within 30 days in culture. IPCs derived from HPCs in FLT3-L/TPO cultures display blood IPC phenotype and have the capacity to produce large amounts of interferon-alpha (IFN-alpha) and to differentiate into mature DCs. This culture system, combined with the use of adult peripheral blood CD34+ HPCs purified from G-CSF-mobilized donors, permits the generation of more than 10(9) IPCs from a single blood donor.

Eosinophil-derived neurotoxin (EDN), an antimicrobial protein with chemotactic activities for dendritic cells

Recent publications have highlighted the chemotactic activities of antimicrobial proteins derived from the granules of neutrophils and basophils. Eosinophil granules also contain antimicrobial proteins. One of them is eosinophil-derived neurotoxin (EDN), a protein belonging to the ribonuclease A (RNase A) superfamily, which has recently been found to have antiviral activity in vitro. We found that EDN was selectively chemotactic for dendritic cells (DCs). The DC chemotactic activity of EDN was inhibited by either pretreatment of DCs with pertussis toxin or by simultaneous addition of placental RNase inhibitor to inhibit the activity of EDN. EDN was not chemotactic for leukocytes other than DCs. Mouse eosinophil-associated RNase 2 (mEAR2), one of a cluster of divergent orthologs of human EDN, was also chemotactic for human as well as mouse DCs. Sequence and mutational analysis demonstrated the importance of the N-terminal region of mEAR2 in mediating its chemotactic effect on DCs. EDN also induced the activation of p42/44 mitogen-activated protein kinase (MAPK) in DCs. Furthermore, injection of mEAR2 into the air pouches of mice resulted in the recruitment of DCs into the air pouches. Thus, EDN and its mouse ortholog, mEAR2, are eosinophil granule-derived antimicrobial RNases that function as chemoattractants for DCs in vitro and in vivo.

Optimized culture conditions for the generation of dendritic cells from peripheral blood monocytes

BACKGROUND AND OBJECTIVES

Dendritic cells (DCs) are promising adjuvants for clinical immunotherapy, but they are scantily distributed. Therefore, numerous in vitro methods have been developed to expand these cells while maintaining their normal functions. Current culture systems generally require the use of fetal bovine serum (FBS)-supplemented media in order to attain DCs with high immunostimulatory activity. However, the presence of exogenous animal proteins sets limits for their use in clinical trials. The purpose of this study was to establish a simple, efficient and FBS-free method for the generation of human DCs for clinical application.

MATERIALS AND METHODS

We compared monocyte-derived DCs generated in a standard FBS-supplemented medium vs. DCs generated in an autologous plasma (AutoPl)-supplemented medium, with regard to their yield, function and longevity. Peripheral blood monocytes were isolated from buffy coats by two consecutive 2-h adherence steps in tissue culture flasks. The adherent cells were differentiated into DCs within 2 weeks by adding granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), c-kit ligand and tumour necrosis factor-alpha (TNF-alpha). Every 2-3 days, the cells in suspension were analysed for their immunophenotype and apoptosis rate by flow cytometry. Their function was demonstrated by their allostimulatory and migratory capacity, as well as by their proteolytic activity.

RESULTS

We show that more than 30 x 10(6) DCs can be achieved per unit of buffy coat using either AutoPl- or FBS-supplemented media. The purity of the DCs was 53.4% and 65% (P > 0.05) in AutoPl- and FBS-based medium, respectively. DCs grown in AutoPl media showed a CD80high CD83+ CD86high CD14neg HLA-DR+ CD1aneg phenotype, while FBS-generated DCs exhibited a CD80high CD83+ CD86high CD14neg HLA-DR+ CD1ahigh phenotype. The apoptosis rate in both culture conditions increased from 10% to 25% over 1 week. AutoPl-generated DCs were shown to be equally strong stimulators for proliferation of allogeneic T lymphocytes as FBS-generated DCs. In addition, the capacity to migrate in response to macrophage inflammatory protein-1alpha (MIP-1alpha) and stromal-cell-derived factor 1alpha (SDF-1alpha) was similar in both groups, whereas the response to MIP-3beta was reduced in AutoPl-derived cells. Zymography analysis of supernatants from 5-day-old cultures demonstrated that AutoPl-generated DCs produced higher amounts of matrix metalloproteinases, suggesting that they have an enhanced capability to traffic through peripheral tissues.

