Circulating senescent myeloid cells drive blood brain barrier breakdown and neurodegeneration

Neurodegenerative diseases (ND) are characterized by progressive loss of neuronal function. Mechanisms of ND pathogenesis are incompletely understood, hampering the development of effective therapies. Langerhans cell histiocytosis (LCH) is an inflammatory neoplastic disorder caused by hematopoietic progenitors expressing MAPK activating mutations that differentiate into senescent myeloid cells that drive lesion formation. Some patients with LCH subsequently develop progressive and incurable neurodegeneration (LCH-ND). Here, we show that LCH-ND is caused by myeloid cells that are clonal with peripheral LCH cells. We discovered that circulating BRAF V600E $^{+}$ myeloid cells cause the breakdown of the blood-brain barrier (BBB), enhancing migration into the brain parenchyma where they differentiate into senescent, inflammatory CD11a $^{+}$ macrophages that accumulate in the brainstem and cerebellum. Blocking MAPK activity and senescence programs reduced parenchymal infiltration, neuroinflammation, neuronal damage and improved neurological outcome in preclinical LCH-ND. MAPK activation and senescence programs in circulating myeloid cells represent novel and targetable mechanisms of ND

CNS Langerhans cell histiocytosis: Common hematopoietic origin for LCH-associated neurodegeneration and mass lesions

BACKGROUND Central nervous system Langerhans cell histiocytosis (CNS-LCH) brain involvement may include mass lesions and/or a neurodegenerative disease (LCH-ND) of unknown etiology. The goal of this study was to define the mechanisms of pathogenesis that drive CNS-LCH. METHODS Cerebrospinal fluid (CSF) biomarkers including CSF proteins and extracellular BRAFV600E DNA were analyzed in CSF from patients with CNS-LCH lesions compared with patients with brain tumors and other neurodegenerative conditions. Additionally, the presence of BRAFV600E was tested in peripheral mononuclear blood cells (PBMCs) as well as brain biopsies from LCH-ND patients, and the response to BRAF-V600E inhibitor was evaluated in 4 patients with progressive disease. RESULTS Osteopontin was the only consistently elevated CSF protein in patients with CNS-LCH compared with patients with other brain pathologies. BRAFV600E DNA was detected in CSF of only 2/20 (10%) cases, both with LCH-ND and active lesions outside the CNS. However, BRAFV600E PBMCs were detected with significantly higher frequency at all stages of therapy in LCH patients who developed LCH-ND. Brain biopsies of patients with LCH-ND demonstrated diffuse perivascular infiltration by BRAFV600E cells with monocyte phenotype (CD14 CD33 CD163 P2RY12 ) and associated osteopontin expression. Three of 4 patients with LCH-ND treated with BRAF-V600E inhibitor experienced significant clinical and radiologic improvement. CONCLUSION In LCH-ND patients, BRAFV600E cells in PBMCs and infiltrating myeloid/monocytic cells in the brain is consistent with LCH-ND as an active demyelinating process arising from a mutated hematopoietic precursor from which LCH lesion CD207 cells are also derived. Therapy directed against myeloid precursors with activated MAPK signaling may be effective for LCH-ND. Cancer 2018. © 2018 American Cancer Society

Prognostic significance of transcription factors FOXA1 and GATA-3 in ductal carcinoma in situ in terms of recurrence and estrogen receptor status

Aim: The aim was to analyze the expression of novel biological transcription markers, forkhead-box A1 (FOXA1), GATA binding protein 3 (GATA-3), and established markers such as Ki-67 (MIB-1) and human epidermal growth factor receptor 2 (HER2) in estrogen receptor (ER(+)) and ER(-) ductal carcinoma in situ (DCIS) patients with/without recurrence.Methods: Two hundred and ninety-one cases of DCIS were retrieved from our pathology database, with complete data available for 219 cases. The follow-up period is from 1988 to 2009. Recurrence is defined in terms of DCIS or invasive carcinoma (IC). No recurrence was seen in 88% (196/219) of cases; 12% (26/219) had a recurrence (IC: 13, DCIS: 13). We are reporting the results of biological marker expression in terms of recurrence and ER status.Results: Our study demonstrates strong expression of GATA-3 in the ER(+) DCIS in recurrence and nonrecurrence groups similar to previously described in IC. A reduced expression of GATA-3 was observed in ER(-) recurrence and nonrecurrence groups. A strong HER2 protein expression, as well as high proliferation index, was seen in recurrence group (DCIS and IC). FOXA1 expression is reduced across the groups though not statistically significant.Conclusion: This is the first study to analyze novel transcription markers FOXA1 and GATA-3 in DCIS. Further work needs to be done on a larger cohort of DCIS cases with recurrence to better understand, which variables are best able to predict recurrence and guide therapy decision strategies. Maintenance of FOXA1 and GATA-3 expression in ER(-) DCIS may offer new promising targets for therapy in future

