Correlation of thymic pathology with HLA in myasthenia gravis

Unraveling molecular networks in thymic epithelial tumors: deciphering the unique signatures

Thymic epithelial tumors (TETs) are a rare and diverse group of neoplasms characterized by distinct molecular signatures. This review delves into the complex molecular networks of TETs, highlighting key aspects such as chromosomal abnormalities, molecular subtypes, aberrant gene mutations and expressions, structural gene rearrangements, and epigenetic changes. Additionally, the influence of the dynamic tumor microenvironment on TET behavior and therapeutic responses is examined. A thorough understanding of these facets elucidates TET pathogenesis, offering avenues for enhancing diagnostic accuracy, refining prognostic assessments, and tailoring targeted therapeutic strategies. Our review underscores the importance of deciphering TETs' unique molecular signatures to advance personalized treatment paradigms and improve patient outcomes. We also discuss future research directions and anticipated challenges in this intriguing field.

Myasthenia gravis-specific aberrant neuromuscular gene expression by medullary thymic epithelial cells in thymoma

Myasthenia gravis (MG) is a neurological disease caused by autoantibodies against neuromuscular-associated proteins. While MG frequently develops in thymoma patients, the etiologic factors for MG are not well understood. Here, by constructing a comprehensive atlas of thymoma using bulk and single-cell RNA-sequencing, we identify ectopic expression of neuromuscular molecules in MG-type thymoma. These molecules are found within a distinct subpopulation of medullary thymic epithelial cells (mTECs), which we name neuromuscular mTECs (nmTECs). MG-thymoma also exhibits microenvironments dedicated to autoantibody production, including ectopic germinal center formation, T follicular helper cell accumulation, and type 2 conventional dendritic cell migration. Cell–cell interaction analysis also predicts the interaction between nmTECs and T/B cells via CXCL12-CXCR4. The enrichment of nmTECs presenting neuromuscular molecules within MG-thymoma is further confirmed immunohistochemically and by cellular composition estimation from the MG-thymoma transcriptome. Altogether, this study suggests that nmTECs have a significant function in MG pathogenesis via ectopic expression of neuromuscular molecules.

Hypofractionated Radiation Therapy Combined With Weekly Chemotherapy in Patients With Unresectable or Recurrent Thymic Epithelial Tumor: A Prospective, Single-Arm Phase 2 Study (GASTO-1042)

PURPOSE

This prospective phase 2 study aimed to evaluate the efficacy and safety of hypofractionated radiation therapy (HRT) combined with concurrent weekly chemotherapy in patients with unresectable or recurrent thymic epithelial tumors (TETs).

METHODS AND MATERIALS

Patients with unresectable or recurrent intrathoracic TETs that could be encompassed within the radiation fields were enrolled. HRT using intensity modulated radiation therapy (IMRT) technique was administered with 3 different levels of radiation doses (51 Gy/17 fractions (fx), 48 Gy/12 fx, and 45 Gy/9 fx; biologically effective dose of 66.3-67.5Gy), combined with weekly docetaxel (25 mg/m²) and nedaplatin (25 mg/m²). Weekly thymosin α1 (1.6 mg) was administered from the start to 2 months after radiation therapy. The objective response rate (ORR), progression-free survival (PFS), overall survival (OS), health-related quality of life (QOL), and toxicity were recorded.

RESULTS

Fifty eligible patients enrolled from August 1, 2018, to July 1, 2020, were analyzed. Most patients (82.0%) had stage IVB tumors. Patients had IMRT-HRT (36-51 Gy in 9-17 fx, median biologically effective dose of 67.2 Gy) and concurrent weekly docetaxel/nedaplatin (2-4 cycles). During a median follow-up of 25.0 months (14.0-40.0), the ORR was 83.7%, the 2-year PFS was 59.1%, and the 2-year OS was 90.0%. There was 1 (2.0%) in-field recurrence while 19 (38.0%) patients developed out-of-field recurrence. Grade 3 pneumonitis was observed in 1 patient (2.0%). The ORR, 2-year PFS, 2-year OS, and toxicity were similar among 3 dose levels. Fourteen (28.0%) patients had 2 to 4 courses of radiation therapy because of recurrent diseases. Only 1 suffered from grade 1 pulmonary fibrosis during follow-up. Most patients (88%) maintained a stable QOL within 1 year after radiation therapy.

CONCLUSIONS

IMRT-HRT and concurrent weekly docetaxel/nedaplatin was effective and well tolerated in unresectable or recurrent TETs. Considering the common out-of-field recurrence, this combined regimen could be an option for repeated radiation therapy. Thymosin α1 might help lower the incidence of pneumonitis and maintain the QOL.

