Pathogenesis Of Langerhans Cell Histiocytosis Research Articles

Differential Gene Analysis of Langerhans Cell Histiocytosis and the Significance of MMP1-Targeted Drug Repositioning.

Langerhans cell histiocytosis (LCH) is a rare condition predominantly affecting young children. Activation of the MAPK pathway has offered key new insights into the pathogenesis of LCH; however, the precise mechanisms underlying its occurrence and development are still far from being completely elucidated. There is still a relapse/reactivation rate in patients with multisystem LCH. Therefore, this study aimed to investigate other potential LCH pathophysiologies and prospective therapeutic targets. The gene expression omnibus (GEO) database was used to retrieve gene expression profiles of LCH (GSE16395). Three distinct types of analyses were performed after identifying the common differentially expressed genes (DEGs) in LCH: hub gene identification, functional annotation, module construction, drug repositioning, and expression analysis via immunohistochemistry (IHC). We identified 417 common DEGs and 50 central hub genes. This functional study highlighted the significance of keratinization, skin development, and inflammation. In addition, we predicted new drug candidates (RS2 drugs targeting matrix metalloprotease1, MMP1) that could be used for LCH treatment. Finally, gene-miRNA and gene-TF networks and immune cell infiltration were analyzed for MMP1-related genes. MMP1 expression levels in LCH tissues were validated by IHC. Our study identified the central communal genes and novel drug candidates. These shared pathways and hub genes offer new perspectives on future mechanisms of action and therapeutic targets.

Langerhans cell histiocytosis: NACHO update on progress, chaos, and opportunity on the path to rational cures.

Langerhans cell histiocytosis (LCH) is a myeloid neoplastic disorder characterized by lesions with CD1a-positive/Langerin (CD207)-positive histiocytes and inflammatory infiltrate that can cause local tissue damage and systemic inflammation. Clinical presentations range from single lesions with minimal impact to life-threatening disseminated disease. Therapy for systemic LCH has been established through serial trials empirically testing different chemotherapy agents and durations of therapy. However, fewer than 50% of patients who have disseminated disease are cured with the current standard-of-care vinblastine/prednisone/(mercaptopurine), and treatment failure is associated with long-term morbidity, including the risk of LCH-associated neurodegeneration. Historically, the nature of LCH-whether a reactive condition versus a neoplastic/malignant condition-was uncertain. Over the past 15 years, seminal discoveries have broadly defined LCH pathogenesis; specifically, activating mitogen-activated protein kinase pathway mutations (most frequently, BRAFV600E) in myeloid precursors drive lesion formation. LCH therefore is a clonal neoplastic disorder, although secondary inflammatory features contribute to the disease. These paradigm-changing insights offer a promise of rational cures for patients based on individual mutations, clonal reservoirs, and extent of disease. However, the pace of clinical trial development behind lags the kinetics of translational discovery. In this review, the authors discuss the current understanding of LCH biology, clinical characteristics, therapeutic strategies, and opportunities to improve outcomes for every patient through coordinated agent prioritization and clinical trial efforts.

Langerhans Cell Histiocytosis With Unusual Hexagonal Crystals in Addition to Usual Charcot-Leyden Crystals. Report of a Patient With Possible Process of Crystal Formation and Clinical Significance of a "Necrotic" Change.

Langerhans cell histiocytosis is a rare neoplastic disorder characterized by the proliferation of Langerhans cells and often accompanied by eosinophil infiltration. Charcot-Leyden crystals, composed of galectin 10, are occasionally observed in Langerhans cell histiocytosis; however, histological images are rarely reported. We herein present a patient with Langerhans cell histiocytosis with Charcot-Leyden crystals and hexagonal crystals by describing the histologic and immunohistochemical features of a lymph node. A unique distribution of Charcot-Leyden crystals and hexagonal crystals was observed in this patient, shedding light on their possible formation process of the latter. We discuss the biological significance of eosinophilic abscesses in Langerhans cell histiocytosis and propose that these crystals may be linked to extracellular trap-cell death (ETosis). This example challenges the conventional characterization of "necrosis" in Langerhans cell histiocytosis and underscores the importance of recognizing ETosis as a potential mechanism involved in the pathogenesis of Langerhans cell histiocytosis. Further studies are underway to validate significance of these findings in a larger cohort of Langerhans cell histiocytosis patients.

