Three-color flow cytometric study on lymphocytes derived from thymic diseases

Autoimmunity in thymic epithelial tumors: a not yet clarified pathologic paradigm associated with several unmet clinical needs

Thymic epithelial tumors (TETs) are rare mediastinal cancers originating from the thymus, classified in two main histotypes: thymoma and thymic carcinoma (TC). TETs affect a primary lymphoid organ playing a critical role in keeping T-cell homeostasis and ensuring an adequate immunological tolerance against "self". In particular, thymomas and not TC are frequently associated with autoimmune diseases (ADs), with Myasthenia Gravis being the most common AD present in 30% of patients with thymoma. This comorbidity, in addition to negatively affecting the quality and duration of patients' life, reduces the spectrum of the available therapeutic options. Indeed, the presence of autoimmunity represents an exclusion criteria for the administration of the newest immunotherapeutic treatments with checkpoint inhibitors. The pathophysiological correlation between TETs and autoimmunity remains a mystery. Several studies have demonstrated the presence of a residual and active thymopoiesis in adult patients affected by thymomas, especially in mixed and lymphocytic-rich thymomas, currently known as type AB and B thymomas. The aim of this review is to provide the state of art in regard to the histological features of the different TET histotype, to the role of the different immune cells infiltrating tumor microenvironments and their impact in the break of central immunologic thymic tolerance in thymomas. We discuss here both cellular and molecular immunologic mechanisms inducing the onset of autoimmunity in TETs, limiting the portfolio of therapeutic strategies against TETs and greatly impacting the prognosis of associated autoimmune diseases.

Flow Cytometric Analysis of Mediastinal Masses in Cats: A Retrospective Study

Mediastinal masses occur in dogs and cats and are often investigated with cytology. However, discrimination between the two most common lesions (thymoma and lymphoma) may be challenging, especially when small/medium lymphocytes represent the prevalent population. The aim of the present study is to describe the flow cytometric aspects of mediastinal masses in cats and to assess the ability of flow cytometry (FC) to differentiate lymphoma from non-lymphomatous lesions. We retrospectively describe FC features of fine needle aspiration cytology from cats with mediastinal masses. Cases were grouped in lymphoma and non-lymphoma based on results of cytology, histopathology, PCR for antigen receptor rearrangement (PARR), clinical presentation, and follow-up. Scatter properties, positivities to CD5, CD4, CD8, CD21, CD18, and their co-expressions were recorded using a multicolour approach. Twenty cats were included, 12 lymphomas and eight non-lymphomatous cases. Forward scatter (FSC) of lymphoid cells was higher in the lymphoma group. Double positive CD4+CD8+ T-cells were the dominant population in eight out of 12 lymphomas, whereas non-lymphomatous lesions showed no dominant lymphoid population in five out of eight cases. Unlike dogs, the high prevalence of CD4+CD8+ lymphomas in cats it makes difficult to differentiate lymphoma from non-lymphomatous lesions using FC alone. FC may add interesting information to refine diagnosis in some cases, but PARR and histopathology remain mandatory to solve differential in case of expansion of small–medium sized double positive lymphoid cells.

Immunotherapeutic potential of CD4 and CD8 single-positive T cells in thymic epithelial tumors

Indications for current immune checkpoint inhibitors are expanding and now include thymic epithelial tumors (TETs). Although clinical trials on immune checkpoint inhibitors for TETs are ongoing, a rationale has not yet been established for immunotherapy for TETs. Therefore, we herein performed phenotypic and functional analyses of T cells in surgically resected TET tissues with a focus on the anti-tumor properties of T cells to TETs as a step towards establishing a rationale for immunotherapy for TETs. We examined T-cell profiles in surgically resected TET tissues, particularly CD4 and CD8 single-positive T cells, using flow cytometry. In the functional analysis of T cells in TETs, we investigated not only cytokine production by T cells, but also their cytotoxicity using bispecific T-cell engager technology. The cluster analysis of T-cell profiles based on flow cytometric data revealed that type B3 thymoma and thymic carcinoma (B3/C) belonged to the hot cluster characterized by a high proportion of Tim-3+ and CD103+ in CD4 and CD8 single-positive T cells. Enhancements in cytokine production and the cytotoxicity of T cells by the anti-PD-1 antibody were significantly greater in B3/C. These results indicate the potential of immunotherapy for patients with B3/C.