Bone marrow-derived myeloid progenitors as driver mutation carriers in high- and low-risk Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a myeloid neoplasia, driven by sporadic activating mutations in the MAPK pathway. The misguided myeloid dendritic cell (DC) model proposes that high-risk, multisystem, risk-organ-positive (MS-RO+) LCH results from driver mutation in a bone marrow (BM)-resident multipotent hematopoietic progenitor, while low-risk, MS-RO2 and single-system LCH would result from driver mutation in a circulating or tissue-resident, DC-committed precursor. We have examined the CD34+c-Kit+Flt3+ myeloid progenitor population as potential mutation carrier in all LCH disease manifestations. This population contains oligopotent progenitors ofmonocytes (Mo's)/macrophages (MFs), osteoclasts (OCs), and DCs. CD34+c-Kit+Flt3+ cells from BM of MS-RO+ LCH patients produced Langerhans cell (LC)-like cells in vitro. Both LC-like and DC offspring from this progenitor carried the BRAF mutation, confirming their common origin. In both high- and low-risk LCH patients, CD34+c-Kit+Flt3+ progenitor frequency in blood was higher than in healthy donors. In oneMS-RO+ LCHpatient, CD34+c-Kit+Flt3+ cell frequency in blood and its BRAF-mutated offspring reported response to chemotherapy. CD34+c-Kit+Flt3+ progenitors from blood of both high- and low-risk LCH patients gave rise to DCs and LC-like cells in vitro, but the driver mutation was not easily detectable, likely due to low frequency of mutated progenitors. Mutant BRAF alleles were found in Mo's /MFs, DCs, LC-like cells, and/or OC-like cells in lesions and/or Mo and DCs in blood of multiple low-risk patients.We therefore hypothesize that in both high- and low-risk LCH, the driver mutation is present in a BM-resident myeloid progenitor that can be mobilized to the blood

Interleukin-18 diagnostically distinguishes and pathogenically promotes human and murine macrophage activation syndrome

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperferritinemic systemic inflammatory disorders. Although profound cytotoxic impairment causes familial HLH (fHLH), the mechanisms driving non-fHLH and MAS are largely unknown. MAS occurs in patients with suspected rheumatic disease, but the mechanistic basis for its distinction is unclear. Recently, a syndrome of recurrent MAS with infantile enterocolitis caused by NLRC4 inflammasome hyperactivity highlighted the potential importance of interleukin-18 (IL-18). We tested this association in hyperferritinemic and autoinflammatory patients and found a dramatic correlation of MAS risk with chronic (sometimes lifelong) elevation of mature IL-18, particularly with IL-18 unbound by IL-18 binding protein, or free IL-18. In a mouse engineered to carry a disease-causing germ line NLRC4T337S mutation, we observed inflammasome-dependent, chronic IL-18 elevation. Surprisingly, this NLRC4T337S-induced systemic IL-18 elevation derived entirely from intestinal epithelia. NLRC4T337S intestines were histologically normal but showed increased epithelial turnover and upregulation of interferon-γ-induced genes. Assessing cellular and tissue expression, classical inflammasome components such as Il1b, Nlrp3, and Mefv predominated in neutrophils, whereas Nlrc4 and Il18 were distinctly epithelial. Demonstrating the importance of free IL-18, Il18 transgenic mice exhibited free IL-18 elevation and more severe experimental MAS. NLRC4T337S mice, whose free IL-18 levels were normal, did not. Thus, we describe a unique connection between MAS risk and chronic IL-18, identify epithelial inflammasome hyperactivity as a potential source, and demonstrate the pathogenicity of free IL-18. These data suggest an IL-18-driven pathway, complementary to the cytotoxic impairment of fHLH, with potential as a distinguishing biomarker and therapeutic target in MAS

Expert consensus recommendations for the diagnosis and treatment of Langerhans cell histiocytosis in adults.

Langerhans cell histiocytosis (LCH) can affect children and adults with wide variety of clinical manifestations, including unifocal, single-system multifocal, single-system pulmonary (smoking-associated), or multisystem disease. The existing paradigms in the management of LCH in adults are mostly derived from the pediatric literature. Over the last decade, the discovery of clonality and MAPK-ERK pathway mutations in most cases led to the recognition of LCH as a hematopoietic neoplasm, opening the doors for treatment with targeted therapies. These advances have necessitated an update of the existing recommendations for the diagnosis and treatment of LCH in adults. This document presents consensus recommendations that resulted from the discussions at the annual Histiocyte Society meeting in 2019, encompassing clinical features, classification, diagnostic criteria, treatment algorithm, and response assessment for adults with LCH. The recommendations favor the use of 18F-Fluorodeoxyglucose positron emission tomography based imaging for staging and response assessment in majority of cases. Most adults with unifocal disease may be cured by local therapies, while the first-line treatment for single-system pulmonary LCH remains smoking cessation. Among patients not amenable or unresponsive to these treatments and/or have multifocal and multisystem disease, systemic treatments are recommended. Preferred systemic treatments in adults with LCH include cladribine or cytarabine, with emerging role of targeted (BRAF- and MEK-inhibitor) therapies. Despite documented response to treatments, many patients struggle with high symptom burden from pain, fatigue, and mood disorders that should be acknowledged and managed appropriately

Childhood-onset Erdheim-Chester disease in the molecular era: clinical phenotypes and long-term outcomes of 21 patients

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BRAF V600E-induced senescence drives Langerhans cell histiocytosis pathophysiology

Langerhans cell histiocytosis (LCH) is a potentially fatal condition characterized by granulomatous lesions with characteristic clonal mononuclear phagocytes (MNPs) harboring activating somatic mutations in mitogen-activated protein kinase (MAPK) pathway genes, most notably BRAFV600E. We recently discovered that the BRAFV600E mutation can also affect multipotent hematopoietic progenitor cells (HPCs) in multisystem LCH disease. How the BRAFV600E mutation in HPCs leads to LCH is not known. Here we show that enforced expression of the BRAFV600E mutation in early mouse and human multipotent HPCs induced a senescence program that led to HPC growth arrest, apoptosis resistance and a senescence-associated secretory phenotype (SASP). SASP, in turn, promoted HPC skewing toward the MNP lineage, leading to the accumulation of senescent MNPs in tissue and the formation of LCH lesions. Accordingly, elimination of senescent cells using INK-ATTAC transgenic mice, as well as pharmacologic blockade of SASP, improved LCH disease in mice. These results identify senescent cells as a new target for the treatment of LCH