Diverse and Targetable Kinase Alterations Drive Histiocytic Neoplasms.

UNLABELLED: Histiocytic neoplasms are clonal, hematopoietic disorders characterized by an accumulation of abnormal, monocyte-derived dendritic cells or macrophages in Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (non-LCH), respectively. The discovery of BRAF(V600E) mutations in approximately 50% of these patients provided the first molecular therapeutic target in histiocytosis. However, recurrent driving mutations in the majority of patients with BRAF(V600E)-wild-type non-LCH are unknown, and recurrent cooperating mutations in non-MAP kinase pathways are undefined for the histiocytic neoplasms. Through combined whole-exome and transcriptome sequencing, we identified recurrent kinase fusions involving BRAF, ALK, and NTRK1, as well as recurrent, activating MAP2K1 and ARAF mutations in patients with BRAF(V600E)-wild-type non-LCH. In addition to MAP kinase pathway lesions, recurrently altered genes involving diverse cellular pathways were identified. Treatment of patients with MAP2K1- and ARAF-mutated non-LCH using MEK and RAF inhibitors, respectively, resulted in clinical efficacy, demonstrating the importance of detecting and targeting diverse kinase alterations in these disorders. SIGNIFICANCE: We provide the first description of kinase fusions in systemic histiocytic neoplasms and activating ARAF and MAP2K1 mutations in non-Langerhans histiocytic neoplasms. Refractory patients with MAP2K1- and ARAF-mutant histiocytoses had clinical responses to MEK inhibition and sorafenib, respectively, highlighting the importance of comprehensive genomic analysis of these disorders.

Elevated sphingomyelinase and hypercytokinemia in hemophagocytic lymphohistiocytosis.

PURPOSE: Ceramide generated from sphingomyelinase activation has been reported to play a role in cytokine-mediated events. Secretory sphingomyelinase (S-SMase), a product of the acid sphingomyelinase gene, has been found to be derived from many cell types and to exist in human serum. The purpose of the current study was to investigate the serum level of S-SMase. PATIENTS AND METHODS: Three patients with hypercytokinemia caused by hemophagocytic lymphohistiocytosis (HLH) were studied. Serum samples were collected from the three patients with HLH, patients with a deficiency of acid sphingomyelinase, or type B Niemann-Pick disease, and normal controls. The S-SMase activities were determined using 14C-sphingomyelin as a substrate. RESULTS: The serum S-SMase activities were increased 10-to 20-fold in the sera from the three patients with HLH (P < 0.0001). The high S-SMase activity was decreased to the normal level along with the clinical improvement of HLH. CONCLUSIONS: Increased release of S-SMase from cells into the circulation is observed in patients with active HLH. The authors suggest that S-SMase is related to the pathophysiology of hypercytokinemia.

Neuron-specific enolase in hemophagocytic lymphohistiocytosis: a potential indicator for macrophage activation?

To determine the pathogenesis of hemophagocytic lymphohistiocytosis (HLH), serum levels of neuron-specific enolase (NSE) and cytokine profiles were investigated. Serum concentrations of NSE and several cytokines were measured by immunoassays, and the association was evaluated in 18 HLH patients. Serum NSE levels increased (> 10 ng/mL) in 27/29 samples (93%) during the active febrile phase, the mean level of which (35.9 ng/mL) was much higher than that during the remission phase (11.2 ng/mL) (P = .001). The peak levels of NSE in 11 patients who required cytotoxic agents were higher than those in 7 patients without chemotherapy, 64.6 +/- 49.4 and 17.9 +/- 12.9, respectively (P = .265). The NSE levels correlated positively with the levels of interferon (IFN)-gamma (Pearson's correlation coefficient [r] = 0.408, P = .044), soluble interleukin-2 receptor (sIL-2R) (r = 0.464, P = .048), lactate dehydrogenase (r = 0.830, P < .00001), aspartate aminotransferase (r = 0.531, P = .003), and ferritin (r = 0.715, P < .00001), and correlated negatively with platelet count (r = -0.422, P = .021), but not with other parameters, including tumor necrosis factor-alpha, IL-1 beta, IL-18, soluble Fas ligand and C-reactive protein. Multiple regression analysis indicated that the correlation of NSE with platelet count was independent of other correlations. Sequential NSE changes well reflected the clinical course of patients. Immunohistochemical staining revealed an appreciable number of NSE-positive histiocytes in bone marrow specimens with florid hemophagocytosis. These results suggest that the circulating NSE originated from macrophages stimulated with IFN-gamma/sIL-2R, and partly from the destruction of platelets. Serum NSE level may be a useful marker for predicting the disease progression of HLH.

Platelet-activating factor acetylhydrolase and haemophagocytosis in the sepsis syndrome.

Sepsis syndrome (SS) is associated with depressed PAF acetylhydrolase, the enzyme responsible for the degradation of platelet activating factor. PAF acetylhydrolase is in a large part produced by macrophages, whose inadequate activation with haemophagocytosis is frequent in patients with SS. The aim of this study was to test the hypothesis that PAF acetylhydrolase levels could be affected in these critically ill patients, because of the large amounts produced by activated macrophages in vitro and in vivo in animal models. The levels of serum PAF acetylhydrolase were assessed in 90 SS patients, who were divided into three groups: patients with (n = 34) or without haemophagocytosis (n = 31), and patients without thrombocytopenia (n = 25) who were used as a control group. The number of organ dysfunctions was matched between patients with haemophagocytosis and controls. Normal reference values were obtained in 59 randomly selected blood donors. Circulating levels of PAF acetylhydrolase were significantly (p = 0.0001) decreased in patients with SS (57+/-3 nmol/ml/min, n = 90) when compared with healthy subjects (69+/-3 nmol/ml/min, n = 59). PAF acetylhydrolase levels were greater in the presence of a haemophagocytosis but without statistical significance (64.2+/-6.5 vs. 50.1+/-2.8:p = 0.25). Despite the fact that macrophagic activation stimulates the in vitro release of PAF acetylhydrolase, no difference was found between patients with or without haemophagocytosis. The mechanism and the role of the PAF acetylhydrolase reduction in SS patients remain to be determined.

