Neoplastic T cells in angioimmunoblastic T-cell lymphoma express CD10

Clonal Hematopoiesis and Bone Marrow Infiltration in Patients With Follicular Helper T-Cell Lymphoma of Angioimmunoblastic Type

Follicular helper T-cell (TFH) lymphoma harbors recurrent mutations of RHOAG17V, IDH2R172, TET2, and DNMT3A. TET2 and DNMT3A mutations are the most frequently affected genes in clonal hematopoiesis (CH). The aim of our study was to investigate the frequency of CH in bone marrow biopsies (BMB) of TFH/angioimmunoblastic T-cell lymphoma (TFH-AITL) patients and its association with myeloid neoplasms. A total of 29 BMB from 22 patients with a diagnosis of TFH-AITL were analyzed by next-generation sequencing (NGS) with a custom panel. Morphologically, 5 BMB revealed that TFH-AITL infiltrates of >5% of bone marrow (BM) cellularity confirmed in 4 cases by NGS-based T-cell clonality. IDH2R172 was demonstrated only in 1 (3%) of 29, and RHOAG17V in 2 (7%) of 29 samples. TET2 and DNMT3A were identified in 24 (83%) of 29 and 17 (59%) of 29 BMB, respectively. In the parallel lymph node the frequencies of mutations were 27% (IDH2R172), 64% (RHOAG17V), 86% (TET2), and 50% (DNMT3A). TET2 and/or DNMT3A mutations identical in lymph node and BMB were present in 18 (82%) of 22 patients, regardless of BM infiltration. In 3 cases the CH mutations were detected 13, 41, and 145 months before TFH-AITL diagnosis. Cases with TET2/DNMT3A mutations and BM variant allele frequencies >40% (7/18, 39%) showed lower blood counts. However, only low platelet count was statistically significant (P = .024). Myeloid neoplasms and/or myelodysplastic syndrome-related mutations were identified in 4 cases (4/22; 18%); all with high TET2 variant allele frequencies (>40%; P = .0114). In conclusion, CH is present in 82% of TFH-AITL and can be demonstrated up to 145 months before TFH-AITL diagnosis. NGS T-cell clonality analysis is an excellent tool to confirm TFH-AITL BM infiltration. Concurrent myeloid neoplasms were identified in 18% of the cases and were associated with TET2 mutations with high allelic burden (>40%). We demonstrated that myeloid neoplasms might occur simultaneously or precede the diagnosis of TFH lymphoma.

Comparison of Follicular Helper T-Cell Markers with the Expression of the Follicular Homing Marker CXCR5 in Peripheral T-Cell Lymphomas-A Reappraisal of Follicular Helper T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCLs) expressing multiple follicular T helper (TFH) cell-related antigens are now classified as TFH lymphomas (TFHL), including angioimmunoblastic, follicular, and not otherwise specified (NOS) types. CXCR5 is the TFH cell-defining chemokine receptor that, together with its ligand CXCL13, plays a critical role in the development of follicles and the positioning of TFH and B cells within follicles. A comprehensive immunomorphologic study was performed to investigate the expression pattern of CXCR5 in a large cohort of nodal PTCLs, particularly those with a TFH cell phenotype, and to compare its expression with six other TFH cell-related antigens. We found that CXCR5 is widely expressed in neoplastic TFH cells, except in TFHL-NOS, and represents a specific marker of this lymphoma entity. Our results suggest that CXCR5 directs the distribution of neoplastic T cells in the affected lymph nodes and may influence the formation of the pathognomic pathological FDC network.

Clinical features and prognostic outcomes of angioimmunoblastic T cell lymphoma in an Asian multicenter study

In our Asian multicenter retrospective study, we investigated the clinical prognostic factors affecting the outcomes of AITL patients and identified a novel prognostic index relevant in the Asian context. In our 174-patient cohort, the median PFS and OS was 1.8 years and 5.6 years respectively. Age > 60, bone marrow involvement, total white cell count >12 × 109/L and raised serum lactate dehydrogenase were associated with poorer PFS and OS in multivariate analyses. This allowed for a prognostic index (AITL-PI) differentiating patients into low (0-1 factors, n = 64), moderate (2 factors, n = 59) and high-risk (3-4 factors, n = 49) subgroups with 5-year OS of 84.0%, 44.0% and 28.0% respectively (p < 0.0001). POD24 proved to be strongly prognostic (5-year OS 24% vs 89%, p < 0.0001). Exploratory gene expression studies were performed and disparate immune cell profiles and cell signaling signatures were seen in the low risk group as compared to the intermediate and high risk groups.

A comparison of the International Consensus and 5th WHO classifications of T-cell lymphomas and histiocytic/dendritic cell tumours

Since the publication in 2017 of the revised 4th Edition of the World Health Organization (WHO) classification of haematolymphoid tumours, here referred to as WHO-HAEM4, significant clinicopathological, immunophenotypic and molecular advances have been made in the field of lymphomas, contributing to refining the diagnostic criteria of several diseases, upgrading entities previously defined as provisional and identifying new entities. This process has resulted in two recent classification proposals of lymphoid neoplasms: the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In this paper, we review and compare the two classifications in terms of diagnostic criteria and entity definition, focusing on T-cell lymphomas and histiocytic/dendritic cell tumours. Moreover, we update the genetic data of the various pathological entities. The main goal is to provide a tool to facilitate the work of the pathologists, haematologists and researchers involved in the diagnosis and treatment of these haematological malignancies.

Role of cytokine in malignant T-cell metabolism and subsequent alternation in T-cell tumor microenvironment

T cells are an important component of adaptive immunity and T-cell-derived lymphomas are very complex due to many functional sub-types and functional elasticity of T-cells. As with other tumors, tissues specific factors are crucial in the development of T-cell lymphomas. In addition to neoplastic cells, T- cell lymphomas consist of a tumor micro-environment composed of normal cells and stroma. Numerous studies established the qualitative and quantitative differences between the tumor microenvironment and normal cell surroundings. Interaction between the various component of the tumor microenvironment is crucial since tumor cells can change the microenvironment and vice versa. In normal T-cell development, T-cells must respond to various stimulants deferentially and during these courses of adaptation. T-cells undergo various metabolic alterations. From the stage of quiescence to attention of fully active form T-cells undergoes various stage in terms of metabolic activity. Predominantly quiescent T-cells have ATP-generating metabolism while during the proliferative stage, their metabolism tilted towards the growth-promoting pathways. In addition to this, a functionally different subset of T-cells requires to activate the different metabolic pathways, and consequently, this regulation of the metabolic pathway control activation and function of T-cells. So, it is obvious that dynamic, and well-regulated metabolic pathways are important for the normal functioning of T-cells and their interaction with the microenvironment. There are various cell signaling mechanisms of metabolism are involved in this regulation and more and more studies have suggested the involvement of additional signaling in the development of the overall metabolic phenotype of T cells. These important signaling mediators include cytokines and hormones. The impact and role of these mediators especially the cytokines on the interplay between T-cell metabolism and the interaction of T-cells with their micro-environments in the context of T-cells lymphomas are discussed in this review article.

