Establishment of a human thymic myoid cell line. Phenotypic and functional characteristics

Targeting autoimmune mechanisms by precision medicine in Myasthenia Gravis

Myasthenia Gravis (MG) is a chronic disabling autoimmune disease caused by autoantibodies to the neuromuscular junction (NMJ), characterized clinically by fluctuating weakness and early fatigability of ocular, skeletal and bulbar muscles. Despite being commonly considered a prototypic autoimmune disorder, MG is a complex and heterogeneous condition, presenting with variable clinical phenotypes, likely due to distinct pathophysiological settings related with different immunoreactivities, symptoms' distribution, disease severity, age at onset, thymic histopathology and response to therapies. Current treatment of MG based on international consensus guidelines allows to effectively control symptoms, but most patients do not reach complete stable remission and require life-long immunosuppressive (IS) therapies. Moreover, a proportion of them is refractory to conventional IS treatment, highlighting the need for more specific and tailored strategies. Precision medicine is a new frontier of medicine that promises to greatly increase therapeutic success in several diseases, including autoimmune conditions. In MG, B cell activation, antibody recycling and NMJ damage by the complement system are crucial mechanisms, and their targeting by innovative biological drugs has been proven to be effective and safe in clinical trials. The switch from conventional IS to novel precision medicine approaches based on these drugs could prospectively and significantly improve MG care. In this review, we provide an overview of key immunopathogenetic processes underlying MG, and discuss on emerging biological drugs targeting them. We also discuss on future direction of research to address the need for patients' stratification in endotypes according with genetic and molecular biomarkers for successful clinical decision making within precision medicine workflow.

Selected Case From the Arkadi M. Rywlin International Pathology Slide Seminar: Atypical Thymoma With Rhabdomyomatous Differentiation

Thymic epithelial neoplasms with foci of rhabdomyomatous differentiation are rare. A case is presented of a primary thymic epithelial neoplasm showing the features of an atypical spindle cell thymoma that contained foci of bland-appearing rhabdomyomatous cells. The histologic and immunohistochemical features of this tumor are discussed along with a review of the literature and the comments from the AMR members to the case.

Pathophysiological mechanisms of autoimmunity

Autoimmune diseases (AIDs) are chronic disorders characterized by inflammatory reactions against self-antigens that can be either systemic or organ specific. AIDs can differ in their epidemiologic features and clinical presentations, yet all share a remarkable complexity. AIDs result from an interplay of genetic and epigenetic factors with environmental components that are associated with imbalances in the immune system. Many of the pathogenic mechanisms of AIDs are also implicated in myasthenia gravis (MG), an AID in which inflammation of the thymus leads to a neuromuscular disorder. Our goal here is to highlight the similarities and differences between MG and other AIDs by reviewing the common transcriptome signatures and the development of germinal centers and by discussing some unresolved questions about autoimmune mechanisms. This review will propose hypotheses to explain the origin of regulatory T (T_reg ) cell defects and the causes of chronicity and specificity of AIDs.

Thymic Germinal Centers and Corticosteroids in Myasthenia Gravis: an Immunopathological Study in 1035 Cases and a Critical Review

The most common form of Myasthenia gravis (MG) is due to anti-acetylcholine receptor (AChR) antibodies and is frequently associated with thymic pathology. In this review, we discuss the immunopathological characteristics and molecular mechanisms of thymic follicular hyperplasia, the effects of corticosteroids on this thymic pathology, and the role of thymic epithelial cells (TEC), a key player in the inflammatory thymic mechanisms. This review is based not only on the literature data but also on thymic transcriptome results and analyses of pathological and immunological correlations in a vast cohort of 1035 MG patients without thymoma. We show that among patients presenting a thymic hyperplasia with germinal centers (GC), 80 % are females, indicating that thymic follicular hyperplasia is mainly a disease of women. The presence of anti-AChR antibodies is correlated with the degree of follicular hyperplasia, suggesting that the thymus is a source of anti-AChR antibodies. The degree of hyperplasia is not dependent upon the time from the onset, implying that either the antigen is chronically expressed and/or that the mechanisms of the resolution of the GC are not efficiently controlled. Glucocorticoids, a conventional therapy in MG, induce a significant reduction in the GC number, together with changes in the expression of chemokines and angiogenesis. These changes are likely related to the acetylation molecular process, overrepresented in corticosteroid-treated patients, and essential for gene regulation. Altogether, based on the pathological and molecular thymic abnormalities found in MG patients, this review provides some explanations for the benefit of thymectomy in early-onset MG patients.

Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society

Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4(+) T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and

Targeted killing of rhabdomyosarcoma cells by a MAP-based human cytolytic fusion protein

The treatment of rhabdomyosarcoma (RMS) is challenging, and the prognosis remains especially poor for high-grade RMS with metastasis. The conventional treatment of RMS is based on multi-agent chemotherapy combined with resection and radiotherapy, which are often marked by low success rate. Alternative therapeutic options include the combination of standard treatments with immunotherapy. We generated a microtubule-associated protein (MAP)-based fully human cytolytic fusion protein (hCFP) targeting the fetal acetylcholine receptor, which is expressed on RMS cells. We were able to express and purify functional scFv35-MAP from Escherichia coli cells. Moreover, we found that scFv35-MAP is rapidly internalized by target cells after binding its receptor, and exhibits specific cytotoxicity toward FL-OH1 and RD cells in vitro. We also confirmed that scFv35-MAP induces apoptosis in FL-OH1 and RD cells. The in vivo potential of scFv35-MAP will need to be considered in further studies.

Human thymus medullary epithelial cells promote regulatory T-cell generation by stimulating interleukin-2 production via ICOS ligand

Natural thymic T regulatory (tTreg) cells maintain tolerance to self-antigen. These cells are generated in the thymus, but how this generation occurs is still controversial. Furthermore, the contribution of thymus epithelial cells to this process is still unclear, especially in humans. Using an exceptional panel of human thymic samples, we demonstrated that medullary thymus epithelial cells (mTECs) promote the generation of tTreg cells and favor their function. These effects were mediated through soluble factors and were mTEC specific since other cell types had no such effect. By evaluating the effects of mTECs on the absolute number of Treg cells and their state of proliferation or cell death, we conclude that mTECs promote the proliferation of newly generated CD25+ cells from CD4+CD25- cells and protect Treg cells from cell death. This observation implicates Bcl-2 and mitochondrial membrane potential changes, indicating that the intrinsic cell death pathway is involved in Treg protection by mTECs. Interestingly, when the mTECs were cultured directly with purified Treg cells, they were able to promote their phenotype but not their expansion, suggesting that CD4+CD25- cells have a role in the expansion process. To explore the mechanisms involved, several neutralizing antibodies were tested. The effects of mTECs on Treg cells were essentially due to interleukin (IL)-2 overproduction by thymus CD4+ T cells. We then searched for a soluble factor produced by mTECs able to increase IL-2 production by CD4+ cells and could identify the inducible T-cell costimulator ligand (ICOSL). Our data strongly suggest a « ménage à trois »: mTEC cells (via ICOSL) induce overproduction of IL-2 by CD25- T cells leading to the expansion of tTreg cells. Altogether, these results demonstrate for the first time a role of mTECs in promoting Treg cell expansion in the human thymus and implicate IL-2 and ICOSL in this process.

Terminally differentiated epithelial cells of the thymic medulla and skin express nicotinic acetylcholine receptor subunit α 3

In the thymus, T cell maturation is influenced by cholinergic signaling, and the predominantly expressed receptor is the α3-subunit of nicotinic acetylcholine receptors, encoded by the chrna3 gene. We here determined its cellular distribution utilizing an appropriate eGFP-expressing reporter mouse strain. Neither T cells (CD4, CD8) nor mesenchymal cells (desmin-positive) expressed eGFP. In the thymic medulla, eGFP-positive cells either were scattered or, more frequently, formed small clusters resembling Hassall's corpuscles. Immunolabeling revealed that these cells were indeed terminally differentiated epithelial cells expressing keratin 10 (K10) but neither typical cortical (K8, K18) nor medullary keratins (K5, K14). These labeling patterns reflected those in the epidermis of the skin, where overlap of K10 and eGFP expression was seen in the stratum granulosum, whereas underlying basal cells displayed K5-immunoreactivity. A substantial portion of thymic eGFP-positive cells was also immunoreactive to chromogranin A, a peptide previously reported in epidermal keratinocytes in the stratum granulosum. Its fragment catestatin has multiple biological activities, including suppression of proinflammatory cytokine release from macrophages and inhibition of α3β4 nAChR. The present findings suggest that its thymic production and/or release are under cholinergic control involving nAChR containing the α3-subunit.