Expanded Assessments of Germline Genetic Variants Identify Additional Risk Loci for Langerhans Cell Histiocytosis

Introduction: Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by lesions including pathogenic CD207+ dendritic cells among an inflammatory infiltrate. Sequencing studies have identified recurrent, mutually exclusive somatic activating mutations in MAPK pathway genes in ~85% of LCH lesions, including BRAF V600E in 50-65%. Despite advances to elucidate the somatic mutational landscape underlying LCH pathogenesis, germline risk factors remain largely unknown. We previously conducted the first genome-wide association study (GWAS) of LCH and identified and validated a risk variant in SMAD6 (rs12438941, G->A) associated with a 3-fold increase in LCH risk. Our current objective is to further elucidate the role of SMAD6 variation on LCH risk and identify novel LCH susceptibility loci. Methods: Independent of our discovery GWAS, we sequenced SMAD6 in 466 additional LCH cases and compared them to aggregate-level SMAD6 data from ~15,694 non-cancer controls in gnomAD v2.1.1. Targeted sequencing of SMAD6 was conducted among these cases with ~200x coverage at the Avera Institute of Human Genetics. In parallel, we conducted a GWAS of 319 of those cases and leveraged controlled-access data from 9,921 controls in the ADDHealth study. Genotyping of the 319 cases was also performed at the Avera Institute for Human Genetics on the Illumina Infinium Global Screening Array. We evaluated the role of common variants (minor allele frequency >5%) on LCH risk and applied principal components analysis to account for potential population stratification. A genome-wide threshold of significance was applied at P-value<5.0x10 -8, and threshold of suggestive significance at P-value<1.0x10 -6. Analyses were conducted in Plink and STATAv17.1. Results: The case-control study of targeted SMAD6 identified novel SMAD6 variants associated with LCH risk ( P-values ranging from 4.54x10 -28 to 2.9x10 -4), including our original GWAS locus. All cases with two copies of the alternate alleles in the top 2 SNPs had BRAF V600E + lesions. In terms of the new GWAS, 31 novel loci were associated with LCH at P-value=5x10 -8, including 2 separate loci on Chr 9, with the top hit being intergenic between KCNV2 and VLDLR on Chr 9 and the second being intergenic between OLFM1 and LOC401557. Other identified top hits suggest putative biologic significance in terms of LCH pathogenesis. Conclusion: We identified additional support that inherited genetic variation impacts LCH risk. We are concurrently assessing the role of ancestry-specific loci on LCH risk and analyzing newly generated SMAD6 targeted sequence and GWAS data in an independent set of case-parent trios (n=185) to integrate with the findings reported here. Next steps include a meta-analysis of our discovery GWAS, the new GWAS reported here, and the recently genotyped new set of 185 case-parent trios. We also aim to determine the role of variants on clinical characteristics (e.g., ancestry, age at onset, BRAF V600E). Our work suggests an important and complex role of germline variants and ancestry in LCH pathogenesis.

The Relationship of Prognostic Factors with Regulatory T cells in Langerhans Cell Histiocytosis

Aim: Langerhans cell histiocytosis(LCH), is a clonal disorder characterized by abnormal proliferation of dendritic cells, which has an intense inflammatory microenvironment. There is limited information about contribution of microenvironment to this rare disease. We aimed to compare regulatory T cells in microenvironment and BRAFV600E mutation with prognostic data.
 Material and Methods: Overall, 26 cases were included to the study. The number FOXP3+ regulatory T cell(Treg)and presence of BRAFV600E mutation were assessed according to age, gender, localization, unifocal or multifocal, involvement of organ at risk, and recurrence status in a histochemical manner. 
 Results: The number of adult cases was higher than pediatric cases. Bone was the most common localization, and 81% of cases were unifocal. Risk organ involvement was observed in 3 cases, 2 of which showed recurrence. It was found that the number of FOXP3+ Tregs was higher in adults, those with unifocal localization, and those with bone involvement. In addition, the number of FOXP3+ Tregs was higher in the group with recurrence than those without recurrence. BRAFV600E mutation was higher in children when compared to adults (p=0.003), but, no significant correlation was found when compared with remaining prognostic parameters (p>0.05). 
 Conclusions: Although BRAFV600E mutation is more common in pediatric patients, it can also be seen in adult patients. The number of FOXP3+ Tregs is proportional to CD3+ and CD4+ cells. T cells, which present at varying rates in microenvironment, play an essential role in the pathogenesis of LCH.

