Homeostasis of Langerhans and dendritic cells in health and disease

PhD ThesisDendritic Cells (DC) play a pivotal role in both the initiation of immunity and its regulation through tolerance induction. They represent potential targets or tools of therapy in autoimmunity, allergy, cancer, and transplant medicine. Despite recent progress in mapping tissue DC subsets in human, their ontogeny and mechanisms of homeostasis remain elusive. The conventional view is that maintenance of tissue DC and macrophages is dependent on constant replenishment from circulating monocyte precursors. This concept was derived from in vitro data and mouse models under perturbed conditions. While these observations may reflect events in inflammation, studies in murine steady-state biology have challenged this, with data indicating at least three ways in which DC may persist independently of monocytes: 1, tissue DC are replaced by non-monocyte, blood-borne precursors; 2, embryological cells seed tissues and persist in adulthood; 3, DC, or their immediate precursors, self-renew in tissues. These mechanisms may not be mutually exclusive. Although much has been gained from the study of DC kinetics in human transplant, these conditions are, at least in part, inflammatory. To understand the steady-state homeostasis of DC and epidermal Langerhans cells (LC) in human tissues, a number of approaches were taken. Firstly, a comprehensive ‘DC profile’ of normal human tissues was developed, starting with detailed characterization of DC, monocyte and macrophage populations in human peripheral blood (PB) and skin. This lead to the identification of new DC subsets in peripheral tissue. Cells with DC precursor potential were then sought, through analysis of their growth factor receptor expression and ability to enter into cell cycle. Correlative data was gathered to suggest relationships between potential blood borne DC precursors and skin APC. The CD34+ haematopoietic compartment was examined to identify potential DC progenitors. The granulocyte/macrophage progenitor (GMP) and a more recently described multilymphoid progenitor (MLP) were identified and shown also to be present in PB. CD34+ cells were identified in peripheral tissue. While cell and gene knockout experiments have significantly advanced understanding of murine DC, these experiments are not possible in human. The second approach was therefore to undertake a search for subjects with spontaneous DC or monocyte deficiencies. Two novel syndromes were identified; Dendritic Cell, Monocyte, B and NK Lymphoid (DCML) deficiency (4 subjects) and autosomal recessive IRF8 deficiency (1 subject). In both cases, severe depletion of peripheral blood monocyte and DC subsets was associated with absence of tissue DC but preservation of LC and some tissue macrophages. Examination of CD34+ stem cell compartments revealed distinct stem cell defects resulting in loss of MLP and depletion of GMP in DCML deficiency, but accumulation of these subsets in IRF8 deficiency. As predicted by mouse models, DC deficiency was associated with a reduction in circulating regulatory T cells, in the context of elevated Flt3-ligand. Finally, lesions of Langerhans Cell Histiocytosis (LCH), a histiocytic disorder presenting with pathological accumulation of langerin+ DC in tissues, were studied. Analysis of langerin distribution in normal skin and lung identified a langerin+ DC, independent of LC. In keeping with in vitro culture data, preliminary observations show that langerin may be up-regulated on mDC in inflammatory conditions. These data suggest that langerin expression in LCH lesions may reflect its upregulation, rather than determine the LC origin of LCH cells. A variety of techniques have been used to explore DC in normal tissue, novel syndromes of DC deficiency and Langerhans cell histiocytosis. These studies provide new insights into the ontogeny and homeostasis of human DC and LC.The Medical Research Council: The Histiocytosis Association of America: The Newcastle Health Care Charity: Tyneside Leukaemia Research Association: The British Society of Haematology

Targeted treatment of brainstem neurohistiocytosis guided by urinary cell-free DNA

OBJECTIVE: To identify a treatment-responsive BRAF(V600E) mutation in brainstem neurohistiocytosis, where no lesional tissue was readily obtainable, using a cell-free DNA approach. METHODS: Cell-free DNA was extracted from urine and allele-specific PCR for the BRAF(V600E) mutation was performed. Response to conventional treatment (corticosteroids and interferon) and targeted treatment with a BRAF inhibitor was assessed by clinical evaluation, gadolinium-enhanced MRI brain scan, and serial testing of urinary cell-free DNA for mutant alleles. RESULTS: BRAF(V600E) mutation could be readily identified in urinary cell-free DNA at an allele frequency of 4.2%. Treatment of Erdheim-Chester disease with corticosteroids and interferon was ineffective and associated with disease progression. Treatment with BRAF inhibitors was associated with clinical improvement and near-complete radiologic remission. Following 6 months of BRAF inhibitor therapy, no enhancing lesions could be detected in the brain and mutant alleles were cleared from the urine. CONCLUSIONS: Analysis of urinary cell-free DNA using allele-specific PCR for BRAF(V600E) mutations allows rapid noninvasive identification of a highly treatment-responsive pathway, leading to clinical and radiologic remission of disease. Our case demonstrates that this assay may have a particular role in challenging neurohistiocytosis cases, where attempts at obtaining lesional tissue have failed or are not feasible. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence. This is a single observation study without controls

