Germinal-Center T-Helper-Cell Markers PD-1 and CXCL13 Are Both Expressed by Neoplastic Cells in Angioimmunoblastic T-Cell Lymphoma

scRNA-seq reveals the landscape of immune repertoire of PBMNCs in iMCD

The etiology of idiopathic multicentric Castleman disease (iMCD) is poorly understood, and the identification of targetable disease mediators remains an unmet clinical need. Thus, we firstly employed single-cell RNA sequencing (scRNA-seq) to elucidate the landscape of the immune repertoire of peripheral blood mononuclear cells (PBMNCs) in iMCD and to identify additional driver cytokines/cells/pathways to address IL-6 blockade-refractory cases. We revealed that the inflammatory cytokine storm observed in iMCD was a significant phenomenon pervasive across all immune cells. B-plasma cell subsets was the main source of IL-6. The IL-6 signaling pathway was significantly activated across a spectrum of immune cells. Systemic upregulation of CXCL13 is mainly driven by peripheral helper T (Tph) and regulatory T (Treg) cells. Notably, a significant positive interaction was observed between CXCL13-expressing T cells and IL-6 signaling-activated B cells. This study provides an immune perspective on PBMNCs in iMCD at the single-cell level, unveiling pathways or targets characterized by atypical inflammatory expression that could potentially serve as promising candidates for therapeutic intervention in iMCD.

Role and application of chemokine CXCL13 in central nervous system lymphoma

Chemokine ligand 13 (CXCL13) and its chemokine receptor 5 (CXCR5) both play significant roles in the tumor microenvironment (TME). CXCL13 in cerebrospinal fluid (CSF) has recently been found to have significant diagnostic and prognostic value in primary and secondary central nervous system (CNS) diffuse large B-cell lymphoma (DLBCL), and the CXCL13-CXCR5 axis has been shown to play an important chemotactic role in the TME of CNS-DLBCL. In this review, we first describe the clinical value of CXCL13 in CSF as a prognostic and diagnostic biomarker for CNS-DLBCL. In addition, this review also discusses the specific mechanisms associated with the CXCL13-CXCR5 axis in tumor immunity of primary diffuse large B cell lymphoma of the central nervous system (PCNS-DLBCL) by reviewing the specific mechanisms of this axis in the immune microenvironment of DLBCL and CNS inflammation, as well as the prospects for the use of CXCL13-CXCR5 axis in immunotherapy in PCNS-DLBCL.

SOHO State of the Art Updates and Next Questions | New Pathways and New Targets in PTCL: Staying on Target

While the peripheral T-cell lymphomas (PTCL) remain a therapeutic challenge, and increasingly account for a disproportionate number of lymphoma-related deaths, improved understanding of disease pathogenesis and classification, and the development of novel therapeutic agents over the past decade, all provide reasons for a more optimistic outlook in the next. Despite their genetic and molecular heterogeneity, many PTCL are dependent upon signaling input provided by antigen, costimulatory, and cytokine receptors. While gain-of-function alterations effecting these pathways are recurrently observed in many PTCL, more often than not, signaling remains ligand-and tumor microenvironment (TME)-dependent. Consequently, the TME and its constituents are increasingly recognized as "on target". Utilizing a "3 signal" model, we will review new-and old-therapeutic targets that are relevant for the more common nodal PTCL subtypes.

Angioimmunoblastic T-cell lymphoma with predominant CD8+ tumor-infiltrating T-cells is a distinct immune pattern with an immunosuppressive microenvironment

Background

Angioimmunoblastic T-cell lymphoma (AITL) has a rich tumor microenvironment (TME) that typically harbors plenty of CD4+tumor infiltrating lymphocytes, (TIL)-T-cells (so called common AITL). Nonetheless, AITL with large numbers of CD8+TIL-Ts that outnumber CD4+cells have been observed (CD8-predominant AITL). However, detailed comparison of CD8-predominant AITL and common AITL are still lacking.

Methods

We compared clinicopathological features, TIL subsets, TME T cell receptor-β (TRB), and immunoglobulin heavy chain (IGH) repertoires, and gene expression profiles in six CD8-predominant and 12 common AITLs using case-control matching (2014 to 2019).

Results

Comparing with common AITLs, CD8-predominant AITLs showed more frequent edema (P = 0.011), effusion (P = 0.026), high elevated plasma EBV-DNA (P = 0.008), and shorter survival (P = 0.034). Moreover, they had more pronounced eosinophil increase (P = 0.004) and a higher Ki67 index (P = 0.041). Flow cytometry revealed an inverted CD4/CD8 ratio in TIL-Ts and lower TIL-B proportions (P = 0.041). TRB repertoire metrics deteriorated, including lower productive clones (P = 0.014) and higher clonality score (P = 0.019). The IGH repertoire was also narrowed, showing a higher proportion of the top 10 clones (P = 0.002) and lower entropy (P = 0.027). Gene expression analysis showed significant enrichment for upregulated negative regulation of immune system processes and downregulated T-cell activation and immune cell differentiation.

Conclusion

Our findings demonstrated that CD8-predominant AITL is a distinct immune pattern of AITL characterized by anti-tumor immunity impairment and an immunosuppressive microenvironment. These characteristics can interpret its severe clinical manifestations and poor outcomes.

Expression of immune checkpoint regulators, programmed death-ligand 1 (PD-L1/PD-1), cytotoxic T lymphocyte antigen 4 (CTLA-4), and indolaimine-2, 3-deoxygenase (IDO) in uterine mesenchymal tumors

BACKGROUND

Immune checkpoints including programmed death-ligand 1/programmed death-1/ (PD-L1/PD-1), cytotoxic T lymphocyte antigen 4 (CTLA-4), and indolaimine-2, 3-deoxygenase (IDO) have recently emerged as effective candidates for treatment against a range of human malignancies. We have investigated their expression in the uterine mesenchymal tumors.

METHODS

Sixty-eight mesenchymal tumors were categorized into 6 diagnostic groups. We assessed PD-L1, PD-1, CTLA-4, and IDO expression on paraffin embedded tissue blocks of the uterine tumors using the respective antibodies. Immunohistochemical (IHC) stains were classified as positive when the reactions were present in at least 1% of the cell membranes for PD-L1/PD-1 or in cytoplasm for CTLA-4 and IDO, regardless of intensity. Student's t-test and McNemar's chi-square tests were carried out to analyze the results.

RESULTS

The mesenchymal neoplasms had expressed the immune checkpoints in the tumor and/or the lymphoid cells at the rate of 49% and 54% respectively. The tumor cells were positive in 10 (18%, PD-L1), 0 (0%, PD-1), 18 (32%, CTLA-4), and 13 (23%, IDO) cases while the infiltrating lymphoid cells were positive in 10 (18%, PD-L1), 23 (40%, PD-1), 18 (32%, CTLA-4), and 13 (23%, IDO) cases. Overall, comparison of paired tumor vs lymphoid cells resulted in p-values of ≤ 0.04.

CONCLUSIONS

Nearly 50% of the uterine tumors express at least one of the immune checkpoints in tumor and/or the infiltrating lymphoid cells. However, expression of the proteins in the two cellular components are mutually exclusive. Namely, when tumor cells express an immune checkpoint, the infiltrating lymphoid cells do not, and vice versa. Since the leiomyosarcomas are reportedly resistant to the immunotherapy when PD-L1 is expressed in the tumor cells, it can be posited that presence of the IHC positive lymphoid cells may be a better indicator of response to the treatment.