Investigational drugs for the treatment of thymic cancer: a focus on phase 1 and 2 clinical trials

INTRODUCTION

Thymic epithelial tumors (TETs) are rare tumors of thymic epithelial cells. Treatment options for advanced disease patients who failed standard platinum-based chemotherapy are limited.

AREAS COVERED

Phase I and II trials published in the last five years testing new systemic treatments for advanced TET patients are discussed, as well as ongoing trials. A PubMed database literature review was conducted for articles published between January 2016 and December 2021, and ongoing clinical trials were retrieved from ClinicalTrials.gov database.

EXPERT OPINION

The most promising classes of new drugs in TET patients are angiogenesis inhibitors and immune checkpoint antibodies (ICIs). Sunitinib and Lenvatinib showed response rates of 26% and 38%, respectively, and ICIs showed durable responses in 20-25% in thymic carcinoma patients (TCs). Both approaches are mainly active in TCs, therefore new treatment options for thymomas is an unmet medical need.Two major new therapeutic strategies are ICIs combinations with other drugs and drugs that target pathways that are dysregulated in TETs.Future challenges include the development of preclinical models to help identify novel targets and test new treatment strategies, and randomized clinical trials to provide reliable evidence based on survival endpoints.

SARS-CoV-2 Proteome Harbors Peptides Which Are Able to Trigger Autoimmunity Responses: Implications for Infection, Vaccination, and Population Coverage

Autoimmune diseases (ADs) could occur due to infectious diseases and vaccination programs. Since millions of people are expected to be infected with SARS-CoV-2 and vaccinated against it, autoimmune consequences seem inevitable. Therefore, we have investigated the whole proteome of the SARS-CoV-2 for its ability to trigger ADs. In this regard, the entire proteome of the SARS-CoV-2 was chopped into more than 48000 peptides. The produced peptides were searched against the entire human proteome to find shared peptides with similar experimentally confirmed T-cell and B-cell epitopes. The obtained peptides were checked for their ability to bind to HLA molecules. The possible population coverage was calculated for the most potent peptides. The obtained results indicated that the SARS-CoV-2 and human proteomes share 23 peptides originated from ORF1ab polyprotein, nonstructural protein NS7a, Surface glycoprotein, and Envelope protein of SARS-CoV-2. Among these peptides, 21 peptides had experimentally confirmed equivalent epitopes. Amongst, only nine peptides were predicted to bind to HLAs with known global allele frequency data, and three peptides were able to bind to experimentally confirmed HLAs of equivalent epitopes. Given the HLAs which have already been reported to be associated with ADs, the ESGLKTIL, RYPANSIV, NVAITRAK, and RRARSVAS were determined to be the most harmful peptides of the SARS-CoV-2 proteome. It would be expected that the COVID-19 pandemic and the vaccination against this pathogen could significantly increase the ADs incidences, especially in populations harboring HLA-B*08:01, HLA-A*024:02, HLA-A*11:01 and HLA-B*27:05. The Southeast Asia, East Asia, and Oceania are at higher risk of AD development.

Old but gold: the role of drug combinations in improving response to immune check-point inhibitors in thoracic malignancies beyond NSCLC

The introduction of immune checkpoint inhibitors (ICIs) in non-oncogene addicted non-small cell lung cancer (NSCLC) has revolutionized the treatment scenario and led to a meaningful improvement in patient prognosis. Disappointingly, the success of ICI therapy in NSCLC has not been fully replicated in other thoracic malignancies as small cell lung cancer (SCLC), malignant pleural mesothelioma (MPM), and thymic epithelial tumors (TETs), due to the peculiar biological features of these disease and to the difficulties in the conduction of well-designed, biomarker-driven clinical trials. Therefore, combination strategies of ICIs plus conventional therapies (either chemotherapy, alternative ICIs or targeted agents) have been implemented. Although first approvals of ICI therapy have been recently granted in SCLC and MPM (in combination with chemotherapy and different ICIs), results remain somewhat modest and limited to a small proportion of patients. This work reviews the trial results of ICI therapy in mesothelioma, SCLC, and TETs and discusses the potential of combining ICIs with old drugs.