Follicular helper T-cell lymphomas: disease spectrum, relationship with clonal hematopoiesis, and mimics. A report of the 2022 EA4HP/SH lymphoma workshop

Follicular helper T-cell lymphomas (TFH lymphomas) were discussed in session V of the lymphoma workshop of the European Association for Haematopathology (EA4HP)/Society for Hematopathology (SH) 2022 meeting in Florence, Italy. The session focused on the morphologic spectrum of TFH lymphoma, including its three subtypes: angioimmunoblastic-type (AITL), follicular-type, and not otherwise specified (NOS). The submitted cases encompassed classic examples of TFH lymphoma and unusual cases such as those with early or indolent presentations, associated B-cell proliferations, or Hodgkin/Reed-Sternberg-like cells. The relationship between TFH lymphoma and clonal hematopoiesis was highlighted by several cases documenting divergent evolution of myeloid neoplasm and AITL from shared clonal mutations. The distinction between TFH lymphoma and peripheral T-cell lymphoma, not otherwise specified (PTCL, NOS), was stressed, and many challenging examples were presented. Various cases highlighted the difficulties of differentiating TFH lymphoma from other established types of lymphoma and reactive conditions. Cutaneous T-cell lymphoma expressing TFH markers, particularly when resulting in lymph node involvement, should be distinguished from TFH lymphomas. Additional immunophenotyping and next-generation sequencing studies were performed on various cases in this session, highlighting the importance of these technologies to our current understanding and classification of TFH lymphomas.

DNMT3AR882H accelerates angioimmunoblastic T-cell lymphoma in mice

DNA methylation-related genes, including TET2, IDH2, and DNMT3A are highly frequently mutated in angioimmunoblastic T-cell lymphoma (AITL), an aggressive malignancy of T follicular helper (Tfh) cells associated with aberrant immune features. It has been shown that TET2 loss cooperates with RHOA^G17V to promote AITL in mice but the functional role of DNMT3A mutations in AITL remains unclear. Here, we report that DNMT3A^R882H, the most common mutation of DNMT3A in AITL, accelerates the development of Tet2^-/-; RHOA^G17V AITL in mice, indicated by the expansion of malignant Tfh cells and aberrant B cells, skin rash, and significantly shortened disease-free survival. To understand the underlying cellular and molecular mechanisms, we performed single-cell transcriptome analyses of lymph nodes of mice transplanted with Tet2^-/-, Tet2^-/-; RHOA^G17V or DNMT3A^R882H; Tet2^-/-; RHOA^G17V hematopoietic stem and progenitor cells. These single-cell landscapes reveal that DNMT3A mutation further activates Tfh cells and leads to rapid and terminal differentiation of B cells, probably through enhancing the interacting PD1/PD-L1, ICOS/ICOSL, CD28/CD86, and ICAM1/ITGAL pairs. Our study establishes the functional roles of DNMT3A mutation in AITL and sheds light on the molecular mechanisms of this disease.

[Classification of peripheral T-cell lymphomas : News and open questions]

Recently, two new classifications were released: the International Consensus Classification (ICC) drafted by the Clinical Advisory Committee and the short version of the 5th Edition of the WHO classification of hematolymphoid tumors. In light of new clinical, morphological, and molecular data, both classifications also revised the classification of peripheral T‑cell lymphomas. In addition to relatively minor changes in terminology and disease definitions, both new classifications mirror the considerable gain of knowledge on the genetic alterations of different T‑cell lymphoma entities. The present review summarizes the most important changes for T‑cell lymphomas in both classifications, the differences between the classifications, and diagnostically relevant issues.

Angioimmunoblastic T-cell lymphoma and correlated neoplasms with T-cell follicular helper phenotype: from molecular mechanisms to therapeutic advances

Angioimmunoblastic T-cell lymphoma (AITL) is the second most frequent subtype of mature T-cell lymphoma (MTCL) in the Western world. It derives from the monoclonal proliferation of T-follicular helper (TFH) cells and is characterized by an exacerbated inflammatory response and immune dysregulation, with predisposition to autoimmunity phenomena and recurrent infections. Its genesis is based on a multistep integrative model, where age-related and initiator mutations involve epigenetic regulatory genes, such as TET-2 and DNMT3A. Subsequently, driver-mutations, such as RhoA G17V and IDH-2 R172K/S promote the expansion of clonal TFH-cells ("second-hit"), that finally begin to secrete cytokines and chemokines, such as IL-6, IL-21, CXCL-13 and VEGF, modulating a network of complex relationships between TFH-cells and a defective tumor microenvironment (TME), characterized by expansion of follicular dendritic cells (FDC), vessels and EBV-positive immunoblasts. This unique pathogenesis leads to peculiar clinical manifestations, generating the so-called "immunodysplastic syndrome", typical of AITL. Its differential diagnosis is broad, involving viral infections, collagenosis and adverse drug reactions, which led many authors to use the term "many-faced lymphoma" when referring to AITL. Although great advances in its biological knowledge have been obtained in the last two decades, its treatment is still an unmet medical need, with highly reserved clinical outcomes. Outside the setting of clinical trials, AITL patients are still treated with multidrug therapy based on anthracyclines (CHOP-like), followed by up-front consolidation with autologous stem cell transplantation (ASCT). In this setting, the estimated 5-year overall survival (OS) is around 30-40%. New drugs, such as hypomethylating agents (HMAs) and histone deacetylase inhibitors (HDAi), have been used for relapsed/refractory (R/R) disease with promising results. Such agents have their use based on a biological rationale, have significant potential to improve the outcomes of patients with AITL and may represent a paradigm shift in the therapeutic approach to this lymphoma in the near future.

Pathologic and molecular insights in nodal T-follicular helper cell lymphomas

T-follicular helper (TFH) cells are one of the T-cell subsets with a critical role in the regulation of germinal center (GC) reactions. TFH cells contribute to the positive selection of GC B-cells and promote plasma cell differentiation and antibody production. TFH cells express a unique phenotype characterized by PD-1^hi, ICOS^hi, CD40L^hi, CD95^hi, CTLA^hi, CCR7^lo, and CXCR5^hi . Three main subtypes of nodal TFH lymphomas have been described: 1) angioimmunoblastic-type, 2) follicular-type, and 3) not otherwise specified (NOS). The diagnosis of these neoplasms can be challenging, and it is rendered based on a combination of clinical, laboratory, histopathologic, immunophenotypic, and molecular findings. The markers most frequently used to identify a TFH immunophenotype in paraffin-embedded tissue sections include PD-1, CXCL13, CXCR5, ICOS, BCL6, and CD10. These neoplasms feature a characteristic and similar, but not identical, mutational landscape with mutations in epigenetic modifiers (TET2, DNMT3A, IDH2), RHOA, and T-cell receptor signaling genes. Here, we briefly review the biology of TFH cells and present a summary of the current pathologic, molecular, and genetic features of nodal lymphomas. We want to highlight the importance of performing a consistent panel of TFH immunostains and mutational studies in TCLs to identify TFH lymphomas.

Types of T-cell lymphoma-a cytogenetic perspective

T cell lymphoma, a type of non-Hodgkin lymphomas is a rare form of malignancy with poor outcomes. TCLS are a heterogeneous group of lymphoid malignancies that occur in nodal and extranodal sites. There are two main types of TCLs namely T-lymphoblastic lymphoma/leukemia and Peripheral T-cell lymphomas classified based on clinical manifestations and cytogenetic mutations. The use of advance technology like karyotyping, fluorescent in situ hybridization (FISH), comparative genomic hybridization (CGH) has allowed us to study TCLs in detail and to observe a different biochemical change that occurs in different TCLs allowing us to classify and treat them differently. This review focuses on the different mutations occurring in different TCLs and how they help us distinguish one type from another.

The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Lymphoid Neoplasms

We herein present an overview of the upcoming 5^th edition of the World Health Organization Classification of Haematolymphoid Tumours focussing on lymphoid neoplasms. Myeloid and histiocytic neoplasms will be presented in a separate accompanying article. Besides listing the entities of the classification, we highlight and explain changes from the revised 4^th edition. These include reorganization of entities by a hierarchical system as is adopted throughout the 5^th edition of the WHO classification of tumours of all organ systems, modification of nomenclature for some entities, revision of diagnostic criteria or subtypes, deletion of certain entities, and introduction of new entities, as well as inclusion of tumour-like lesions, mesenchymal lesions specific to lymph node and spleen, and germline predisposition syndromes associated with the lymphoid neoplasms.