CXCL13-CXCR5 axis: Regulation in inflammatory diseases and cancer

Chemokine C-X-C motif ligand 13 (CXCL13), originally identified as a B-cell chemokine, plays an important role in the immune system. The interaction between CXCL13 and its receptor, the G-protein coupled receptor (GPCR) CXCR5, builds a signaling network that regulates not only normal organisms but also the development of many diseases. However, the precise action mechanism remains unclear. In this review, we discussed the functional mechanisms of the CXCL13-CXCR5 axis under normal conditions, with special focus on its association with diseases. For certain refractory diseases, we emphasize the diagnostic and therapeutic role of CXCL13-CXCR5 axis.

Cutaneous Reactive B-cell Lymphoid Proliferations

Cutaneous lymphoid hyperplasia (CLH), also known as cutaneous pseudolymphoma, is a spectrum of benign conditions characterized by reactive B- and T-cell cutaneous lymphocytic infiltrates. B-cell lymphoid proliferations are a heterogenous group of non-neoplastic cutaneous diseases that must be histopathologically distinguished from cutaneous B-cell lymphomas. These proliferations can be observed as reactive phenomena to infections, medications, allergens, neoplasms, and more. Further, there are many inflammatory conditions that present with reactive B-cell infiltrates, including actinic prurigo, Zoon balanitis, Rosai-Dorfman, and cutaneous plasmacytosis. This review summarizes multiple cutaneous B-cell lymphoid proliferations within the major categories of reactive and disease-associated CLH. Further we discuss major discriminating features of atypical CLH and malignancy. Understanding the specific patterns of B-cell CLH is essential for the proper diagnosis and treatment of patients presenting with such lesions.

The lymph node transcriptome of unicentric and idiopathic multicentric Castleman disease

Castleman disease is a polyclonal lymphoproliferative disorder characterized by unicentric or multicentric lymphadenopathy with characteristic histomorphological features, in addition to variable inflammatory symptomatology. The molecular mechanisms and etiologies of unicentric Castleman disease (UCD) and idiopathic multicentric Castleman disease (iMCD) are poorly understood, and identification of targetable disease mediators remains an unmet clinical need. We performed whole exome sequencing on lymph node biopsies from patients with UCD and iMCD and compared the transcriptomic profiles to that of benign control lymph nodes. We identified significantly upregulated genes in UCD (n=443), iMCD (n=316) or both disease subtypes (n=51) and downregulated genes in UCD (n=321), iMCD (n=105) or both (n=10). The transcriptomes of UCD and iMCD showed enrichment and upregulation of elements of the complement cascade. By immunohistochemistry, C4d deposits indicative of complement activation were found to be present in UCD and iMCD, mostly within abnormally regressed germinal centers, but also in association with plasma cell clusters, endothelial cells and stroma cell proliferations. Other enriched gene sets included collagen organization, S1P3 pathway and VEGFR pathway in UCD; and humoral response, oxidative phosphorylation and proteosome in iMCD. Analysis of cytokine transcripts showed upregulation of CXCL13 but not IL6 in UCD and iMCD. Among angiogenic mediators, the VEGFR1 ligand placental growth factor (PGF) was upregulated in both disease subtypes. We hereby report for the first time the whole lymph node transcriptomes of UCD and iMCD, underscoring findings that could aid in the discovery of targetable disease mediators.

Melanoma Immunotherapy and Precision Medicine in the Era of Tumor Micro-Tissue Engineering: Where Are We Now and Where Are We Going?

Malignant melanoma still remains a cancer with very poor survival rates, although it is at the forefront of personalized medicine. Most patients show partial responses and disease progressed due to adaptative resistance mechanisms, preventing long-lasting clinical benefits to the current treatments. The response to therapies can be shaped by not only taking into account cancer cell heterogeneity and plasticity, but also by its structural context as well as the cellular component of the tumor microenvironment (TME). Here, we review the recent development in the field of immunotherapy and target-based therapy and how, in the era of tumor micro-tissue engineering, ex-vivo assays could help to enhance our melanoma biology knowledge in its complexity, translating it in the development of successful therapeutic strategies, as well as in the prediction of therapeutic benefits.

Markers of Follicular Helper T Cells Are Occasionally Expressed in T-Cell or Histiocyte-Rich Large B-Cell Lymphoma, Classic Hodgkin Lymphoma, and Atypical Paracortical HyperplasiaA Diagnostic Pitfall For T-Cell Lymphomas of T Follicular Helper Origin

OBJECTIVES

Follicular helper T cell (TFH) markers are expressed in angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma of the TFH phenotype (PTCL-TFH). However, differential expression and coexpression of these markers in benign and other malignant lymphoid proliferations have not been well studied.

METHODS

We performed programmed death-1 (PD-1), C-X-C motif chemokine ligand 13 (CXCL13), inducible costimulator (ICOS), CD10, and B-cell lymphoma 6 protein (BCL-6) immunohistochemistry on AITL, PTCL not otherwise specified (PTCL-NOS), PTCL-TFH, T-cell or histiocyte-rich large B-cell lymphoma (THRLBCL), classic Hodgkin lymphoma (CHL), atypical paracortical hyperplasia (PCH), progressive transformation of germinal centers (PTGC), and reactive follicular hyperplasia (RFH).

RESULTS

CXCL13 and ICOS were more sensitive but less specific for AITL than PD-1, CD10, and BCL-6. Moreover, 74% of AITL (none of PTCL-NOS or PTCL-TFH) coexpressed more than 2 TFH markers. In background T cells of THRLBCL, 70% of cases coexpressed more than 1 marker. The background T cells of CHL expressed all TFH markers except CD10 in all cases. In addition, 13% of PCH cases coexpressed more than 1 marker. In RFH and PTGC, all markers were expressed mainly in germinal centers with rare extrafollicular staining.

CONCLUSIONS

AITL, PTCL-NOS, and PTCL-TFH show differential expression of TFH markers. AITL frequently coexpresses more than 2 TFH markers. TFH markers can be expressed in PCH and in background T cells of THRLBCL and CHL. Consequently, caution should be used before a diagnosis of AITL is established, particularly with limited samples.

CXCL13 Signaling in the Tumor Microenvironment

Chemokines have emerged as important players in tumorigenic process. An extensive body of literature generated over the last two or three decades strongly implicate abnormally activated or functionally disrupted chemokine signaling in liaising most-if not all-hallmark processes of cancer. It is well-known that chemokine signaling networks within the tumor microenvironment are highly versatile and context-dependent: exert both pro-tumoral and antitumoral activities. The C-X-C motif chemokine ligand 13 (CXCL13), and its cognate receptor CXCR5, represents an emerging example of chemokine signaling axes, which express the ability to modulate tumor growth and progression in either way. Collateral evidence indicate that CXCL13-CXCR5 axis may directly modulate tumor growth by inducing proliferation of cancer cells, as well as promoting invasive phenotypes and preventing their apoptosis. In addition, CXCL13-CXCR5 axis may also indirectly modulate tumor growth by regulating noncancerous cells, particularly the immune cells, within the tumor microenvironment. Here, we review the role of CXCL13, together with CXCR5, in the human tumor microenvironment. We first elaborate their patterns of expression, regulation, and biological functions in normal physiology. We then consider how their aberrant activity, as a result of differential overexpression or co-expression, may directly or indirectly modulate the growth of tumors through effects on both cancerous and noncancerous cells.

