Pathogenesis Of Angioimmunoblastic T-cell Lymphoma Research Articles

Role of the S1P Signaling Pathway in the Pathogenesis of Angioimmunoblastic T-Cell Lymphoma

Peripheral T cell lymphomas (PTCLs) are a group of aggressive lymphoid malignancies originating from mature T cells. Angioimmunoblastic T-cell lymphomas (AITL) represent 20% to 30% of all PTCL diagnoses and are associated with autoimmune features, poor response to chemotherapy, and dismal prognosis. Molecular profiling of AITL has identified T-follicular helper (TFH) cells as the cell of origin of AITL, while mutational analysis has identified frequent alterations in epigenetic regulators ( TET2, DNMT3A, and IDH2) and elements of the TCR pathway as drivers of AITL transformation. Our group identified the highly recurrent RHOA G17V mutation as a defining hallmark of AITL and other T-cell lymphomas of TFH-cell origin (Palomero et al., 2014). Using a novel conditional knockin mouse model, we demonstrated that expression of Rhoa G17V in CD4+ T-cells induces TFH cell specification and promotes AITL lymphomagenesis in the context of loss of Tet2 (Cortes et al., 2018). Recently, we have identified that Rhoa G17V regulates the expression of the sphingosine-1-phosphate (S1P) receptor 1 (S1PR1) one of the five members of the receptor family of S1P, which plays an essential role in immune response and lymphocyte trafficking. During thymic T-cell development, expression of Rhoa G17V in CD4+ cells inhibited S1PR1 downregulation after the double positive stage leading to altered positive selection, reduced CD4+ single positive cell numbers and premature thymic egress of autorreactive T-cells which results in the development of systemic inflammation and autoimmunity. In our Tet2 −/− RHOA G17V AITL tumor model, constitutive activation of S1P receptors supported activation of the STAT3 and NFkB pathway and enhanced migration of malignant cells to peripheral organs. Mechanistically, expression of Rhoa G17V in mature CD4+ T-cells impaired re-phosphorylation of the Ezrin-Radoxin-Moesin (ERM) complex independently of ROCK signaling and led to the activation and increased migration of CD4+ T-cells. Importantly, blockade of S1PR1 signaling by fingolimod induced anti-tumor activity in Tet2 −/− RHOA G17V lymphoma-bearing mice in vivo with significant reductions in tumor burden associated with increased apoptosis and decreased STAT3 phosphorylation. Furthermore, analysis of a panel of primary tumors from AITL patients using a multiplexed staining panel and PhenoImager platform revealed significantly higher S1PR1 expression in AITL tumor cells than normal TFH cells from benign reactive lymph nodes. Our findings highlight the role of S1P signaling pathway in the pathogenesis of RHOA G17V-driven AITLs and the potential therapeutic benefit of targeting this pathway.

INSM1 Expression in Mesenchymal Tumors and Its Clinicopathological Significance.

Insulinoma-associated protein 1 (INSM1) has been identified as a nuclear marker of neuroendocrine tumors. Although INSM1 appears to be a subtle and specific biomarker for neuroendocrine tumor, its expression and clinicopathological significance in mesenchymal tumors remain unclear. We analyzed INSM1 mRNA level in GEO database and conducted immunohistological staining to detect the expression of INSM1 on 576 mesenchymal tumors from pathology department of Tongji Hospital. At transcription level, INSM1 expression in AITL (angioimmunoblastic T-cell lymphoma) was higher than their adjacent normal tissues as well as Hodgkin's lymphoma. Moreover, INSM1 expression in well-differentiated liposarcoma (WDLPS) was significantly higher than normal fat (P = 0.014) and dedifferentiated liposarcoma (DDLPS) (P = 0.0248). At protein level, the positive rate of INSM1 in AITL was 18/48 (47.4%), while in DDLPS was 9/20 (45%). INSM1 expression in AITL was significantly higher than Hodgkin's lymphoma (P = 0.008). And INSM1 expression in WDLPS was significantly lower than DDLPS (P = 0.015). The combination of GEO data and immunohistochemistry data indicated that the expression level of INSM1 was higher in AITL compared with normal control, suggesting that INSM1 may be involved in pathogenesis of AITL. The abnormal expression of INSM1 was found in WDLPS, and the positive rate of INSM1 was higher in DDLPS than in WDLPS. INSM1 may be involved in the regulation of liposarcoma development. There were significant differences in the expression of INSM1 between AITL and Hodgkin's lymphoma and WDLPS and DDLPS. These findings may assist in the differential diagnosis of these tumors when common markers are difficult to identify, enriching the diagnostic index system of mesenchymal tumors.