Human Germinal Center-associated Lymphoma (HGAL) Is a Reliable Marker of Normal and Neoplastic Follicular Helper T Cells Including Angioimmunoblastic T-Cell Lymphoma

The diagnosis of angioimmunoblastic T-cell lymphoma (AITL) is complex and requires the demonstration of a T-follicular helper (TFH) phenotype. Immunophenotypic markers that detect the TFH phenotype are highly variable, thereby necessitating the use of 3 to 5 TFH markers to substantiate a TFH phenotype. We tested the utility of germinal center markers human germinal center-associated lymphoma (HGAL) and LIM-domain only 2 (LMO2) in detecting a TFH phenotype. We compared their staining to that of 6 TFH markers in current use, PD-1, ICOS, CXCL13, SAP, CD10, and BCL6, in a cohort of 23 AITL. Our results show that although both markers can detect a TFH phenotype, HGAL was superior to LMO2 in the percent of cells stained and the intensity of staining, 2 variables used to generate H-scores. Using H-scores as the metric, HGAL was most comparable to BCL6 among the currently used TFH markers and was more sensitive than CXCL13, SAP, CD10, and LMO2. PD-1 and ICOS emerged as the most robust of the 8 markers tested in this study in detecting a TFH phenotype. We conclude that HGAL is a reliable marker of TFH cells and can aid in the diagnosis of lymphomas of TFH derivation, particularly in the recognition of early patterns of AITL.

Recent Advances in Diagnosis and Therapy of Angioimmunoblastic T Cell Lymphoma

Angioimmunoblastic T cell lymphoma (AITL) is a common subtype of mature peripheral T cell lymphoma (PTCL). As per the 2016 World Health Organization classification, AITL is now considered as a subtype of nodal T cell lymphoma with follicular helper T cells. The diagnosis is challenging and requires a constellation of clinical, laboratory and histopathological findings. Significant progress in the molecular pathophysiology of AITL has been achieved in the past two decades. Characteristic genomic features have been recognized that could provide a potential platform for better diagnosis and future prognostic models. Frontline therapy for AITL was mainly depending on chemotherapy and the management of relapsed or refractory AITL is still unsatisfactory with a very poor prognosis. Upfront transplantation offers better survival. Novel agents have been introduced recently with promising outcomes. Several clinical trials of combinations using novel agents are underway. Herein, we briefly review recent advances in AITL diagnosis and the evolving treatment landscape.

Mutation analysis links angioimmunoblastic T-cell lymphoma to clonal hematopoiesis and smoking

Background

Although advance has been made in understanding the pathogenesis of mature T-cell neoplasms, the initiation and progression of angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), remain poorly understood. A subset of AITL/PTCL-NOS patients develop concomitant hematologic neoplasms (CHN), and a biomarker to predict this risk is lacking.

Methods

We generated and analyzed the mutation profiles through 537-gene targeted sequencing of the primary tumors and matched bone marrow/peripheral blood samples in 25 patients with AITL and two with PTCL-NOS.

Results

Clonal hematopoiesis (CH)-associated genomic alterations, found in 70.4% of the AITL/PTCL-NOS patients, were shared among CH and T-cell lymphoma, as well as concomitant myeloid neoplasms or diffuse large B-cell lymphoma (DLBCL) that developed before or after AITL. Aberrant AID/APOBEC activity-associated and tobacco smoking-associated mutational signatures were respectively enriched in the early CH-associated mutations and late non-CH-associated mutations during AITL/PTCL-NOS development. Moreover, analysis showed that the presence of CH harboring ≥2 pathogenic TET2 variants with ≥15% of allele burden conferred higher risk for CHN (p=0.0006, hazard ratio = 14.01, positive predictive value = 88.9%, negative predictive value = 92.1%).

Conclusions

We provided genetic evidence that AITL/PTCL-NOS, CH, and CHN can frequently arise from common mutated hematopoietic precursor clones. Our data also suggests smoking exposure as a potential risk factor for AITL/PTCL-NOS progression. These findings provide insights into the cell origin and etiology of AITL and PTCL-NOS and provide a novel stratification biomarker for CHN risk in AITL patients.

Funding

R01 grant (CA194547) from the National Cancer Institute to WT.

Update on the Classification and Diagnostic Approaches of Mature T-Cell Lymphomas

CONTEXT.—

In the 2017 revised World Health Organization classification of tumors of hematopoietic and lymphoid tissues, some mature T-cell lymphomas are reclassified and a few new provisional entities are established based on new data from clinical and laboratory studies. T follicular helper cell lymphoma is identified by T follicular helper cell markers. Anaplastic large cell lymphoma, ALK negative, is a better-defined entity based on genetic abnormalities, and breast implant-associated anaplastic large cell lymphoma is recognized as a provisional entity. The gastrointestinal T-cell lymphomas are reclassified, with addition of a new provisional entity, indolent T-cell lymphoproliferative disorder of the gastrointestinal tract, characterized by an indolent clinical course.

OBJECTIVE.—

To review the diagnostic approaches of reclassified and newly established entities of mature T-cell lymphomas, focusing on significant immunophenotypic features and molecular genetic abnormalities. Relevant new discoveries after the publication of the 2017 World Health Organization classification are included.

DATA SOURCES.—

Information from the literature most relevant to 2017 World Health Organization revised classification and publications after 2016.

CONCLUSIONS.—

Incorporating clinical, morphologic, and immunophenotypic features usually provides sufficient evidence to reach a preliminary diagnosis of mature T-cell lymphoma. Molecular genetic studies can be very helpful for the final diagnosis and classification, especially in challenging cases. Some molecular genetic features have been found in breast implant-associated anaplastic large cell lymphoma, distinct from anaplastic large cell lymphoma, ALK negative. Immunohistochemical staining of 4 markers may enable further subtyping of peripheral T-cell lymphomas.

Angioimmunoblastic T-cell lymphoma diagnosed from pleural fluid by integration of morphologic, immunophenotypic, and molecular findings

An 88-year-old man with end-stage renal disease on hemodialysis presented with shortness of breath and was found to have lower extremity edema and bilateral pleural effusions on a chest X-ray. A therapeutic and diagnostic thoracentesis was performed, and cytologic examination revealed atypical mononuclear cells. Based on this, flow cytometry was performed on the pleural fluid, along with immunostains on the cellblock and a next-generation sequencing (NGS) panel. A definitive diagnosis of angioimmunoblastic T-cell lymphoma (AITL) was made based on demonstrating an atypical T follicular helper cell population expressing CD10, BCL6, CXCL13, CD200, CD57, and PD1, and detection of pathogenic variants in RHOA, IDH2, and TET2. This case represents the first reported case where a primary diagnosis of AITL was made on a body fluid specimen and highlights how immunophenotyping and NGS can provide a definitive diagnosis of AITL on a cytologic specimen.

How I Diagnose Angioimmunoblastic T-Cell Lymphoma

OBJECTIVES

Angioimmunoblastic T-cell lymphoma (AITL) is a subtype of peripheral T-cell lymphoma derived from T-follicular helper cells. For pathologists, diagnosing AITL may be challenging due to its wide clinical and histopathologic spectrum, which can mimic a variety of reactive and neoplastic processes.

METHODS

We summarize and discuss the clinicopathologic features of AITL, emphasizing diagnostic tools available to the practicing pathologist. Common diagnostic dilemmas are discussed.

RESULTS

AITL exhibits various histologic patterns and is often associated with a prominent microenvironment that can obscure the neoplastic cells. Atypical B-cell proliferations, which can take a number of forms, are common in AITL, and clonal B-cell expansion can be seen. The atypical B cells can closely resemble Hodgkin/Reed-Sternberg cells, leading to misdiagnosis as classic Hodgkin lymphoma. Molecular studies have revealed recurrent genetic alterations, which can aid in differential diagnosis, particularly in problematic cases.