Expression of the checkpoint receptors LAG-3, TIM-3 and VISTA in peripheral T cell lymphomas

AIMS

Peripheral T cell lymphomas represent approximately 10%-15% of non-Hodgkin lymphomas and are characterised by an aggressive clinical courses and poor outcomes. Ligands provided by constituents of the tumour microenvironment engage receptors expressed by malignant T cells, promoting tumour growth and chemotherapy resistance. In addition to stimulatory receptors that promote the growth and survival of malignant T cells, recent studies suggest that homologous inhibitory receptors may have an opposing effect and function as tumour suppressors. For example, recent data suggest that programmed cell death 1 blockade may lead to increased lymphoma growth. Therefore, the identification of alternative checkpoint receptors in T cell lymphoproliferative neoplasms is an important and clinically relevant question.

METHODS

The checkpoint receptors T cell immunoglobulin-3 (TIM-3), V-domain Ig-containing suppressor of T cell activation (VISTA) and lymphocyte-activation gene 3 (LAG-3) play fundamental roles in peripheral tolerance, and their ligands are exploited by many solid tumours to evade host immunity. However, their expression in T cell lymphoproliferative neoplasms has not been evaluated. In this study, we evaluated the expression of TIM-3, VISTA and LAG-3 in a cohort of peripheral T cell lymphomas cases by immunohistochemistry and flow cytometric analysis.

RESULTS

Our results demonstrate that TIM-3, VISTA and LAG-3 expression is rarely identified within a large cohort of T cell lymphomas and its tumour microenvironment.

CONCLUSIONS

Our data suggest that immune-regulatory roles for TIM-3, VISTA and LAG-3 may be predominant in lymphomas subsets different than the ones analysed in the current study. However, a potential role for these checkpoint receptors as tumour suppressors in T cell lymphomas remains to be elucidated.

GATA-3 in T-cell lymphoproliferative disorders

GATA-3 regulates the differentiation, proliferation, survival, and function of peripheral T cells and their thymic progenitors. Recent findings, reviewed here, not only implicate GATA-3 in the pathogenesis of molecularly, genetically, and clinically distinct T-cell lymphoproliferative disorders, but also have significant diagnostic, prognostic, and therapeutic implications.

Extreme Peripheral Blood Plasmacytosis Mimicking Plasma Cell Leukemia as a Presenting Feature of Angioimmunoblastic T-Cell Lymphoma (AITL)

Angioimmunoblastic T-cell lymphoma (AITL) is one of four major subtypes of nodal peripheral T cell lymphoma, characterized by its cell of origin, the follicular helper T-cell (T_FH). Patients typically present with prominent constitutional (B) symptoms, generalized lymphadenopathy, hepatosplenomegaly, cytopenias, and rash. Here we present a case of a 62-year-old male with progressive cervical adenopathy, fevers and weight loss presenting with extreme polyclonal plasmacytosis and high plasma EBV viral load. While the initial presentation appeared to mimic plasma cell leukemia or severe infection, lymph node biopsy and bone marrow biopsy confirmed a diagnosis of AITL. This case highlights the heterogeneity of the clinical presentation of AITL to enable physicians to more promptly recognize, diagnose and initiate treatment.

Identification of hub genes and key pathways associated with angioimmunoblastic T-cell lymphoma using weighted gene co-expression network analysis

Background: Angioimmunoblastic T-cell lymphoma (AITL) is an aggressive subtype of peripheral T-cell lymphoma (PTCL) that has a poor 5-year overall survival rate due to its lack of precise therapeutic targets. Identifying potential prognostic markers of AITL may provide information regarding the development of precision medicine. Methods: RNA sequence data from PTCL and patient clinic traits were obtained from the Gene Expression Omnibus (GEO) database. Differentially expressed gene (DEG) analysis and weighted gene co-expression network analysis (WGCNA) were performed to identify DEGs between the different PTCL subtypes and investigate the relationship underlying co-expression modules and clinic traits. Gene ontology (GO) and protein-protein interaction (PPI) network analyses based on DAVID and the STRING website, respectively, were utilized to deeply excavate hub genes. Results: After removing the outliers from the GSE65823, GSE58445, GSE19069, and GSE6338 datasets using the results from an unsupervised cluster heatmap, 50 AITL samples and 55 anaplastic large cell lymphoma (ALCL) samples were screened. A total of 677 upregulated DEGs and 237 downregulated DEGs were identified in AITL and used to construct a PPI network complex. Using WGCNA, 12 identified co-expression modules were constructed from the 5468 genes with the top 10% of variance, and 192 genes from the Turquoise and Brown modules were with a Gene Significance (GS) cut-off threshold >0.6. Eleven hub genes (CDH1, LAT, LPAR1, CXCL13, CD27, ICAM2, CD3E, CCL19, CTLA-4, CXCR5, and C3) were identified. Only CTLA-4 overexpressed was found to be a poor prognostic factor according to survival analysis. Gene set enrichment analysis (GSEA) identified and validated the intersection of key pathways (T cell receptor, primary immunodeficiency, and chemokine signaling pathways). Conclusion: Our findings provide the framework for the identification of AITL co-expression gene modules and identify key pathways and driving genes that may be novel treatment targets and helpful for the development of a prognostic evaluation index.

Monoclonal plasma cell infiltrates in the setting of cutaneous follicular helper T cell lymphoproliferative disorders

There is a growing recognition that some primary cutaneous T cell lymphomas of the skin exhibit a follicular helper T cell phenotype best exemplified by primary cutaneous CD4+ small/medium sized pleomorphic T cell lymphoma. The follicular helper T cells is an evolutionary function in a common TH1 cell under the influence of other cell types most notably monocyte derived dendritic cells but also plasma cells. In addition, the skin defines a characteristic organ site of involvement for angioimmunoblastic T-cell lymphoma (AITL); the first recognized form of follicular helper T cell lymphoma. One of the hallmarks of the follicular helper T cell lymphomas a significant degree of post germinal center B cell hyperplasia. We encountered 7 cases of primary cutaneous follicular helper T cell and four cases of AITL, in which the biopsies contained a light chain restricted plasma cell infiltrate in the skin. There were no features that suggested an atypical or more aggressive clinical course in association with the identification of this light chain restricted plasmacytic infiltrates except one case of AITL in whom a diffuse large cell B cell lymphoma subsequently developed. There was no association with Epstein-Barr virus (EBV) infection light chain restricted plasma cell infiltrate in any of the eleven cases. The basis of these infiltrates is likely a reciprocal functional one reflecting the role of follicular helper T cells in the induction of B cell hyperplasia and the role of plasma cells as a countercheck balance controlling the extent of follicular helper T cell hyperplasia. B cell clonality, plasma cell atypia and blastic B cell transformation can occur without implying a malignant transformation.

CXCL13/CXCR5 signaling axis in cancer

The tumor microenvironment comprises stromal and tumor cells which interact with each other through complex cross-talks that are mediated by a variety of growth factors, cytokines, and chemokines. The chemokine ligand 13 (CXCL13) and its chemokine receptor 5 (CXCR5) are among the key chemotactic factors which play crucial roles in deriving cancer cell biology. CXCL13/CXCR5 signaling axis makes pivotal contributions to the development and progression of several human cancers. In this review, we discuss how CXCL13/CXCR5 signaling modulates cancer cell ability to grow, proliferate, invade, and metastasize. Furthermore, we also discuss the preliminary evidence on context-dependent functioning of this axis within the tumor-immune microenvironment, thus, highlighting its potential dichotomy with respect to anticancer immunity and cancer immune-evasion mechanisms. At the end, we briefly shed light on the therapeutic potential or implications of targeting CXCL13/CXCR5 axis within the tumor microenvironment.