High-Throughput Sequence Analysis of Peripheral T-Cell Lymphomas Indicates Subtype-Specific Viral Gene Expression Patterns and Immune Cell Microenvironments.

Certain peripheral T-cell lymphomas (PTCLs) have been associated with viral infection, particularly infection with Epstein-Barr virus (EBV). However, a comprehensive virome analysis across PTCLs has not previously been reported. Here we utilized published whole-transcriptome RNA sequencing (RNA-seq) data sets from seven different PTCL studies and new RNA-seq data from our laboratory to screen for virus association, to analyze viral gene expression, and to assess B- and T-cell receptor diversity paradigms across PTCL subtypes. In addition to identifying EBV in angioimmunoblastic T-cell lymphoma (AITL) and extranodal NK/T-cell lymphoma (ENKTL), two PTCL subtypes with well-established EBV associations, we also detected EBV in several cases of anaplastic large-cell lymphoma (ALCL), and we found evidence of infection by the oncogenic viruses Kaposi's sarcoma-associated herpesvirus and human T-cell leukemia virus type 1 in isolated PTCL cases. In AITLs, EBV gene expression analysis showed expression of immediate early, early, and late lytic genes, suggesting either low-level lytic gene expression or productive infection in a subset of EBV-infected B-lymphocyte stromal cells. Deconvolution of immune cell subpopulations demonstrated a greater B-cell signal in AITLs than in other PTCL subtypes, consistent with a larger role for B-cell support in the pathogenesis of AITL. Reconstructed T-cell receptor (TCR) and B-cell receptor (BCR) repertoires demonstrated increased BCR diversity in AITLs, consistent with a possible EBV-driven polyclonal response. These findings indicate potential alternative roles for EBV in PTCLs, in addition to the canonical oncogenic mechanisms associated with EBV latent infection. Our findings also suggest the involvement of other viruses in PTCL pathogenesis and demonstrate immunological alterations associated with these cancers.IMPORTANCE In this study, we utilized next-generation sequencing data from 7 different studies of peripheral T-cell lymphoma (PTCL) patient samples to globally assess viral associations, provide insights into the contributions of EBV gene expression to the tumor phenotype, and assess the unique roles of EBV in modulating the immune cell tumor microenvironment. These studies revealed potential roles for EBV replication genes in some PTCL subtypes, the possible role of additional human tumor viruses in rare cases of PTCLs, and a role for EBV in providing a unique immune microenvironmental niche in one subtype of PTCLs. Together, these studies provide new insights into the understudied role of tumor viruses in PTCLs.

Candidate susceptibility variants in angioimmunoblastic T-cell lymphoma.

Angioimmunoblastic T-cell lymphoma (AITL) is a subtype of peripheral T-cell lymphoma with a poor prognosis: the 5-year survival rate is approximately 30%. Somatic driver mutations have been found in TET2, IDH2, DNMT3A, RHOA, FYN, PLCG1, and CD28, whereas germline susceptibility to AITL has to our knowledge not been studied. The homogenous Finnish population is well suited for studies on genetic predisposition. Here, we performed an exome-wide rare variant analysis in 23 AITL patients. No germline mutations were found in the driver genes, implying that they are not frequently involved in genetic AITL predisposition. Potentially pathogenic variants present in at least two patients and showing significant (p < 0.01) enrichment in our sample set were found in ten genes: POLK, PRKCB, ZNF676, PRRC2B, PCDHGB6, GNL3L, TTC36, OTOG, OSGEPL1, and RASSF9. The most significantly enriched variants, causing p.Lys469Ter in a splice variant of POLK and p.Pro588His in PRKCB, are intriguing candidates as Polk deficient mice display a spontaneous mutator phenotype, whereas PRKCB was recently shown to be somatically mutated in 33% of another peripheral T-cell lymphoma, adult T-cell lymphoma. If validated, our findings would provide new insight into the pathogenesis of AITL, as well as tools for early detection in susceptible individuals.

