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Trained immunity (TI) is a proinflammatory program induced in monocyte/macrophages upon sensing of specific pathogens and is characterized by immunometabolic and epigenetic changes that enhance cytokine production. Maladaptive activation of TI (ie, in the absence of infection) may result in detrimental inflammation and development of disease; however, the exact role and extent of inappropriate activation of TI in the pathogenesis of human diseases is undetermined. In this study, we uncovered the oncogene-induced, maladaptive induction of TI in the pathogenesis of a human inflammatory myeloid neoplasm (Erdheim-Chester disease, [ECD]), characterized by the BRAFV600E oncogenic mutation in monocyte/macrophages and excess cytokine production. Mechanistically, myeloid cells expressing BRAFV600E exhibit all molecular features of TI: activation of the AKT/mammalian target of rapamycin signaling axis; increased glycolysis, glutaminolysis, and cholesterol synthesis; epigenetic changes on promoters of genes encoding cytokines; and enhanced cytokine production leading to hyperinflammatory responses. In patients with ECD, effective therapeutic strategies combat this maladaptive TI phenotype; in addition, pharmacologic inhibition of immunometabolic changes underlying TI (ie, glycolysis) effectively dampens cytokine production by myeloid cells. This study revealed the deleterious potential of inappropriate activation of TI in the pathogenesis of human inflammatory myeloid neoplasms and the opportunity for inhibition of TI in conditions characterized by maladaptive myeloid-driven inflammation., (© 2021 by The American Society of Hematology.)

Langerhans cell histiocytosis (LCH) and the non-LCH neoplasm Erdheim-Chester disease (ECD) are heterogeneous neoplastic disorders marked by infiltration of pathologic macrophage-, dendritic cell-, or monocyte-derived cells in tissues driven by recurrent mutations activating MAPK signaling. Although recent data indicate that at least a proportion of LCH and ECD patients have detectable activating kinase mutations in circulating hematopoietic cells and bone marrow-based hematopoietic progenitors, functional evidence of the cell of origin of histiocytosis from actual patient materials has long been elusive. Here, we provide evidence for mutations in MAPK signaling intermediates in CD34 + cells from patients with ECD and LCH/ECD, including detection of shared origin of LCH and acute myelomonocytic leukemia driven by TET2 -mutant CD34 + cell progenitors in one patient. We also demonstrate functional self-renewal capacity for CD34 + cells to drive the development of histiocytosis in xenotransplantation assays in vivo. These data indicate that the cell of origin of at least a proportion of patients with systemic histiocytoses resides in hematopoietic progenitor cells prior to committed monocyte/macrophage or dendritic cell differentiation and provide the first example of a patient-derived xenotransplantation model for a human histiocytic neoplasm., (© 2017 by The American Society of Hematology.)

Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD) are rare histiocytic disorders induced by somatic mutation of MAPK pathway genes. BRAF V600E 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, BRAF V600E allele-specific polymerase chain reaction was used to map the neoplastic clone in 20 adults with LCH, ECD, and HCL. BRAF V600E 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 BRAF V600E 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., (© 2017 by The American Society of Hematology.)