Cutaneous localization of angioimmunoblastic T-cell lymphoma may masquerade as B-cell lymphoma or classical Hodgkin lymphoma: A histologic diagnostic pitfall

BACKGROUND

We report the cases of three patients presenting skin lesions whose biopsies showed nodular polymorphic infiltrates consisting of lymphocytes, plasma cells, histiocytes, eosinophils, B blasts, and Hodgkin Reed-Sternberg (HRS)-like cells. Two of them were initially diagnosed as classical Hodgkin lymphoma (cHL), on the other hand, the last one as a B-cell lymphoma. All patients have been treated for angioimmunoblastic T-cell lymphoma (AITL).

METHODS

We performed a second review of the skin biopsies with further immunophenotypic molecular analyses. Scrupulous observation revealed, in the background of the three cases, atypical small to medium-sized lymphocytes carrying a CD3+, CD4+ T-cell phenotype and expressing PD1 and CXCL13 follicular helper T-cell markers. The two lesions initially diagnosed as cHL showed scattered HRS-like cells with CD30+, CD15+, PAX5+, CD20-, Epstein Barr Virus (EBV) + classical phenotype. The case initially diagnosed as B-cell lymphoma showed a diffuse B-cell proliferation associated with small B-cell and medium to large-sized B blasts that were positive for EBV.

CONCLUSION

Those cases highlighted that atypical T-cells may be obscured by B-cell proliferation mimicking cHL or B-cell lymphoma in cutaneous localization of AITL and confirmed the requirement of collecting clinical information before performing a diagnosis.

T Cells That Help B Cells in Chronically Inflamed Tissues

Chronically inflamed tissues commonly accrue lymphocyte aggregates that facilitate local T cell-B cell interactions. These aggregates can range from small, loosely arranged lymphocyte clusters to large, organized ectopic lymphoid structures. In some cases, ectopic lymphoid structures develop germinal centers that house prototypical T follicular helper (Tfh) cells with high expression of Bcl6, CXCR5, PD-1, and ICOS. However, in many chronically inflamed tissues, the T cells that interact with B cells show substantial differences from Tfh cells in their surface phenotypes, migratory capacity, and transcriptional regulation. This review discusses observations from multiple diseases and models in which tissue-infiltrating T cells produce factors associated with B cell help, including IL-21 and the B cell chemoattractant CXCL13, yet vary dramatically in their resemblance to Tfh cells. Particular attention is given to the PD-1^hi CXCR5⁻ Bcl6^low T peripheral helper (Tph) cell population in rheumatoid arthritis, which infiltrates inflamed synovium through expression of chemokine receptors such as CCR2 and augments synovial B cell responses via CXCL13 and IL-21. The factors that regulate CD4⁺ T cell production of CXCL13 and IL-21 in these settings are also discussed. Understanding the range of T cell populations that can provide help to B cells within chronically inflamed tissues is essential to recognize these cells in diverse inflammatory conditions and to optimize either broad or selective therapeutic targeting of B cell-helper T cells.

CUTANEOUS MANIFESTATIONS OF ANGIOIMMUNOBLASTIC T-CELL LYMPHOMA

Background: Angioimmunoblast T-cell lymphoma (AITL) is a rare T-cell lymphoproliferative disease that is accompanied by generalized lymphadenopathy, hepatosplenomegaly, intoxication symptoms and extranodal lesions. The extranodal manifestations of the disease frequently involve various skin changes. One of the first such manifestations is maculopapular rashes observed in about half of AITL patients and usually preceding the appearance of lymphadenopathy. Other forms of skin lesions accompany the disease considerably less frequently.Aim: To characterize the range of skin changes in patients suffering from AITL, to establish a correspondence between the nature of skin changes and their histological picture.Materials and methods: 54 AITL patients were being treated at the National Research Centre for Hematology from 2000 to 2017, with the male/female ratio being 30/24. The median age was 61 (29–81) years.Results: Changes in the skin were observed in 24 (44.4 %) of 54 AITL patients, out of whom 18 (75 %) and 6 (25 %) were male and female patients, respectively. Maculopapular rash was observed in 22 (91.7 %) out of 24 patients. The morphological and molecular investigations of skin biopsy specimens exhibiting maculopapular rash demonstrated nonspecific reactive changes. Patients with maculopapular rash demonstrated an increase in the level of total (polyclonal) IgE. Specific skin lesions detected in 8 (14.8 %) cases were represented by a ‘livedo reticularis’, focal skin hyperpigmentation, erythroderma, left eyelid tumour and tumour in 3, 2, 1, 1 and 1 cases, respectively.Conclusion: Maculopapular rash frequently observed in AITL patients is a reactive process not associated with a specific skin lesion. Specific skin lesions in AITL are much less common and can be represented by various forms. In some AITL cases, skin changes of the reactive and tumour nature can be simultaneously observed. 

Development of small-molecule immune checkpoint inhibitors of PD-1/PD-L1 as a new therapeutic strategy for tumour immunotherapy

Cancer immunotherapy has been increasingly utilised to treat advanced malignancies. The signalling network of immune checkpoints has attracted considerable attention. Immune checkpoint inhibitors are revolutionising the treatment options and expectations for patients with cancer. The reported clinical success of targeting the T-cell immune checkpoint receptors PD-1/PD-L1 has demonstrated the importance of immune modulation. Indeed, antibodies binding to PD-1 or PD-L1 have shown remarkable efficacy. However, antibody drugs have many disadvantages, such as their production cost, stability, and immunogenicity and, therefore, small-molecule inhibitors of PD-1 and its ligand PD-L1 are being introduced. Small-molecule inhibitors could offer inherent advantages in terms of pharmacokinetics and druggability, thereby providing additional methods for cancer treatment and achieving better therapeutic effects. In this review, we first discuss how PD-1/PD-L1-targeting inhibitors modulate the relationship between immune cells and tumour cells in tumour immunotherapy. Second, we discuss how the immunomodulatory potential of these inhibitors can be exploited via rational combinations with immunotherapy and targeted therapy. Third, this review is the first to summarise the current clinical and preclinical evidence regarding small-molecule inhibitors of the PD-1/PD-L1 immune checkpoint, considering features and responses related to the tumours and to the host immune system.

Ex Vivo Profiling of PD-1 Blockade Using Organotypic Tumor Spheroids

Ex vivo systems that incorporate features of the tumor microenvironment and model the dynamic response to immune checkpoint blockade (ICB) may facilitate efforts in precision immuno-oncology and the development of effective combination therapies. Here, we demonstrate the ability to interrogate ex vivo response to ICB using murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS). MDOTS/PDOTS isolated from mouse and human tumors retain autologous lymphoid and myeloid cell populations and respond to ICB in short-term three-dimensional microfluidic culture. Response and resistance to ICB was recapitulated using MDOTS derived from established immunocompetent mouse tumor models. MDOTS profiling demonstrated that TBK1/IKKε inhibition enhanced response to PD-1 blockade, which effectively predicted tumor response in vivo Systematic profiling of secreted cytokines in PDOTS captured key features associated with response and resistance to PD-1 blockade. Thus, MDOTS/PDOTS profiling represents a novel platform to evaluate ICB using established murine models as well as clinically relevant patient specimens.Significance: Resistance to PD-1 blockade remains a challenge for many patients, and biomarkers to guide treatment are lacking. Here, we demonstrate feasibility of ex vivo profiling of PD-1 blockade to interrogate the tumor immune microenvironment, develop therapeutic combinations, and facilitate precision immuno-oncology efforts. Cancer Discov; 8(2); 196-215. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Deng et al., p. 216This article is highlighted in the In This Issue feature, p. 127.