Thymic epithelial tumors: From biology to treatment

In the last few years, meaningful advances have been made in the knowledge of the biology of Thymic Epithelial Tumors (TETs). Data available suggest that in most cases, the different histological subtypes could be distinct biological entities, characterized by specific molecular aberrations, rather than representing a histological continuum of diseases. Recurrent gene mutations in Thymomas and Thymic Carcinoma have been identified, but we still do not know the exact role played by these mutations in TETs pathogenesis. Relevant new data are now available on the pathogenetic mechanisms underlying the association between TETs and autoimmune diseases that warrant further investigations for the potential therapeutic implications. The progress in knowledge of the molecular pathways involved in TETs pathogenesis, allowed to identify and to test target therapies potentially active in such diseases. Platinum-based chemotherapy remains the standard first line treatment for patients with advanced or metastatic TETs. However, some promising data have been reported on the activity of new target therapies, including anti-angiogenic drugs, Cycline Dependent Kinases and PI3K/mTOR inhibitors, as well as of Immune-checkpoint inhibitors. A number of new drugs and combinations are currently under evaluation. The efficacy of new drugs should be balanced with their toxicity profiles, in such complex patients that seem to be more susceptible to develop drug-related toxicities, in particular with immunotherapies.

Associations between HLA and autoimmune neurological diseases with autoantibodies

Recently, several autoimmune neurological diseases have been defined by the presence of autoantibodies against different antigens of the nervous system. These autoantibodies have been demonstrated to be specific and useful biomarkers, and most of them are also pathogenic. These aspects have increased the value of autoantibodies in neurological practice, as they enable to establish more accurate diagnosis and to better understand the underlying mechanisms of the autoimmune neurological diseases when they are compared to those lacking them. Nevertheless, the exact mechanisms leading to the autoimmune response are still obscure. Genetic predisposition is likely to play a role in autoimmunity, HLA being the most reported genetic factor. Herein, we review the current knowledge about associations between HLA and autoimmune neurological diseases with autoantibodies. We report the main alleles and haplotypes, and discuss the clinical and pathogenic implications of these findings.

Human Leucocyte Antigen B50 Is Associated with Conversion to Generalized Myasthenia Gravis in Patients with Pure Ocular Onset

OBJECTIVES

The aim of this study was to investigate the associations between major histocompatibility complex (MHC) class I and II alleles and disease characteristics in Turkish patients with myasthenia gravis (MG).

SUBJECTS AND METHODS

The MHC class I and II alleles of 108 unrelated MG patients were genotyped. The human leucocyte antigen (HLA) distribution of all MG patients and subgroups of MG patients (grouped according to disease characteristics) was compared to that of 250 healthy controls.

RESULTS

Overall distributions of HLA-B*61 and C*05 were more frequent in MG patients (7.4 vs. 2.0% and 14.8 vs. 6.8%, respectively) than in non-MG patients. Subgroup analyses revealed that HLA-DRB1*14 and DQB1*02 alleles were more frequent in early-onset MG [n = 10 (20.8%) vs. n = 25 (10.0%) and n = 21 (43.8%) vs. n = 59 (23.6%)]. In patients seropositive for anti-AchR antibodies, the frequencies of HLA-B*50 and C*05 were higher. HLA-C*05, DRB1*01, and DRB1*11 were higher in patients with ocular MG. In addition, HLA-A*01, A*31, B*08, and DRB1*14 were higher among patients with thymic hyperplasia, whereas DQB1*03 was lower. However, all of these differences lost significance after correction of the p value for multiple comparisons. No allele association was found among patients with thymoma. Strikingly, patients with generalized MG who had pure ocular symptoms at disease onset had significantly increased HLA-B*50 compared to the controls (corrected p < 0.001, OR = 9.92; 95% CI 3.05-32.22).

CONCLUSION

The HLA-B*50 allele was associated with conversion to generalized disease in patients with pure ocular symptoms at disease onset. This finding could extend our understanding of the complex interactions between the pathogenesis of MG and genetic heritage.

Identification and characterisation of peptide binding motifs of six autoimmune disease-associated human leukocyte antigen-class I molecules including HLA-B*39:06