The BRAF V600E mutation is one of the most common mutations implicated in the development of several types of cancer including colorectal cancer (CRC), where it is associated with aggressive disease phenotypes and poor outcomes. The status of the BRAF V600E mutation is frequently determined by direct DNA sequencing. However, no previous study has sought to quantify the BRAF V600E protein in cancer specimens. Here, we evaluated immunoenrichment coupled with two MS-based quantitative techniques, namely multiple reaction monitoring (MRM) and single ion monitoring conjugated accurate inclusion mass screening (SIM-AIMS), to detect and precisely quantify wild-type (WT) and V600E mutant BRAF proteins in DNA sequence-confirmed CRC tissue specimens. WT and V600E BRAF proteins were immunoprecipitated from a CRC cell line (HT-29), and their representative peptides ((592)IGDFGLATVK(601) and (592)IGDFGLATEK(601), respectively) were confirmed by LC-MS/MS analysis and then quantified by MRM or SIM-AIMS with spiked stable isotope-labeled peptide standards. Both assays worked well for measuring WT BRAF from different amounts of HT-29 cell lysates, but the MRM assay was more sensitive than SIM-AIMS assay for quantifying lower levels of V600E BRAF. In protein extracts (2 mg) from 11 CRC tissue specimens, the MRM assay could measure WT BRAF in all 11 cases (0.32-1.66 ng) and the V600E BRAF in two cases (0.1-0.13 ng; mutant-to-WT ratio, 0.16-0.17). The SIM-AIMS assay could also detect WT and V600E BRAF in CRC specimens, but the measured levels of both targets were lower than those determined by MRM assay. Collectively, this study provides an effective method to precisely quantify WT and V600E BRAF proteins in complex biological samples using immunoenrichment-coupled targeted MS. Since the V600E BRAF protein has emerged as an important therapeutic target for cancer, the developed assay should facilitate future BRAF-related basic and clinical studies., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Since 2006 when we last reviewed the literature concerning the use of purine analogues in hairy cell leukaemia (HCL), results from several new and updated series have been published. Here we examine these reports and consider their implications for patient management. The two purine analogues pentostatin and cladribine remain the first-line treatments of choice for all patients with HCL. Although they have not been compared in randomised trials, they appear to be equally effective. A complete response is important for the long-term outcome and we look at how best this can be achieved. Evidence is emerging which supports the use of either purine analogue plus an anti-CD20 monoclonal antibody after relapse, though questions remain concerning the scheduling of the monoclonal antibody. Patients refractory to the purine analogues may require alternative agents., (Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Hairy cell leukemia (HCL) is an indolent B-cell malignancy effectively treated but not often cured by purine analog therapy; after multiple courses of purine analogs, patients can become purine analog resistant and in need of alternative therapies. Complete remission to single-agent purine analog is often accompanied by minimal residual disease (MRD), residual HCL cells detectable by immunologic methods, considered a risk factor for eventual relapse. Several different non-chemotherapy approaches are being used to target relapsed and refractory HCL, including inhibitors of BRAF, but so far only monoclonal antibody (MAb)-based approaches have been reported to eliminate MRD in a high percentage of patients. One of the MAb-based options for HCL currently under clinical investigation involves recombinant immunotoxins, containing a fragment of a MAb and a bacterial toxin. The bacterial toxin, a highly potent fragment from Pseudomonas exotoxin, catalytically ADP-ribosylates elongation factor 2 (EF2), resulting in protein synthesis inhibition and apoptotic cell death. Recombinant immunotoxins tested in HCL patients include LMB-2, targeting CD25, and BL22, targeting CD22. An affinity matured version of BL22, termed moxetumomab pasudotox (formerly HA22 or CAT-8015) achieved high CR rates in phase I, and is currently undergoing multicenter Phase 3 testing. Phase I testing was without dose-limiting toxicity, although 2 patients had grade 2 hemolytic uremic syndrome (HUS) with transient grade 1 abnormalities in platelets and creatinine. Preclinical work is underway to identify residues on moxetumomab pasudotox leading to immunogenicity. Moxetumomab pasudotox is undergoing pivotal testing for relapsed and refractory HCL., (Published by Elsevier Ltd.)