Angioimmunoblastic T cell lymphoma: novel molecular insights by mutation profiling.

Angioimmunoblastic T cell lymphoma (AITL) originates from follicular helper T-cells and is characterised by a polymorphic infiltrate with the neoplastic T-cells forming small clusters around the follicle and high endothelial venules. Despite the recent advances in its phenotypic characterisation, the genetics and molecular mechanisms underlying AITL are not fully understood. In the present study, we performed whole exome sequencing in 9 cases of AITL from Taiwan (n = 6) and U.K. (n = 3). We confirmed frequent mutations in TET2 (9/9), DNMT3A (3/9), IDH2 (3/9), RHOA (3/9) and PLCG1 (2/9) as recently reported by others. More importantly, we identified mutations in TNFRSF21 (1/9), CCND3 (1/9) and SAMSN1 (1/9), which are not yet seen or strongly implicated in the pathogenesis of AITL. Among the pathogenic mutations identified in AITL, mutations in DNA methylation regulators TET2 and DNMT3A occur early in hematopoietic stem cells as shown by previous studies, and these genetic events enhance the self-renewal of hematopoietic stem cells, but are unlikely to have any major impact on T-cell differentiation. Mutations in RHOA, PLCG1 and TNFRSF21 (DR6), which encode proteins critical for T-cell biology, most likely promote T-cell differentiation and malignant transformation, consequently generating the malignant phenotype. Our findings extend the molecular insights into the multistage development of AITL.

Role and Mechanisms of Rhoa G17V in the Pathogenesis of AITL

Peripheral T cell lymphomas (PTCL) are a heterogeneous group of lymphoid tumors resulting from the malignant transformation of mature T-cells. Among these, angioimmunoblastic T-cell lymphoma (AITL), which accounts for almost 20% of PTCL cases, represents one of the most aggressive forms of non-Hodgkin lymphoma with a dismal survival rate of 30% at 5 years. AITL tumors are characterized by loss of function mutations in the Ten-Eleven Translocation 2 (TET2) epigenetic tumor suppressor and a highly recurrent mutation (p.Gly17Val, G17V) in the RHOA small GTPase gene, present in almost 70% of AITL cases. Immunohistochemical analyses and gene expression profiling studies have established follicular T helper cells (Tfh), a as the cell of origin of AITL. Tfh cells are a CD4+ T-cell population characterized by high levels of expression of the chemokine receptor CXCR5, the inhibitory receptor PD-1 and the transcription factor BCL6. To investigate the specific role and mechanisms of RHOA G17V in AITL we first generated a conditional inducible Rhoa G17V knock-in mouse by introducing a floxed Rhoa wild type minigene upstream of the Rhoa G17V mutant exon in the endogenous RhoA locus by homologous recombination. RhoA G17V conditional knockin mice express wild type RhoA but switch to express the mutant G17V allele upon expression of Cre recombinase. Crossing this line with a CD4CreERT2 strain, which expresses a tamoxifen-inducible form of Cre, results in tamoxifen inducible selective activation of Rhoa G17V specifically in CD4 T-cells. Given the close association of the RHOA G17V mutation with AITL we hypothesized that expression of mutant Rhoa G17V could promote Tfh cell polarization and transformation, explaining the high prevalence of this mutation in AITL cases. Notably, tamoxifen-induced expression of Rhoa G17V in CD4CreERT2 RhoA G17V knockin mice resulted in spontaneous accumulation of Tfh cells expressing Cxcr5, Pd-1 and Bcl6 in absence of immunization. Mechanistically, RhoA G17V Tfh cells expressed increased levels of the ICOS receptor, a major factor in Tfh development, and showed enhanced ICOS signaling. Moreover, suppression of ICOS signaling with an anti-ICOSL blocking antibody impaired Rhoa G17V-induced Tfh polarization. Next, we analyzed the specific interaction of RHOA G17V and loss of Tet2 in AITL. Expression of mutant RHOA G17V in hematopoietic progenitors from Tet2 knockout mice resulted in the specific development of AITL with a median latency of 14 months. Tet2-/- RHOA G17V tumors are clonal and transplantable and present typical AITL Tfh-like features including expression of CXCR5, PD-1, BCL6 and ICOS, and are critically dependent on ICOS signaling for growth and proliferation in vivo. In all, our results demonstrate an instructive role for the RHOA G17Vmutation in Tfh cell fate specification and in AITL transformation and support an oncogenic role for ICOS signaling in the pathogenesis of AITL. The AITL animal model reported here may facilitate the preclinical testing of new therapeutic approaches for the treatment of this disease. DisclosuresNo relevant conflicts of interest to declare.