CONCLUSIONS

Our findings indicate that plastic-adherent peripheral blood cells, when cultured with GM-CSF, IL-4, c-kit-ligand and TNF-alpha in autologous human plasma-supplemented media, are a potent source of functional DCS that may be of value for human therapy.

Modulation of antitumor immune responses by hematopoietic cytokines

BACKGROUND

Advances in immunotherapy for the treatment of patients with malignant disease have led to increasingly successful use of these methods in the clinical setting. This review presents findings from recent studies that have explored improved methods for the presentation of tumor-associated antigens and for the restoration of tumor specific immune responses using cytokine therapy.

METHODS

A review of human clinical trial research on immune cytokines from 1995 (MEDLINE) to the present was conducted. Particular attention was focused on articles that reported results from Phase II or later clinical studies in patients with malignant disease.

RESULTS

The defects in cellular immunity commonly seen in patients with malignancies often are expressed as tumor specific anergy. Reversing patient tolerance to tumor antigens may be accomplished by treatment with immunoregulatory cytokines, such as Flt-3 and granulocyte-macrophage-colony stimulating factor, that mature and activate dendritic cells. Published clinical studies indicate that granulocyte-macrophage-colony stimulating factor stimulates antigen-presenting cells and has promising antitumor activity as an adjunct or as stand-alone therapy for patients with malignant disease, including leukemia, melanoma, breast carcinoma, prostate carcinoma, and renal cell carcinoma.

CONCLUSIONS

Immune-modulating cytokines may be used alone or in combination with other treatments to help restore immune function, improve response to tumor-associated antigens, and reduce the toxic effects of standard antitumor therapies. The evolving understanding of how dendritic cells regulate immune responses and promising results from published studies of immune-enhancing cytokines in the treatment of patients with malignant disease support the conduct of randomized clinical trials to confirm the clinical benefit of these immunotherapeutic strategies.

Towards determining the differentiation program of antigen-presenting dendritic cells by transcriptional profiling

Dendritic cells (DC) represent professional antigen-presenting cells that develop from hematopoietic progenitors through successive steps of differentiation. Employing DNA microarray technology, we analysed the specific changes in gene expression that occur when human progenitor cells differentiate into DC. CD34 progenitor cells were first amplified in vitro with stem cell factor (SCF), Flt3 ligand (FL), thrombopoietin and IL-6/soluble IL-6 receptor fusion protein, and cells were then induced to differentiate into DC with IL-4 and GM-CSF. DC maturation was induced by TNFalpha. Progenitor cells and DC were subjected to transcriptional profiling by DNA microarrays that represent 13000 human genes. Our analysis revealed specific changes in the expression of a large number of cell surface antigens including molecules involved in antigen uptake and processing, cell migration and antigen presentation. Genes encoding such molecules were upregulated during DC differentiation as were genes encoding cytokines, cytokine receptors, chemokines and chemokine receptors. Stem cell genes and genes related to the multilineage differentiation potential and proliferative state of progenitor cells were downregulated. Our analysis also provides information on the expression profiles of transcriptional regulators such as the NF-kappaB/rel and STAT transcription factors. Interestingly, NF-kappaB/rel factors were found to be expressed in both progenitor cells and DC at similar levels and were induced by TNFalpha. In contrast, expression of STAT factors increased during DC differentiation and their expression was virtually unaffected by TNFalpha.

Rapid and efficient generation of lentivirally gene-modified dendritic cells from DC progenitors with bone marrow stromal cells