Implication of double-stranded RNA signaling in the etiology of autoimmune myasthenia gravis

OBJECTIVE

Myasthenia gravis (MG) is an autoimmune disease mediated mainly by anti-acetylcholine receptor (AChR) antibodies. The thymus plays a primary role in MG pathogenesis. As we recently showed an inflammatory and antiviral signature in MG thymuses, we investigated whether pathogen-sensing molecules could contribute to an anti-AChR response.

METHODS

We studied the effects of toll-like receptor agonists on the expression of α-AChR and various tissue-specific antigens (TSAs) in human thymic epithelial cell (TEC) cultures. As polyinosinic-polycytidylic acid (poly[I:C]), which mimics double-stranded RNA (dsRNA), stimulated specifically α-AChR expression, the signaling pathways involved were investigated. In parallel, we analyzed the expression of dsRNA-signaling components in the thymus of MG patients, and the relevance of our data was investigated in vivo in poly(I:C)-injected mice.

RESULTS

We demonstrate that dsRNA signaling induced by poly(I:C) specifically triggers the overexpression of α-AChR in TECs and not of other TSAs. A poly(I:C) effect was also observed on MG TECs. This induction is mediated through toll-like receptor 3 (TLR3) and protein kinase R (PKR), and by the release of interferon (IFN)-β. In parallel, human MG thymuses also display an overexpression of TLR3, PKR, and IFN-β. In addition, poly(I:C) injections specifically increase thymic expression of α-AChR in wild-type mice, but not in IFN-I receptor knockout mice. These injections also lead to an anti-AChR autoimmune response characterized by a significant production of serum anti-AChR antibodies and a specific proliferation of B cells.

INTERPRETATION

Because anti-AChR antibodies are highly specific for MG and are pathogenic, dsRNA-signaling activation could contribute to the etiology of MG.

Targeting the fetal acetylcholine receptor in rhabdomyosarcoma

INTRODUCTION

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood and adolescence. Recent efforts to enhance overall survival of patients with clinically advanced RMS have failed and there is a demand for conceptually novel treatments. Immune therapeutic options targeting the fetal nicotinic acetylcholine receptor (fnAChR), which is broadly expressed on RMS, are novel approaches to overcome the therapeutic resistance of RMS. Expression of the fnAChR is restricted to developing fetal muscles, some apparently dispensable ocular muscle fibers and thymic myoid cells. Therefore, after-birth fnAChR is a tumor-associated and almost tumor-specific antigen on RMS cells.

AREAS COVERED

This review gives an overview on nAChR function and expression pattern in RMS tumor cells, and deals with the immunological significance of fnAChR-expressing cells, including the risk of anti-nAChR autoimmunity as a potential side effect of fnAChR-directed immunotherapies. The article also addresses the advantages and disadvantages of vaccination strategies, immunotoxins and chimeric T cells targeting the fnAChR.

EXPERT OPINION

Finally, we suggest technical and biological strategies to improve the available immunotherapeutic tools including increasing the in vivo expression of the target fnAChR on RMS cells.

Neutralizing anti-gH antibody of Varicella-zoster virus modulates distribution of gH and induces gene regulation, mimicking latency

The anti-glycoprotein H (gH) monoclonal antibody (anti-gH-MAb) that neutralizes varicella-zoster virus (VZV) inhibited cell-to-cell infection, resulting in a single infected cell without apoptosis or necrosis, and the number of infectious cells in cultures treated with anti-gH-MAb declined to undetectable levels in 7 to 10 days. Anti-gH-MAb modulated the wide cytoplasmic distribution of gH colocalized with glycoprotein E (gE) to the cytoplasmic compartment with endoplasmic reticulum (ER) and Golgi markers near the nucleus, while gE retained its cytoplasmic distribution. Thus, the disintegrated distribution of gH and gE caused the loss of cellular infectivity. After 4 weeks of treatment with anti-gH-MAb, no infectious virus was recovered, even after cultivation without anti-gH-MAb for another 8 weeks or various other treatments. Cells were infected with Oka varicella vaccine expressing hepatitis B surface antigen (ROka) and treated with anti-gH-MAb for 4 weeks, and ROka was recovered from the quiescently infected cells by superinfection with the parent Oka vaccine. Among the genes 21, 29, 62, 63, and 66, transcripts of gene 63 were the most frequently detected, and products from the genes 63 and 62, but not gE, were detected mainly in the cytoplasm of quiescently infected cells, in contrast to their nuclear localization in lytically infected cells. The patterns of transcripts and products from the quiescently infected cells were similar to those of latent VZV in human ganglia. Thus, anti-gH-MAb treatment resulted in the antigenic modulation and dormancy of infectivity of VZV. Antigenic modulation by anti-gH-MAb illuminates a new aspect in pathogenesis in VZV infection and the gene regulation of VZV during latency in human ganglia.