Thymic hyperplasia following double immune checkpoint inhibitor therapy in two patients with stage IV melanoma

Hyperplasia of the thymus is commonly seen in myasthenia gravis and other autoimmune disorders. Thymic size also varies with age, corticosteroid use, infections, and inflammatory disease. Although thymic hyperplasia has been described following chemotherapy, there is no known association of true thymic hyperplasia with immune checkpoint inhibitor therapy. We present two cases of suspected true thymic hyperplasia in patients with stage IV melanoma who were treated with the combination of nivolumab and ipilimumab, which was complicated by immune-related toxicity requiring corticosteroid therapy, and then subsequently also by secondary hypoadrenalism requiring replacement hydrocortisone. In one patient, histological and flurocytometric analyses of an incisional biopsy of the thymus revealed findings consistent with true thymic hyperplasia. In the other case, the stable fluorodeoxyglucose positron emission tomography/Computed tomography (FDG-PET/CT) findings were consistent also with true thymic hyperplasia. These are the first described cases of true thymic hyperplasia following combination immune checkpoint inhibitor therapy for metastatic melanoma. We hypothesize that the true thymic hyperplasia in these cases results from initial lymphocyte depletion caused by intense corticosteroid therapy followed by rebound thymic hyperplasia during the period of relative hypocortisolism, which may have been aggravated by the onset of secondary hypoadrenalism.

Diagnosis of intrathyroidal ectopic thymus in thyroid fine needle aspiration samples

Aims

Intrathyroidal ectopic thymus (ITET) is a rare cause of paediatric thyroid nodules. Although ultrasonography of ITET demonstrates a characteristic appearance similar to that of normal thymus, accurate differentiation from other thyroid nodule etiologies by ultrasonography is difficult, and so that fine needle aspiration (FNA) is usually performed for further analysis. The aim of this study was to evaluate the utility of flow cytometry (FCM) in confirming the diagnosis of ITET in thyroid FNA samples.

Methods

Five cases of ITET were retrieved from our thyroid FNA database within a 3-year period. Their clinical information, ultrasonographic features, cytology and FCM findings were retrospectively reviewed. The FCM results were compared with those of 22 T-cell acute lymphoblastic leukaemia/lymphoblastic lymphoma (T-ALL/LBL) cases.

Results

The FNA smears of all five ITET cases demonstrated abundant lymphocytes of variable sizes, which included some immature lymphoid cells. No Hassall’s bodies or atypical epithelioid cells were recognised. By multicolour FCM analysis including antibodies against CD1a, CD2, CD3, CD4, CD5, CD7, CD8, CD10, CD34, TDT and TCR, all ITET cases showed antigen expression patterns consistent with normal thymocyte maturation. All T-ALL/LBL cases exhibited significant immunophenotypic aberrancy.

Conclusions

The diagnosis of ITET based on FNA cytology is often inconclusive. The presence of immature lymphocytes often raises the concern for LBL. FCM with adequate antigen coverage can reliably distinguish ITET from T-ALL/LBL and make the diagnosis of ITET in FNA samples. Avoiding unnecessary further invasive procedures, providing reassurance to clinician and patient, the accurate diagnosis of ITET by FCM in FNA samples is clinically important.