Langerhans cell histiocytosis: current advances in molecular pathogenesis.

Langerhans cell histiocytosis (LCH) is a rare and clinically heterogeneous hematological disease characterized by the accumulation of mononuclear phagocytes in various tissues and organs. LCH is often characterized by activating mutations of the mitogen-activated protein kinase (MAPK) pathway with BRAFV600E being the most recurrent mutation. Although this discovery has greatly helped in understanding the disease and in developing better investigational tools, the process of malignant transformation and the cell of origin are still not fully understood. In this review, we focus on the newest updates regarding the molecular pathogenesis of LCH and novel suggested pathways with treatment potential.

Resistance to BRAF inhibitors in a patient with <i>BRAF</i> V600E-positive Langerhans cell histiocytosis

Here we report a clinical case of a patient with BRAF-positive Langerhans cell histiocytosis treated with combination therapy including trametinib. As the patient was undergoing long-term therapy with a BRAF inhibitor, his underlying disease reactivated. Hence it was suggested that the child might have become resistant to the treatment as a result of a subclonal mutation. It was concluded that this event undermined the efficacy of long-term therapy with BRAF inhibitors and highlighted the need for further study of possible molecular genetic mechanisms involved in the pathogenesis of Langerhans cell histiocytosis, as well as the need for the development of new treatment approaches. The patient's parents gave consent to the use of their child's data, including photographs, for research purposes and in publications.

Possible involvement of CXCR3-CXCR6 + CD4 + T cells in Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is a condition characterized by proliferation of Langerhans cells and wide-range pathologies, ranging from single granulomatous lesions to multi-organ involvement, associated with tissue destruction. LCH pathogenesis remains obscure although association with interleukin (IL)-17A has been reported. We report here a case that illustrates the potential pathogenic role of helper T17 (Th17) cells in LCH-related bone destruction. The patient was a 66-year-old woman. The clinical course included craniectomy and bone mass excision in X-9, diagnosis of LCH confirmed by histopathology, followed by 26-month chemotherapy. In August X, the patient was diagnosed with complete central diabetes insipidus. Symptoms improved after treatment with desmopressin. Pituitary magnetic resonance imaging showed swelling extending from the suprasellar region to the pituitary stalk, suggestive of LCH recurrence. This was followed by chemotherapy combined with mercaptopurine hydrate. RESULTS: Subsequent peripheral blood lymphocyte analysis showed marked increase in activated Th17 cells (CXCR3-CXCR6+ CD4+ T cells). Double staining for CD4 and IL-17 by immunofluorescence of pathological tissue samples obtained during temporal bone mass excision, which confirmed the diagnosis of LCH in X-9, showed areas of combined presence of CD4-positive cells and IL-17-positive cells. Chemotherapy resulted in size reduction of the pituitary lesion and decrease in peripheral blood-activated Th17 cells. We found abundant peripheral blood-activated Th17 cells and high percentages of IL-17-producing cells in osteolytic bone lesions in LCH. This finding, together with the decrease in peripheral blood-activated Th17 cells following chemotherapy, suggests the potential involvement of activated Th17 cells in LCH-related osteolysis.

Fine-Mapping of SMAD6 Sequence Data Identifies Additional Putative Risk Loci for Langerhans Cell Histiocytosis