The first histological and immunohistochemical examination of thymus in a case of fetus in fetu

Fetus in fetu (FIF) is a rare condition with less than 150 cases reported in the world to the best of our knowledge. It is a malformed monozygotic twin ("non-dominant twin"), which is found inside the body of a living child or sometimes in an adult ("dominant twin"). Different organs can be seen in these fetuses; vertebral column limbs, central nervous system, gastrointestinal tract, vessels, and genitourinary tract. In the literature, we found only two cases of fetus in fetu with the present thymic tissue. In this paper, the thymus of non-dominant twin exteriorized from the mediastini of dominant twin, was analyzed by histological and imunohistochemical methods. Even though the majority of organs did not develop normally in the mentioned case, thymic tissue was proved to be present in many body parts of the non-dominant twin. In spite of the fact that the cortex and the medulla were not so distinguishable as in the normal thymuses, presence of many basic cell populations was demonstrated: thymic epithelial cells (AE1/AE3 positive cells), T (CD45RO positive) and B (CD20 positive) cells, macrophages (CD68 positive cells), dendritic cells (S100 positive cells) and myoid cells (desmin positive). The Hassall's bodies were localized mostly in the medulla, however in sporadic cases they occurred in the area close to the connective tissue septa. The superficial epithelial cells of the Hassall's corpuscules as well as their internal contents, were markedly stained by alcian blue, and the cystic formations, found inside the Hassall's bodies, contained PAS-positive substance, similar to Hassall's bodies of normal thymuses. This fact indicates that although development of the parasitic twin is incomplete, all three germ layers participate on its development.

IL-2 and proteoglycans synergistically induce antigen-specific B-cell responses--a possible immune response in the hyperplastic myasthenia thymus

To understand developmental mechanisms of effector B-cells in the hyperplastic MG thymus, we have evaluated immunological roles of IL-2 and the 100-kDa haemopoietic biglycan, because the number of their producers increases pathologically there. When these two factors were added to an immune system together, the number of antibody-producing cells was markedly increased in a synergistic fashion. Further, IL-2 and the conditioned medium of myoid cells induced immunoglobulin isotype switches, suggesting that new B-cell stimulatory microenvironments were generated in the hyperplastic thymus. In relation to this, we also discuss a new biological feature, an immunomodulator, of conventional biglycan and decorin.

Regulatory and pathogenic mechanisms in human autoimmune myasthenia gravis

The thymus is frequently hyperplastic in young female myasthenia gravis (MG) patients presenting with anti-acetylcholine receptor (AChR) antibodies. This thymic pathology is characterized by the presence of ectopic germinal centers (GCs) containing B cells involved at least partially in the production of pathogenic anti-AChR antibodies. Our recent studies have furthered our understanding of the mechanisms leading to GC formation in the hyperplastic thymus. First, we showed that CXCL13 and CCL21, chemokines involved in GC formation, are overexpressed in MG thymus. Second, we demonstrated an increase in pro-inflammatory activity in the thymus from MG patients and its partial normalization by glucocorticoids, as evidenced by gene expression profile. Third, we found that pro-inflammatory cytokines are able to upregulate the expression of AChR subunits in thymic epithelial and myoid cells. Fourth, we showed that the function of T regulatory (Treg) cells, whose role is to downregulate the immune response, is severely impaired in the thymus of MG patients; such a defect could explain the chronic immune activation observed consistently in MG thymic hyperplasia. Altogether, these new data suggest that CXCL13 and CCL21, which are produced in excess in MG thymus, attract peripheral B cells and activated T cells, which are maintained chronically activated in the inflammatory thymic environment because of the defect in suppressive activity of Treg cells. Presence of AChR in the thymus and upregulation of its expression by the pro-inflammatory environment contribute to the triggering and maintenance of the anti-AChR autoimmune response.