Diagnosis and subclassification of thymoma by minimally invasive fine needle aspiration directed by endobronchial ultrasound: a review and discussion of four cases

Thymomas have been classified by the World Health Organisation (WHO) into six groups, based on the morphology of epithelial cells and the ratio between epithelial cells and lymphocytes within the tumour. Among 1458 consecutive cases of endobronchial ultrasound transbronchial needle aspiration (EBUS-TBNA) performed in a tertiary referral centre between February 2008 and February 2012, we have encountered four cases of thymic neoplasms. We discuss the cytomorphological features of three cases of type B thymoma (one each of B1, B2 and B3 subtypes) and one case of thymic carcinoma diagnosed on EBUS-TBNA using cell blocks, immunocytochemistry and flow cytometry which allowed preoperative chemotherapy to be carried out in two cases, diagnosis to be made after unsatisfactory surgical mediastinoscopy in the third and diagnosis of lymph node metastasis of the thymic carcinoma in the fourth. The differential diagnosis and criteria for subclassification of thymomas are discussed; although subclassification of these cases was possible in these cases, and tumours other than thymoma excluded, additional cases would be necessary to assess the potential accuracy of EBUS-TBNA. These, to the best of our knowledge, represent the first cases of thymoma that were diagnosed and subclassified according to WHO criteria using multimodality evaluation of EBUS-derived cytological aspirates.

Respiratory Tract and Mediastinum

Normal cytology, abnormal and atypical cells, non-cellular components, and infectious cell changes are largely described together with benign, malignant, and neuroendocrine lesions regarding exfoliative and aspiration cytology of the lung. A separate section broadly addresses diagnostic findings and differential diagnoses in bronchoalveolar washings.

The section ‘Fine needle aspiration biopsy of mediastinal disorders’ covers in particular biopsy techniques, accuracy of liquid-based cytology, and the complex lesions of the thymus gland. Cytodiagnostic algorithms of the major benign and malignant pulmonary and mediastinal lesions and their respective differential diagnoses are additionally presented in synoptic setups.

Regulation of Th-POK and Runx3 in T cell development in human thymoma

Thymoma is a thymic epithelial neoplasm which induces T cell development. However, the frequency of mature CD4(+) T cells in thymomas is lower than in normal thymi. Recently, CD4/CD8 lineage commitment has been elucidated in animal model. The zinc finger transcription factor Th-POK is a critical factor to CD4(+) T cell development in CD4/CD8 lineage commitment, whereas CD8(+) T cell development requires the transcription factor Runx3. These factors antagonize in CD4/CD8 lineage commitment. In this study, we examined Th-POK and Runx3 mRNA expression in the T cell subsets of human normal thymus and thymoma. A quantitative reverse transcriptase-polymerase chain reaction examination revealed that Th-POK expression in normal thymi was higher in the CD4(+)CD8(-) subset than in the CD4(+)CD8(+) and CD4(-)CD8(+) subsets. In thymomas, Th-POK expression in the CD4(+)CD8(-) subset was significantly lower than that in normal thymi, and was significantly correlated with the proportion of CD3(+) cells in the CD4(+)CD8(-) subset. However, Th-POK expressions of the CD3(+)CD4(+)CD8(+) and CD3(+)CD4(+)CD8(-) subsets were not impaired in thymomas compared to normal thymi. These results suggest that thymoma neoplastic epithelial cells can induce Th-POK expression similarly to the normal thymic epithelial cells. In addition, there was no significant difference in Runx3 expression between normal thymi and thymomas. Therefore, CD4/CD8 lineage commitment dependent on Th-POK and Runx3 system seems to be working even in the neoplastic environment formed by human thymomas.

Immunological function of thymoma and pathogenesis of paraneoplastic myasthenia gravis

Thymoma and thymic carcinoma are the representative tumors arising from the thymic epithelium. Thymoma is well known for association with autoimmune diseases including myasthenia gravis, suggesting its biological activity. Herein, recent progress in research of thymoma is reviewed with reference to its immunological function. Myasthenia gravis is frequently associated with WHO type B1 and B2 thymomas. These types of thymomas hold a significant number of CD4(+)CD8(+) double-positive T cells, and at the same time, the neoplastic epithelial cells express HLA-DR molecules at a slightly reduced level compared with the normal thymus. The impaired expression of HLA-DR molecules in neoplastic epithelial cells of thymomas possibly affects positive selection of CD4(+)CD8(-) single-positive T cells and may result in alteration of its repertoire. The function of thymoma neoplastic cells as the cortical epithelium of the thymus and the morphological resemblance of thymomas to the cortex suggest that thymoma is of cortical epithelial origin; this might imply that thymoma lacks the functional medulla where professional antigen-presenting cells are engaged in negative selection. These findings suggest that thymoma generates autoreactive T cells causing autoimmunity. Further investigation on immunological function of thymoma is supposed to elucidate the pathogenesis of thymoma-related autoimmunity and the high affinity of thymoma with myasthenia gravis. In addition, studying the biology of thymoma is also expected to contribute to further understanding of T-cell development and immunological tolerance in the human, because thymoma can be considered an acquired thymus.

