Langerhans Cell Histiocytosis Lesions Research Articles

Regulatory T-cell expansion in oral and maxillofacial Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a rare myeloid-origin neoplasm characterized by the expansion and dissemination of CD1 a+/CD207+ dendritic cells (LCH cells), but the rarity of its occurrence has long impeded progress in understanding its pathology. We focus on the potentially important role that regulatory T cells (T-reg) play in the oral and maxillofacial LCH tumor microenvironment (TME). Nine cases of oral and maxillofacial LCH, diagnosed from 2009 to 2019, were collected retrospectively from the affiliated hospitals of Southern Medical University. Immunohistochemistry was conducted characterizing T cells and T-reg phenotype. Data were evaluated by 1-sample Wilcoxon's test. Significantly increased frequency and abnormal distributions of T-reg were identified in all the LCH lesion sections. Proliferating T-reg account for a mean average of 11.5% of the total T-cell subsets, with significant difference (Wilcoxon's test; P < .05). T-reg expansion in the localized inflammatory TME leads to a failure of immune regulation by suppressing antitumor response, which can be a latent and significant factor contributing to LCH progression. However, T-reg may also acquire the capability for aiding in initiating T-cell responses under the "cytokine storm" at the beginning of LCH onset. T-reg might contribute to the augmentation of tissue repair by transforming growth factor-β (TGF-β), explaining the self-limiting character of 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.

Langerhans Cell Histiocytosis With Vertebral Involvement Diagnosed and Treated Over the Last 15 Years in a Single Canadian Pediatric Academic Institution.

We report 11 children with vertebral lesion of Langerhans cell histiocytosis (LCH) diagnosed and treated between 2000 and 2015. Vertebral lesions were usually present at LCH diagnosis. No child developed neurologic symptoms. Among 29 vertebral lesions, only 2 were unstable. Chemotherapy was used in all children but 3. A LCH recurrence was observed in 6 patients, involving vertebrae in 4 cases. All children were disease-free at their last follow-up. Sequelae were more often radiologic than clinical. Since potential recurrences and incomplete bone regeneration exist, discussion about optimal treatment and long-term follow-up of vertebral lesions are essential.

Genetic landscape of adult Langerhans cell histiocytosis with lung involvement

The clinical significance of the BRAF V600E mutation in adult Langerhans cell histiocytosis (LCH), including pulmonary Langerhans cell histiocytosis (PLCH), is not well understood. Similarly, the spectrum of molecular alterations involved in adult LCH has not been fully delineated. To address these issues, we genotyped a large number of adult LCH biopsies and searched for an association of identified molecular alterations with clinical presentation and disease outcome.Biopsies from 117 adult LCH patients, 83 with PLCH (median age 36.4 years, 56 females, 38 multisystem disease, 79 single system disease, 65 current smokers) were genotyped for the BRAF V600E mutation. In 69 cases, LCH lesions were also genotyped by whole-exome sequencing (WES) or targeted gene panel next-generation sequencing (NGS). Cox models were used to estimate the association of baseline characteristics with the hazard of LCH progression.MAPK pathway alterations were detected in 59 out of 69 cases (86%) (BRAF V600E mutation: 36%, BRAF N486_P490 deletion: 28%, MAP2K1 mutations: 15%, isolated NRAS Q61 mutations: 4%), while KRAS mutations were virtually absent in PLCH lesions. The BRAF V600E mutation was not associated with LCH presentation at diagnosis, including smoking status and lung function, in PLCH patients. BRAF V600E status did not influence the risk of LCH progression over time.Thus, MAPK alterations are present in most lesions from adult LCH patients, particularly in PLCH. Unlike reports in paediatric LCH, BRAF V600E genotyping did not provide additional information on disease outcome. The search for alterations involved in the MAPK pathway, including BRAF deletions, is useful for guiding targeted treatment in selected patients with refractory progressive LCH.

Added Value of 18F-FDG PET/CT in Initial Evaluation of Osseous Lesions of Langerhans Cell Histiocytosis in Children.