A Clinicopathologic Study of Lennert Lymphoma and Possible Prognostic Factors: The Importance of Follicular Helper T-cell Markers and the Association With Angioimmunoblastic T-cell Lymphoma

Lennert lymphoma (LeL) is a variant of peripheral T-cell lymphoma, not otherwise specified. Few clinicopathologic studies have investigated LeL, which is a rare disease. Here, we analyzed the clinicopathologic features of 26 patients with LeL to identify potential prognostic factors. Neoplastic cells positive for CD4, CD8, CD4/CD8, TIA-1, and granzyme B were observed in 21 (80.8%), 4 (15.4%), 1 (3.8%), 4 (15.3%), and 0 (0.0%) patients, respectively. Regarding follicular helper T-cell (TFH) markers, neoplastic cells positive for programmed cell death-1 (PD-1), CXCL13, CD10, and BCL6 were observed in 14 (53.8%), 13 (50.0%), 1 (3.8%), and 0 (0.0%) patients, respectively. Patients with positivity for at least 1 TFH cell marker (PD-1, CXCL13, CD10, and/or BCL6) were defined as being TFH cell marker-positive (n=15) and had a worse prognosis than TFH cell marker-negative patients (n=11) (P=0.011). Clinicopathologic characteristics did not differ significantly between TFH cell marker-positive and marker-negative LeL patients. Moreover, prognosis did not differ significantly between TFH cell marker-positive LeL patients and patients with angioimmunoblastic T-cell lymphoma (AITL) (n=42). Nevertheless, as compared with AITL, TFH cell marker-positive LeL was associated with significantly lower frequencies of B symptoms, skin rash, high-intermediate-risk or high-risk international prognostic index values, expanded follicular dendritic cell meshworks, polymorphic infiltrate, clear cells, and positivity for CD10 and BCL6. Although it may be difficult to definitively distinguish between TFH cell marker-positive LeL and AITL, our results suggest that TFH cell markers are useful for identifying LeL patients who will experience unfavorable outcomes.

Immune checkpoint blockade: the role of PD-1-PD-L axis in lymphoid malignancies

The co-inhibitory receptor programmed cell death (PD)-1, expressed by immune effector cells, is credited with a protective role for normal tissue during immune responses, by limiting the extent of effector activation. Its presently known ligands, programmed death ligands (PD-Ls) 1 and 2, are expressed by a variety of cells including cancer cells, suggesting a role for these molecules as an immune evasion mechanism. Blocking of the PD-1-PD-L signaling axis has recently been shown to be effective and was clinically approved in relapsed/refractory tumors such as malignant melanoma and lung cancer, but also classical Hodgkin’s lymphoma. A plethora of trials exploring PD-1 blockade in cancer are ongoing. Here, we review the role of PD-1 signaling in lymphoid malignancies, and the latest results of trials investigating PD-1 or PD-L1 blocking agents in this group of diseases. Early phase studies proved very promising, leading to the clinical approval of a PD-1 blocking agent in Hodgkin’s lymphoma, and Phase III clinical studies are either planned or ongoing in most lymphoid malignancies.

Diagnosis of chronic lymphoproliferative disorders by flow cytometry using four-color combinations for immunophenotyping: A proposal of the brazilian group of flow cytometry (GBCFLUX)

BACKGROUND

Multiparametric flow cytometry (MFC) is a powerful tool for the diagnosis of hematological malignancies and has been useful for the classification of chronic lymphoproliferative disorders (CLPD) according to the WHO criteria. Following the purposes of the Brazilian Group of Flow Cytometry (GBCFLUX), the aim of this report was to standardize the minimum requirements to achieve an accurate diagnosis in CLPDs, considering the different economic possibilities of the laboratories in our country. Most laboratories in Brazil work with 4-fluorescence flow cytometers, which is why the GBCFLUX CLPD Committee has proposed 4-color monoclonal antibody (MoAb) panels.

METHODS/RESULTS

Panels for screening and diagnosis in B, T and NK lymphoproliferative disorders were developed based on the normal differentiation pathways of these cells and the most frequent phenotypic aberrations. Important markers for prognosis and for minimal residual disease (MRD) evaluation were also included. The MoAb panels presented here were designed based on the diagnostic expertise of the participating laboratories and an extensive literature review.

CONCLUSION

The 4-color panels presented to aid in the diagnosis of lymphoproliferative neoplasms by GBCFLUX aim to provide clinical laboratories with a systematic, step-wise, cost-effective, and reproducible approach to obtain an accurate immunophenotypic diagnosis of the most frequent of these disorders. © 2016 International Clinical Cytometry Society.

Pathology of Extranodal Lymphoma

An overview of the pathology of extranodal lymphoma is presented. The emphasis of this presentation is on the classification system of extranodal lymphomas, including both B-cell and T-cell lymphomas, based on their morphology, phenotype, and molecular alterations.

CXCL13 is a plasma biomarker of germinal center activity

Significantly higher levels of plasma CXCL13 [chemokine (C-X-C motif) ligand 13] were associated with the generation of broadly neutralizing antibodies (bnAbs) against HIV in a large longitudinal cohort of HIV-infected individuals. Germinal centers (GCs) perform the remarkable task of optimizing B-cell Ab responses. GCs are required for almost all B-cell receptor affinity maturation and will be a critical parameter to monitor if HIV bnAbs are to be induced by vaccination. However, lymphoid tissue is rarely available from immunized humans, making the monitoring of GC activity by direct assessment of GC B cells and germinal center CD4(+) T follicular helper (GC Tfh) cells problematic. The CXCL13-CXCR5 [chemokine (C-X-C motif) receptor 5] chemokine axis plays a central role in organizing both B-cell follicles and GCs. Because GC Tfh cells can produce CXCL13, we explored the potential use of CXCL13 as a blood biomarker to indicate GC activity. In a series of studies, we found that plasma CXCL13 levels correlated with GC activity in draining lymph nodes of immunized mice, immunized macaques, and HIV-infected humans. Furthermore, plasma CXCL13 levels in immunized humans correlated with the magnitude of Ab responses and the frequency of ICOS(+) (inducible T-cell costimulator) Tfh-like cells in blood. Together, these findings support the potential use of CXCL13 as a plasma biomarker of GC activity in human vaccine trials and other clinical settings.

Expression of follicular helper T-cell markers in primary cutaneous T-cell lymphoma

The follicular helper T cells (TFH) seemed to be expressed in several subsets of T-cell lymphomas. However, their expression in cutaneous T-cell lymphomas (CTCLs) has been rarely described. We investigated the clinical features, histopathological morphology, and expression of TFH markers in CTCLs. Forty-nine patients (24 men and 25 women) diagnosed with CTCL were examined, 25 patients with mycosis fungoides (MF) and 24 with other CTCLs. Immunohistochemical staining for CD10, Bcl-6, inducible costimulator, CXCL13, and PD-1 were performed. Relation between PD-1 and clinical course in MF was evaluated. PD-1 was detected in 21 of 25 (84.0%) MF cases and in 11 of 24 (45.8%) other CTCL cases. Bcl-6, CXCL13, inducible costimulator, and CD10 were occasionally expressed in most T-cell lymphomas, including MF. The staining for PD-1 was negative in all the MF cases with large-cell transformation. No correlation was observed between disease course and PD-1 expression rate in the MF cases. In conclusion, among the TFH markers, PD-1 was most frequently expressed in CTCL. PD-1 was expressed in most MF. PD-1 expression rates were significantly higher in MF than in other CTCLs.

PD-1, S-100 and CD1a expression in pseudolymphomatous folliculitis, primary cutaneous marginal zone B-cell lymphoma (MALT lymphoma) and cutaneous lymphoid hyperplasia

BACKGROUND

Pseudolymphomatous folliculitis is a lymphoid proliferation that clinically and histopathologically mimics primary cutaneous extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma). In this study, we assessed the diagnostic value of three immunohistochemical markers, programmed death-1 (PD-1), CD1a and S100.

