Presence of circulating abnormal CD34+ progenitors in adult Langerhans cell histiocytosis

New insights into the molecular pathogenesis of langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is a rare proliferative disorder characterized by an accumulation of cells sharing the major phenotypic features of cutaneous Langerhans cells. Given its variable clinical evolution, ranging from self-limiting lesions to multisystemic forms with a poor prognosis, in the last decades it has been debated whether LCH might not have a neoplastic rather than an inflammatory nature. However, although the fundamental events underlying the pathogenesis of LCH are still elusive, recent advances have strikingly improved our understanding of the disease. In particular, the identification of multiple interplays between LCH cells and their tumor microenvironment, along with the recognition of the lesional cytokine storm as a key determinant of LCH progression, has substantiated new opportunities for devising targeted therapeutic approaches. Strikingly, the detection of the rapidly accelerated fibrosarcoma isoform B(V600E) gain-of-function mutation as a genetic alteration recurring in more than 50% of patients has fueled the paradoxical picture of LCH as a tumor of the antigen-presenting cells that can evade rejection by the immune system. Thus, new evidence regarding the ontogeny of LCH cells, as well as a better understanding of the putative immune system frustrating strategy in LCH, may help to define the precise pathogenesis.

Cell-specific gene expression in Langerhans cell histiocytosis lesions reveals a distinct profile compared with epidermal Langerhans cells

Langerhans cell histiocytosis (LCH) is a rare disease characterized by heterogeneous lesions containing CD207(+) Langerhans cells (LCs) and lymphocytes that can arise in almost any tissue and cause significant morbidity and mortality. After decades of research, the cause of LCH remains speculative. A prevailing model suggests that LCH arises from malignant transformation and metastasis of epidermal LCs. In this study, CD207(+) cells and CD3(+) T cells were isolated from LCH lesions to determine cell-specific gene expression. Compared with control epidermal CD207(+) cells, the LCH CD207(+) cells yielded 2113 differentially expressed genes (false discovery rate < 0.01). Surprisingly, the expression of many genes previously associated with LCH, including cell-cycle regulators, proinflammatory cytokines, and chemokines, were not significantly different from control LCs in our study. However, several novel genes whose products activate and recruit T cells to sites of inflammation, including SPP1 (osteopontin), were highly overexpressed in LCH CD207(+) cells. Furthermore, several genes associated with immature myeloid dendritic cells were overexpressed in LCH CD207(+) cells. Compared with the peripheral CD3(+) cells from LCH patients, the LCH lesion CD3(+) cells yielded only 162 differentially regulated genes (false discovery rate < 0.01), and the expression profile of the LCH lesion CD3(+) cells was consistent with an activated regulatory T cell phenotype with increased expression of FOXP3, CTLA4, and SPP1. Results from this study support a model of LCH pathogenesis in which lesions do not arise from epidermal LCs but from accumulation of bone marrow-derived immature myeloid dendritic cells that recruit activated lymphocytes.

Langerhans cell histiocytosis: current insights in a molecular age with emphasis on clinical oral and maxillofacial pathology practice

Langerhans cell histiocytosis (LCH) commonly involves the oral and maxillofacial region, and comes to the attention of dental practitioners when a patient presents with orofacial pain and a bony or soft tissue lesion. This is a relatively rare entity, which has made it difficult to investigate the clinical, biologic, and molecular aspects of the disease. Treatment protocols are not well defined, particularly in adults. During the past decade, the Histiocyte Society has formulated various LCH categories, based on risk stratification, and treatment protocols for the pediatric population. Adult trials are currently available through the Histiocyte Society. Although there has been considerable controversy, the neoplastic nature of LCH has been established by demonstrating clonality. LCH symptoms and the development and persistence of LCH lesions have been ascribed to a "chemokine/cytokine storm" due to autocrine and paracrine mechanisms. Discovery of biologic, cytogenetic, and molecular abnormalities in LCH have already affected treatment by providing novel therapeutic targets.

Indeterminate Cell Histiocytosis: A Case Report

Indeterminate cell histiocytosis is a rare neoplasm composed of cells with mixed characteristics of Langerhans cells and non-Langerhans cells. An otherwise healthy, 36-year-old woman presented with asymptomatic generalized papules and nodules that had appeared on all four extremities, the trunk, and cheeks in the previous 6 months. The lesions were firm, painless, non-pruritic, and slightly flesh-yellow or reddish-brown in color. Histopathologic, immunohistochemical examination and electron microscopic studies showed characteristic findings of indeterminate cell histiocytosis: diffuse proliferative histiocytes infiltrating the dermis without epidermotropism or atypia; neoplastic cells expressing markers characteristic of both Langerhans cells (CD1a, S-100) and focal monocytes/macrophages (Factor XIIIa, CD68); and no Birbeck granules within the cytoplasm of the neoplastic cells. Flow cytometry revealed more CD34+ cells in the peripheral blood of the patient than in peripheral blood from a control. Interestingly, the patient responded favorably to psoralen ultraviolet A-range treatment. Herein, we present this case and review the literature.

Malignant Langerhans cell tumor: a case with a favorable outcome associated with the absence of blood dendritic cell proliferation

Malignant Langerhans cell tumor is a rare malignant proliferation of Langerhans cells, with a negative prognosis due to its dissemination throughout the body, leading to death within 1 year. This disease has to be distinguished from Langerhans cell histiocytosis. The favorable evolution of a case of Langerhans cell tumor, characterized by the absence of metastasis 18 months after its occurrence, may be due to the initial treatment, which consisted of complete and large resection of the tumor. The authors searched for abnormal dendritic cells or progenitors in the blood but found no large amounts or proliferation of CD34(+) or CD1a(+) cells at the diagnosis and 1 year later. This case report shows that malignant Langerhans cell tumor is not always a lethal disease. The condition may be related to surgical treatment and the absence of malignant cells in the blood when the diagnosis was performed.

Langerhans cell histiocytosis of the female genital tract: a literature review

Langerhans cell histiocytosis (LCH) is a rare malignant disease involving the accumulation of a monoclonal proliferation of cells in various organs, that phenotypically resemble Langerhans cells (LC). LCH is not merely a hyperplasia of LC, as it typically affects organs that are outside of their normal physiologic distribution. Normal Langerhans cells are bone marrow-derived dendritic cells that populate the epidermis and are distinguished by the presence of Birbeck granules and cell surface protein CD1a. LC act as sentinels; they recognize, internalize, and process antigens encountered in the skin. Upon encountering an antigen, LC become activated with subsequent maturation and induction of their migratory capacity. Langerhans cells in patients with LCH are aberrant and profoundly differ from normal LC. The clinical spectrum of LCH is quite diverse; multiple organs can be affected. "Pure" genital Langerhans cell histiocytosis is a rare presentation, with only 12 previously reported cases. Due to the rarity of this disease, treatment of genital LCH is still very diverse. No modality is proven to be superior in improving patient outcome, and relapses frequently occur after surgery. Dramatic responses of cutaneous and ano-genital lesions to thalidomide and interferons have been reported. We advocate the use of immuno-modulating agents in LCH of the female genital tract first, rather than surgery.