Objectives: To demonstrate the value of FDG PET/CT in evaluation of childhood patient with osseous Langerhans cell histiocytosis (LCH). Patients and Methods: A prospective analysis of 24 pediatric patients with histopathologically proven LCH September 2016 till November 2018. All patients received specific therapy for LCH in the form of chemotherapy &/or surgical resection. Analysis criteria included the following: any focal FDG uptake was considered abnormal when it was greater than that of hepatic uptake or in presence of abnormal changes on CT with any degree of FDG uptake. Results: 17 patients (70.8%) presented with multi-system disease (bone as well as LNs &/or liver, lungs, soft tissueand skin), 5 patients (20.8%) had uni-focal osseous lesions and 2 patients (8.3%) presented by multi-focal bone lesions. FDG PET/CT revealed metabolic changes in osseous lesions detected by anatomical radiographic scan and revealed multiple other lesions as well. No statistically significant association could be detected between neither disease recurrence nor risk of mortality at diagnosis with age, sex, presenting organ, disease extent, risk of mortality, SUV max of leading lesion. Conclusion: PET/CT may be useful as additional imaging to assess known LCH lesions and rule out the presence of other organ infiltration and to provide a reference basis of staging, treatment plan.FDG PET/CT provides the characteristics of lesions in CT scan, but also the lesions activity by FDG uptake. 18F-FDG PET/CT may be incorporated in patientmanagement to facilitate disease stratification and avoid un-necessary interventions.

Creating and Testing a CD207+ Langerhans Cell Histiocytosis-like Cell Line

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by pathological CD207+ dendritic cells (DCs) with persistent mitogen-activated protein kinase (MAPK) activation. Investigations into LCH have historically been challenged by the small percentage of pathologic CD207+ DCs. No cell lines with morphology or function representing LCH lesion CD207+ DCs currently exist. We utilized four strategies to generate cell line(s) mimicking differentiated LCH pathogenic cells. First, CD207+ cells were isolated from the lesion of an LCH patient and cultured in a cytokine cocktail. The cells maintained CD1a and CD207 expression for two weeks, after which there were significant changes in cell morphology and progression to cell death. When a similar approach was implemented to isolate and culture skin CD207+ cells, the cells were viable for only three days, supporting the potential role for somatic activating MAPK mutations in LCH lesion DCs to prolong viability. CD207+ cells were then isolated from HLA-DR+ (lineage negative) cells from the lymphoid stroma of healthy tonsils (tCD207+). The tCD207+ cells were transduced with a lentivirus encoding human telomerase reverse transcriptase (hTERT). These cells, also lacking MAPK activating mutations, died two weeks post-transduction. A fourth approach has been more successful in which tCD207+ cells were cultured in a cytokine cocktail which provided MAPK pathway stimulation. The cells retained CD207 expression and survived in culture for over two weeks. The cells were then immortalized using a lentivirus encoding HOXA9. Immortalized cells maintained CD207 expression. Allele specific MAPK pathway mutations (BRAF and MAP2K1) are being generated by class II CRISPR/Cpf1 genome editing as Cpf1 has been shown to have robust activity to induce specific disruption of only mutant, but not wild-type, BRAF allele. The phenotypic and genomic characteristics of the immortalized cells expressing the different MAPK pathway mutations will be assessed by RHG-banding cytogenetic analysis, fluorescence in situ hybridization, gene expression analysis, and immuno‐cytochemistry and results will be compared to cells isolated from LCH lesions to confirm whether the established cell line may be a viable in vitro mimic of the LCH lesion DC. Disclosures No relevant conflicts of interest to declare.

Blocking MAPK Activation and Immune Checkpoints Reverse Immune Dysfunction and Reduce Disease in a Mouse Model of LCH

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by granulomatous lesions containing pathological CD207+ dendritic cells (DCs) with persistent mitogen-activated protein kinase (MAPK) pathway activation. Standard of care chemotherapy strategies are inadequate or overly toxic for the majority of patients with multisystem disease. The mechanisms underlying development of inflammation in LCH lesions are poorly understood, and potential for immunotherapy has not been determined. Analysis of the LCH lesion identified the most prominent immune cells as T lymphocytes, second only to pathologic CD207+/CD1a+ DCs (LCH DC). Both CD8+ and CD4+ T cells exhibited 'exhausted' phenotypes with high expression of the immune checkpoint inhibitor receptors. LCH DC cells also showed robust expression of ligands to checkpoint inhibitor receptors. Lesion CD8+ T cells exhibited blunted expression of Th1 cytokines with impaired effector function. In contrast, regulatory T cells (Tregs) isolated from LCH lesions demonstrated intact suppressive activity. Treatment of BRAFV600ECD11c LCH mice with anti-PD-1, anti-TIM-3 and MEKi decreased the lesion size: MEKi treatment resulted in reduction of the myeloid compartment; anti-PD-1 and anti-TIM-3 were associated with reduction in the lymphoid compartment. However, combined treatment with MEKi and either anti-PD-1 or anti-TIM-3 significantly decreased both CD8+ T cell and myeloid LCH cells in a synergistic fashion. These results thus indicate MAPK hyperactivation in myeloid LCH cells drives recruitment and activation of functionally exhausted T cells within the LCH microenvironment. While the results from this study did not demonstrate a significant impact of checkpoint inhibition alone on tumor burden in experimental mice, combined MAPK and checkpoint inhibition may be a potentially effective therapeutic strategy for patients with LCH. Disclosures Bollard: self: Patents &amp; Royalties: patent on HIV T cells; NexImmune: Equity Ownership; Torque: Equity Ownership; Cellectis: Membership on an entity's Board of Directors or advisory committees; Caballetta: Equity Ownership; Mana Therapeutics: Equity Ownership.