Vaccines against myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor (AChR) interfering with the neuromuscular transmission. Experimental autoimmune MG serves as an excellent animal model to study possible therapeutic modalities for MG. This review will focus on the different ways to turn off the autoimmune response to AChR, which results in suppression of myasthenia. This paper will describe the use of fragments or peptides derived from the AChR, antigen-presenting cells and anti-T cell receptor antibodies, and will discuss the underlying mechanisms of action. Finally, the authors propose new promising therapeutic prospects, including treatment based on the modulation of regulatory T cells, which have recently been found to be functionally defective in MG patients.

The chemokine CXCL13 is a key molecule in autoimmune myasthenia gravis

Myasthenia gravis (MG) is associated with ectopic germinal centers in the thymus. Thymectomy and glucocorticoids are the main treatments but they induce operative risks and side effects, respectively. The aim of this study was to propose new therapies more efficient for MG. We hypothesized that molecules dysregulated in MG thymus and normalized by glucocorticoids may play a key role in thymic pathogenesis. Using gene chip analysis, we identified 88 genes complying with these criteria, the most remarkable being the B-cell chemoattractant (CXCL13). Its expression was increased in thymus and sera of glucocorticoid-untreated patients and decreased in response to treatment in correlation with clinical improvement. Normal B cells were actively chemoattracted by thymic extracts from glucocorticoid-untreated patients, an effect inhibited by anti-CXCL13 antibodies. In the thymus, CXCL13 was preferentially produced by epithelial cells and overproduced by epithelial cells from MG patients. Altogether, our results suggest that a high CXCL13 production by epithelial cells could be responsible for germinal center formation in MG thymus. Furthermore, they show that this gene is a main target of corticotherapy. Thus, new therapies targeting CXCL13 could be of interest for MG and other autoimmune diseases characterized by ectopic germinal center formation.

Thymic myoid cells protect thymocytes from apoptosis and modulate their differentiation: implication of the ERK and Akt signaling pathways

Thymic myoid cells correspond to a muscle-like cell population present in the thymic medulla. They are well conserved throughout species evolution, but their biological role is not known. We demonstrated that myoid cells protected thymocytes from apoptosis as evidenced by a strong decrease of annexin-V-FITC positive thymocytes. This effect was (1) specific of myoid cells compared to thymic epithelial cells; (2) dependent on direct cell-to-cell contacts and (3) triggered rapidly after 2 h in cocultures. This protective phenomenon was due to the activation of prosurvival mechanisms. Indeed, myoid cells activated extracellular-regulated kinases (ERK1/2) and Akt in thymocytes. Myoid cells also influenced thymocyte maturation. We observed an increase in CD4(+) and a decrease in CD8(+) single positive (SP) thymocytes when cocultured with myoid cells, independently of a CD8(+)SP increased death or a CD4(+)SP overproliferation. Consequently, thymic myoid cells protect thymocytes from apoptosis and could also modulate their differentiation process.

Effects of cytokines on acetylcholine receptor expression: implications for myasthenia gravis

Myasthenia gravis is an autoimmune disease associated with thymic pathologies, including hyperplasia. In this study, we investigated the processes that may lead to thymic overexpression of the triggering Ag, the acetylcholine receptor (AChR). Using microarray technology, we found that IFN-regulated genes are more highly expressed in these pathological thymic tissues compared with age- and sex-matched normal thymus controls. Therefore, we investigated whether proinflammatory cytokines could locally modify AChR expression in myoid and thymic epithelial cells. We found that AChR transcripts are up-regulated by IFN-gamma, and even more so by IFN-gamma and TNF-alpha, as assessed by real-time RT-PCR, with the alpha-AChR subunit being the most sensitive to this regulation. The expression of AChR protein was increased at the cytoplasmic level in thymic epithelial cells and at the membrane in myoid cells. To examine whether IFN-gamma could influence AChR expression in vivo, we analyzed AChR transcripts in IFN-gamma gene knock-out mice, and found a significant decrease in AChR transcript levels in the thymus but not in the muscle, compared with wild-type mice. However, up-regulation of AChR protein expression was found in the muscles of animals with myasthenic symptoms treated with TNF-alpha. Altogether, these results indicate that proinflammatory cytokines influence the expression of AChR in vitro and in vivo. Because proinflammatory cytokine activity is evidenced in the thymus of myasthenia gravis patients, it could influence AChR expression and thereby contribute to the initiation of the autoimmune anti-AChR response.