Since dendritic cells (DC) play pivotal roles in both innate and adaptive immunity, DC can be a good target for immuno-gene therapy. However, the optimal generation method for gene-modified DC has not yet been well exploited. CD34+ cells from cord blood (CB), bone marrow (BM), or peripheral blood (PB) were expanded in a medium containing stem cell factor (SCF), flt 3 ligand (Flt3L) and thrombopoietin (TPO) with or without HESS-5, a murine BM stromal cell line, for 2 weeks (the first expansion step), then differentiated to DC in a medium containing granulocyte-macrophage colony-stimulating factor (GM-CSF), flt 3 ligand (Flt3L), stem cell factor (SCF), tumor necrosis factor-alpha (TNF-alpha), IL-4, and lipopolysaccharide (LPS) for 9 days (the second differentiation step). DC progenitors were transduced with human immunodeficiency virus (HIV) vectors at different time points during the second step. Use of HESS-5 during the first step resulted in more DC generation than without it (cell expansion: CB, 10,461 vs. 354-fold; BM, 962 vs. 225-fold; peripheral blood mononuclear cell (PBMC), 8,506 vs. 240-fold; %DC: CB, 83.4% vs. 76.9%; BM, 83.6 vs. 69.8%; PBMC, 85.9 vs. 60.5%). Gene transduction to the in vitro expanded DC progenitors at day 3 during the second step, resulted in better final yield of the gene-modified DC than that to those at day 0 or day 6 (as much as 44% of DC expressed green fluorescence protein (GFP) as a transgene) and the transduction efficiency correlated with endocytic ability and percent of S phase. DC transduced with an HIV vector encoding a melanoma antigen, MART-1, were adequately recognized by specific anti-MART-1 CTL. The two-step culture method with HESS-5 is useful for rapid expansion of DC progenitors and subsequent lentiviral gene transduction to DC.

Inhibition of the transforming activity of FLT3 internal tandem duplication mutants from AML patients by a tyrosine kinase inhibitor

FLT3 is a receptor tyrosine kinase that may play a role in a significant proportion of leukemias. In addition to being aberrantly expressed in acute leukemias, activating mutations of the FLT3 gene have been found in patients with AML, myelodysplastic syndrome (MDS) and more rarely, ALL. Internal tandem duplications (ITDs) of the FLT3 gene have been detected in 17-34% of patients with AML and portend a poor prognosis for these patients. FLT3 receptors containing ITD mutations (FLT3/ITDs) are constitutively activated in the absence of FLT3 ligand (FL) stimulation leading to the activation of downstream signaling proteins, including ERK and STAT 5. FLT3 activity, therefore, is a logical target for therapeutic intervention. AG1296 is a tyrosine kinase inhibitor of the tyrphostin class that shows inhibitory activity for wild-type FLT3, in addition to the PDGF and c-KIT receptors. We examined the inhibitory effects of AG1296 on FLT3/ITDs isolated from AML patients in the IL-3-dependent cell line, Ba/F3, as well as in primary leukemia samples from AML patients. Immunoprecipitation and immunoblotting analyses demonstrated that FLT3/ITDs were constitutively phosphorylated in the absence of FL. The auto-phosphorylation of FLT3/ITDs was inhibited by AG1296 with an IC(50) of approximately 1 microM. FLT3/ITDs were associated with constitutive phosphorylation of ERK, STAT 5A, STAT 5B, CBL, VAV and SHP2 in Ba/F3 cells. The phosphorylation of these downstream signaling molecules was suppressed in a dose-responsive fashion by AG1296. AG1296 inhibited IL-3 independent growth and induced apoptosis in Ba/F3 cells transformed by FLT3/ITDs. AG1296 also inhibited FLT3 auto-phosphorylation, and induced a cytotoxic effect, in primary AML cells. These findings suggest that inhibiting the activity of FLT3 may have a therapeutic value in some leukemias expressing FLT3/ITDs.

MUTZ-3, a human cell line model for the cytokine-induced differentiation of dendritic cells from CD34+ precursors

Many human myeloid leukemia-derived cell lines possess the ability to acquire a dendritic cell (DC) phenotype. However, cytokine responsiveness is generally poor, requiring direct manipulation of intracellular signaling mechanisms for differentiation. In contrast, the CD34+ human acute myeloid leukemia cell line MUTZ-3 responds to granulocyte macrophage- colony-stimulating factor (GM-CSF), interleukin 4 (IL-4), and tumor necrosis factor alpha (TNFalpha), cytokines known to be pivotal both in vivo and in vitro for DC generation from monocytes and CD34+ stem cells. In all respects, MUTZ-3 cells behave as the immortalized equivalent of CD34+ DC precursors. Upon stimulation with specific cytokine cocktails, they acquire a phenotype consistent with either interstitial- or Langerhans-like DCs and upon maturation (mDC), express CD83. MUTZ-3 DC display the full range of functional antigen processing and presentation pathways. These findings demonstrate the unique suitability of MUTZ-3 cells as an unlimited source of CD34+ DC progenitors for the study of cytokine-induced DC differentiation.