TCR Repertoire Clonality Analysis and Transcriptome Analyses of Immune Infiltrates in Patients with Langerhans Cell Histiocytosis Can Define Prognostic Biomarkers for Future Therapeutic Development

Langerhans Cell Histiocytosis (LCH) is a myeloproliferative disorder, most common in children, with an incidence of approximately 5 cases per million children and 1/10,000 live births per year - similar to the frequency of Hodgkin's lymphoma and AML in children. LCH lesions are comprised of clonal pathologic CD207+ dendritic cells (DCs) harboring mutually exclusive genomic alterations of MAPK pathway members along with a large inflammatory infiltrate comprised of macrophages, multinucleated giant cells, lymphocytes, and eosinophils that do not carry MAPK mutations. Mass cytometry revealed that in systemic LCH lesions, T lymphocytes are the most abundant cellular subsets among immune infiltrates and exhibit an exhausted phenotype characterized by expression of immune inhibitory receptors. Since inflammatory infiltrate composed of cells without MAPK pathway mutation is characteristic of LCH, it is likely that the pathogenic DCs in LCH mediate some of the pathologic manifestations through DC-T cell interactions. However, properties of tumor infiltrating T lymphocytes (TILs) in LCH are poorly understood, In this study we performed Bulk TCR alpha/ beta repertoire profiling using the SMARTer TCR a/b Profiling Kit (Takara Bio ) to identify the CDR3 and full length clonotypes in sorted CD8, CD4 and CD4 CD25 compartments isolated from lesions that were stimulated as well the repertoire from the matching white blood cells. We found that in the sorted CD8 cells and CD4 cells from all patient lesions, there was a characteristic clonality shift where-in the repertoire in the lesions were clonally expanded, and interestingly some of the V, J genes were shared among the patient lesions, In addition to changes in the TCR repertoire, we performed bulk Transcriptome analyses to characterize the functional nature of the T-cell infiltrates, and we find that genes responsible for calcium mobilization and mitochondrial metabolism are significantly downregulated in LCH TILs, even after TCR stimulation. RANKL (encoding receptor activator of nuclear factor kappa-B ligand or tumor necrosis factor ligand superfamily member 11) expression, which is solely dependent on TCR activation‐induced calcium mobilization, is also downregulated in the LCH TILs. RANKL is widely known as a modulator of immune cell function by virtue of influencing the survival and T cell-stimulatory capacity of DCs. Impaired calcium mobilization and mitochondrial metabolism might explain the exhausted phenotype we observe in the LCH TILs. We are currently investigating whether the clonal signatures identified by TCR sequencing in the LCH TILs can be used for prognostic purposes, and the T cell functional states can also be exploited to identify biomarkers that can be used to stratify LCH patients for therapy. Disclosures No relevant conflicts of interest to declare.

Langerhans cell histiocytosis of the jaw, a mimicker of osteomyelitis on CT and MR images: A retrospective analysis.

Differential diagnosis of Langerhans Cell Histiocytosis (LCH) in the jaw is essential for early treatment including systemic therapy. Records of 17 patients (6 men and 11 women; mean age, 14 years) with histologically confirmed LCH were reviewed. All the lesions occurred in the mandible. Most of the cases (n=12) were intraosseous type LCH, only 5 patients had alveolar type LCH. Patients complained of facial swelling and pain most likely. In the 14 patients who underwent CT and/or MR imaging, all LCH lesions were osteolytic, with a mean size of 23 mm. LCH presented as expansile lesions with periosteal new bone formation, perilesional sclerosis, fluid attenuation/signal within the lesion, and inflammatory changes in adjacent soft tissues on CT/MR images. Considering the major symptoms of LCH were swelling and pain, the differential diagnosis of LCH from osteomyelitis might be more difficult. The differential diagnosis for osteolytic lesions of the jaw with surrounding inflammatory changes should include LCH, especially in young patients.