Research on CD8 T cell-mediated inflammatory diseases requires a better understanding of target epitopes and the constraints placed upon these by major histocompatibility complex (MHC) class I binding restrictions, especially those that relate to predisposing alleles. We used linear trap quadrupole fourier transform (LTQ-FT) tandem mass spectrometry to identify naturally processed and presented peptides eluted from the MHC-negative myeloid leukaemia cell line K562 transfected with specific MHC class I genes. We provide information on the peptidome of HLA-B*39:06, which is associated with the autoimmune disease type 1 diabetes, and extend the analysis to include a further five human leukocyte antigen (HLA) alleles (HLA-A*02:01/-A*11:01/-A*24:02/-B*18:01/-B*38:01) studied under identical experimental conditions. We identified a total of 3095 individual peptides with a mascot score ≥40 (HLA-A*02:01 = 569 peptides, -A*11:01 = 904, A*24:02 = 257, -B*18:01 = 615, -B*38:01 = 453, -B*39:06 = 297). Peptides had a preferential length of nine amino acids and originated mainly from cytoplasmic or nuclear proteins. Eluted peptides revealed a strong binding motif with binding anchor positions at position 2 (P2) and the C-terminus (PΩ). Peptides eluted from HLA-A*02:01 showed a P2 preference for leucine (62% of total peptides have Leu at P2) and PΩ preference for valine (49%). Similar data are provided for HLA-A*11:01 (P2:Thr, 29%; PΩ:Lys, 49%), -A*24:02 (P2:Tyr, 78%; PΩ:Phe, 41%), -B*18:01 (P2:Glu, 77%; PΩ:Tyr, 32%), -B*38:01 (P2:His, 51%; PΩ:Leu, 45%) and -B*39:06 (P2:Arg/His, 24%; PΩ:Ala, 64%). This work thus gives an overview of the naturally processed and presented repertoire of several common and autoimmune disease-related HLA alleles, which may be useful in studying autoreactive CD8 T cell responses and the role of HLA in disease susceptibility.

Late-onset myasthenia gravis - CTLA4(low) genotype association and low-for-age thymic output of naïve T cells

Late-onset myasthenia gravis (LOMG) has become the largest MG subgroup, but the underlying pathogenetic mechanisms remain mysterious. Among the few etiological clues are the almost unique serologic parallels between LOMG and thymoma-associated MG (TAMG), notably autoantibodies against acetylcholine receptors, titin, ryanodine receptor, type I interferons or IL-12. This is why we checked LOMG patients for two further peculiar features of TAMG - its associations with the CTLA4(high/gain-of-function) +49A/A genotype and with increased thymic export of naïve T cells into the blood, possibly after defective negative selection in AIRE-deficient thymomas. We analyzed genomic DNA from 116 Caucasian LOMG patients for CTLA4 alleles by PCR/restriction fragment length polymorphism, and blood mononuclear cells for recent thymic emigrants by quantitative PCR for T cell receptor excision circles. In sharp contrast with TAMG, we now find that: i) CTLA4(low) +49G(+) genotypes were more frequent (p = 0.0029) among the 69 LOMG patients with age at onset ≥60 years compared with 172 healthy controls; ii) thymic export of naïve T cells from the non-neoplastic thymuses of 36 LOMG patients was lower (p = 0.0058) at diagnosis than in 77 age-matched controls. These new findings are important because they suggest distinct initiating mechanisms in TAMG and LOMG and hint at aberrant immuno-regulation in the periphery in LOMG. We therefore propose alternate defects in central thymic or peripheral tolerance induction in TAMG and LOMG converging on similar final outcomes. In addition, our data support a 60-year-threshold for onset of 'true LOMG' and an LOMG/early-onset MG overlapping group of patients between 40 and 60.

Correlation between acetylcholine receptor antibody levels and thymic pathology in myasthenia gravis: a review

Myasthenia gravis is the most common chronic autoimmune neuromuscular disease. Anti-acetylcholine receptor (AChR) antibodies are found in at least 80% of patients with generalized myasthenia and have been implicated in disease pathogenesis. Thymic abnormalities are frequently found in seropositive patients, and the thymus is thought to be involved in generation of autoimmunity. This article reviews existing literature on the role of AChR antibodies in the pathogenesis of myasthenia gravis, and the correlation between AChR antibody titers and thymic pathology. Most studies found that highest titers are seen in thymic hyperplasia, followed by intermediate titers in thymoma, and lowest titers in atrophic or normal thymus. One publication found no difference between titers in thymoma and normal thymus.

Late onset myasthenia gravis is associated with HLA DRB1*15:01 in the Norwegian population

Background

Acquired myasthenia gravis (MG) is a rare antibody-mediated autoimmune disease caused by impaired neuromuscular transmission, leading to abnormal muscle fatigability. The aetiology is complex, including genetic risk factors of the human leukocyte antigen (HLA) complex and unknown environmental factors. Although associations between the HLA complex and MG are well established, not all involved components of the HLA predisposition to this heterogeneous disease have been revealed. Well-powered and comprehensive HLA analyses of subgroups in MG are warranted, especially in late onset MG.