Background: Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by lesions including pathogenic CD207+ dendritic cells among an inflammatory infiltrate. Sequencing studies have identified recurrent, mutually exclusive somatic activating mutations in MAPK pathway genes in ~85% of LCH lesions, including BRAF V600E in 50-65%. Despite advances to elucidate the somatic mutational landscape underlying LCH pathogenesis, germline risk factors remain largely unknown. We previously conducted a genome-wide association study of LCH and identified and validated a risk variant in SMAD6 (rs12438941, G->A) associated with a 3.7-fold increase in LCH risk. SMAD6 inhibits bone morphogenetic protein and transforming growth factor-beta (TGF-β)/activin signaling, which are determinants of physiologic myeloid dendritic cell differentiation, and is in close proximity to MAP2K1. Notably, this risk allele is more common in Hispanics, who are at the highest risk of developing LCH, and absent in those of African ancestry who experience the lowest risk of LCH. Our current objective is to further analyze risk of acquiring LCH associated with SMAD6 variations. Methods: Four-hundred and sixty-seven cases diagnosed with LCH were recruited at Texas Children's Hospital. Targeted sequencing of SMAD6 was conducted among cases with ~200x coverage at the Avera Institute of Human Genetics. We accessed aggregate-level SMAD6 sequence data at 940 overlapping loci in SMAD6 from a median of 15,694 non-cancer controls in gnomAD v2.1.1. Variants were pruned using SNPclip due to high linkage disequilibrium (LD; r2 > 0.8) (n = 216 removed), low minor allele frequency (MAF < 0.01) (n = 326 removed), absence from 1000Genomes (n = 240 removed), non-biallelic (n = 3 removed), and absence from dbSNP155 (GRCh37; n = 1 removed). The Fisher's exact test was applied to 154 SMAD6 variants with a Bonferroni critical P-value of 3.2 x 10-4 to assess any association between SMAD6 variation and case status. Sequence data were analyzed in SAS v9.2. Results: In this case-control analysis, 49 variants within SMAD6 were significantly associated with LCH risk (P-values ranging from 4.54 x 10-28 to 2.9 x 10-4), including our previously identified risk locus (P-value: 8.55 x 10-14). Most (48) of the hits were intronic, and one was in the 5' UTR (p = 2.88 x 10-5). The top 4 SNPs had low MAF globally (range 2-9%) but were enriched in the 1000 Genomes AMR (Admixed American superpopulation) population (range 15-23%). The top two SNPs are in high LD in some populations (r2: MXL (Mexican ancestry from Los Angeles) = 0.71, ASW (Americans of African Ancestry in the Southwest USA) = 1.0, PEL (Peruvian from Lima, Peru) = 0.92), but not globally. The third SNP was also in moderately high LD with the peak SNP in some populations (r2: MXL= 0.28, ASW = 0.83, PEL = 0.51). The fourth SNP, which was the variant that was previously identified in our LCH GWAS, has only moderate LD with the peak SNP in some populations (r2: MXL= 0.31, CLM (Colombian from Medellian, Colombia) = 0.3, PEL = 0.13), suggesting that these may be independent signals, and/or that specific SNPs contribute to LCH risk differentially based on ancestry. Conclusions: We identified additional support for associations of germline SMAD6 variants with LCH susceptibility. Our previous risk locus was again enriched among those who develop LCH, and a cluster of loci surrounding our risk locus was identified using this sequence-based approach. Next steps include functional annotation of top hits, analyses to assess whether top hits are associated with LCH patient or clinical characteristics (e.g., genomic ancestry, BRAF V600E mutation status, risk organ involvement), and burden analysis to investigate highly penetrant variants. Overall, this study suggests potential contributions of germline genomics in LCH pathogenesis that may identify a functional role for SMAD6 and account for different incidence rates according to race/ethnicity.

Plasma Signaling Factors in Patients With Langerhans Cell Histiocytosis (LCH) Correlate With Relative Frequencies of LCH Cells and T Cells Within Lesions.

Langerhans cell histiocytosis (LCH) lesions contain an inflammatory infiltrate of immune cells including myeloid-derived LCH cells. Cell-signaling proteins within the lesion environment suggest that LCH cells and T cells contribute majorly to the inflammation. Foxp3+ regulatory T cells (Tregs) are enriched in lesions and blood from patients with LCH and are likely involved in LCH pathogenesis. In contrast, mucosal associated invariant T (MAIT) cells are reduced in blood from these patients and the consequence of this is unknown. Serum/plasma levels of cytokines have been associated with LCH disease extent and may play a role in the recruitment of cells to lesions. We investigated whether plasma signaling factors differed between patients with active and non-active LCH. Cell-signaling factors (38 analytes total) were measured in patient plasma and cell populations from matched lesions and/or peripheral blood were enumerated. This study aimed at understanding whether plasma factors corresponded with LCH cells and/or LCH-associated T cell subsets in patients with LCH. We identified several associations between plasma factors and lesional/circulating immune cell populations, thus highlighting new factors as potentially important in LCH pathogenesis. This study highlights plasma cell-signaling factors that are associated with LCH cells, MAIT cells or Tregs in patients, thus they are potentially important in LCH pathogenesis. Further study into these associations is needed to determine whether these factors may become suitable prognostic indicators or therapeutic targets to benefit patients.

Radiologic zebra line sign in a patient with Langerhans cell histiocytosis on bisphosphonate therapy.