Langerhans Cell Histiocytosis in the Pediatric Population: Treatment of Isolated Craniofacial Lesions.

Langerhans cell histiocytosis (LCH) commonly affects the craniofacial skeleton and prognosis depends on location, extension, and recurrence of the disease. The aim of our study is to better define the treatment of single craniofacial lesions, as to date different treatment modalities have been suggested and recurrence rates for both unifocal and multifocal bony lesion range between 10% and 70%. Between 2000 and 2014, we retrospectively reviewed clinical findings, anatomic location, extent of the disease, therapy, and outcomes in 24 pediatric patients with histologically confirmed LCH. Seventeen patients (67%) had craniofacial involvement, of which 13 had single system involvement and 4 had multisystem involvement. Eight patients (33%) had no craniofacial involvement. Eleven patients affected by unifocal cranial lesions were treated with resection and reconstruction. One patient with a unifocal mastoid lesion was treated with chemotherapy alone (vinblastine and prednisone). Four patients with mandible lesions were treated with curettage alone.There were no recurrences in patients treated with excision alone. One patient (25%) treated with curettage recurred. Two patients with diffuse disease manifested organ dysfunction and diabetes insipidus. Chemotherapy was tolerated in 12 patients treated.Our findings suggest that resection of isolated LCH lesions of the cranium is safe and chemotherapy is effective and well tolerated for nonsurgical cases.

Comparison of whole-body MRI, bone scan, and radiographic skeletal survey for lesion detection and risk stratification of Langerhans Cell Histiocytosis

Accurate risk stratification according to the extent of Langerhans cell histiocytosis (LCH) determined on whole-body evaluation is important for determining the treatment plans and prognosis in patients with LCH. This study aimed to compare the lesion detectability and the accuracy of risk stratification of skeletal survey, bone scan, and whole-body magnetic resonance imaging (WB-MRI) in patients with LCH. Patients with newly-diagnosed LCH who underwent all three imaging modalities were retrospectively included (n = 46). The sensitivity and mean number of false-positives per patient for LCH lesions, and the accuracy of risk stratification of each modality were assessed. WB-MRI had significantly higher sensitivity (99.0%; 95% confidence interval, 93.2–99.9%) than skeletal survey (56.6%; p < 0.0001) and bone scan (38.4%; p < 0.0001) for LCH lesions, and there were no significant differences in the number of false-positives per patient (p > 0.017). WB-MRI tended to have higher accuracy for the risk stratification than skeletal survey and bone scan (concordance rate of 0.98, 0.91, and 0.83, respectively), although the differences were not significant (overall p-value 0.066). In conclusion, WB-MRI had higher detectability for LCH lesions than skeletal survey and bone scan, while the three whole-body imaging modalities had comparable accuracy in the initial risk stratification of LCH.

Atteintes ostéoarticulaires au cours des histiocytoses

Histiocytoses are heterogeneous diseases characterized by the accumulation of histiocytes in various organs. The detection of somatic molecular alterations in some of these led to a new classification, published in 2016. In this review, we describe bone involvement of L-group histiocytosis (Langerhans-cell histiocytosis (LCH) and Erdheim-Chester disease (ECD)), and Destombes-Rosai-Dorfman disease (RDD). The osseous lesions of LCH consist of unilateral or multifocal, hypermetabolic lesions on bone C-computed tomography (CT)-scan or 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), mainly affecting flat bones and vertebrae, and more rarely long bones, with a risk of fracture. ECD bone involvement is characterized by metaphyso-diaphyseal sclerotic, hypermetabolic lesions, present in more than 90 % of cases, and constituting an iconic feature of this disease. Limbs bone pain may be suggestive of ECD, and is sometimes the first sign of the disease. RDD is characterized by multifocal bone involvement of the limbs or spine, associated in typical forms with node involvement. Treatments options vary for these 3 types of histiocytoses, and range from abstention to chemotherapy in LCH, from immunomodulatory treatments to targeted therapies in ECD, and from abstention, corticosteroid therapy, immunosuppressive drugs, to chemotherapies in RDD.