The curious origins of angioimmunoblastic T-cell lymphoma.

Once an obscure disease, recent studies have transformed our understanding of angioimmunoblastic T-cell lymphoma (AITL). In this review, we summarize new major advances in the genetics and biology of AITL. Genome wide sequencing studies have dissected the repertoire of the genetic alterations driving AITL uncovering a highly recurrent Gly17Val somatic mutation in the small GTPase RHOA and major role for mutations in epigenetic regulators, such as TET2, DNMT3A and IDH2, and signaling factors (e.g., FYN and CD28). These findings support a multistep model of follicular T helper cell transformation in AITL and pinpoint novel candidates for the development of targeted therapies in this disease. AITL originates from follicular T helper cells and is characterized by the presence of RHOA G17V mutation together with genetic alterations in TET2, DNMT3A, and IDH2. Research efforts now focus on the elucidation of the specific roles and interplay of these genetic alterations in the pathogenesis of AITL.

Epstein-Barr Virus-Positivity in Tumor has no Correlation with the Clinical Outcomes of Patients with Angioimmunoblastic T-cell Lymphoma

Background/AimsEpstein-Barr virus (EBV) is involved in the pathogenesis of angioimmunoblastic T-cell lymphoma (AILT), but its precise role and prognostic impact are not clear. This study aimed to evaluate the incidence of EBV-postitivity in the tumor and bone marrow (BM) samples from AILT patients, and their correlations with the clinical variables and patient survival.MethodsSeventy AILT cases were identified over a period of 8 years. Twenty seven cases were investigated for their EBV tumor status, and 10 BM samples of these patients were investigated for their EBV status with using in situ hybridization (ISH). EBV PCR was performed for the BM mononuclear cells in 8 cases.ResultsAmong the 27 tumor specimens, ten (37%) were EBV-positive. Only CD20-negativity in tumor correlated with the EBV-positivity (p=0.035). In 13 (48%) patients, gross tumor involvement was recognized by hematoxylin-eosin staining at the time of diagnosis. Among the 10 patients who had additional BM slides available, there were 3 with BM involvement, and none showed EBV positive results on ISH. EBV PCR of the BM mononuclear cells revealed one-positive case among 8 patients. This patient was negative for both BM involvement and EBV ISH. The median overall survival of the 25 treated patients was 48.9 months (95% CI: 18.6~79.2 months). Neither overall survival nor progression-free survival was related with EBV-positivity of the tumor.ConclusionsEBV-positivity of tumor had no impact on the prognosis of AILT patients.

The gene expression profile of nodal peripheral T-cell lymphoma demonstrates a molecular link between angioimmunoblastic T-cell lymphoma (AITL) and follicular helper T (TFH) cells