A 3-year-old boy was diagnosed with multi-system Langerhans cell histiocytosis (LCH) with bone, skin, lung, lymph node, and bone marrow involvement at 8 months of age. He achieved non-active disease (NAD) after chemotherapy with prednisolone, vincristine, and cytarabine. However, the patient presented with bone lesion relapse. Despite re-initiation of vinblastine and prednisolone, his bone lesion progressed, prompting treatment with three cycles of cladribine. While it provided some improvement, he presented with bone lesion relapse soon after cladribine therapy. Due to the recurrence of the bone lesion, we administered bisphosphonate therapy using monthly zoledronic acid for 6 months in addition to conventional chemotherapy, which resolved his bone lesion. The patient achieved NAD for 1 year. While he did not present with bone pain, radiographs obtained during bisphosphonate therapy revealed a “dense metaphyseal band sign,” also known as “zebra line sign,” at the tibia and fibula (Figure 1A−D). Nevertheless, 2 years after initiation of bisphosphonate therapy, his growth remained steady (Figure 1E). LCH is characterized as both neoplastic and inflammatory disease. Osteoclasts are crucial in the pathogenesis of LCH, especially in lytic bone lesions. Previous reports revealed that bisphosphonate therapy, including pamidronate and zoledronate, was effective in patients with LCH. Bisphosphonates reduce the activity of osteoclasts by inhibiting their recruitment, thereby resulting in the uncoupling of bone remodeling. The zebra line sign refers to the line of cartilage calcification persisting from the metaphysis into the diaphysis [1, 2]. This radiologic finding reflects the administration of bisphosphonate [3]. Although the zebra line sign seems to be a normal reaction to bisphosphonate therapy, hematology-oncology specialists are not familiar with this finding. In addition, the long-term side effects (e.g., short stature and fracture) remain unknown. This study highlights the importance of long-term follow-up to evaluate the safety profile of bisphosphonates in patients with LCH. The authors declare no conflict of interest.

Immune Checkpoint Inhibitors Restore Function of Lesion Infiltrating T Lymphocytes in Langerhans Cell Histiocytosis

Langerhans Cell Histiocytosis (LCH) is characterized by inflammatory lesions with pathologic CD207+ dendritic cells (DCs) and constitutively activated ERK. LCH lesions are associated with a local cytokine storm and exhibit a heterogeneous collection of inflammatory infiltrates (eosinophils, neutrophils and lymphocytes). The critical role of the immune system in regulating tumor growth and progression has been highlighted with the extraordinary impact of dis-inhibiting cytotoxic T cells in some adult cancers. However, the mechanisms behind tumor formation, both accumulation of pathologic CD207+ DCs as well as recruitment of inflammatory infiltrate in LCH, remain to be defined. Mutually exclusive somatic mutations in MAPK pathway genes have been identified in approximately 75% of LCH cases, including recurrent BRAF -V600Eand MAP2K1 mutations. However, the inflammatory infiltrate within LCH lesions is composed of cells without any BRAF mutation or ERK activation. We hypothesized that the pathologic inflammation in LCH is orchestrated by interactions between the pathologic MAPK-activated DCs and normal immune cells. Defining the nature and function of infiltrating T cells in LCH has the potential to not only provide insights into mechanisms of pathogenesis and potential therapeutic targets, but may also inform novel physiologic mechanisms of DC-mediated T cell function. Clonality, investigated by exploring T cell receptor beta (TCRB) rearrangement in LCH patients, identified clonal populations among LCH lesion-infiltrating CD3+ T cells. The complementarity-determining region 3 (CDR3) of the TCRBV07 gene demonstrated marked monoclonal expansion, suggesting a potential involvement of antigen selection in the pathogenesis of LCH. High dimensional mass cytometric analysis identified multiple tumor-infiltrating T lymphocyte subsets in LCH. Functional analysis indicated hypercytokinemia and defective alloreactive CD8 effector T cells. Spanning tree progression of density normalized events (SPADE) analysis of infiltrating CD3+ T cells revealed high expression of T cell immunoglobulin mucin (TIM-3), lymphocyte activated gene 3 (LAG3) and programmed cell death protein 1 (PD-1) compared to healthy controls, indicating that effector T cell exhaustion might be an important mechanism of immune dysregulation in LCH patients. In addition we found pathologic DCs in LCH lesions expressing ligands for the inhibitory receptors (PDL-1/L2, Galectin-9 and MHC Class II). We also found that patients harboring BRAF -V600E mutation express higher ligand expression compared to patients with wild type BRAF . Checkpoint inhibitor therapy by inhibiting PD-1 in an ex vivo setting to reinvigorate exhausted T cells only partially rescued CD8 effector cells alloreactivity in LCH patients. We are currently evaluating the efficacy of combination therapy in restoring effector T lymphocyte function. The results from this study thus support a model in which LCH lesion DCs with activated MAPK signaling select and recruit activated T cells with potential for clonal expansion to LCH lesions. While the CD207+ DCs in LCH lesions is histologically uniform across the disease spectrum, the composition of the immune microenvironment is variable. The variability of the inhibitory receptor ligand expression in BRAF -V600E vs BRAF wild-type lesions suggests that specific mechanisms of MAPK activation may have some distinct impact on T cell recruitment and activation. Finding more effective ways to reinvigorate T cells and have them regain functions could prove to be incredibly useful for efficacious therapeutic intervention in patients with LCH. DisclosuresNo relevant conflicts of interest to declare.