CONCLUSIONS

Given the complex diagnostic challenges in AITL, an integrated approach, incorporating clinical, morphologic, immunophenotypic, and molecular findings, is helpful to reach an accurate diagnosis.

Progression of AITL-like tumors in mice is driven by Tfh signature proteins and T-B cross talk

Angioimmunoblastic T-cell lymphoma (AITL) is an aggressive peripheral T-cell lymphoma driven by a pool of neoplastic cells originating from T follicular helper (Tfh) cells and concomitant expansion of B cells. Conventional chemotherapies for AITL have shown limited efficacy, and as such, there is a need for improved therapeutic options. Because AITL originates from Tfh cells, we hypothesized that AITL tumors continue to rely on essential Tfh components and intimate T-cell-B-cell (T-B) interactions. Using a spontaneous AITL mouse model (Roquinsan/+ mice), we found that acute loss of Bcl6 activity in growing tumors drastically reduced tumor size, demonstrating that AITL-like tumors critically depend on the Tfh lineage-defining transcription factor Bcl6. Because Bcl6 can upregulate expression of signaling lymphocytic activation molecule-associated protein (SAP), which is known to promote T-B conjugation, we next targeted the SAP-encoding Sh2d1a gene. We observed that Sh2d1a deletion from CD4+ T cells in fully developed tumors also led to tumor regression. Further, we provide evidence that tumor progression depends on T-B cross talk facilitated by SAP and high-affinity LFA-1. In our study, AITL-like tumors relied heavily on molecular pathways that support Tfh cell identity and T-B collaboration, revealing potential therapeutic targets for AITL.

Clinicopathological Implications of RHOA Mutations in Angioimmunoblastic T-Cell Lymphoma: A Meta-analysis: RHOA mutations in AITL

BACKGROUND

Studies have recently shown that RHOA mutations play a crucial role in angioimmunoblastic T-cell lymphoma (AITL) pathogenesis. We aimed to pool data from these studies to provide a comparison of clinicopathological features between the RHOA mutant and RHOA wild-type groups in the AITL population.

METHODS

We searched PubMed and Web of Science for the keywords "RHOA AND lymphoma" and selected only studies reporting the clinical significance of RHOA mutations in AITL. We calculated the odds ratios (OR) or the mean difference with 95% CI using a random effect model.

RESULTS

Our pooled results showed a significant association between RHOA mutations and a T-follicular helper cell (TFH) phenotype, especially CD10 (OR, 5.16; 95% CI, 2.32-11.46), IDH2 mutations (OR, 10.70; 95% CI, 4.22-27.15), and TET2 mutations (OR, 7.03; 95% CI, 2.14-23.12). Although DNMT3A together with TET2 and IDH2 mutations are epigenetic gene alterations, we found an insignificant association between RHOA and DNMT3A mutations (OR, 1.72; 95% CI, 0.73-4.05). No significant associations of RHOA mutations with other clinicopathological features and overall survival were found.

CONCLUSIONS

RHOA mutations are strongly correlated with a T-follicular helper cell phenotype and epigenetic mutations such as TET2 and IDH2. Further studies with large AITL samples should be conducted to validate the relationship of TET2, DNMT3A, and RHOA co-mutations.

Management of Angioimmunoblastic T-Cell Lymphoma (AITL) and other T Follicular Helper Cell lymphomas (TFH PTCL)

Despite the remarkable improvements in the treatment and outcome of patients with aggressive B-cell lymphoma, the peripheral T-cell lymphomas (PTCL) continue to carry a poor prognosis with the presently available treatment options. The PTCL are very rare diseases that account for only 10,000 to 15,000 new cases per year in the United States. The World Health Organization's 2016 classification describes 29 distinct subtypes of PTCL, thus making these both rate and incredibly heterogenous. The 2 most common forms of PTCL, for example, peripheral T-cell lymphoma-not otherwise specified and angioimmunoblastic T-cell lymphoma , have an incidence of only 2500 and 1800 cases per year respectively, in the United States.

Management of ALCL and other CD30+ peripheral T-cell lymphomas with a focus on Brentuximab vedotin

Peripheral T-cell lymphomas (PTCL) are rare lymphoproliferative disorders with poor outcomes and high rates of relapse. Incidence varies although the most common subtypes include PTCL-not-otherwise specified, anaplastic large cell lymphoma, and angioimmunoblastic T-cell lymphoma. Anaplastic large cell lymphoma is characterized by near-universal CD30 expression and serves as a prototypic model for other CD30-expressing lymphomas. Historically, these neoplasms have been treated with regimens used in the treatment of aggressive B-cell lymphomas. Over the last decade, brentuximab vedotin, an antibody-drug conjugate, has been investigated to treat peripheral T-cell lymphomas expressing CD30. While first studied in the relapsed and refractory setting, it was later studied in the frontline setting in the ECHELON-2 trial with positive results and is now an approved treatment for CD30-expressing peripheral T-cell lymphomas. Other treatment options in the relapsed and refractory setting include histone deacetylase inhibitors, pralatrexate, and salvage multiagent chemotherapy regimens. Current research is underway regarding combination therapies and the use of other novel agents.

Clinicopathological characterization of follicular helper T-cell-derived peripheral T-cell lymphoma involving Waldeyer's ring

Follicular helper T-cell-derived peripheral T-cell lymphoma (TFH-derived PTCL) initially present in the Waldeyer's ring is a rare condition with a challenging diagnosis. This study aimed to evaluate the clinicopathological characteristics and diagnosis of Waldeyer's ring TFH-derived PTCL and raise awareness of this type of lymphoma. A series of 13 cases of Waldeyer's ring TFH-derived PTCL were retrospectively analyzed. Clinically, most patients presented with localized manifestations, such as painless cervical lymphadenopathy (7/13), pharyngalgia (6/13), and nasal obstruction (3/13), and systemic symptoms were uncommon. Macroscopically, plump mass (9/13) and nodular lesions (3/13) covered with intact and tense mucosa were the main findings on fiberoptic laryngoscopy examination. Pathologically, diffuse infiltration with atypical lymphocytes in the lamina propria (10/13) was the most common growth pattern. Clear cells (9/13) and vascular proliferation (11/13) within a polymorphic inflammatory background (11/13) were frequently observed. All cases expressed at least two TFH markers: PD-1 in 92.3% (12/13), BCL6 in 69.2% (9/13), CXCL13 in 53.8% (7/13), and CD10 in 46% (6/13). Targeted next-generation sequencing analysis identified frequent mutations, including TET2 (10/11), RHOA (6/11), DNMT3A (3/11), and IDH2 (2/11). The overall survival rate at 2 years was 35.5%, and survival analysis revealed that patients with localized disease showed better overall survival (P = 0.022). In conclusion, careful morphological observation combined with immunohistochemistry and molecular analysis would help in diagnosis of TFH-derived PTCL involving the Waldeyer's ring, which is a rare condition that frequently presents with atypical clinical manifestations.

Reactive Eosinophil Proliferations in Tissue and the Lymphocytic Variant of Hypereosinophilic Syndrome

OBJECTIVES

The 2019 Society for Hematopathology and European Association for Haematopathology Workshop reviewed the spectrum of neoplastic, nonneoplastic, and borderline entities associated with reactive eosinophilia in tissue.

METHODS

The workshop panel reviewed 46 cases covered in 2 workshop sessions.

RESULTS

The 46 cases were presented with their consensus diagnoses during the workshop. Reactive eosinophilia in lymph nodes and other tissues may be accompanied by or be distinct from peripheral blood eosinophilia. Reactive etiologies included inflammatory disorders such as Kimura disease and IgG4-related disease, which may show overlapping pathologic features and reactions to infectious agents and hypersensitivity (covered in a separate review). Hodgkin, T-cell, and B-cell lymphomas and histiocytic neoplasms can result in reactive eosinophilia. The spectrum of these diseases is discussed and illustrated through representative cases.

