Profound systemic alteration of the immune phenotype and an immunoglobulin switch in Erdheim-Chester disease in 78 patients from a single center.

Erdheim-Chester disease (ECD) is a rare, systemic, non-Langerhans cell histiocytosis neoplasm, which is characterized by the infiltration of CD63+ CD1a- histiocytes in multiple tissues. The BRAFV600E mutation is frequently present in individuals with ECD and has been detected in hematopoietic stem cells and immune cells from the myeloid and systemic compartments. Immune cells and pro-inflammatory cytokines are present in lesions, suggesting that ECD involves immune cell recruitment. Although a systemic cytokine T-helper-1-oriented signature has been reported in ECD, the immune cell network orchestrating the immune response in ECD has yet to be described. To address this issue, the phenotypes of circulating leukocytes were investigated in a large, single-center cohort of 78 patients with ECD and compared with those of a group of 21 control individuals. Major perturbations in the abundance of systemic immune cells were detected in patients with ECD, with decreases in circulating plasmacytoid, myeloid 1, and myeloid 2 dendritic cells, mostly in BRAFV600E carriers, in comparison with individuals in the control group. Similarly, marked decreases in blood Thelper, cytotoxic, and B-lymphocyte numbers were observed in patients with ECD, relative to the control group. Measurement of circulating immunoglobulin concentrations revealed an immunoglobulin G switch, from IgG1 to IgG4 subclasses, which are more frequently associated with the BRAF mutation. First-line therapies, including pegylated interferon-a and vemurafenib, were able to correct most of these alterations. This study reveals a profound disturbance in the systemic immune phenotype in patients with ECD, providing important new information, helping to understand the physiopathological mechanisms involved in this rare disease and improving the therapeutic management of patients.

Hypoalphalipoproteinemia and BRAFV600E Mutation Are Major Predictors of Aortic Infiltration in the Erdheim-Chester Disease.

Objective- Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis characterized by the infiltration of multiple tissues with lipid-laden histiocytes. Cardiovascular involvement is frequent in ECD and leads to a severe prognosis. The objective of this study was to determine whether an alteration of lipid metabolism participates in the lipid accumulation in histiocytes and the cardiovascular involvement in ECD. Approach and Results- An analysis of plasma lipid levels indicated that male ECD patients carrying the BRAFV600E (B-Raf proto-oncogene, serine/threonine kinase) mutation exhibited hypoalphalipoproteinemia, as demonstrated by low plasma HDL-C (high-density lipoprotein cholesterol) levels. Capacity of sera from male BRAFV600E ECD patients to mediate free cholesterol efflux from human macrophages was reduced compared with control individuals. Cardiovascular involvement was detected in 84% of the ECD patients, and we reported that the presence of the BRAFV600E mutation and hypoalphalipoproteinemia is an independent determinant of aortic infiltration in ECD. Phenotyping of blood CD14+ cells, the precursors of histiocytes, enabled the identification of a specific inflammatory signature associated with aortic infiltration which was partially affected by the HDL phenotype. Finally, the treatment with vemurafenib, an inhibitor of the BRAFV600E mutation, restored the defective sera cholesterol efflux capacity and reduced the aortic infiltration. Conclusions- Our findings indicate that hypoalphalipoproteinemia in male ECD patients carrying the BRAFV600E mutation favors the formation of lipid-laden histiocytes. In addition, we identified the BRAF status and the HDL phenotype as independent determinants of the aortic involvement in ECD with a potential role of HDL in modulating the infiltration of blood CD14+ cells into the aorta.