Transcriptional Profiles, Lineage Tracing with BRAF-V600E and HLA-DQB2 Expression Support a Model of Blood CD1c+ Cells As Precursors to LCH Lesion CD207+ Cells

Purpose: Langerhans Cell Histiocytosis (LCH) is characterized by granulomatous lesions that include pathologic CD1a+/CD207+dendritic cells (DC). Activating somatic MAPK pathway gene mutations have been identified in hematopoietic stem cells and lesion DCs in patients with high-risk LCH, though the differentiation pathway remains uncertain. The purpose of this study was to define the origin of LCH lesion CD1a+/CD207+ cells.Methods: We compared transcriptomes of LCH lesion CD1a+/CD207+ cells to established gene signatures from human peripheral blood and tissue myeloid populations including CD14+ monocytes, CD16+ monocytes, CD14+ DCs, macrophages, epidermal Langerhans cells, CD1c+ myeloid dendritic cells (mDCs) and CD141+mDCs. Additionally, quantitative PCR of BRAF-V600E and HLA-DQB2, and HLA-DQB2 surface expression were used to identify clonal lesion and peripheral blood monocyte and dendritic cell populations.Results: When comparing lesion CD1a+/CD207+ cells to blood and tissue DC/monocyte populations, the CD1c+ mDC gene signature was most similar to gene expression profile of lesion CD1a+/CD207+ cells. In order to further test the hypothesis that LCH CD1a+/CD207+ cells arise from CD1c+mDCs, we investigated subpopulations within the LCH lesions for the BRAF-V600E allele and found that, in addition to LCH CD1a+ and CD1a+/CD207+ DCs, BRAF-V600E was also identified in LCH lesional CD1c+ mDCs. Furthermore, HLA-DQB2, highly expressed in LCH CD1a+/CD207+ cells, was also expressed in LCH lesion CD1c+ cells, but not in any other lesion myeloid subpopulations. Furthermore, HLA-DQB2 was expressed only in peripheral blood of patients with active high-risk LCH, and HLA-DQB2+ CD1c+ blood cells were highly enriched for the BRAF-V600E allele.Conclusion: These data support a model where blood CD1c+ mDCs with hyperactive ERK migrate to lesion sites and differentiate into LCH CD1a+/CD207+ cells. If differentiation from CD1c+ DCs to CD1a+/CD207+ cells is critical to LCH pathogenesis, blocking this process may represent a novel therapeutic opportunity. DisclosuresNo relevant conflicts of interest to declare.

Hepatic Langerhans cell histiocytosis: A review.

Hepatic Langerhans cell histiocytosis (LCH) is characterized by proliferation and accumulation of Langerhans cells in the liver, causing liver dysfunction or forming a mass lesion. The liver can be involved in isolation, or be affected along with other organs. A common clinical hepatic presentation is cholestasis with pruritis, fatigue and direct hyperbilirubinemia. In late stages, there may be hypoalbuminemia. Liver biopsy may be required for the diagnosis of hepatic LCH. Histologic finding may be diverse, including lobular Langerhans cell infiltrate with mixed inflammatory background, primary biliary cholangitis-like pattern, sclerosing cholangitis-like pattern, and even cirrhosis at later stages. Because of its non-specific injury patterns with broad differential diagnosis, establishing a diagnosis of hepatic LCH can be challenging. Hepatic LCH can easily be missed unless this diagnosis is considered at the time of biopsy interpretation. A definitive diagnosis relies on positive staining with CD1a and S100 antigen. Liver involvement is a high risk feature in LCH. The overall prognosis of hepatic LCH is poor. Treating at an early stage may improve the outcome. Systemic chemotherapy is the mainstay of treatment and liver transplantation may be offered. New molecular markers involved in pathogenesis of LCH are being explored with a potential for targeted therapy. However, further studies are needed to improve outcome.