Isolation and phenotypical characterization of mesenchymal stem cells from human fetal thymus

Stem cells from human fetal thymus ectomesenchyma capable of forming colonies during in vitro culturing were isolated and characterized. Selection of culturing conditions showed that the growth and phenotypical characteristics of these cultures depended on seeding density and presence of basic fibroblast growth factor in the medium. After nonspecific inhibition of proliferation clonogenic cultures of thymic mesenchymal stem cells differentiated into myoblasts, formed characteristic myotubes, and expressed specific myogenesis markers. Colonies of thymic mesenchymal stem cells differentiated into chondrogenic, osteogenic, and adipogenic lines under conditions described for bone marrow mesenchymal stem cells. Cytofluorometric analysis of surface epitopes of thymic mesenchymal stem cells showed that the majority of cells expressed mesenchymal markers Thy-1, CD44, and CD105. Testing for CD34, CD38, CD45, and HLA-DR were negative in all cases. The main cell population (70-95%) did not express MHCl antigens during long-term culturing.

Novel Cationic Lipids Incorporating an Acid-Sensitive Acylhydrazone Linker: Synthesis and Transfection Properties

Cationic lipid-mediated gene transfection involves uptake of the lipid/DNA complexes via endocytosis, a cellular pathway characterized by a significant drop in pH. Thus, in the present study, we aimed to explore the impact on transfection efficiency of the inclusion of an acid-sensitive acylhydrazone function in the cationic lipid structure. We synthesized and evaluated the transfection properties of a series of four cationic steroid derivatives characterized by an acylhydrazone linkage connecting a guanidinium-based headgroup to a saturated cholestanone or an unsaturated cholest-4-enone hydrophobic domain. Acid-catalyzed hydrolysis was confirmed for all lipids, its rate being highest for those with a cholestanone moiety. The compound bis-guanidinium bis(2-aminoethyl)amine hydrazone (BGBH)-cholest-4-enone was found to mediate efficient gene transfection into various mammalian cell lines in vitro and into the mouse airways in vivo. In vitro transfection studies with BGBH-cholest-4-enone formulations also showed that incorporation of a degradable acylhydrazone bond led to low cytotoxicity and impacted the intracellular trafficking of the lipoplexes. Thus, our work allowed us to identify a cationic lipid structure with an acid-cleavable acylhydrazone linker capable of mediating efficient gene transfection in vitro and in vivo and it thereby provides a basis for further development of related acid-sensitive gene delivery systems.

Rhabdomyomatous Carcinoma of the Thymus

Myoid cells have been described in the thymus in association with a variety of benign and malignant conditions. The presence of a benign rhabdomyomatous component in a malignant primary thymic epithelial neoplasm, however, is extremely rare. A case of poorly differentiated carcinoma of the thymus arising in the posterior mediastinum containing a prominent rhabdomyomatous component is described. The patient, a 70-year-old woman, was seen for a large posterior mediastinal mass. An open chest biopsy revealed an extensively necrotic tumor composed of islands of atypical cells with vesicular nuclei and prominent nucleoli with numerous mitotic figures admixed with abortive glandular structures. Interspersed with the malignant epithelial components were islands of large cells containing brightly eosinophilic cytoplasm and small, round, excentrically placed nuclei. Immunohistochemical studies showed strong positivity of the epithelial cells for cytokeratin and strong positivity of the myoid cells for pan-actin, desmin, and myogenin. The possible relationship of the rhabdomyomatous component of this tumor with the myoid cells of the thymus is discussed.

Determinação imunohistoquímica da presença de células mióides em pacientes submetidos à timectomia

OBJETIVO: Detectar e quantificar células mióides em timos de pacientes com miastenia grave, estabelecendo possível correlação entre a quantidade de células mióides com variáveis demográficas e clínico-patológicas. MÉTODO: Foram analisados por meio de método imuno-histoquímico com anticorpo antidesmina (clone D33; marca Dako), timos de 22 pacientes (16 mulheres e seis homens, entre 12 e 61 anos) submetidos à timectomia, entre 1981 e 1995, no Serviço de Cirurgia Torácica do Hospital Heliópolis como parte do tratamento de miastenia grave. RESULTADOS: As maiores médias de células mióides foram encontrados em timos dos pacientes da raça negra (29,4:17,8), do sexo feminino (23,2:13,0) e com faixa etária entre 60 e 80 anos (média de 33,0). Pela classificação clínica da Fundação de Miastenia Grave da América (MGFA), a maior média de células mióides (26,7) encontra-se na classe IIIa, sendo do tipo histológico de hiperplasia verdadeira (média 42,0). As células mióides foram identificadas em 11 timos com hiperplasia linfóide, três hiperplasias verdadeiras e em quatro timos normais. Os timomas malignos (três) e um timo normal não apresentaram células mióides. CONCLUSÕES: As células mióides podem ser identificadas e quantificadas pelo método imuno-histoquímico com anticorpo antidesmina, porém não existe correlação entre a quantidade de células mióides e as variáveis demográficas, clínico-patológicas. Elas não foram identificadas no timoma fusocelular.