CONCLUSIONS

Reactive eosinophilia in lymph nodes and tissues may be related to both nonneoplastic and neoplastic lymphoid proliferations and histiocytic and nonhematolymphoid processes. Understanding the differential diagnosis of reactive eosinophilia and the potential for overlapping clinical and pathologic findings is critical in reaching the correct diagnosis so that patients can be treated appropriately.

Case Report: Composite Angioimmunoblastic T-Cell Lymphoma and Epstein-Barr Virus-Positive B-Cell Lymphoproliferative Disorder as Other Iatrogenic Immunodeficiency-Associated Lymphoproliferative Disorders

Immunosuppressants are widely used to treat patients with rheumatoid arthritis (RA), and their adverse effects have been known to cause other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPDs). We report a patient with RA who had been treated with methotrexate (MTX) and tacrolimus (TAC) and who developed whole body lymphadenopathy. We simultaneously confirmed angioimmunoblastic T-cell lymphoma (AITL) through a right cervical lymph node biopsy and Epstein-Barr virus-positive B-cell lymphoproliferative disorder (EBV-positive B-LPD) through a bone marrow examination. After cessation of immunosuppressant therapy, both LPDs completely disappeared. Patients with AITL are occasionally reported to develop B-cell lymphoma through reactivation of the EBV, which leads to clonal expansion in the microenvironment. Immunohistochemistry results revealed that both LPD components were positive for EBV-encoded RNA. Moreover, in this patient, the plasma EBV DNA level was found to be high; therefore, EBV infection was a probable etiology. Synchronous coexistence of AITL and B-LPD as an OIIA-LPD has rarely been reported. This case report is the first to discuss the disappearance of both LPDs on withdrawal of immunosuppressants only. AITL occasionally accompany B-LPD; however, this composite lymphoma comprised AITL and B-LPD, and OIIA-LPDs should not be overlooked.

A comprehensive analysis of RHOA mutation positive and negative angioimmunoblastic T-cell lymphomas by targeted deep sequencing, expression profiling and single cell digital image analysis

Angioimmunoblastic T-cell lymphoma (AITL) is a uniquely aggressive mature T-cell neoplasm. In recent years, recurrent genetic mutations in ras homolog family member A (RHOA), tet methylcytosine dioxygenase 2 (TET2), DNA methyltransferase 3 alpha (DNMT3A) and isocitrate dehydrogenase [NADP(+)] 2 (IDH2) have been identified as associated with AITL. However, a deep molecular study assessing both DNA mutations and RNA expression profile combined with digital image analysis is lacking. The present study aimed to evaluate the significance of molecular and morphologic features by high resolution digital image analysis in several cases of AITL. To do so, a total of 18 separate tissues from 10 patients with AITL were collected and analyzed. The results identified recurrent mutations in RHOA, TET2, DNMT3A, and IDH2, and demonstrated increased DNA mutations in coding, promoter and CCCTC binding factor (CTCF) binding sites in RHOA mutated AITLs vs. RHOA non-mutated cases, as well as increased overall survival in RHOA mutated patients. In addition, single cell computational digital image analysis morphologically characterized RHOA mutated AITL cells as distinct from cells from RHOA mutation negative patients. Computational analysis of single cell morphological parameters revealed that RHOA mutated cells have decreased eccentricity (more circular) compared with RHOA non-mutated AITL cells. In conclusion, the results from the present study expand our understanding of AITL and demonstrate that there are specific cell biological and morphological manifestations of RHOA mutations in cases of AITL.

Advances in understanding of angioimmunoblastic T-cell lymphoma

It has been nearly half a century since angioimmunoblastic T-cell lymphoma (AITL) was characterized in the early 1970’s. Our understanding of the disease has dramatically changed due to multiple discoveries and insights. One of the key features of AITL is aberrant immune activity. Although AITL is now understood to be a neoplastic disease, pathologists appreciated that it was an inflammatory condition. The more we understand AITL at cellular and genetic levels, the more we view it as both a neoplastic and an inflammatory disease. Here, we review recent progress in our understanding of AITL, focusing on as yet unsolved questions.

Atypical lymphoid hyperplasia in a patient undergoing tonsillectomy for severe obstructive sleep apnea

Tonsillectomy is a common procedure in the pediatric population, with subsequent microscopic examination of the specimen for cancer and other rare diagnoses occurring routinely. A 17 year-old female with a history of autoimmune vasculitis underwent adenotonsillectomy for severe obstructive sleep apnea. Pathology demonstrated small, medium and large lymphocytes and plasma cells obscuring the lymphoid follicles and germinal centers, with few Epstein-Barr virus positive lymphocytes. Tingible body macrophages were seen in the vaguely nodular areas. This reactive histologic pattern represents an atypical lymphoproliferative disorder never before documented in tonsils. Histopathologic images will be shown.

Combination of multicolor flow cytometry for circulating lymphoma cells and tests for the RHOAG17V and IDH2R172 hot-spot mutations in plasma cell-free DNA as liquid biopsy for the diagnosis of angioimmunoblastic T-cell lymphoma

We applied two-step multicolor flow cytometry (FCM) for circulating lymphoma cells in the blood of 20 patients with angioimmunoblastic T-cell lymphoma (AITL) and confirmed neoplastic T-cells in all. Eleven exhibited dim expression of CD3 and 7 lost its expression. The proportion of CD10⁺ lymphoma cells ranged widely from 0 to 100%, with a median of 15.7%. Ten patients demonstrated expansion of a single T-cell receptor β-chain repertoire. Lymphoma cells comprised 0.01 to 18.22% (median, 0.26%) of white cells and the absolute numbers ranged from 0.5 to 1491.6 cells (median, 29.3 cells) per microliter of blood. We next found that 14 (70%) and 3 (15%) patients carried RHOA^G17V and IDH2^R172 mutations, respectively, in cell-free DNA (cfDNA) in the plasma. The combination of multicolor FCM of the blood, and tests for RHOA^G17V and IDH2^R172 hot-spot mutations in plasma cfDNA provides a blood-based 'liquid biopsy' for the diagnosis of AITL.

Angioimmunoblastic T-cell lymphoma-like lymphadenopathy in mice transgenic for human RHOA with p.Gly17Val mutation

A missense mutation in RHOA encoding p.Gly17 Val has been reported to occur frequently in angioimmunoblastic T-cell lymphoma (AITL). Here, we describe a murine model which expresses the human RHOA mutant gene product in a T-cell specific manner and develops AITL-like symptoms. Most transgenic mice feature with latency one or two enlarged lymph nodes characterized by aberrant lymph node architecture, extensive lymphocytic infiltration, extrafollicular meshwork of follicular dendritic cells (FDC) and arborized endothelial venules. Importantly, we provide evidence for expansion of PD-1+ follicular helper T (Tfh) cells which are the neoplastic cells of AITL. In addition, we saw proliferation of B-cells leading to hypergammaglobulinemia and the presence of dominant T cell clonal populations. Transplantation of lymph node cells to immunocompromised mice partly recreated lymphadenopathy after a long latency and with low penetrance suggesting that cells have undergone partial transformation to a premalignant state. Transcriptomic profiling revealed that the gene expression pattern within affected lymph nodes of the mice closely resembles that of AITL patients with the identical RHOA p.Gly17 Val mutation. The murine model should, therefore, be useful in dissecting pathogenesis of AITL at the molecular level particularly for the cases with the RHOA p.Gly17Val mutation.