METHODS

We evaluated 25 cases of cutaneous lymphoid proliferations with established diagnoses, including 9 patients with pseudolymphomatous folliculitis, 11 with MALT lymphoma, and 5 with cutaneous lymphoid hyperplasia (CLH). The clinical, histopathologic and immunohistochemical characteristics were reviewed and three major characteristics assessed: (a) proportion of T cells expressing PD-1, (b) pattern of expression of CD1a by dendritic cells and (c) pattern of expression of S100 by dendritic cells.

RESULTS

We found pseudolymphomatous folliculitis to have a significant increase in PD-1+ T cells compared with MALT lymphoma (p < 0.0001). The pattern of CD1a staining is also informative: MALT lymphoma is significantly more likely to demonstrate a peripheral concentration of CD1a+ dendritic cells around lymphoid nodules than pseudolymphomatous folliculitis (p < 0.0003) or CLH (p < 0.05). Pseudolymphomatous folliculitis demonstrates an interstitial distribution of CD1a+ cells more often than MALT lymphoma (p < 0.04). S100 staining was not a helpful discriminator.

CONCLUSIONS

Histopathologic factors including PD-1 and CD1a staining patterns may allow for more certainty in distinguishing lymphoid hyperplasia, including pseudolymphomatous folliculitis, from MALT lymphoma.

Presence of antigen-experienced T cells with low grade of differentiation and proliferative potential in chronic Chagas disease myocarditis

BACKGROUND

The main consequence of chronic Trypanosoma cruzi infection is the development of myocarditis in approximately 20-30% of infected individuals but not until 10-20 years after the initial infection. We have previously shown that circulating interferon-γ-secreting T cells responsive to Trypanosoma cruzi antigens in chronic Chagas disease patients display a low grade of differentiation and the frequency of these T lymphocytes decreases along with the severity of heart disease. This study thought to explore the expression of inhibitory receptors, transcription factors of type 1 or regulatory T cells, and markers of T cell differentiation, immunosenescence or active cell cycle in cardiac explants from patients with advanced Chagas disease myocarditis.

METHODOLOGY/PRINCIPAL FINDINGS

The expression of different markers for T and B cells as well as for macrophages was evaluated by immunohistochemistry and immunofluorescence techniques in cardiac explants from patients with advanced chronic Chagas disease submitted to heart transplantation. Most infiltrating cells displayed markers of antigen-experienced T cells (CD3(+), CD4(+), CD8(+), CD45RO(+)) with a low grade of differentiation (CD27(+), CD57(-), CD45RA(-), PD(-)1(-)). A skewed T helper1/T cytotoxic 1 profile was supported by the expression of T-bet; whereas FOXP3(+) cells were scarce and located only in areas of severe myocarditis. In addition, a significant proliferative capacity of CD3(+) T cells, assessed by Ki67 staining, was found.

CONCLUSIONS/SIGNIFICANCE

The quality of T cell responses and immunoregulatory mechanisms might determine the pattern of the cellular response and the severity of disease in chronic Trypanosoma cruzi infection.

Large B-cell lymphomas poor in B cells and rich in PD-1+ T cells can mimic T-cell lymphomas

OBJECTIVES

To characterize the clinicopathologic features of cases of large B-cell lymphomas, poor in B cells and densely rich in programmed cell death-1 (PD-1)+ reactive T cells, which can mimic T-cell lymphomas.

METHODS

A single-institute retrospective review of cases between 2010 and 2013 was performed.

RESULTS

Of 178 cases of large B-cell lymphomas, eight cases of large B-cell lymphomas poor in B cells and diffusely rich in sheets of PD-1+ T cells were identified. These cases either were initially misdiagnosed as a T-cell lymphoma or substantiated a broader differential diagnosis including a T-cell lymphoma. Five cases were T-cell histiocyte-rich large B-cell lymphomas, and three cases were diagnosed as large B-cell lymphomas rich in T cells. In three of these cases, a subset of the PD-1+ T cells showed either morphologic nuclear atypia or atypical expression of T-cell antigens on flow cytometry and/or immunohistochemistry.

CONCLUSIONS

Large B-cell lymphomas poor in B cells and rich in T cells can have diffuse sheets of reactive PD-1+ T cells, some with atypical morphologic and immunophenotypic features mimicking a T-cell lymphoma. Careful assessment of the immunoarchitecture and background inflammatory and stromal cells can prevent erroneous diagnoses in such cases.

Utility of CD279/PD-1 immunohistochemistry in the evaluation of benign and neoplastic T-cell-rich bone marrow infiltrates

OBJECTIVES

CD279 expression is used to help identify angioimmunoblastic T-cell lymphoma (AITL) or other T-cell lymphomas of T-follicular helper (TFH) cell origin; however, its utility in assessing lymphoid infiltrates in the bone marrow (BM) is not well established.

METHODS

Immunohistochemistry for CD279 was performed on normal staging BM and in BM with benign lymphoid aggregates (LAs), AITLs, and other T-cell lymphomas.

RESULTS

Seven of 10 staging BMs demonstrated scattered, usually weakly CD279+ cells. Thirty-four of 38 BMs had scattered weakly/variably intense CD279+ cells within LAs, but only four contained 11% to 25% CD279+ cells. Three of four AITLs were strongly CD279+, but one contained only around 10% CD279+ cells. Eleven of the other 38 T-cell lymphomas were CD279+, including five possible AITLs; four peripheral T-cell lymphomas, not otherwise specified; and two T-cell large granular lymphocytic leukemias.

CONCLUSIONS

Although useful in assessing selected BM lymphoid infiltrates, CD279 expression may be limited in AITLs, is not specific for TFH lymphomas, and can be seen in benign lymphoid infiltrates, although without extensive strong positivity.

Diagnostic accuracy of a defined immunophenotypic and molecular genetic approach for peripheral T/NK-cell lymphomas. A North American PTCL study group project

The diagnosis of peripheral T-cell and NK-cell lymphomas (PTNKCL) is difficult with few standards for required ancillary studies. We evaluated a series of PTNKCLs using a tiered approach to immunohistochemistry and molecular genetic characterization to document diagnostic accuracy and clinical relevance. Seven hematopathologists reviewed 374 cases that included PTNKCL and non-PTNKCL cases to mimic diagnostic practice. Cases received tier 0, 1, and 2 diagnoses by 3 independent pathologists, on the basis of hematoxylin and eosin stains and progressive immunohistochemistry panels. A tier 2b diagnosis was rendered when gene rearrangement data were available, and a final consensus diagnosis was rendered after discussion of each case. Across all 374 cases, consensus agreement was 92.5%. For PTNKCLs, World Health Organization subclassification was possible in 16.5%, 37.1%, 82.8%, and 85.9% of individual reviewer diagnoses at tier 0, 1, 2, and 2b, respectively. Gene rearrangement contributed to a change in diagnosis in 51 of 647 (8%) individual reviews. Following this algorithm may provide prognostic information on the basis of individual marker expression in common PTNKCL types (CD4 in peripheral T-cell lymphoma, not otherwise specified and PD-1 in angioimmunoblastic T-cell lymphoma). This evidence-based approach to the diagnosis of PTNKCL informs practicing pathologists, clinical trial designers, and policy-makers regarding required ancillary studies.