Ectopic cervico-mediastinal thymoma confirmed by flow cytometric analysis of tumor-derived lymphocytes

Ectopic cervical or cervico-mediastinal thymomas are very rare and most of them are asymptomatic, except for the presence of a cervical mass. We present the case of a 71-year-old man with an ectopic cervico-mediastinal thymoma threatening superior vena cava syndrome. He had a slight headache and presented with venous dilatation on the chest wall. A computed tomographic scan and magnetic resonance imaging of the chest demonstrated a mass extending from the right neck to the hilum, that indented the trachea and compressed and displaced the brachiocephalic veins anteriorly. Under a right hemicollar incision and median sternotomy, the mass was resected en bloc together with the thymus. The resected specimen was an encapsulated mass measuring 11x7x4 cm. The pathological diagnosis was type AB, non-invasive thymoma, confirmed by 3-color flow cytometry of tumor-derived lymphocytes. Flow cytometry using biopsy material may contribute to the preoperative diagnosis of ectopic thymoma.

Amygdaloid kindled seizures can induce functional and pathological changes in thymus of rat: role of the sympathetic nervous system

The present study sought to determine the effects of long-term kindled seizures of the basal amygdala upon immune function in rat, utilizing the thymus, as a principal target for study. Histopathology from kindled Sprague-Dawley rats revealed the presence of epithelial cell thymoma in 70% of these rats. The results revealed an increased rate of apoptosis and proliferation in thymic epithelial cells. Analysis of thymocytes indicated a decrease in the ratio of CD4 to CD8 positive T cells and reduced proliferative response to T-cell mitogens. To determine whether these effects were mediated through the sympathetic nervous system, animals were treated with guanethidine, which blocked the development of epithelial cell thymomas, while mifepristone treatment, employed to determine the possible role of the hypothalamic-pituitary axis, was ineffective in attenuating thymoma development. Thus, the present study demonstrated that functional and pathological changes in the thymus during kindled seizures are mediated through the sympathetic nervous system.

Role of positive selection of thymoma-associated T cells in the pathogenesis of myasthenia gravis

BACKGROUND

A human thymoma is a thymic epithelial neoplasm and is characterized by its frequent association with myasthenia gravis. The histological characteristic of thymoma is coexistence of a large number of lymphocytes, including CD4(+)CD8(+) double positive T cells, phenotypes of the cortical thymocytes. To elucidate the role of these T lymphocytes in the pathogenesis of thymoma-associated myasthenia gravis, we examined the usage of alphabeta or gammadelta T cell receptor of the T lymphocytes in thymoma in conjunction with the positive selection event.

MATERIALS AND METHODS

Thymomas were obtained from 28 patients. Nine patients were associated with myasthenia gravis. Lymphocytes were freshly isolated from the tumor tissue and were subjected to four-color flow cytometric analysis.

RESULTS

The average proportion of TCRalphabeta(+) cells in thymomas associated with myasthenia gravis was 47.0% and was significantly higher (P = 0.0008) than that without myasthenia gravis (23.4%). Positive selection event was then examined in terms of CD69, a positive selection marker. The mean proportion of TCRalphabeta(+)CD69(+)CD4(+)CD8(-) cells in the myasthenic thymomas (8.22%) was significantly greater (P = 0.015) than the nonmyasthenic thymomas (2.99%). On the other hand, there was not a significant difference in the mean proportion of TCRalphabeta(+)CD69(+)CD4(-)CD8(+) cells between the myasthenic and the nonmyasthenic thymomas.