Methodology/Principal Findings

This case-control association study is of a large population-based Norwegian cohort of 369 MG patients and 651 healthy controls. We performed comprehensive genotyping of four classical HLA loci (HLA-A, -B, -C and -DRB1) and showed that the DRB1*15:01 allele conferred the strongest risk in late onset MG (LOMG; onset ≥60years) (OR 2.38, p_c7.4×10⁻⁵). DRB1*13:01 was found to be a protective allele for both early onset MG (EOMG) and LOMG (OR 0.31, p_c 4.71×10⁻⁴), a finding not previously described. No significant association was found to the DRB1*07:01 allele (p_nc = 0.18) in a subset of nonthymomatous anti-titin antibody positive LOMG as reported by others. HLA-B*08 was mapped to give the strongest contribution to EOMG, supporting previous studies.

Conclusion

The results from this study provide important new information concerning the susceptibility of HLA alleles in Caucasian MG, with highlights on DRB1*15:01 as being a major risk allele in LOMG.

Thymoma and autoimmunity

The thymus is a central lymphatic organ that is responsible for many immunological functions, including the production of mature, functional T cells and the induction of self-tolerance. Benign or malignant tumors may originate from the thymus gland, with thymoma being the most common and accounting for 50% of anterior mediastinal tumors. Malignancies linked to thymoma include the loss of self-tolerance and the presence of autoimmunity. In this review, we compiled the current scientific evidence detailing the various interactions between thymoma and autoimmune diseases, including myasthenia gravis, systemic lupus erythematosus, inappropriate antidiuretic hormone secretion, pure red cell aplasia, pernicious anemia, pemphigus and autoimmune thyroid diseases. In recent years, several mechanisms have been proposed to explain these interactions. Most are based on the assumption that the 'sick' thymus, like the 'normal' thymus, can generate mature T cells; however, the T cells generated by the sick thymus are impaired and thus may exert cellular autoreactivity. Here, we present several theories that may shed light on the loss of self-tolerance associated with this epithelial tumor of the thymus.

Thymoma and paraneoplastic myasthenia gravis

Paraneoplastic autoimmune diseases associate occasionally with small cell lung cancers and gynecologic tumors. However, myasthenia gravis (MG) occurs in at least 30% of all patients with thymomas (usually present at MG diagnosis). These epithelial neoplasms almost always have numerous admixed maturing polyclonal T cells (thymocytes). This thymopoiesis-and export of mature CD4(+)T cells-particularly associates with MG, though there are rare/puzzling exceptions in apparently pure epithelial WHO type A thymomas. Other features potentially leading to inefficient self-tolerance induction include defective epithelial expression of the autoimmune regulator (AIRE) gene and/or of major histocompatibility complex class II molecules in thymomas, absence of myoid cells, failure to generate FOXP3(+) regulatory T cells, and genetic polymorphisms affecting T-cell signaling. However, the strong focus on MG/neuromuscular targets remains unexplained and suggests some biased autoantigen expression, T-cell selection, or autoimmunization within thymomas. There must be further clues in the intriguing serological and cellular parallels in some patients with late-onset MG but without thymomas-and in others with AIRE mutations-and in the contrasts with early-onset MG, as discussed here.

Thymopoiesis, regulatory T cells, and TCRVbeta expression in thymoma with and without myasthenia gravis, and modulatory effects of steroid therapy

We analyzed thymocyte and thymic regulatory T cell (CD4SPCD25+Foxp3+cells, Treg) development in thymoma with and without myasthenia gravis (MG, MG-thymoma, non-MG-thymoma) and in MG-associated non-neoplastic thymus (MG-NNT). An increased number of immature CD4+CD8(-)CD3(-) thymocytes through the CD4+CD8+ to CD4+CD8(-) transition and an abnormal T cell receptor Vbeta (TCRVbeta) development through the CD4+CD8+ to CD4(-)CD8+ transition were seen both in MG-and non-MG-thymomas. Terminal thymopoiesis, i.e., CD45RA+ cells within the CD4+CD8(-)CD3+ and CD8+CD4(-)CD3+ subsets, was skewed towards the CD4+ compartment in MG-thymoma and CD8+ compartment in non-MG-thymoma, but thymic export was increased only in the latter in keeping with the hypothesis that CD8+ lymphocytes may play a role in the initial stages of autosensitization and in disagreement with the relevance of an increased output of CD4+ T lymphocytes in paraneoplastic MG. Treg level in normal thymus and MG-NNT and both MG- and non-MG-thymoma was similar, and TCRVbeta development in Treg cells was slightly altered in thymoma but irrespective of MG presence. Thus, the relevance of a defective Treg development in MG context remains to be established. Most alterations in thymopoiesis were corrected by therapeutic corticosteroid administration, and the effects of steroid administration may be mediated by thymic microenvironment.