Ikaros family zinc finger 1 regulates dendritic cell development and function in humans

Ikaros family zinc finger 1 (IKZF1) is a haematopoietic transcription factor required for mammalian B-cell development. IKZF1 deficiency also reduces plasmacytoid dendritic cell (pDC) numbers in mice, but its effects on human DC development are unknown. Here we show that heterozygous mutation of IKZF1 in human decreases pDC numbers and expands conventional DC1 (cDC1). Lenalidomide, a drug that induces proteosomal degradation of IKZF1, also decreases pDC numbers in vivo, and reduces the ratio of pDC/cDC1 differentiated from progenitor cells in vitro in a dose-dependent manner. In addition, non-classical monocytes are reduced by IKZF1 deficiency in vivo. DC and monocytes from patients with IKZF1 deficiency or lenalidomide-treated cultures secrete less IFN-alpha, TNF and IL-12. These results indicate that human DC development and function are regulated by IKZF1, providing further insights into the consequences of IKZF1 mutation on immune function and the mechanism of immunomodulation by lenalidomide

Single-gene association between GATA-2 and autoimmune hepatitis:a novel genetic insight highlighting immunologic pathways to disease

AbstractBackground & AimsAutoimmune hepatitis (AIH), an immune-mediated liver disease, originates as a consequence of interacting genetic and environmental risk factors. Treatment remains non-specific and prone to side effects. Deficiencies in regulatory T cell (Treg) function are hypothesized to contribute to the pathogenesis of AIH.MethodsWe describe an adult patient who presented with AIH in the context of monocytopenia. The patient was characterized by GATA2 gene sequencing, flow cytometry of peripheral blood for leucocyte subsets, ELISA for serum Flt-3 ligand, and immunohistochemistry of liver biopsy tissue.ResultsSequencing confirmed a GATA2 mutation. Peripheral Treg were absent in the context of a preserved total T cell count. Immunostaining for the Treg transcription factor FOXP3 was reduced in liver tissue as compared to a control AIH specimen. There were marked deficiencies in multiple antigen-presenting cell subsets and Flt-3 ligand was elevated. These findings are consistent with previous reports of GATA2 dysfunction.ConclusionsThe association of a GATA2 mutation with AIH is previously unrecognized. GATA2 encodes a hematopoietic cell transcription factor, and mutations may manifest as monocytopenia, dendritic and B cell deficiencies, myelodysplasia, and immunodeficiency. Tregs may be depleted as in this case. Our findings provide support for the role of Tregs in AIH, complement reports of other deficiencies in T cell regulation causing AIH-like syndromes, and support the rationale of attempting to modulate the Treg axis for the therapeutic benefit of AIH patients

Hematopoietic origin of Langerhans cell histiocytosis and Erdheim-Chester disease in adults.

Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD) are rare histiocytic disorders induced by somatic mutation of MAPK pathway genes. BRAFV600E mutation is the most common mutation in both conditions and also occurs in the hematopoietic neoplasm hairy cell leukemia (HCL). It is not known if adult LCH or ECD arises from hematopoietic stem cells (HSCs), nor which potential blood borne precursors lead to the formation of histiocytic lesions. In this study, BRAFV600E allele-specific polymerase chain reaction was used to map the neoplastic clone in 20 adults with LCH, ECD, and HCL. BRAFV600E was tracked to classical monocytes, nonclassical monocytes, and CD1c+ myeloid dendritic cells (DCs) in the blood, and mutations were observed in HSCs and myeloid progenitors in the bone marrow of 4 patients. The pattern of involvement of peripheral blood myeloid cells was indistinguishable between LCH and ECD, although the histiocytic disorders were distinct to HCL. As reported in children, detection of BRAFV600E in peripheral blood of adults was a marker of active multisystem LCH. The healthy counterparts of myeloid cells affected by BRAF mutation had a range of differentiation potentials depending on exogenous signals. CD1c+ DCs acquired high langerin and CD1a with granulocyte-macrophage colony-stimulating factor and transforming growth factor β alone, whereas CD14+ classical monocytes required additional notch ligation. Both classical and nonclassical monocytes, but not CD1c+ DCs, made foamy macrophages easily in vitro with macrophage colony-stimulating factor and human serum. These studies are consistent with a hematopoietic origin and >1 immediate cellular precursor in both LCH and ECD