CONCLUSIONS

The possible role of development of TCRalphabeta(+) T cells, especially the role of positive selection of TCRalphabeta(+)CD4(+)CD8(-) T cells in thymoma, was suggested in the pathogenesis of thymoma-associated myasthenia gravis.

A homozygous and a heterozygous defect of the winged helix DNA-binding domain of the fork head (FH) gene in tailless and tailed rat siblings: resultant lymphocyte-rich thymoma connected with renal tubule amyloid beta (Abeta) deposits

OBJECTIVE

To investigate the cause of thymoma connected with renal amyloid beta (Abeta) overproduction.

DESIGN AND METHODS

Pathologic, immune-fluorescence analyses, flow cytometry (FCM) analyses, polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR were applied for tailless and tailed Lewis/Sea rat siblings at the age of 6 months.

RESULTS

A homozygous defect of the winged helix DNA-binding domain of the fork head (FH) gene was detected in the RT-PCR of the tailless rat kidney and liver. Lymphocyte-rich thymoma was found in both rats, but was more prominent in the tailless rat. FCM showed that CD4+ and CD8a+ cells constituted of more than 90% of the thymus lymphocytes in both rats. Abeta deposits in the renal tubules of both rats were shown by positive staining with antihuman Abeta (11-28) antibody (Ab) together with the activation of the kidney presenilin (PSEN) genes. The mRNA level of transthyretin (TTR) was suppressed moderately with age by the homozygous FH1 gene defect.

CONCLUSIONS

Both homozygous and heterozygous defects of the DNA-binding domain of the FH gene caused lymphocyte-rich thymoma and renal Abeta overproduction.

A study on CD45 isoform expression during T-cell development and selection events in the human thymus

CD45 molecules are known to appear as various isoforms generated by alternative splicing of variable exons 4, 5, and 6, but the detailed profile of CD45 isoform expression during thymocyte development has not been revealed. We examined the CD45 isoforms expressed in the various human thymocytes' subsets defined by CD3, CD4, and CD8 expressions using RT-PCR and 4-color flow cytometry. RT-PCR study revealed that RABC, RAB, RBC, RB, and R0 isoforms were expressed in thymocytes while any of RAC, RA, or RC isoforms were not detected. RABC, RAB and RBC isoforms were expressed at CD3(-)CD4(-)CD8(-) and CD3(+)CD4(+)CD8(-) stages, but were barely detectable at CD3(-)CD4(+)CD8(+) stage. RB isoform was consistently expressed at a relatively high level at all stages. R0 isoform was expressed at a low level at CD3(-)CD4(-)CD8(-) and CD3(-)CD4(+)CD8(-) stages but upregulated at CD3(+)CD4(+)CD8(+) and CD3(+)CD4(+)CD8(-) stages. In combination with the results obtained by 4-color flow cytometric study, CD45 isoform expression on human thymocytes were determined to be RABC(+)RAB(+/-)RBC(+)RB(+)R0(+/-) at CD3(-)CD4(-)CD8(-) stage, RABC(-)RAB(-)RBC(-)RB(+)R0(+) at CD3(-)CD4(+)CD8(-) and CD3(-)CD4(+)CD8(+) stages, RABC(+/-)RAB(+)RBC(+)RB(++)R0(++) at CD3(+)CD4(+)CD8(+) stage, and RABC(+)RAB(+)RBC(+)RB(++)R0(+) at CD3(+)CD4(+)CD8(-) stage. Bcl-2 expression was upregulated between CD3(-)CD4(+)CD8(+)CD45R0(+) and CD3(+)CD4(+)CD8(+)CD45R0(+) stages. Expression of CD45R0 epitope was upregulated between CD3(-)CD4(+)CD8(+)CD69(-) and CD3(+)CD4(+)CD8(+)CD69(+) stages while CD45RA epitope expression was unchanged. Thus, when thymocytes are positively selected, CD45R0 isoform expression seems to be upregulated while CD45RABC isoform expression stays at a very low level. In summary, various isoforms of CD45 were shown to be tightly regulated during thymocyte development and through the selection process.