Myasthenia gravis in a patient with pauciarticular juvenile chronic arthritis

There have been reported cases of children with histories of pauciarticular juvenile chronic arthritis (JCA) later developing myasthenia gravis (MG) as young adults. This is intriguing because it had been considered rare to diagnose a second autoimmune disease in a patient with pauciarticular JCA, unlike in those with adult-onset rheumatoid arthritis. We report a case of MG in a 20-year-old woman with a history of pauciarticular JCA. She presented with bilateral ptosis, weakness, and a history of dysphagia. The diagnosis was confirmed with positive serum acetylcholine receptor antibodies (2000 nm/L) and electromyography showing a decremental response to repetitive muscle stimulation. The patient's inflammatory arthritis was quiescent at diagnosis. The patient underwent a surgical thymectomy and was treated with pyridostigmine, intravenous immunoglobulin, and corticosteroids with a fluctuating clinical course. Previous cases have been reported of MG associated with this subtype of JCA, suggesting a connection in autoimmune pathology. The earlier recognition and management of MG in a patient with pauciarticular JCA presenting with weakness may improve the prognosis of this disease.

HLA-DQ Polymorphism in Turkish Patients With Myasthenia Gravis

Genetic susceptibility to myasthenia gravis (MG) is reported frequently and varies depending on the clinical presentation of the patients. HLA-DQ genotyping was performed in 132 patients using polymerase chain reaction and sequence-specific oligonucleotide hybridizations in the Turkish population for the first time in this study. Antibody positivities against acetylcholine receptor and titin were 81 and 27%, respectively. Sixty-five percent of the patients had disease onset before 40 years of age (EOMG). Overall distribution of DQA1*0103 (odds ratio (OR): 0.5) and DQB1*0502 (OR: 1.9) alleles was different in patients and an ethnically matched healthy control group. Among the subgroups, DQB1*02 was significantly more frequent in EOMG (OR: 1.8), in women with MG (OR: 2.4), and in women with EOMG (OR: 2.8), whereas DQA1*0102 and DQB1*502 (OR: 2.3 for both) were increased and DQA1*0103 (OR: 0.04) was decreased in men with MG. Seropositivity was associated with both DQA1*03 (OR: 12.1) and DQB1*0302 (OR: 14.2) in the patient group. DQA1*02 (OR: 4.9) was associated with the presence of anti-titin antibodies, whereas DQA1*0101 (OR: 3.7) and *0102 (OR: 2.9) were more frequent in patients without this antibody. The presence of thymoma in MG was positively associated with DQB1*0301 (OR: 2.8), and DQB1*02 (OR: 0.3) was significantly less frequent in this group. The HLA-DQ associations in subgroups of MG suggest that the heterogeneity of the disease may be influenced by different genes or even by different alleles. DQ alleles have proved to be relatively informative polymorphisms in studying MG.

HLA and smoking in prediction and prognosis of small cell lung cancer in autoimmune Lambert–Eaton myasthenic syndrome

Patients with small cell lung cancer (SCLC) survive longer if they have the antibody-mediated Lambert-Eaton myasthenic syndrome (LEMS), making this autoimmune disorder a prototype disease for studying cancer immunosurveillance. Patients with nontumor LEMS (NT-LEMS) never develop SCLC but are otherwise indistinguishable clinically. Therefore, we have compared immunogenetic factors in SCLC-LEMS and NT-LEMS and studied their role in the pathogenesis of LEMS and survival from SCLC. In 48 British and 29 Dutch Caucasian LEMS patients, we studied clinical symptoms, antibody titers, HLA types and alleles at six nearby located microsatellite loci. Highly significant associations were found in NT-LEMS, which appeared strongest with HLA-B8, but also involved HLA-DQ2, -DR3 and six flanking microsatellite alleles. SCLC-LEMS patients were not different from controls. Smoking was a strong predictor of SCLC. In contrast, HLA-B8 positivity correlated with a decreased risk of SCLC even among the smokers. Moreover, in SCLC-LEMS patients, HLA-B8 positivity correlated with prolonged survival after LEMS onset. We propose that two distinct immunopathogenetic routes can lead to one clinically and serologically indistinguishable autoimmune myasthenic syndrome. HLA-DR3-B8 is strongly associated with LEMS in nontumor patients only. In other LEMS patients, SCLC apparently provides a powerful autoimmunogenic stimulus that overrides HLA restrictions in breaking tolerance to calcium channels. Moreover, negativity for HLA-B8 combined with smoking behavior points more strongly to an underlying SCLC and predicts a worse prognosis in SCLC-LEMS patients.