Thymic myoid cells express high levels of muscle genes

To explore the possible contribution of thymic myoid cells in tolerance induction mechanisms, we quantified by real-time RT-PCR, the expression of 12 muscle genes (the five subunits of acetylcholine receptor, Musk, rapsyn, utrophin, ErbB2, ErbB3, troponin T, and MCK) in a human thymic myoid cell line (MITC), compared to thymic epithelial cells (TEC) and thymocytes. Although expression of all the genes analyzed was detected in TEC and thymocytes, the level of expression in these cells was much lower than in MITC, except for -AChR, utrophin and ErbB3 genes. Since myoid cells express high level of most muscle genes and are consistently found in the thymic medulla, they may contribute to the mechanisms involved in the induction and maintenance of immune tolerance.

Aminoglycoside-derived cationic lipids as efficient vectors for gene transfection in vitro and in vivo

BACKGROUND

Cationic lipids are at present very actively investigated for gene transfer studies and gene therapy applications. Basically, they rely on the formation of DNA/lipid aggregates via electrostatic interactions between their cationic headgroup and the negatively charged DNA. Although their structure/activity relationships are not well understood, it is generally agreed that the nature of the positive headgroup impacts on their transfection activity. Thus, we have directed our efforts toward the development of cationic lipids with novel cationic moieties. In the present work, we have explored the transfection potential of the lipophilic derivatives of the aminoglycoside kanamycin A. Indeed, aminoglycosides, which are natural polyamines known to bind to nucleic acids, provide a favorable scaffold for the synthesis of a variety of cationic lipids because of their structural features and multifunctional nature.

METHODS AND RESULTS

We report here the synthesis of a cationic cholesterol derivative characterized by a kanamycin A headgroup and of its polyguanidinylated derivative. The amino-sugar-based cationic lipid is highly efficient for gene transfection into a variety of mammalian cell lines when used either alone or as a liposomal formulation with the neutral phospholipid dioleoylphosphatidylethanolamine (DOPE). Its polyguanidinylated derivative was also found to mediate in vitro gene transfection. In addition, colloidally stable kanamycin-cholesterol/DOPE lipoplexes were found to be efficient for gene transfection into the mouse airways in vivo.

CONCLUSIONS

These results reveal the usefulness of cationic lipids characterized by headgroups composed of an aminoglycoside or its guanidinylated derivative for gene transfection in vitro and in vivo.

Human thymuses express incomplete sets of muscle acetylcholine receptor subunit transcripts that seldom include the delta subunit

In myasthenia gravis (MG) the muscle acetylcholine receptor (AChR) is the target of an immune response that might begin in the thymus. The thymus expresses binding sites for specific ligands of muscle AChR, a complex protein composed of alpha, beta, gamma (or epsilon) and delta subunits. The thymus expresses the AChR alpha subunit, but there is controversy regarding the expression in the thymus of the gamma, epsilon and delta subunits. We investigated the presence of messenger RNA (mRNA) for the different muscle AChR subunits in thymus tissue from 20 healthy subjects and 13 myasthenic patients. We detected mRNA for the alpha and epsilon subunits in all samples, for the beta subunit in all but one sample and for the gamma subunit in most samples although at lower levels than the epsilon subunit. Myasthenic thymuses expressed levels of gamma subunit mRNA similar to control thymuses but more abundant epsilon subunit mRNA. None of the myasthenic thymuses and only two control thymuses expressed detectable delta subunit mRNA. This supports the hypothesis that human thymus may express AChR proteins that do not include the delta subunit. Such receptors, which would have different antigenic structure than the muscle AChRs, might have a role in triggering the autoimmune response that causes MG.