Langerhans Cell Histiocytosis in Adults: Treatment Opportunities of Today

Langerhans cell histiocytosis (LCH) is an extremely rare disease associated with tissue infiltration by pathological cells which are phenotypically similar to normal Langerhans cells. Standard therapy of LCH in adults has not been developed so far, due to the lack of sufficient evidence base for different treatment methods. In clinical practice, cytostatic treatment is applied along with new approaches using signaling pathway inhibitors involved in LCH pathogenesis. This literature review covers currently existing methods of LCH therapy in adults and their feasibility in clinical practice.

Differential In Situ Cytokine Profiles of Langerhans-Like Cells and T Cells in Langerhans Cell Histiocytosis: Abundant Expression of Cytokines Relevant to Disease and Treatment

AbstractThe pathogenesis of Langerhans cell histiocytosis (LCH) remains poorly understood. To further elucidate LCH pathogenesis, we analyzed the expression of 10 cytokines relevant to cellular recruitment and activation at the protein level in 14 patients and identified the lesional cells responsible for cytokine production in situ by immunohistochemistry. The cytokines investigated included the hematopoietic growth factors interleukin-3 (IL-3), IL-7, and granulocyte-macrophage colony-stimulating factor (GM-CSF); the lymphocyte regulatory cytokines IL-2, IL-4, and IL-10; the inflammatory regulators IL-1α and tumor necrosis factor-α (TNF-α); and the effector cell-activating cytokines IL-5 and interferon-γ (IFN-γ). In all specimens, CD1a+ histiocytes (LCH cells) and CD3+ T cells produced large amounts of cytokines, creating a true cytokine storm. IL-2, IL-4, IL-5, and TNF-α were produced exclusively by T cells, whereas only IL-1α was produced by LCH cells. Equal numbers of LCH cells, T cells, and macrophages produced GM-CSF and IFN-γ. Equal numbers of LCH cells and macrophages produced IL-10, whereas IL-3 was produced by T cells and macrophages. IL-7 was only produced by macrophages. Eosinophils, present in some specimens, were partially responsible for the production of IL-5, IFN-γ, GM-CSF, IL-10, IL-3, and IL-7. Expression of all cytokines, abundant in most biopsies, was irrespective of age, gender, or site of biopsy. These findings emphasize the role of T cells in LCH. The juxtaposition of T cells and LCH cells suggests that both cells interact in a cytokine amplification cascade, resulting from stimulation of autocrine and paracrine stimulatory loops. This cascade can be linked directly to the development of LCH through recruitment, maturation, and proliferation of LCH cells. The cytokines studied are known to be involved in the development of other characteristic features of LCH, such as fibrosis, necrosis, and osteolysis.

HISTIOCYTOSIS OF LANGERHANS CELLS IN A NEWBORN: A CASE REPORT

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplastic proliferation with variable clinical behavior; the male:female ratio is 1.6:1.0. The pathogenesis of LCH is imperfectly understood. A newborn boy, 1 month old, had a small focal lesion with a papillomatous surface, was cured, and the tissue removed was granulomatous, friable, and bleeding. The microscopic examination revealed histiocytes with abundant eosinophilic cytoplasm and lobulated or coffee bean-like nucleus admixed with a variable number of eosinophils, lymphocytes, and neutrophils. In a immunohistochemical study, cells were positive for CD1A, S100, CD68, and fascin. The patient was referred to the onco-hematology service of a pediatric hospital and had his body fully examined, without other lesions being identified. After a 2-year follow-up, there was no recurrence. At the site where the lesion was cured, an ulcer remained, through which the early eruption of the tooth 84 occurred. This tooth is currently present.

Immunohistochemical characterization of immune cell infiltration in paediatric and adult Langerhans cell histiocytosis.