HLA class II genotypes in Mexican Mestizo patients with myasthenia gravis

Myasthenia gravis is an autoimmune, heterogeneous disorder, characterized by the presence of antibodies against acetylcholine receptors at the neuromuscular junction. There is a strong evidence that an individual's genetic composition is an important predisposing factor for the development of the disease. To correlate HLA class II genotypes with thymic pathology in Mexican Mestizo patients who had been subjected to thymectomy. HLA class II genes were analyzed in 60 patients and in 99 healthy ethnically matched controls. Thymic hyperplasia, atrophy, thymoma, and normal histology were encountered in 56, 33, 8 and 2% of patients, respectively. HLA-DR11 was significantly increased in patients with thymoma compared with healthy controls (pC = 0.001, OR = 13.35, 95% CI 3.5-51.3), compared with the subgroup of hyperplasia patients (pC = 0.005, OR = 15.5, 95% CI 2.78-95.58) and with the atrophy subgroup (pC = 0.04, OR = 10.5, 95% CI 1.75-70.95). This study provides the evidence of an association between HLA class II alleles with clinical and genetic heterogeneity in myasthenia gravis, particularly in those with thymoma (HLA-DR11).

The Role of Thymomas in the Development of Myasthenia Gravis

Thymic pathology occurs in 80-90% of myasthenia gravis patients. Significant associations between different thymic alterations and clinical findings are discussed. To highlight peculiarities in thymoma-associated myasthenia gravis, we briefly review myasthenia gravis associated with thymic lymphofollicular hyperplasia (TFH) and thymic atrophy.

Genetics of autoimmune myasthenia gravis, a model for antibody-mediated autoimmunity in man

Autoimmune myasthenia gravis is an antibody-mediated autoimmune disease of the neuromuscular junction aimed at the muscle acetylcholine receptor. Recent genetic analyses focusing on a nonclass II HLA-linked locus, MYAS1, and on one of the genes encoding the AChR self-antigen, CHRNA1, are discussed.

Recall immune memory: a new tool for generating late onset autoimmune myasthenia gravis

Most patients with autoimmune myasthenia gravis (MG) produce autoantibodies against their muscle acetylcholine receptors (AChR), causing debilitating muscle weakness. Approximately 60% of MG patients first exhibit myasthenic symptoms after the age of 40. Yet, in the C57BL/6 mouse model of MG, older mice are resistant to induction of myasthenia gravis. To understand the immunological basis for this resistance, the effects of age on the B-cell responses to AChR from Torpedo californica, the inducing antigen, were addressed. As expected, the primary B-cell response was lower in 20-month-old mice than in 2-month-old mice; the isotype profile was not altered by age. When mice were re-immunized, the anti-T-AChR titers increased in both young and old animals, suggesting that a memory response was elicited. Importantly, memory B-cells activated in young animals were largely resistant to the age-associated loss of immune function and the recall memory response was vigorous. Furthermore, the antibodies produced in re-stimulated older mice were functional, as evidenced by the appearance of MG symptoms in some of these animals. Thus, by eliciting a recall memory response, the first examples of late onset MG in mice have been generated. By analogy, late onset MG in humans may be due to re-activation of B-cell responses initiated at a younger age.

A limited epidemiological study of seropositive myasthenia gravis in Tayside

Myasthenia gravis is an acquired disorder of the neuromuscular junction characterised by fatiguable weakness of the limbs, bulbar and facial muscles and may be complicated by respiratory muscle weakness and failure. One often confirms the diagnosis by a simple serological test looking for the presence of the nicotinic acetylcholine receptor antibody. However, seronegative myasthenia constitutes about 20% of cases and in the case of ocular myasthenia, only 50% will have the antibody. Therefore, the diagnosis can be less than straightforward especially if the patient presents with vague symptoms such as fatigue or presents to specialities other than neurology or ophthalmology. The fact that the diagnosis may prove to be challenging, compounded by the fact that the condition is relatively rare and that the antibody to the acetylcholine receptor is not always present, epidemiological data is often less than precise and indeed difficult to acquire. We felt it was necessary to try to establish the epidemiological data on seropositive myasthenia gravis in Tayside, (this has never been carried out) bearing in mind the above pitfalls, and see how the incidence compares with similar and previous studies.