Application of a 5 Marker Panel to the Routine Diagnosis of Peripheral T-Cell Lymphoma With T-Follicular Helper Phenotype

The 2017 World Health Organization update introduced a new category of nodal peripheral T-cell lymphoma with T-follicular helper phenotype (PTCL-TFH) defined by expression of at least 2 or 3 TFH markers. Our study assesses the utility of an immunohistochemical panel of 5 TFH markers (CD10, BCL6, PD-1, CXCL13, and ICOS) for identification of TFH phenotype in angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified (NOS). Immunohistochemical for the 5 markers was performed on 22 cases of AITL and 29 cases of PTCL-NOS. Cases were reviewed for morphologic features characteristic of AITL. All AITL cases showed expression of ≥2 TFH markers. This panel resulted in reclassification of 41% PTCL-NOS cases to PTCL-TFH. Positive percent agreement for the TFH phenotype is 97% for PD1, 94% for ICOS, 44% for CD10 and CXCL13, and 29% for BCL6. Negative percent agreement for TFH phenotype is 100% for CD10, BCL6, and CXCL13, 82% for ICOS and 71% for PD1. AITL cases were more likely than PTCL-TFH cases to contain expanded CD21-positive follicular dendritic cell meshworks, clear cell cytology and polymorphous inflammatory background; however, there was a significant (P<0.005) Kruskal-Wallis trend in all morphologic variables between the 3 groups suggesting a continuum from PTCL-NOS to PTCL-TFH to AITL. The median number of morphologic features of AITL also correlated significantly with number of TFH markers positive (Spearman coefficient ρ=0.759). In summary, the stain panel chosen will have an impact on cases classified as PTCL-TFH. This entity may exist along a spectrum between PTCL-NOS and AITL.

Immunophenotyping of the PD-L1-positive cells in angioimmunoblastic T cell lymphoma and Hodgkin disease

Objective

Programmed death-1 (PD-1) and its ligand PD-L1 are now used as predictive biomarkers to guide clinical decisions. Precise characterization of PD-L1-positive cells may contribute to our knowledge of which patients derive benefit from the PD-L1 blockade therapy.

Results

To address this issue, we performed immunophenotyping of PD-L1-positive cells in Hodgkin lymphoma and in angioimmunoblastic T cell lymphoma (AITL) employing multiple immunofluorescent immunolabeling. We found that PD-L1-positive cells and PD-1-positive cells both in Hodgkin lymphoma and in AITL belong to two completely different cell lineages. In both lymphomas, PD-1 was found exclusively in T-lymphocytes, whereas PD-L1 was revealed in the tumor microenvironment cells including macrophages. PD-L1 was also detected in CD30-positive cells in Hodgkin lymphoma but not in AITL. The marker of B-cell lineage, CD20, was not detectable in PD-L1-positive cells both in AITL and in Hodgkin. Our study highlights the importance of comprehensive assessment of PD-1/PD-L1 regulatory pathways for employing PD-L1 as a predictive biomarker in clinical practice. PD-L1-antibody therapy is proven in Hodgkin lymphoma. Comparative immunophenotyping of the PD-1/PD-L1 axis provides a support for attempts to prove this principle also for AITL.

The new biology of PTCL-NOS and AITL: current status and future clinical impact

Peripheral T-cell lymphomas (PTCL) comprise a heterogeneous group of aggressive lymphoproliferative disorders almost all of which are associated with poor clinical outcomes. Angioimmunoblastic T-cell lymphoma (AITL) and some peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) have similarities to normal CD4⁺ T-cell subsets in their gene expression profiles. A cell of origin model is, therefore, emerging and is likely to be refined in the future. Follicular helper (Tfh) T cells are now established as the cell of origin of AITL and about 20% of PTCL-NOS. Sequencing studies have identified recurrent genetic alterations in epigenetic modifiers, T-cell receptor signalling pathway intermediates or RHOA, most commonly a specific mutation leading to RHOA G17V. While PTCL-NOS remains a diagnosis of exclusion, advances in genomics have identified subgroups expressing transcription factors TBX 21 (Th1-like origin) and GATA3 (Th2-like origin). These findings suggest new biomarkers and new therapeutic avenues including the hypomethylating agent azacytidine, or inhibitors of proximal T-cell receptor (TCR) signalling and potentially certain monoclonal antibodies. The advances over the past few years, therefore, prompt stratified medicine approaches to test biologically based treatments and determine the clinical utility of the new disease classifications.

Angioimmunoblastic T-cell Lymphoma: An Unusual Case in an Octogenarian

Angioimmunoblastic T-cell lymphoma (AITL) is an unusual subtype of mature peripheral T-cell lymphoma originating from the follicular T-helper cells and is often associated with autoimmune disorders. AITL is an aggressive lymphoma, presenting with constitutional symptoms, generalized lymphadenopathy, and hepatosplenomegaly. Immunohistochemistry and biopsy are diagnostic methods. The treatment modalities range from steroids, immunomodulators, and cytotoxic chemotherapy.

An 87-year-old female presented to the emergency department with cough, dyspnea, dizziness, night sweats, and unintentional weight loss with multiple discrete swellings over her body for a duration of three days. Her physical exam was significant for tachycardia with dry mucous membranes and generalized lymphadenopathy. However, no hepatosplenomegaly was noted. Laboratory investigations revealed neutrophilic leukocytosis (12.8 K/uL), with elevated inflammatory markers (C-reactive protein of 1.39 mg/dL, sedimentation rate of 86 mm/hour). The biopsy of the cervical lymph node revealed atypical lymphoid infiltrates. Flow cytometry showed CD10+ and CD4+/CD8+ T-cells with a minority of CD23+ B-cells, and fluorescence in situ hybridization (FISH) reported gains of the BCL2 gene region on chromosome 18, all of which were suggestive of AITL. She was transferred to an advanced hematology center for staging and targeted therapy.

A careful review of the patient with the prompt clinical and histological examination is essential for the correct diagnosis as the differentials are vast due to its non-specific clinical presentation and accurate treatment is a must for complete remission.

Angioimmunoblastic T-cell lymphoma in Taiwan reveals worse progression-free survival for RHOA G17V mutated subtype

Angioimmunoblastic T-cell lymphoma (AITL) carries genetic mutations of TET2, RHOA, and IDH2, but the prognostic impact of these mutations is not widely investigated. Although one study shows no difference in overall survival between patients with or without RHOA G17V mutation, a poor performance status is associated with RHOA G17V-mutated AITL, which is an independent adverse factor. We retrospectively investigated the prognostic impact of RHOA G17V mutation in AITL patients. A total of 31 cases were enrolled (male-to-female, 2.1; mean age: 62.8 years). RHOA G17V mutation was analyzed by deep sequencing. We found that in contrast to RHOA-wild type, patients with RHOA G17V-mutated AITL more frequently had B symptoms (p = .035), stronger PD1 expression (p = .045), ≥3 TFH markers (p = .011), higher blood vessel density (p<.001), and poorer progression-free survival (p = .046). These results support a role for RHOA genetic testing in AITL patients as ROHA G17V mutation carries a worse prognosis, probably associated with B symptoms and stage IV disease.

Update on peripheral T-cell lymphomas with T-helper phenotype: Are there too many subtypes?

Follicular helper T (T_FH) cells are the providers of T-cell help to B-cells in the development of germinal centers and for the generation of most class-switched antibodies. The markers most commonly associated with T_FH activity are IL21, IL4, CD40L, BCL6, SAP, CXCR5/CXCL13, and ICOS. T-cell lymphoma genomic studies have shown that different T-cell lymphoma types express signatures typical for T_FH cells, this including angioimmunoblastic T-cell lymphoma (AITL), a related condition termed peripheral T-cell lymphoma with T_FH phenotype and primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder. Angioimmunoblastic T-cell lymphoma is a well-established entity, a clinically aggressive disease with a survival of 30% OS after 5 years. Molecular and clinical studies have confirmed this as a well-established clinicopathological entity with relatively specific gene mutations, including mutations found in hematopoietic precursor cells and others. Peripheral T-cell lymphoma with T_FH phenotype is an associated disorder with histology of PTCL but a T_FH phenotype, as defined by the expression of 2-3 immunohistochemical markers. Molecular studies on this entity are showing a partial overlap with AITL. Primary cutaneous CD4+ small/medium lymphoproliferative disorder is an entirely different process that takes place in the skin, showing frank cytologic atypia, monoclonal TCR rearrangement and T_FH phenotype in the context of a clinically benign lesion. Here we review the main clinical, molecular and diagnostic features of these three lymphoproliferative processes.