Co-Expression of CD56 and Production of Transforming Growth Factor Beta By Foxp3 Regulatory T Cells from Langerhans Cell Histiocytosis Lesions

Introduction:Langerhans cell histiocytosis (LCH) is a rare disease involving inflammatory lesions that can occur in essentially any organ of the body. LCH lesions are defined by the presence of CD1a+/CD207+ myeloid lineage cells (LCH cells), which often have mutations within the RAS/RAF/MEK/ERK pathway and constitutive activation of ERK. A range of other immune cells are also present within lesions including an enrichment of Foxp3 regulatory T cells (Tregs).The immune suppressive cytokine transforming growth factor beta (TGF-β), which is commonly produced by Foxp3 Tregs has also been detected within lesions and blood from patients with active LCH disease. Groups have suggested that LCH cells are a source of TGF-β and that TGF-β is one of the drivers of the LCH cell phenotype. Given the enrichment of Foxp3 Tregs and the presence of TGF-β within LCH lesions it is conceivable that Foxp3 Tregs too are a source of TGF-β production.Historically the identification of Foxp3 Tregs has not allowed for functional studies to be conducted because staining for the Foxp3 transcription factor requires cell permeabilization. A newer surrogate gating strategy to detect CD3+CD4+CD25+CD127low lymphocytes allows for downstream functional assays on the Foxp3 Treg population. Our study aimed to better define the role of Tregs in LCH pathogenesis using this surrogate staining method.Results:A surrogate Treg identification method was employed to gate on CD3+CD4+CD25+CD127low lymphocytes in the blood from healthy donors and patients with LCH and in lesions from patients with LCH. Using this gating strategy we identified similarly to previous studies that the proportion of lesional Tregs (median = 12.85 %, IQR = 7.85-26.72 %, n = 6) was significantly (p < 0.0001) increased in the total T cell population when compared to those in the blood from healthy donors (median = 1.02 %, IQR = 0.84-1.20 %, n = 19). The proportion of Tregs in blood from patients with active LCH (median = 1.73 %, IQR = 1.58-3.80 %, n = 8) was also significantly (p = 0.232) increased when compared to those in the blood from healthy donors. We confirmed Foxp3 expression in Tregs in lesions from three independent LCH donors by staining for the transcription factor, and we confirmed that other lesional CD4+ T cells were mostly negative for Foxp3.Due to our interest in unconventional T cells we analysed specimens for CD56 expression in conjunction with investigating Tregs and we unexpectedly found CD56 expression on a considerable proportion of the Treg population in LCH lesions (median = 36.48 %, IQR = 24.94-55.14 %, n = 6). The proportion of Tregs that displayed CD56 expression on their cell surface was significantly higher in the lesions from patients with LCH compared to the blood from healthy donors (median = 2.29 %, IQR = 0.61-4.10 %, n = 15, p = 0.0092) and patients with active LCH (median = 0.57 %, IQR = 0.11-0.85 %, n = 8, p < 0.0001). Additionally, we found that the proportion of CD56+ Tregs in total T cells from LCH lesions was directly correlated to the proportion of total Tregs in overall lesional T cells (r = 1, p = 0.0028). Importantly, we confirmed Foxp3 expression by both the CD56+ and CD56- Treg populations in lesions from three independent LCH donors.We purified and then stimulated Tregs from healthy donors, and CD56+ and CD56- Treg populations from lesions from patients with LCH. Using supernatants from this assay we found that Tregs from lesions from patients with LCH produced active TGF-β when challenged with PMA and ionomycin for 16 hours (CD56+ Tregs n = 3, CD56- Tregs n = 3).Conclusion:We have confirmed that both CD56+ and CD56- Treg populations from the lesions from patients with LCH are able to produce TGF-β. Given their cytokine potential, the functional status of Tregs in LCH lesions is therefore most likely to be suppressive in nature. This means that Tregs are possibly responsible for a component of the well documented expression of TGF-β within lesions. DisclosuresNo relevant conflicts of interest to declare.