Induction of apoptosis and caspase activation in cells obtained from familial haemophagocytic lymphohistiocytosis patients.

Familial haemophagocytic lymphohistiocytosis (FHL) is a rare and uniformly fatal disorder of early childhood characterized by fever, hepatosplenomegaly, cytopenia and widespread infiltration of vital organs by activated lymphocytes and macrophages. In order to test whether the massive accumulation of immune cells in these patients is associated with a perturbation of apoptosis, lymphocytes were isolated from eight patients and subjected to the chemotherapeutic agent etoposide or agonistic anti-Fas monoclonal antibodies in vitro. These stimuli elicited a normal apoptotic response in FHL patient cells when compared to healthy controls, as determined by phosphatidylserine exposure, DNA fragmentation, in vitro cleavage of the caspase-3-like substrate aspartate-glutamate-valine-aspartate-7-amino-4-methyl-coumarin (DEVD-AMC) and proteolysis of the anti-apoptotic protein Bcl-2. In addition, the degree of constitutive and Fas-triggered apoptosis in freshly isolated neutrophils was monitored in three children, with similar results. These studies indicate that immune cells derived from FHL patients are not inherently resistant to apoptosis induction. Specifically, etoposide-induced and Fas-triggered activation of intracellular caspases appears to remain intact in these individuals. However, the degree of spontaneous activation of caspase-3-like enzymes in activated lymphocytes was attenuated in three of the four patients tested prior to initiation of therapy, suggesting a possible biological deficiency in these individuals.

Reduced Tyk2/SHP-1 interaction and lack of SHP-1 mutation in a kindred of familial hemophagocytic lymphohistiocytosis.

Familial hemophagocytic lymphohistiocytosis (FHLH) is an autosomal recessive disease with features similar to those of the murine motheaten phenotype resulting from mutations of protein tyrosine phosphatase SHP-1. This has raised the possibility that defects in SHP-1 or SHP-1-regulated signaling molecules may be present in FHLH. In this study, we examined SHP-1 protein and transcript in the peripheral blood mononuclear cells (PBMC) of an FHLH family. Our results show that the FHLH patient and the parents express comparable levels of a single SHP-1 protein and that the SHP-1 cDNA clone from the patient contains no mutation in the coding region. Interestingly, a reduced association of SHP-1 with the Jak family kinase Tyk2 was detected in the patient and the defect appears to have been inherited from one of the parents. This reduced SHP-1/Tyk2 association is likely due to a defect in Tyk2 or in cellular factors regulating Tyk2, because we found no abnormalities in SHP-1 or in SHP-1 association with the other Jak kinases. These data demonstrate that the SHP-1 gene is intact in FHLH and that the defect in some cases with this disease may involve signaling molecules regulated by SHP-1.

Increasing values of serum acid phosphatase in a child with Mycoplasma pneumoniae-associated hemophagocytic histiocytic syndrome.

We describe a 3 1/2-year-old boy with disseminated histiocytic disease probably induced by Mycoplasma pneumoniae. In this patient, acid phosphatase was elevated in serum and was also detected histochemically in the infiltrating histiocytes. The serum acid phosphatase levels increased as his histiocytosis progressed, apparently mirroring the activity of the disease. This observation suggests that serum acid phosphatase levels should be evaluated further to determine whether they will be a useful indicator of disease in children with different histiocytosis syndromes.

Expression of neuron-specific enolase immunoreactivity by cutaneous and extracutaneous Langerhans-cell histiocytoses ("X").

The immunohistochemical expression of Neuron-Specific Enolase (NSE) and of S100 protein was studied in 10 cases of cutaneous and 19 cases of extracutaneous Langerhans cell histiocytoses (LCH), including acute/proliferative forms (cutaneous Letterer-Siwe disease) and chronic/granulomatous forms (eosinophilic granuloma, Hand-Schüller-Christian disease). Of the LCH cases, 18 (62%) exhibited detectable NSE-immunoreactivity as compared to 82.8% for S100. NSE expression was found more frequently and intensely within acute (as compared to chronic) forms of LCH. This result lends further support to the cellular unicity of LCH, but also suggests some degree of heterogeneity among LCH cells. It can be speculated that NSE-expression is correlated with the proliferation/activation state of (abnormal) Langerhans cells.

Reticulohistiocytoma of the limbus and cornea. A clinicopathologic study of two cases.

Reticulohistiocytoma is a rare, benign histiocytic lesion usually occurring as an isolated skin nodule or as part of a systemic disorder known as "multicentric reticulohistiocytosis." The clinical and histopathologic findings of two women who presented with a single, painless mass localized to the cornea and limbus without skin lesions or systemic disease are reported. Histopathologically, the lesions were composed predominantly of large mononuclear and a few multinucleated cells with finely granular, "ground-glass" cytoplasm and large nuclei with prominent nucleoli. Immunohistochemical and electron microscopic studies conformed the histiocytic nature of these cells. Reticulohistiocytoma should be included in the differential diagnosis of epibulbar benign histiocytic lesions.