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia commonly affecting children with frequent somatic mutations in MAPK pathway genes including BRAFV600E and MAP2K1. Some studies suggest that LCH cells can recruit and modulate inflammatory cells, which could provide reciprocal survival signals. To characterize the immune profile of infiltrating inflammatory cells, and to clarify their participation in LCH pathogenesis, a detailed immunohistochemical analysis was performed. Fifteen (10 children, 5 adults) LCH cases were assessed through macrophage (CD68 and CD163), mature dendritic cell (mDC; CD83 and CD208), regulatory T cell (Treg; CD4, CD25 and FOXP3) and cytotoxic lymphocyte (CL; CD56, CD57, perforin and granzyme B) immunomarkers. Moreover, lymphocytic and LCH markers were also analysed. All cases were S100, CD1a, CD207 and CD4-positive. Bcl-2 and cyclin D1 expression was observed in 13 of 15 cases. In the immune microenvironment, M2-polarized macrophages and Tregs were the predominant cell populations, followed by significantly (P<.005) smaller levels of mDCs and CLs. Additionally, the number of CD3+cells was significantly higher than that of CD20+cells. In the CD3+cell population, there were a significantly higher number of CD4+cells than CD8+cells. While there were no differences when comparing the paediatric and adult populations, FOXP3+cells were significantly higher in patients with multisystem involvement and treated with chemotherapy, than single-site cases and those without chemotherapy. Our results suggest that M2-polarized macrophages and Treg infiltration can promote LCH development and survival, probably through pro-tumoral, immunosuppressive and/or cytokine-mediated mechanisms. This work highlights the need for further exploration of immune-targeted therapy for LCH.

Foxp3+ Tregs from Langerhans cell histiocytosis lesions co-express CD56 and have a definitively regulatory capacity

Langerhans cell histiocytosis (LCH) lesions contain myeloid lineage ‘LCH’ cells. Regulatory T cells (Tregs) are also enriched within lesions, although their role in LCH pathogenesis is unknown. LCH cells are thought to produce the transforming growth factor beta (TGF-β) within lesions, however whether Tregs contribute is unestablished. Using flow cytometry, we analyzed relative frequencies of live Tregs from LCH patients and identified CD56 expression and TGF-β production by lesion Tregs. While CD56+ Tregs were enriched in lesions, overall CD56+ T cells were reduced in the blood from active LCH patients compared to non-active disease patients, and there was a negative correlation between CD8+CD56+ T cells and Tregs. We propose that inducing a Treg phenotype in T cells such as CD56+ T cells may be a mechanism by which LCH cells divert inflammatory T cell responses. Thus, Tregs within LCH lesions are likely an important component in LCH pathogenesis.

Revealing Homologous Clonality By Synchronous Trisomy 8 in Langerhans CELL Histiocytosis and ACUTE Myeloid Leukemia

Purpose Langerhans cell histiocytosis (LCH) is a disorder in which excess immature Langerhans cells build up in the body. Increasing reports have revealed LCH may share a common origin with myeloid-derived malignancies. Here we report a case of a 45-year-old male, diagnosed as synchronous LCH and acute myeloid leukemia (AML). Relevant tests have been performed to investigate the clonal relationship between LCH and AML. Methods The diagnosis of LCH and AML were based on skin and bone marrow biopsy respectively in Beijing Friendship Hospital, Capital Medical University. No cytotoxic drugs were used before the two diseases were diagnosed. Immunophenotyping was run by immunochemistry or flow cytometry. Karyotype analysis was carried out with G-banding, and the findings were confirmed by fluorescence in situ hybridization (FISH). Mutational analysis of BRAF, KRAS and NRAS genes were performed by ARMS-PCR. Additional gene screening was detected by next-generation sequencing (NGS). Results The case expressed CD1a, S-100, Langerin on the Langerhans cells and CD13, CD34, CD38, CD117, MPO on the leukemic blasts. No other intermingling markers was found on the LCH and AML except CD33 and CD68. Cytogenetic studies showed a karyotype with 47, XY, +8[10], and a confirmatory test revealed the existence of trisomy 8 in both skin and bone marrow lesions by FISH. Cell rate of trisomy 8 on skin, bone marrow and oral mucosa were 9%, 49% and 1%. Mutation analysis revealed KRAS c.436G&gt;A:p.A146T (exon4) in AML and LCH cells, but BRAF c.1799T&gt;A:p.V600E (exon15) only in LCH. Conclusion These findings suggest that LCH cells are derived from myeloid precursors in this case, and BRAF mutation may play an important role in pathogenesis of LCH. Disclosures No relevant conflicts of interest to declare.