Acquired Hematologic Disorders of Ras-MAPK Activation

Histiocytic disorders represent a collection of conditions characterized by aberrant function, differentiation and/or proliferation of cells of the mononuclear phagocyte system (MPS). “Histiocyte” is an archaic term (meaning “tissue cell”) used to describe phagocytic cells with mononuclear morphology. Clinical approaches to histiocytic disorders have historically been challenged by incomplete understanding of mechanisms of pathogenesis, with debate over classification as cancer versus immune dysregulation. Langerhans cell histiocytosis (LCH), the most common histiocytic disorder, presents with granulomatous lesions with clonal CD207+ dendritic cells (DCs) that can arise as single lesions or life-threatening disseminated disease. Despite the wide range of clinical presentations, LCH lesions are histologically indistinguishable regardless of disease severity. Erdheim-Chester disease (ECD) arises in adults and is characterized by distribution of inflammatory lesions with CD163+ foamy histiocytes involving bone, retroperitoneum/kidney, skin and/or brain. Juvenile xanthogranuloma (JXG), histologically similar to ECD, is typically skin-limited in children, but may also manifest as life-threatening systemic disease. Classical Rosai-Dorfman disease (RDD) presents in children as lymphadenopathy with CD163+ histiocytes and emperipolesis identified in lymph node biopsy, though RDD likely represents a spectrum of conditions in children and adults with a common histiological endpoint. Classification of histiocytic disorders has been based on phenotype of the pathologic cell: LCH (DC-like), non-LCH (macrophage-like), or malignant histiocytosis. BRAFV600E was the first recurrent somatic mutation identified in LCH and ECD. While occurring in 7% of all human cancers, BRAFV600E mutations are also frequently found in benign conditions such as melanocytic nevi and colon polyps. Whole exome sequencing of LCH, ECD, RDD and JXG biopsies has revealed mutually exclusive MAPK pathway activating mutations within otherwise “quiet” genomic landscapes. In LCH, the stage of myeloid differentiation in which the mutation arises defines the extent of disease, and MAPK activation in precursor cells drives myeloid differentiation, blocks migration, and inhibits apoptosis, resulting in accumulation of resilient pathologic DCs that recruit and activate T cells. These new insights support reclassification of these histiocytic disorders as myeloproliferative neoplasms (MPN). Early phase trials in adults with LCH and ECD and emerging pediatric case studies demonstrate promising responses to MAPK pathway inhibitors, though potential for cure and long-term safety are not known. MAPK pathway activation clearly drives pathogenesis in histiocytic MPNs. However, it remains unclear how pathway activation, in many cases with the same mutation in the same CD34+ hematopoietic stem cell, can produce distinct cellular phenotypes with characteristic tissue distribution. While we now are beginning to understand the framework for mechanisms of pathogenesis of histiocytic disorders, continued research will uncover opportunities to identify additional targets and inform personalized therapeutic strategies based on cell of origin, somatic mutation and inherited risk factors. DisclosuresNo relevant conflicts of interest to declare.

Inherited Genetic Risk Factors and Langerhans Cell Histiocytosis Relapse Events

Introduction: Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by lesions including pathogenic CD207+ dendritic cells among an inflammatory infiltrate, and has a median age at diagnosis of 30 months. Approximately 50% of children with LCH relapse, and 40% experience a second relapse event within two years. Sequencing studies have identified activating somatic mutations in MAPK pathway genes in ~85% of LCH lesions. Notably, LCH cases who are carriers of BRAFV600E+ experience a 2-fold increased risk of relapse. However, the role of inherited genetic effects in LCH relapse remains unknown. Therefore, we conducted a genome-wide association study (GWAS) to characterize the role of inherited genetic variants on risk of LCH relapse.Methods: LCH cases (n=117) for this discovery GWAS were recruited from Texas Children's Hospital, of which 52 patients experienced a relapse event and 65 patients did not. Genotyping was performed on the Illumina Omni5 Quad BeadChip. We tested the association between common variants (minor allele frequency >5%) and LCH relapse risk in PLINK. A genome-wide threshold of significance was applied at P-value<5.0x10-8, and threshold of suggestive significance at P-value<1.0x10-5. Principal component analysis was performed to account for genetic ancestry, with the top two principal components (PCs) accounting for 85% of variability. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) controlling for age at diagnosis, sex, and the top two PCs were estimated using logistic regression. An independent replication set of LCH cases (n=124) were recruited from Texas Children's Hospital to validate discovery GWAS findings.Results: High-quality genotype data for 583,173 germline variants were tested for an association with LCH relapse risk in the discovery GWAS stage. We identified a variant in high linkage disequilibrium with a cluster of loci on Chromosome 9 that surpassed our threshold of suggestive significance (non-coding RNA LOC100506532 rs2182640; P-value=6.98x10-6). This intronic variant was associated with a decreased risk of LCH relapse that remained statistically significant after adjusting for age at diagnosis, sex, and the top two PCs (aOR: 0.16; 95% CI: 0.07-0.35). While this non-coding RNA gene is largely uncharacterized, non-coding RNAs function to regulate gene expression at the transcriptional and post-transcriptional level. Results from validation of this risk locus in an independent replication set are forthcoming.Conclusions: In this genome-wide assessment of inherited genetic variation and LCH relapse, we identified a genomic region that may be associated with LCH relapse. It is unclear which variant in the LOC100506532 cluster is a potentially causal allele. One of these variants may be a proxy for the causal locus, or may act through an effect on other genes in the same region or at distal sites. Notably RXRA, a retinoic acid receptor gene, is located in close proximity (~400kb) to LOC100506532 and regulates gene expression in various biologic processes. Risk variants within this gene have been identified to modulate disease-specific survival in melanoma, another BRAF-driven malignancy. While we are in the process of validating the association between LOC100506532 rs2182640 and LCH relapse risk in an independent replication set, our discovery GWAS results provide initial evidence to suggest that inherited risk factors influence LCH disease severity. DisclosuresNo relevant conflicts of interest to declare.