Differential IRF8 Transcription Factor Requirement Defines Two Pathways of Dendritic Cell Development in Humans

The formation of mammalian dendritic cells (DCs) is controlled by multiple hematopoietic transcription factors, including IRF8. Loss of IRF8 exerts a differential effect on DC subsets, including plasmacytoid DCs (pDCs) and the classical DC lineages cDC1 and cDC2. In humans, cDC2-related subsets have been described including AXL+ SIGLEC6+ pre-DC, DC2 and DC3. The origin of this heterogeneity is unknown. Using highdimensional analysis, in vitro differentiation, and an allelic series of human IRF8 deficiency, we demonstrated that cDC2 (CD1c+ DC) heterogeneity originates from two distinct pathways of development. The lymphoidprimed IRF8hi pathway, marked by CD123 and BTLA, carried pDC, cDC1, and DC2 trajectories, while the common myeloid IRF8lo pathway, expressing SIRPA, formed DC3s and monocytes. We traced distinct trajectories through the granulocyte-macrophage progenitor (GMP) compartment showing that AXL+ SIGLEC6+ pre-DCs mapped exclusively to the DC2 pathway. In keeping with their lower requirement for IRF8, DC3s expand to replace DC2s in human partial IRF8 deficiency

The evolution of cellular deficiency in GATA2 mutation.

To access publisher's full text version of this article click on the hyperlink at the bottom of the pageConstitutive heterozygous GATA2 mutation is associated with deafness, lymphedema, mononuclear cytopenias, infection, myelodysplasia (MDS), and acute myeloid leukemia. In this study, we describe a cross-sectional analysis of 24 patients and 6 relatives with 14 different frameshift or substitution mutations of GATA2. A pattern of dendritic cell, monocyte, B, and natural killer (NK) lymphoid deficiency (DCML deficiency) with elevated Fms-like tyrosine kinase 3 ligand (Flt3L) was observed in all 20 patients phenotyped, including patients with Emberger syndrome, monocytopenia with Mycobacterium avium complex (MonoMAC), and MDS. Four unaffected relatives had a normal phenotype indicating that cellular deficiency may evolve over time or is incompletely penetrant, while 2 developed subclinical cytopenias or elevated Flt3L. Patients with GATA2 mutation maintained higher hemoglobin, neutrophils, and platelets and were younger than controls with acquired MDS and wild-type GATA2. Frameshift mutations were associated with earlier age of clinical presentation than substitution mutations. Elevated Flt3L, loss of bone marrow progenitors, and clonal myelopoiesis were early signs of disease evolution. Clinical progression was associated with increasingly elevated Flt3L, depletion of transitional B cells, CD56(bright) NK cells, naïve T cells, and accumulation of terminally differentiated NK and CD8(+) memory T cells. These studies provide a framework for clinical and laboratory monitoring of patients with GATA2 mutation and may inform therapeutic decision-making.Lymphoma and Leukaemia Research British Society of Hematology Bright Red George Walker Trust Wellcome Trus

Human dermal CD14⁺ cells are a transient population of monocyte-derived macrophages.

Dendritic cells (DCs), monocytes, and macrophages are leukocytes with critical roles in immunity and tolerance. The DC network is evolutionarily conserved; the homologs of human tissue CD141(hi)XCR1⁺ CLEC9A⁺ DCs and CD1c⁺ DCs are murine CD103⁺ DCs and CD64⁻ CD11b⁺ DCs. In addition, human tissues also contain CD14⁺ cells, currently designated as DCs, with an as-yet unknown murine counterpart. Here we have demonstrated that human dermal CD14⁺ cells are a tissue-resident population of monocyte-derived macrophages with a short half-life of <6 days. The decline and reconstitution kinetics of human blood CD14⁺ monocytes and dermal CD14⁺ cells in vivo supported their precursor-progeny relationship. The murine homologs of human dermal CD14⁺ cells are CD11b⁺ CD64⁺ monocyte-derived macrophages. Human and mouse monocytes and macrophages were defined by highly conserved gene transcripts, which were distinct from DCs. The demonstration of monocyte-derived macrophages in the steady state in human tissue supports a conserved organization of human and mouse mononuclear phagocyte system