Hairy cell leukaemia is a rare chronic neoplastic B-cell lymphoproliferation that characteristically involves blood, bone marrow and spleen with liver, lymph node and skin less commonly involved. Histologically, the cells have a characteristic appearance with pale/clear cytoplasm and round or reniform nuclei. In the spleen, the infiltrate involves the red pulp and is frequently associated with areas of haemorrhage (blood lakes). The cells stain for B-cell related antigens as well as with antibodies against tartrate-resistant acid phosphatase, DBA44 (CD72), CD11c, CD25, CD103, CD123, cyclin D1 and annexin A1. Mutation of BRAF -V600E is present and antibody to the mutant protein can be used as a specific marker. Bone marrow biopsy is essential in the initial assessment of disease as the bone marrow may be inaspirable or unrepresentative of degree of marrow infiltration as a result of the tumour associated fibrosis preventing aspiration of the tumour cell component. Bone marrow biopsy is important in the assessment of therapy response but in this context staining for CD11c and Annexin A1 is not helpful as they are also markers of myeloid lineage and identification of low level infiltration may be obscured. In this context staining for CD20 may be used in conjunction with morphological assessment and staining of serial sections for cyclin D1 and DBA44 to identify subtle residual infiltration. Staining for CD79a and CD19 is not recommended as these antibodies will identify plasma cells and can lead to over-estimation of disease. Staining for CD20 should not be used in patients following with anti-CD20 based treatments. Down regulation of cyclin D1 and CD25 has been reported in patients following BRAF inhibitor therapy and assessment of these antigens should not be used in this context. Histologically, hairy cell leukaemia needs to be distinguished from other B-cell lymphoproliferations associated with splenomegaly including splenic marginal zone lymphoma, splenic diffuse red pulp small B-cell lymphoma and hairy cell leukaemia variant. This can be done by assessment of the spleen but as this is now rarely performed in this disorder distinction is almost always possible by a combination of morphological and immunophenotypic studies on bone marrow trephine biopsy, which can be supplemented by assessment of BRAF-V600E mutation assessment in borderline cases., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Since its discovery in 1923 and further characterization in 1958, hairy cell leukemia (HCL) has undergone enormous advances in the understanding of the biology and treatment of the disease. Initially a uniformly fatal disease, new therapies in rapid succession transformed HCL into a chronic disease with a normal life expectancy in many cases. More recently, the identification of BRAFV600E mutations in the majority of patients with classic HCL have enabled targeted therapies as a therapeutic option. Additional discoveries into the biology of the disease have identified new subtypes of HCL. Modern approaches to the evaluation and treatment of HCL include detailed molecular analysis which informs therapeutic options, which may consist of traditional therapies such as purine nucleoside analogs, or targeted therapies with antibodies, BTK inhibitors, or BRAF inhibitors, or combination therapy. Because HCL is a rare disease, continued progress depends on patients being enrolled on clinical trials whenever possible., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Success in the treatment of patients with hairy cell leukemia (HCL) over the last several decades is largely due to the high efficacy of the nucleoside analogs, cladribine and pentostatin. However, the relapse-free survival curves have not shown a plateau and many patients treated with these agents will eventually relapse. Although better understanding of the pathogenic mechanisms in HCL have led to effective and novel options for the treatment of relapse, long term durability of the responses obtained with these agents still remains unclear. Combination of nucleoside analogs with monoclonal antibodies such as rituximab has been shown to be safe and effective and has the potential to supersede the nucleoside analogs as the frontline strategy. Such chemo-immunotherapy approaches are under further investigation and will have to be assessed with socioeconomic considerations in mind. Other novel monoclonal antibodies, approved for the treatment of other lymphoid neoplasms, may also be considered for future studies of chemo-immunotherapy., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This brief review highlights the sequence of therapeutic milestones and advances in our understanding of the biology of hairy cell leukemia (HCL) with a focus on recent molecular findings and how these may be applied to improve disease outcomes in the future. Targeted therapy is discussed in the context of the recently identified BRAF mutation and other genetic findings., Competing Interests: None., (Copyright © 2015. Published by Elsevier Ltd.)

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes cartilage and bone destruction. The mechanisms leading to RA are unknown. There is currently no reliable cure for RA. Early treatment can reduce inflammation, joint damage and bone destruction. Thus, early diagnosis of RA is critical. However, definitive diagnosis of RA can be difficult. Immunologic tests that can be performed for the diagnosis of RA include detection of anti citrullinated protein antibodies (ACPAs). However, one third of RA patients have no ACPAs. To identify new autoantibodies in RA, we used the sera of RA patients to screen protein arrays containing 8000 human proteins. We found and validated two major autoantigens: PAD4 (peptidyl arginine deiminase 4) and BRAF (v raf murine sarcoma viral oncogene homolog B1) catalytic domain. We identified peptide targets of anti PAD4 and BRAF autoantibodies. We observed that anti PAD4 are inhibitory whereas anti BRAF stimulate BRAF activity. Anti PAD4 and anti BRAF antibodies may be used to diagnose RA, particularly in the absence of anti citrullinated protein antibodies., (Copyright © 2012 Elsevier B.V. All rights reserved.)