Heterogeneous immunogenetic background in Japanese adults with myasthenia gravis

The aim of this study was to elucidate the roles of human leukocyte antigen (HLA) class II genes in disease susceptibility in Japanese adult patients with myasthenia gravis (MG). A number of studies have shown that MG is correlated with DR3 in Caucasians. In Japanese, infantile MG is associated with DR9, but the HLA class II alleles associated with adult MG remains unclear. HLA-DRB1 and DQB1 alleles were determined by genotyping in 75 Japanese adult patients with MG and in 115 race-matched healthy adults. No statistically significant difference was observed in the overall prevalences of DRB1 and DQB1 alleles between MG patients and healthy controls, even when the patients and controls were stratified on the basis of their gender. MG patients with DQB1*0604 were younger and those with DQB1*0402 were older at disease onset than those without (P=0.03 and 0.008, respectively). Concomitant autoimmune thyroid disease was associated with DRB1*0803 (P=0.0009, corrected P=0.04). In addition, anti-acetylcholine receptor antibody levels were significantly higher in patients with DQB1*0604 than in those without (P=0.045). These findings indicate that immunogenetic backgrounds in Japanese adult MG patients are heterogeneous and are apparently different from those in Caucasian patients.

Thymomas alter the T-cell subset composition in the blood: a potential mechanism for thymoma-associated autoimmune disease

Thymomas are the only tumors that are proven to generate mature T cells from immature precursors. It is unknown, however, whether intratumorous thymopoiesis has an impact on the peripheral T-cell pool and might thus be related to the high frequency of thymoma-associated myasthenia gravis. This study shows, using fluorescence-activated cell sorting-based analyses and T-cell proliferation assays, that thymopoiesis and T-cell function in thymomas correspond with immunologic alterations in the blood. Specifically, the proportion of circulating CD45RA+CD8+ T cells is significantly increased in patients with thymoma compared with normal controls, in accordance with intratumorous T-cell development that is abnormally skewed toward the CD8+ phenotype. Moreover, it is primarily the proportion of circulating CD45RA+CD8+ T cells that decreases after thymectomy. The results also demonstrate that T cells reactive toward recombinant autoantigens are distributed equally between thymomas and blood, whereas T-cell responses to foreign antigen (ie, tetanus toxoid) are seen only among circulating T cells and not among thymoma-derived T cells. These functional studies support the hypothesis that thymopoiesis occurring within thymomas alters the peripheral T-cell repertoire. Because many thymomas are enriched with autoantigen-specific T cells, a disturbance of circulating T-cell subset composition by export of intratumorous T cells may contribute to paraneoplastic autoimmune disease arising in patients with thymoma.

Thymomas alter the T-cell subset composition in the blood: a potential mechanism for thymoma-associated autoimmune disease

Thymomas are the only tumors that are proven to generate mature T cells from immature precursors. It is unknown, however, whether intratumorous thymopoiesis has an impact on the peripheral T-cell pool and might thus be related to the high frequency of thymoma-associated myasthenia gravis. This study shows, using fluorescence-activated cell sorting-based analyses and T-cell proliferation assays, that thymopoiesis and T-cell function in thymomas correspond with immunologic alterations in the blood. Specifically, the proportion of circulating CD45RA+CD8+ T cells is significantly increased in patients with thymoma compared with normal controls, in accordance with intratumorous T-cell development that is abnormally skewed toward the CD8+ phenotype. Moreover, it is primarily the proportion of circulating CD45RA+CD8+ T cells that decreases after thymectomy. The results also demonstrate that T cells reactive toward recombinant autoantigens are distributed equally between thymomas and blood, whereas T-cell responses to foreign antigen (ie, tetanus toxoid) are seen only among circulating T cells and not among thymoma-derived T cells. These functional studies support the hypothesis that thymopoiesis occurring within thymomas alters the peripheral T-cell repertoire. Because many thymomas are enriched with autoantigen-specific T cells, a disturbance of circulating T-cell subset composition by export of intratumorous T cells may contribute to paraneoplastic autoimmune disease arising in patients with thymoma.

Thymoma

Thymomas are fascinating tumors because of their multifaceted clinical presentation, including an unrivaled frequency of associated paraneoplastic autoimmune diseases and an astounding histologic heterogeneity. Thus, thymomas challenge the clinician, pathologist, and immunologist alike with complex diagnostic and therapeutic problems in almost all fields of medicine, radiology, nuclear medicine, surgery, radiooncology, and pathology. This review highlights recent progress in these fields, including the new World Health Organization's classification of thymomas, and reports on the beginning discovery of the genetic basis of thymoma oncogenesis and the cellular and molecular immunopathology of thymoma-associated paraneoplastic autoimmunity.