Central diabetes insipidus in pediatric patients with Langerhans cell histiocytosis: Results from the JLSG-96/02 studies.

We analyzed central diabetes insipidus (CDI) development in pediatric patients with Langerhans cell histiocytosis (LCH) treated according to the Japan LCH Study Group (JLSG) regimen, which is the combination chemotherapy including cytarabine (Ara-C). Retrospective data from 317 patients (multisystem disease (MS), n=206; multiple focal bone (MFB), n=111) treated according to the JLSG-96/02 regimens were analyzed. The median follow-up duration was 10.6 years (range, 0.1-21.1). A total of 50/317 (15.8%) patients developed CDI (MFB, n=4; MS, n=46). Of the 50 cases, CDI was already present at the time of LCH diagnosis (pre-CDI) in 25, and it newly developed after the diagnosis and initiation of treatment (post-CDI) in the other 25 cases. The cumulative incidence of post-CDI at 10-year calculated by Kaplan-Meier analysis was 9.0% for total and 12.0% for MS patients. A positive correlation with LCH lesions at the CNS risk sites at diagnosis was found in pre-CDI cases (17/164vs 8/171; P=0.0359), but not in post-CDI cases (14/129vs 11/163; P =0.254). Multivariate analysis showed that relapse at the CNS risk sites was significantly associated with post-CDI development (hazard ratio: 4.70; 95% CI, 1.29-17.1, P <0.05). In the JLSG-96/02 studies, CDI developed in 15.8% of the cohort in which half as pre- and the other half as post-CDI. Relapse, particularly at the CNS risk sites, was linked with the development of post-CDI.

Histiocitosis de células de Langerhans multisistémica asociada con papulosis linfomatoide: ¿solo un hallazgo accidental? Presentación de un caso y revisión de la literatura

Langerhans cell histiocytosis (LCH) is a disease characterized by proliferation of CD1a+dendritic cells with local or diffuse organ compromise. The identification of recurrent gene mutations has confirmed the hypothesis of LCH as a true neoplasm. Lymphomatoid papulosis (LyP) belongs to the spectrum of CD30+primary cutaneous lymphomas. LCH has been described in association with other lymphoproliferative disorders. However, lesions constituted by Langerhans cells (LC) have been commonly considered reactive, related to cytokines produced by the lymphoma-microenvironment interaction. Some authors designate these lesions as “Langerhans cells-like lesions”. We present the case of a 28-years-old woman with multisystem LCH and simultaneous PyL lesions with reactive LC hyperplasia.

Comparison between low-dose chemotherapy and surgery for the treatment of extremity-associated solitary bone lesions in children with Langerhans cell histiocytosis in South China: A case-control study