Approach to nodal-based T-cell lymphomas

Peripheral T-cell lymphomas (PTCLs) represent a heterogeneous group of uncommon malignancies derived from mature T cells and usually characterised by an aggressive clinical course. Their clinical presentation, localisation and pattern of dissemination are highly variable, but the majority of cases present as nodal diseases. The recently revised classification of lymphomas has incorporated many new molecular genetic data derived from gene expression profiling and next generation sequencing studies, which refine the definition and diagnostic criteria of several entities. Nevertheless, the distinction of PTCL from various reactive conditions, and the diagnosis of PTCL subtypes remains notably challenging. Here, an updated summary of the clinicopathological and molecular features of the most common nodal-based PTCLs (angioimmunoblastic T-cell lymphoma and other nodal lymphomas derived from follicular T helper cells, anaplastic large cell lymphomas and peripheral T-cell lymphoma, not otherwise specified) is presented. Practical recommendations in the diagnostic approach to nodal T-cell lymphoproliferations are presented, including indications for the appropriate use and interpretation of ancillary studies. Finally, we discuss commonly encountered diagnostic problems, including pitfalls and mimics in the differential diagnosis with various reactive conditions, and the criteria that allow proper identification of distinct PTCL entities.

Relapsed angioimmunoblastic T-cell lymphoma with large pericardial effusion

T-cell lymphomas comprise 10% to 15% of all lymphoid malignancies and affect precursor or mature T cells; the latter are referred to as peripheral T-cell lymphomas. We present a case of a subtype, angioimmunoblastic T-cell lymphoma, in which a patient previously treated with chemotherapy and autologous stem cell transplant relapsed with B symptoms and large pericardial/pleural effusions. Recurrent lymphoma was confirmed on pericardial tissue biopsy. Treatment was trialed with lenalidomide and the effusions resolved. Five months later she died from septic shock and multiorgan failure. Our case highlights the need for rapid evaluation of B symptoms and/or new effusions in patients with a known history of angioimmunoblastic T-cell lymphoma.

Bone Marrow Infiltration of Angioimmunoblastic T-Cell Lymphoma: Identification and Prognostic Impact of Histologic Patterns and Diagnostic Application of Ancillary Phenotypic and Molecular Analyses

CONTEXT.—

Angioimmunoblastic T-cell lymphomas originate from T follicular helper cells and express respective markers (BCL6, CD10, CXCL13, ICOS, and PD-1). Although commonly present, bone marrow involvement by angioimmunoblastic T-cell lymphoma can be diagnostically challenging. Additionally, only little is known about the distribution of T follicular helper cells in healthy and reactively changed bone marrows or in samples affected by other lymphomas.

OBJECTIVE.—

To establish a diagnostic approach to reliably identify bone marrow infiltration of angioimmunoblastic T-cell lymphoma.

DESIGN.—

We analyzed the morphologic infiltration pattern and the expression of T follicular helper-cell markers in 42 matched paired lymph node and bone marrow samples and applied comparative clonality testing. Furthermore, we studied the expression of BCL6 and PD-1 in a control cohort of healthy, reactively changed, and otherwise affected bone marrows.

RESULTS.—

We identified 3 different bone marrow infiltration patterns correlating with overall survival (interstitial/micronodular infiltration with or without eosinophilia and diffuse infiltration with eosinophilia). The matched pairs showed a consistent (co)expression of PD-1 and BCL6 with a generally weaker expression in the bone marrow than in the lymph nodes. Comparative clonality testing was helpful in only a minority of cases. Infiltrates of the most important differential diagnoses contained either PD-1- or BCL6-positive tumor-infiltrating cells, but no coexpressing cells.

CONCLUSIONS.—

Bone marrow infiltration by angioimmunoblastic T-cell lymphoma displays 3 different patterns that correlate with prognosis. BCL6 and PD-1 can be reliably used to identify lymphoma infiltrates and to help rule out several differential diagnoses. Comparative clonality testing rarely provides additional value and cannot replace morphologic and phenotypic analyses.

The pathological features of angioimmunoblastic T-cell lymphomas with IDH2R172 mutations

Angioimmunoblastic T-cell lymphoma is a peripheral T-cell lymphoma derived from follicular T-helper cells. High-throughput genomic sequencing studies have shown that angioimmunoblastic T-cell lymphoma carries frequent mutations in RHOA^G17V and IDH2^R172 genes. The clinico-pathological features of angioimmunoblastic T-cell lymphoma cases with RHOA^G17V mutations have been addressed; however, similar studies for IDH2 mutated cases are lacking. Therefore, the aim of the present study was to evaluate the pathological features of angioimmunoblastic T-cell lymphoma with IDH2 mutations. In order to identify cases with IDH2 mutations, 50 cases previously diagnosed as angioimmunoblastic T-cell lymphoma were subjected to next-generation sequencing analysis using a custom panel covering four genes frequently mutated in angioimmunoblastic T-cell lymphoma including DNMT3A, TET2, IDH2 and RHOA. All cases were analyzed for PD1, ICOS, CXCL13, CD10, BCL6, CD21, CD23 and EBER in situ hybridization. Mutational analysis recognized three groups. Group 1: IDH2^R172 mutations were identified in 20 cases (40%). All cases carried RHOA^G17V mutations. Group 2: RHOA^G17V mutations without IDH2^R172 mutation were identified in 16 cases (32%), and Group 3: 14 cases (28%) without RHOA^G17V or IDH2^R172 mutations. Morphologically, angioimmunoblastic T-cell lymphoma cases with IDH2^R172 mutations were characterized by the presence of medium to large clear cells (p = 0.00001), and a follicular T-helper phenotype with the particular feature of strong CD10 (p = 0.0268) and CXCL13 expression (p = 0.0346). Interestingly, TET2 mutations were identified in 32 of 33 (97%) cases with IDH2^R172 and/or RHOA^G17V mutations whereas only 55% of angioimmunoblastic T-cell lymphoma cases wild-type for these two genes carried TET2 mutations (p = 0.0022). In contrast, DNMT3A mutations were found in 48% of the cases and were equally distributed in the three groups. In conclusion, our results support the results of gene expression profiling studies suggesting that IDH2^R172 mutations define a unique subgroup within angioimmunoblastic T-cell lymphoma with strong follicular T-helper-like phenotype and characteristic morphological features.

Cutaneous lesions of angioimmunoblastic T-cell lymphoma: Clinical, pathological, and immunophenotypic features

BACKGROUND

Angioimmunoblastic T-cell lymphoma (AITL) is a systemic peripheral T-cell lymphoma with a follicular helper T-cell (T_FH ) immunophenotype that frequently involves the skin. However, the histopathology of cutaneous involvement by AITL has not been fully established.

METHODS

We reviewed the clinicopathological features of 19 patients seen at our institution with AITL involving the skin. Pan-T-cell and T_FH marker expression was evaluated by immunohistochemistry. Epstein-Barr virus (EBV) was detected using in situ hybridization (ISH) for Epstein-Barr virus-encoded small RNA (EBER). T-cell receptor (TCR) gene rearrangement was evaluated by PCR.

