Angioimmunoblastic T-cell lymphoma contains multiple clonal T-cell populations derived from a common TET2 mutant progenitor cell.

Angioimmunoblastic T-cell lymphoma (AITL) is a neoplastic proliferation of T follicular helper cells with clinical and histological presentations suggesting a role of antigenic drive in its development. Genetically, it is characterized by a stepwise acquisition of somatic mutations, with early mutations involving epigenetic regulators (TET2, DNMT3A) and occurring in haematopoietic stem cells, with subsequent changes involving signaling molecules (RHOA, VAV1, PLCG1, CD28) critical for T-cell biology. To search for evidence of potential oncogenic cooperation between genetic changes and intrinsic T cell receptor (TCR) signaling, we investigated somatic mutations and T-cell receptor β (TRB) rearrangement in 119 AITL, 11 peripheral T-cell lymphomas with T follicular helper phenotype (PTCL-TFH), and 25 PTCL-NOS using Fluidigm polymerase chain reaction (PCR) and Illumina MiSeq sequencing. We confirmed frequent TET2, DNMT3A, and RHOA mutations in AITL (72%, 34%, 61%) and PTCL-TFH (73%, 36%, 45%) and showed multiple TET2 mutations (2 or 3) in 57% of the involved AITL and PTCL-TFH. Clonal TRB rearrangement was seen in 76 cases with multiple functional rearrangements (2-4) in 18 cases (24%). In selected cases, we confirmed bi-clonal T-cell populations and further demonstrated that these independent T-cell populations harboured identical TET2 mutations by using BaseScope in situ hybridization, suggesting their derivation from a common TET2 mutant progenitor cell population. Furthermore, both T-cell populations expressed CD4. Finally, in comparison with tonsillar TFH cells, both AITL and PTCL-TFH showed a significant overrepresentation of several TRB variable family members, particularly TRBV19*01. Our findings suggest the presence of parallel neoplastic evolutions from a common TET2 mutant haematopoietic progenitor pool in AITL and PTCL-TFH, albeit to be confirmed in a large series of cases. The biased TRBV usage in these lymphomas suggests that antigenic stimulation may play an important role in predilection of T cells to clonal expansion and malignant transformation. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Yao WQ ，Wu F ，Zhang W ，Chuang SS ，Thompson JS ，Chen Z ，Zhang SW ，Clipson A ，Wang M ，Liu H ，Bibawi H ，Huang Y ，Campos L ，Grant JW ，Wright P ，Ei-Daly H ，Rásó-Barnett L ，Farkas L ，Follows GA ，Gao Z ，Attygalle AD ，Ashton-Key M ，Liu W ，Du MQ ... -  《-》

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.

Harland L ，Borgmann V ，Otto F ，Overkamp M ，Bonzheim I ，Fend F ，Quintanilla-Martinez L ，Nann D ... -  《-》

Parallel evolution of two distinct lymphoid proliferations in clonal haematopoiesis.

Angioimmunoblastic T-cell lymphoma (AITL) is genetically characterized by TET2 and DNMT3A mutations occurring in haematopoietic progenitor cells, and late events (e.g. the RHOA-G17V mutation) associated with malignant transformation. As TET2/DNMT3A-mutated progenitor cells can differentiate into multilineage progenies and give rise to both AITL and myeloid neoplasms, they may also have the potential to lead to other metachronous/synchronous neoplasms. We report two cases showing parallel evolution of two distinct potentially neoplastic lymphoid proliferations from a common mutated haematopoietic progenitor cell population. Both cases presented with generalized lymphadenopathy. In case 1 (a 67-year-old female), an initial lymph node (LN) biopsy was dismissed as reactive, but a repeat biopsy showed a nodal marginal zone lymphoma (NMZL)-like proliferation with an increase in the number of T-follicular helper (TFH) cells. Immunohistochemistry, and clonality and mutational analyses by targeted sequencing of both whole tissue sections and microdissected NMZL-like lesions, demonstrated a clonal B-cell proliferation that harboured the BRAF-G469R mutation and shared TET2 and DNMT3A mutations with an underlying RHOA-G17V-mutant TFH proliferation. Review of the original LN biopsy showed histological and immunophenotypic features of AITL. In case 2 (a 66-year-old male), cytotoxic T-cell lymphoma with an increase in the number of Epstein-Barr virus-positive large B cells was diagnosed on initial biopsy. On review together with the relapsed biopsy, we identified an additional occult neoplastic TFH proliferation/smouldering AITL. Both T-cell proliferations shared TET2 and DNMT3A mutations while RHOA-G17V was confined to the smouldering AITL. In addition to demonstrating diagnostic challenges, these cases expand the potential of clonal haematopoiesis in the development of different lineage neoplastic proliferations.

Attygalle AD ，Dobson R ，Chak PK ，Vroobel KM ，Wren D ，Mugalaasi H ，Morgan Y ，Kaur M ，Ahmad R ，Chen Z ，Naresh KN ，Du MQ ... -  《-》

BCL6 locus is hypermethylated in angioimmunoblastic T-cell lymphoma.

Nishizawa S ，Sakata-Yanagimoto M ，Hattori K ，Muto H ，Nguyen T ，Izutsu K ，Yoshida K ，Ogawa S ，Nakamura N ，Chiba S ... -  《-》

[Analysis of clinicopathological and molecular abnormalities of angioimmunoblastic T-cell lymphoma].

Shi YF ，Wang HJ ，Liu WP ，Mi L ，Long MP ，Liu YF ，Lai YM ，Zhou LX ，Diao XT ，Li XH ... -  《-》