BackgroundThe treatment algorithm for solitary bone lesions of Langerhans cell histiocytosis (SBL-LCH) in children extremities still remains controversial. We conducted a retrospective case-control study to compare the feasibility of low-dose chemotherapy (LDC) and surgery for SBL-LCH in children extremities. Patients and methodsThis study compares 43 pediatric patients starting LDC with a surgery control group (n = 44), matched for gender, age, follow-up time, and lesion sites and sizes, treated between 2001 and 2015 at our institution. Hospital stay (HS), time to symptom relief (TTSR), recovery time (RT), complications, relapse-free survival (RFS), health-related quality of life (HRQOL) and cost-effectiveness were analyzed for each strategy. ResultsHS, TTSR and RT in the LDC group were shorter than those in the surgery group (p < 0.01). Chemotherapy-related complications included nausea (16.30%), aminotransferase elevation (9.30%), slight hair loss (11.63%), decline in immune function (23.26%), growth retardation (16.30%), and moon face (9.30%). Chemotherapy-related side effects were mild and well tolerated. Pathologic fractures (6.81%), loosening of instrumentation (6.00%,), surgical site infection (4.00%) and rejection of bone grafting (9.09%) developed in surgery patients. LDC treatment resulted in a longer RFS (87 months) than surgery alone (59 months) (p = 0.011). Furthermore, compared with surgery patients, patients in the LDC group had a better HRQOL at 3 months’ follow-up for the physical, role, emotional and social function domains assessed (p < 0.001, p = 0.001, p < 0.001 and p = 0.003, respectively) according to the European Organisation for Research and Treatment of Cancer QLQ-C30® survey. However, HRQOL scores at 2 years’ follow-up were similar between the two groups. The incremental cost-effectiveness ratio (ICER) was ¥−137,030/quality-adjusted life year (QALY) for LDC versus surgery. ConclusionsCompared with surgery, LDC promotes more rapid recovery, is less invasive, is characterized by increased safety and a superior HRQOL, and is a more cost-effective treatment strategy for pediatric patients with SBL-LCH in the extremities.

Isolated Langerhans Cell Histiocytosis of Thyroid-Masquerading as a Thyroid Neoplasm - A Rare Case Report

Langerhans Cell Histiocytosis (LCH) is a rare neoplastic disease of unknown etiology characterized by oligoclonal proliferation of langerhans cells with a varying incidence rate of 4-5.4 per 1 million individuals. LCH occurs in localised and multifocal forms. LCH lesions were first described in the year 1893, they are composed of large histiocytes with abundant cytoplasm intermixed with lymphocytes and eosinophils. Diabetes insipidus is the most common endocrinological abnormality of LCH. Other manifestations such as hypothalamic/pituitary axis disturbance and anterior pituitary deficiency can occur resulting in secondary or tertiary hypothyroidism. Cases of LCH with isolated thyroid involvement are very rare. We present a case of LCH, in a 42-year-old female who had a nodular thyroid swelling since one and a half year with euthyroid status. Total thyroidectomy specimen was received with a clinical diagnosis of thyroid neoplasm. Histopathology revealed langerhans histiocytes both mononucleated and multinucleated with prominent nuclear grooves, accompanied by good number of eosinophils and lymphocytes. Histopathology diagnosis of LCH was given supported by IHC S-100 and CD 1a positivity. Since, it’s a rare entity it needs to be distinguished from its closer mimics non Hodgkin’s lymphoma and Rosai Dorfman’s disease. Treatment of choice is surgical resection, but there is no evidence of improved outcome on usage of adjuvant chemoradiotherapy for primary thyroid LCH post resection. So, more case reports and articles are recommended to acess treatment regimen for better outcome.

RAF/MEK/extracellular signal-related kinase pathway suppresses dendritic cell migration and traps dendritic cells in Langerhans cell histiocytosis lesions.

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia characterized by granulomatous lesions containing pathological CD207+ dendritic cells (DCs) with constitutively activated mitogen-activated protein kinase (MAPK) pathway signaling. Approximately 60% of LCH patients harbor somatic BRAFV600E mutations localizing to CD207+ DCs within lesions. However, the mechanisms driving BRAFV600E+ LCH cell accumulation in lesions remain unknown. Here we show that sustained extracellular signal-related kinase activity induced by BRAFV600E inhibits C-C motif chemokine receptor 7 (CCR7)-mediated DC migration, trapping DCs in tissue lesions. Additionally, BRAFV600E increases expression of BCL2-like protein 1 (BCL2L1) in DCs, resulting in resistance to apoptosis. Pharmacological MAPK inhibition restores migration and apoptosis potential in a mouse LCH model, as well as in primary human LCH cells. We also demonstrate that MEK inhibitor-loaded nanoparticles have the capacity to concentrate drug delivery to phagocytic cells, significantly reducing off-target toxicity. Collectively, our results indicate that MAPK tightly suppresses DC migration and augments DC survival, rendering DCs in LCH lesions trapped and resistant to cell death.