Serum IgA level, monocyte count, and international prognostic index are independently associated with overall survival in patients with HTLV-I-negative nodal peripheral T cell lymphoma

Peripheral T cell lymphomas (PTCL) account for 10-15 % of non-Hodgkin's lymphomas and are associated with poor prognosis. Although many prognostic factors for PTCL have been proposed, the heterogeneity of PTCL seems to be an obstacle in the establishment of clinically useful prognostic system, such as the International Prognostic Index (IPI) in diffuse large B cell lymphoma. PTCL with nodal manifestation include the HTLV-I-negative histologic subtypes of PTCL not otherwise specified (PTCL-NOS), angioimmunoblastic T cell lymphoma (AITL), and anaplastic large cell lymphoma (ALCL). As PTCL-NOS encompasses a group of similar tumors and mostly shares their clinical pictures, we retrospectively analyzed clinical data from 77 patients diagnosed with ALCL, AITL, and PTCL-NOS at Kobe City Medical Center General Hospital from May 1994 to February 2012 to identify the prognostic factor for nodal PTCL. The median age of patients was 64 years, ranging from 23 to 83 years. With a median follow-up of 50 months, 5-year overall survival (OS) was 43 %. Multivariate analysis identified high-risk IPI (hazard ratio (HR), 4.04; P = 0.015), absolute monocyte count > 0.8 × 10(9)/L (HR, 3.44; P = 0.001), and serum concentration of IgA > 410 mg/dL (HR, 2.31; P = 0.013) as poor prognostic factors for OS. Thus, we have identified novel prognostic factors of monocyte count and serum IgA level for nodal PTCL. Although conventional prognostic models mainly reflect both tumor characteristics and host factors, the present model indicates the importance of host immune response as the unfavorable prognosis.

Cytopathology in the diagnosis of lymphoma

FNA is a simple, safe, and an inexpensive sampling technique that plays an important role in the evaluation of lymphadenopathy. The key to enhancing the accuracy of FNA diagnosis of lymphoma is the multi parameter approach in which the cytomorphologic features are evaluated in correlation with the results of ancillary studies and clinical context. A full understanding of the current lymphoma classification, clinical features associated with each lymphoma subtype and the impact of the diagnosis on patient management is essential in FNA diagnosis of lymphoma. It is also important to recognize the limitations of FNA in the primary diagnosis of some subtypes of lymphoma, and tissue biopsy should be recommended for a definitive diagnosis and subclassification in such cases.

CD200 flow cytometric assessment and semiquantitative immunohistochemical staining distinguishes hairy cell leukemia from hairy cell leukemia-variant and other B-cell lymphoproliferative disorders

OBJECTIVES

To evaluate CD200 expression in B-cell proliferative disorders.

METHODS

We analyzed 180 recent specimens of B-cell neoplasms for CD200 expression by flow cytometric immunophenotypic analysis, which is better able to assess relative intensity of staining than immunohistochemical staining.

RESULTS

We found that hairy cell leukemia exhibits a high level of staining for CD200 in comparison to other B-cell lymphoproliferative disorders, including hairy cell leukemia-variant (HCL-V), marginal zone lymphoma, and lymphoplasmacytic lymphoma. We confirmed this observation by semiquantitative immunohistochemical staining.

CONCLUSIONS

Assessment of the CD200 expression level is helpful to distinguish HCL from HCL-V and other B-cell lymphoproliferative disorders and in the differential diagnosis of B-cell neoplasms in general.

Programmed death 1 and B and T lymphocyte attenuator immunoreceptors and their association with malignant T-lymphoproliferative disorders: brief review

Malignant T-cell lymphoproliferative diseases are relatively rare. T cells are activated through the T-cell receptor with the aid of costimulating molecules that can be either excitatory or inhibitory. Such pathways have been also implicated in mechanisms of malignant T-cell lymphoproliferative diseases' persistence and relapse by circumventing immune responses. To date, three major immunoinhibitory molecules have been recognized, namely programmed cell death-1 (PD-1), B and T lymphocyte attenuator (BTLA) and cytotoxic T lymphocyte antigen 4 (CTLA-4). Although CTLA-4 is considered the 'gatekeeper' of immune tolerance, PD-1 negatively regulates immune responses broadly, whereas BTLA activation has been shown to inhibit CD8+ cancer-specific T cells. Both PD-1 and BTLA downregulate proximal T-cell receptor signalling cascade and are involved in immune evasion of leukaemias and lymphomas, even after allogeneic stem cell transplantation. These immunoregulatory molecules can have seemingly a synergistic effect on weakening the immune response of patients with haematological malignancies, and their manipulation represents a very active field of preclinical as well as clinical interest.

Peripheral blood sCD3⁻ CD4⁺ T cells: a useful diagnostic tool in angioimmunoblastic T cell lymphoma

Angioimmunoblastic T cell lymphoma (AITL) belongs to the subgroup of mature T cell lymphomas according to the World Health Organization and is one of the common T cell lymphomas in Western countries. Particularly in cases in which histological confirmation cannot be easily achieved, immunophenotyping of peripheral blood can give important information for the differential diagnosis of AITL. sCD3⁻ CD4⁺ T cells are a typical feature of AILT in flow cytometry of peripheral blood. In this retrospective study, the diagnostic value of flow cytometry for the diagnosis 'AITL' was assessed by comparing the frequency of sCD3⁻ CD4⁺ T cells in leukemic AITL patients and in patients with other leukemic CD4⁺ T cell lymphomas. Immunophenotyping of peripheral blood by flow cytometry was performed in a lymphocyte gate using fluorochrome-labelled antibodies against CD3, CD2, CD4, CD5, CD7, CD8, CD10, CD14, CD16, CD19, CD56, CD57 and T cell receptor. In 17/17 leukemic AITL patients, a small but distinct population of sCD3⁻ CD4⁺ T cells was detected (mean percentage of sCD3⁻ CD4⁺ T cells in the lymphocyte gate: 11.9 ± 15.4%, range 0.1-51.8%). In contrast, sCD3⁻ CD4⁺ T cells were found in only 1/40 patients with other leukemic CD4⁺ T cell lymphomas (one patient with mycosis fungoides). sCD3⁻ CD4⁺ T cells have a high positive predictive value (94%) for the diagnosis 'AITL'. Flow cytometry is particularly useful in the differential diagnosis of AITL, even if the aberrant T cell population has a very low frequency. Further biological characterization of this subfraction of lymphoma cells is warranted.

Pathobiology of T-cell and NK-cell lymphomas

T-cell and NK-cell lymphomas are uncommon lymphomas with an aggressive clinical course. The causes and precise cellular origins of most T-cell lymphomas are still not well defined. The WHO classification utilizes morphologic and immunophenotypic features in conjunction with clinical aspects and in some instances genetics to delineate a prognostically and therapeutically meaningful categorization. The anatomic localization of neoplastic T-cells and NK-cells parallels in part their proposed normal cellular counterparts and functions. T-cells of the adaptive immune system are mainly based in lymph nodes and peripheral blood, whereas lymphomas derived from T-cells and NK-cells of the innate immune system are mainly extranodal. This approach allows for better understanding of some of the manifestations of the T-cell and NK-cell lymphomas, including their cellular distribution, some aspects of morphology and even associated clinical findings.