RESULTS

AITL affected both trunk and extremities in 15/19 cases (79%). Perivascular infiltration by small and/or medium-sized lymphocytes was seen in 18/19 (95%). Granulomatous inflammation was identified in 4/19 (21%). Aberrant loss of CD2, CD5, or CD7 was identified in 1/18 (6%), 2/18 (11%), or 7/19 (37%) cases, respectively. Seventeen of eighteen evaluable cases (95%) expressed 2 to 3 T_FH markers: PD-1 in 19/19 (100%), BCL6 in 94% (17/18), and CD10 in 37% (7/19). EBV-positive cells were detected in 3/18 (17%) with varying density. Clonal TCR gene rearrangement was identified in 9/11 (82%).

CONCLUSIONS

Cutaneous involvement by AITL shows relatively non-specific histopathological features. However, an immunohistochemical panel including T_FH markers and EBER ISH is useful in differential diagnosis.

Structural and diffusion weighted MRI demonstrates responses to ibrutinib in a mouse model of follicular helper (Tfh) T-cell lymphoma

Recent analyses of the genetics of peripheral T-cell lymphoma (PTCL) have shown that a large proportion of cases are derived from normal follicular helper (Tfh) T-cells. The sanroque mouse strain bears a mutation that increases Tfh cell number and heterozygous animals (Roquin^san/+) develop lymphomas similar to human Tfh lymphoma. Here we demonstrate the usefulness of Roquin^san/+ animals as a pre-clinical model of Tfh lymphoma. Long latency of development and incomplete penetrance in this strain suggests the lymphomas are genetically diverse. We carried out preliminary genetic characterisation by whole exome sequencing and detected tumor specific mutations in Hsp90ab1, Ccnb3 and RhoA. Interleukin-2-inducible kinase (ITK) is expressed in Tfh lymphoma and is a potential therapeutic agent. A preclinical study of ibrutinib, a small molecule inhibitor of mouse and human ITK, in established lymphoma was carried out and showed lymphoma regression in 8/12 (67%) mice. Using T2-weighted MRI to assess lymph node volume and diffusion weighted MRI scanning as a measure of function, we showed that treatment increased mean apparent diffusion coefficient (ADC) suggesting cell death, and that change in ADC following treatment correlated with change in lymphoma volume. We suggest that heterozygous sanroque mice are a useful model of Tfh cell derived lymphomas in an immunocompetent animal.

PD-1 Tumor Suppressor Signaling in T Cell Lymphomas

The inhibitory receptor PD-1 is critical to balancing antigen-induced T cell activation; its inhibition is currently being explored to enhance antitumor T cell immunity with certain successful outcomes. However, PD-1 has also emerged as a central tumor suppressor in T cell lymphomas, where the tumor cell originates from a T cell itself. These aggressive cancers are frequently characterized by oncogenic mutations in T cell receptor (TCR) signaling pathways. PD-1 activity within malignant T cells can negatively regulate the PI3K/AKT and PKCθ/NF-κB tumor survival pathways and PD-1 is frequently inactivated in this human malignancy. This review summarizes current insights into oncogenic T cell signaling, discusses tumor-suppressive functions and mechanisms of PD-1 in T cell lymphomagenesis, and addresses potential unwanted effects caused by PD-1 checkpoint inhibition.

Angioimmunoblastic T-Cell Lymphoma

Angioimmunoblastic T-cell lymphoma (AITL) is one of the most common types of T-cell lymphoma, representing about 15-20% of cases of peripheral T-cell lymphoma (PTCL). It is characterized by a unique clinical presentation and distinct pathologic and molecular features. Classes of drugs particularly active in AITL are emerging; however, treatment of relapsed and refractory disease remains a challenge. This chapter reviews the epidemiology, clinical presentation, pathogenesis, diagnosis, and treatment of AITL.

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.

Multiple Ways to Detect IDH2 Mutations in Angioimmunoblastic T-Cell Lymphoma from Immunohistochemistry to Next-Generation Sequencing

Angioimmunoblastic T-cell lymphoma (AITL) is a peripheral T-cell lymphoma associated with chemoresistance and a poor prognosis. Various nonsynonymous mutations in the R172 residue of IDH2 are present in 20% to 30% of AITL patients. In addition to their diagnostic value, these mutations are potentially targetable, especially by isocitrate dehydrogenase (IDH) 2 inhibitor, and therefore their identification in a routine setting is clinically relevant. However, in AITL, the neoplastic cells may be scarce, making the identification of molecular anomalies difficult. We evaluated the diagnostic value of different methods to detect IDH2 mutations in formalin-fixed, paraffin-embedded tumor samples. Immunohistochemistry with an anti-IDH2 R172K antibody, Sanger sequencing, high-resolution melting PCR, allele-specific real-time quantitative PCR, and next-generation sequencing (NGS) were applied to biopsy specimens from 42 AITL patients. We demonstrate that the IDH2 R172K antibody is specific to this amino acid substitution and highly sensitive for the detection of the IDH2^R172K variant, the most frequent substitution in this disease. In our study, NGS and allele-specific real-time quantitative PCR displayed a good sensitivity, detecting 96% and 92% of IDH2 mutations, respectively, in contrast to Sanger sequencing and high-resolution melting PCR, which showed a significantly lower detection rate (58% and 42%, respectively). These results suggest that a combination of immunohistochemistry and AS-PCR or NGS should be considered for the identification of IDH2 mutations in AITL in a routine setting.

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. 

Aggressive Angioimmunoblastic T Cell Lymphomas (AITL) with Soft Tissue Extranodal Mass Varied Histopathological Patterns with Peripheral Blood, Bone Marrow, and Splenic Involvement and Review of Literature

Angioimmunoblastic T cell lymphoma (AITL) is a peripheral T cell non-Hodgkin lymphoma with an aggressive fatal course and it has varied clinical presentation with an uncommon presentation when they present as soft tissue masses or when there is spill in the peripheral blood or there are composite lymphomas that are rare presentations. Common presentations include lymphadenopathy, fever and systemic symptoms, hemolytic anemias, skin rashes, and rheumatoid arthritis. The classical histopathology is absence of follicles in lymph nodes with presence of high endothelial venules and the tumor cells of small to medium-sized lymphocytes with pale cytoplasm mixed with reactive T cells. On immunohistochemistry, the cells are positive for CD3, CD4, CD10, BCL2, and CXCL13. In this observational study, the clinicopathologic presentation and the immunohistochemical profile of five cases who initially presented with a soft tissue mass which is an extremely rare presentation of this rare type of non-Hodgkin lymphoma that was diagnosed at our center with peripheral blood and bone marrow involvement and the clinicopathologic presentation, immunohistochemical profile, and response to treatment on follow-up are correlated with the literature review. One case had a fulminant and aggressive course and was fatal within 2 months of diagnosis. The rest of the four cases are on regular chemotherapy and follow-up. Our five cases had presented with soft tissue masses, two in the axillary regio,n two in the hand, and one in the scapular region with an extranodal presentation, and there was associated lymphadenopathy which developed subsequently with classic histomorphology and immunohistochemical findings. The age range was 46-54 years and all five cases were males. Three cases were with anemia (hemoglobin range 6.5-8.0 mg/dl) and all five cases were having peripheral blood plasmacytosis. Histopathology was classic with paracortical involvement with polymorphous population of cells with neoplastic lymphocytes of small and large sizes with numerous arborizing blood vessels which correspond to high endothelial venules. Microscopically, three architectural patterns; pattern I was seen in three cases (60%) and then pattern II and III in one case each (20% each). Immunohistochemistry revealed CD4+, CD8-, CXCL13+, CD10+, BCL6+, CD19, CD20, CD1a, Tdt, CD21, and CD23+ in follicular dendritic cells. AITL is a rare and aggressive non-Hodgkin lymphoma with varied clinical presentation with classic histomorphology with various patterns which may cause diagnostic dilemma and immunophenotypic findings, and prompt and early diagnosis is mandatory for institution of therapy.