AbstractThe molecular alterations underlying the pathogenesis of angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma, unspecified (PTCL-u) are largely unknown. In order to characterize the ontogeny and molecular differences between both entities, a series of AITLs (n = 18) and PTCLs-u (n = 16) was analyzed using gene expression profiling. Unsupervised clustering correlated with the pathological classification and with CD30 expression in PTCL-u. The molecular profile of AITLs was characterized by a strong microenvironment imprint (overexpression of B-cell– and follicular dendritic cell–related genes, chemokines, and genes related to extracellular matrix and vascular biology), and overexpression of several genes characteristic of normal follicular helper T (TFH) cells (CXCL13, BCL6, PDCD1, CD40L, NFATC1). By gene set enrichment analysis, the AITL molecular signature was significantly enriched in published TFH-specific genes. The enrichment was higher for sorted AITL cells than for tissue samples. Overexpression of several TFH genes was validated by immunohistochemistry in AITLs. A few cases with molecular TFH-like features were identified among CD30− PTCLs-u. Our findings strongly support that TFH cells represent the normal counterpart of AITL, and suggest that the AITL spectrum may be wider than suspected, as a subset of CD30− PTCLs-u may derive from or be related to AITL.

Bcl-6 expression in reactive follicular hyperplasia, follicular lymphoma, and angioimmunoblastic T-cell lymphoma with hyperplastic germinal centers: Heterogeneity of intrafollicular T-cells and their altered distribution in the pathogenesis of angioimmunoblastic T-cell lymphoma

Background: The Bcl-6 gene product, a nuclear phosphoprotein, is expressed independently of Bcl-6 gene rearrangement. In lymph nodes, expression of Bcl-6 protein is restricted to germinal center (GC) B-cells and 10% to 15% of CD3 CD4 + intrafollicular T cells. Interfollicular cells are negative for Bcl-6 protein, except for rare CD3 + CD4 + T cells. Recently, we reported cases of angioimmunoblastic T-cell lymphoma (AITL) with hyperplastic GCs (AITL/GC), and observed that borders of enlarged GCs were ill defined, with features suggestive of an outward migration of GC cells to surrounding interfollicular zones. This prompted a study of follicular borders with Bcl-6 staining in reactive follicular hyperplasias and follicular lymphomas to compare with AITL/GC. Materials and Methods: Formalin-fixed paraffin sections were used for immunostaining of Bcl-6. Six cases of AITL/GC, 12 nonspecific reactive follicular hyperplasia (FH), 7 HIV adenopathy, 10 follicular lymphoma (FL), and 8 typical AITL (ie, AITL without GC) were studied. Double staining for Bcl-6/CD20, Bcl-6/CD3, and Bcl-6/CD57 was performed in selected cases. Results: In FH and HIV adenopathy, staining for Bcl-6 revealed densely populated GCs with well-defined and regular GC borders, whereas Bcl-6 + cells were rare in the interfollicular areas. An occasional GC with an ill-defined border was invariably surrounded by a broad mantle zone; those with indistinct mantle zones had well-defined, regular borders. In FL, follicles were densely populated, and their borders were irregular, with some Bcl-6 + cells in the interfollicular zones. In AITL/GC, GCs were less dense, GC borders were ill defined and irregular, and the number of interfollicular Bcl-6 + cells was markedly increased. Double staining revealed that these interfollicular Bcl-6 + cells in AITL/GC were Bcl-6 +/CD3 +/CD20 −/CD57 − T cells. Moreover, CD3 + intrafollicular T cells were depleted in AITL/GC, whereas they were abundant in FH. Intrafollicular CD57 + cells did not stain for Bcl-6, and were also depleted in AITL/GC. In typical AITL, some neoplastic cells were positive for Bcl-6, showing variable degrees of staining. Conclusions: (1) GCs of AITL/GC differed from those of other reactive follicular hyperplasias and follicular lymphomas, and staining for Bcl-6 was useful to discern them. (2) Intrafollicular CD3 + T cells, many of which were also positive for Bcl-6, were markedly depleted in AITL/GC, with increased interfollicular Bcl-6 +/CD3 + cells, suggesting an outward migration of intrafollicular T cells in this condition. (3) Interfollicular Bcl-6 +/CD3 + cells in AITL/GC were too numerous to be accounted for by migration alone, suggesting local proliferation. (4) Intrafollicular CD57 + cells were negative for Bcl-6, indicating heterogeneity of the intrafollicular T-cell population. (5) Some neoplastic cells in AITL stained for Bcl-6, suggesting up-regulation of Bcl-6 expression in this tumor.