Follicular center helper T-cell (TFH) marker positive mycosis fungoides/Sezary syndrome

We identified 11 patients with CD10(+) cutaneous T-cell lymphoma by flow cytometry. All cases were CD4(+) and CD8(-). Three patients had extensive lymphadenopathy, systemic symptoms and an aggressive clinical course consistent with angioimmunoblastic T-cell lymphoma or peripheral T-cell lymphoma. However, 8 of the 11 patients had a prolonged disease course with gross morphology, histology and tumor cell phenotype indistinguishable from mycosis fungoides or Sezary syndrome. Immunohistochemical studies confirmed CD10 expression in seven of the eight cases and revealed the lymphoma cells were Bcl-6(+), PD-1(+), and EBV(-). Two had significant expression of CXCL-13(+). The findings indicate that lymphoma cells from mycosis fungoides or Sezary syndrome may express follicular center helper T-cell markers CD10, Bcl-6, and PD-1 and occasionally CXCL-13. The expression of these markers in some cases of mycosis fungoides/Sezary syndrome suggests follicular center helper T-cell differentiation and may lead to confusion in distinguishing mycosis fungoides/Sezary syndrome from other follicular center helper T-cell marker positive T-cell lymphomas with cutaneous manifestations.

Follicular T-cell lymphoma: a member of an emerging family of follicular helper T-cell derived T-cell lymphomas

Unlike B-cell lymphomas, where knowledge of normal B-cell origin and differentiation has greatly contributed to their classification, the current classification of peripheral T-cell lymphomas is limited by a lack of understanding of their cellular origin. In the current World Health Organization classification of lymphomas, follicular T-cell lymphoma was formally recognized as a morphologic variant of peripheral T-cell lymphoma, not otherwise specified. There is growing evidence, however, that follicular T-cell lymphoma may be a unique clinicopathologic entity based on its morphologic features and derivation from follicular helper T-cells. In addition, there are abundant recent data supporting the concept that follicular helper T-cells can give rise to other types of T-cell lymphoma, including angioimmunoblastic T-cell lymphoma, primary cutaneous CD4+ small/medium T-cell lymphoma, and a subset of neoplasms, in addition to follicular T-cell lymphoma, currently classified as peripheral T-cell lymphoma, not otherwise specified. In this review, we focus primarily on the clinicopathologic, immunophenotypic, and molecular features of follicular T-cell lymphoma and discuss its potential relationship with other types of T-cell lymphoma thought to be derived from follicular helper T-cells.

EuroFlow antibody panels for standardized n-dimensional flow cytometric immunophenotyping of normal, reactive and malignant leukocytes

Most consensus leukemia & lymphoma antibody panels consist of lists of markers based on expert opinions, but they have not been validated. Here we present the validated EuroFlow 8-color antibody panels for immunophenotyping of hematological malignancies. The single-tube screening panels and multi-tube classification panels fit into the EuroFlow diagnostic algorithm with entries defined by clinical and laboratory parameters. The panels were constructed in 2-7 sequential design-evaluation-redesign rounds, using novel Infinicyt software tools for multivariate data analysis. Two groups of markers are combined in each 8-color tube: (i) backbone markers to identify distinct cell populations in a sample, and (ii) markers for characterization of specific cell populations. In multi-tube panels, the backbone markers were optimally placed at the same fluorochrome position in every tube, to provide identical multidimensional localization of the target cell population(s). The characterization markers were positioned according to the diagnostic utility of the combined markers. Each proposed antibody combination was tested against reference databases of normal and malignant cells from healthy subjects and WHO-based disease entities, respectively. The EuroFlow studies resulted in validated and flexible 8-color antibody panels for multidimensional identification and characterization of normal and aberrant cells, optimally suited for immunophenotypic screening and classification of hematological malignancies.

The darker side of follicular helper T cells: from autoimmunity to immunodeficiency

Follicular helper T (T(FH)) cells represent a distinct subset of CD4⁺ helper T (T(H)) cells specialized in providing help to B cells. They are characterized by their unique transcriptional profile (Bcl6), surface marker expression (CXCR5, PD-1, ICOS and CD40L) and cytokine production pattern (IL-21 and IL-6). T(FH) cells provide help to B cells both to form germinal centers (GCs) and to differentiate into memory B cells and plasma cells for generation of humoral responses. However, there is emerging evidence that implicates T(FH) cells in the development of various human pathologies, such as autoimmune diseases, immunodeficiency and lymphoma. This review focuses on the current progress in this area including mouse and human studies. A clearer understanding of the mechanisms of T(FH) cell-mediated immunity and pathology may be exploited for rational development of therapeutic strategies.

Atypical angioimmunoblastic T-cell lymphomas masquerading as systemic polyclonal B-immunoblastic proliferation

Angioimmunoblastic T cell lymphoma (AITL) is a relatively rare peripheral T cell lymphoma derived from follicular T helper cells. AITL has a varied presentation, both clinically and morphologically. AITL can pose a diagnostic challenge as it may be difficult to identify and characterize the neoplastic cells among the polymorphous infiltrates composed of polyclonal B immunoblasts and plasma cells. In AITL, the reactive B cell and plasma cell proliferation is secondary to dysregulated secretion of cytokines such as interleukin-6 by the neoplastic follicular T helper cells. SPBIP is a condition of unknown etiopathogenesis characterized by systemic involvement by polyclonal B immunoblasts and plasma cells. We report two cases of AITL, which are presented with atypical findings making it difficult to diagnose. The cases had features similar to SPBIP. Our cases highlight the importance of screening cases of polyclonal plasmacytosis and SPBIP like cases for underlying AITL.

Clinicopathologic analysis of peripheral T-cell lymphoma, follicular variant, and comparison with angioimmunoblastic T-cell lymphoma: Bcl-6 expression might affect progression between these disorders

We examined clinicopathologic findings in 17 cases of peripheral T-cell lymphoma, follicular variant (f-PTCL), and compared these findings with angioimmunoblastic T-cell lymphoma (AITL) to determine whether they were identical to the spectrum of changes seen in AITL and how each of the findings in f-PTCL were related to the characteristics of AITL. Almost all f-PTCL cases showed pathologic characteristics of AITL and immunohistochemical positivities in lymphoma cells for CD4, CD10, Bcl-6, PD-1, and CXCL13. Except for pathologic characteristics, clinicopathologic findings in f-PTCL had few significant differences from AITL. The positive rate for Bcl-6 expression in neoplastic cells was significantly associated with the frequency of polymorphic infiltrates, vascular proliferation, B-immunoblasts, clear cells, Epstein-Barr virus-positive lymphocytes, hepatosplenomegaly, and skin rash. Our study confirmed the continuity between f-PTCL and AITL. Moreover, Bcl-6 expression in f-PTCL was statistically associated with the characteristics of AITL.

CXCL13 as a novel marker for diagnosis and disease monitoring in pediatric PTLD

Posttransplant lymphoproliferative disease (PTLD) is a severe complication of immunosuppressive treatment in organ-grafted children. Early diagnosis of PTLD is hampered by both unspecific clinical symptoms and lack of easy accessible markers. The homeostatic chemokine CXCL13, which plays a crucial role in B-cell homing and lymphoid organ development, is expressed in some lymphomatous diseases. This study aims to investigate whether serum CXCL13 (sCXCL13) levels correlate with occurrence and regression of PTLD in pediatric solid-organ graft recipients. Serum samples from PTLD patients (n = 21), patients with Epstein-Barr virus (EBV) reactivation (n = 18), and healthy age-matched controls (n = 19) were tested for CXCL13 using a commercially available ELISA kit. sCXCL13 levels were significantly higher in PTLD patients than in healthy children. PTLD patients had also higher sCXCL13 values than pediatric solid-organ recipients with EBV reactivation. An increase in sCXCL13 levels was observed from EBV reactivation to PTLD diagnosis in most cases. Elevated sCXCL13 levels were detected up to 2 years prior to PTLD diagnosis and correlated well with response to cytoreductive treatment in individual patients. sCXCL13, thus, may be a readily available surrogate marker for the diagnosis of PTLD and for monitoring of response to treatment in patients with initially elevated sCXCL13 levels.