Identification of novel STAT5B mutations and characterization of TCR\u03b2 signatures in CD4+ T-cell large granular lymphocyte leukemia

Dipabarna Bhattacharya,Daehong Kim,Gregorio Barilà,Enrico Tiacci,Gianluca Schiavoni,Fumihiro Ishida,Giulia Calabretto,Renato Zambello,Antonella Teramo,Tiina Kelkka,Gianpietro Semenzato,Jani Huuhtanen,Toru Kawakami,Jason Theodoropoulos,Hayakazu Nakazawa ,Cristina Vicenzetto,Monica Facco,Vanessa Rebecca Gasparini,Brunangelo Falini,Satu Mustjoki

doi:10.1038/s41408-022-00630-8

Abstract

CD4+ T-cell large granular lymphocyte leukemia (T-LGLL) is a rare subtype of T-LGLL with unknown etiology. In this study, we molecularly characterized a cohort of patients (n = 35) by studying their T-cell receptor (TCR) repertoire and the presence of somatic STAT5B mutations. In addition to the previously described gain-of-function mutations (N642H, Y665F, Q706L, S715F), we discovered six novel STAT5B mutations (Q220H, E433K, T628S, P658R, P702A, and V712E). Multiple STAT5B mutations were present in 22% (5/23) of STAT5B mutated CD4+ T-LGLL cases, either coexisting in one clone or in distinct clones. Patients with STAT5B mutations had increased lymphocyte and LGL counts when compared to STAT5B wild-type patients. TCRβ sequencing showed that, in addition to large LGL expansions, non-leukemic T cell repertoires were more clonal in CD4+ T-LGLL compared to healthy. Interestingly, 25% (15/59) of CD4+ T-LGLL clonotypes were found, albeit in much lower frequencies, in the non-leukemic CD4+ T cell repertoires of the CD4+ T-LGLL patients. Additionally, we further confirmed the previously reported clonal dominance of TRBV6-expressing clones in CD4+ T-LGLL. In conclusion, CD4+ T-LGLL patients have a typical TCR and mutation profile suggestive of aberrant antigen response underlying the disease.

Highlights

T-cell large granular lymphocyte leukemia (T-LGLL) is a rare lymphoproliferative disease characterized by chronic expansion of clonal, mature cytotoxic T cells in the peripheral blood and bone marrow [1]
Besides the previously identified STAT5B mutations in CD4+ T-LGLL (N642H, Y665F, Q706L, and S715F [4]), we discovered additional six novel somatic STAT5B mutations in the cohort
Somatic STAT5B mutations were initially described in CD8+ T-LGLL [9], but follow-up analyses have revealed that they more often occur in CD4+ and immature T-cell malignancies [4, 33, 38–42]

Summary

Introduction

T-cell large granular lymphocyte leukemia (T-LGLL) is a rare lymphoproliferative disease characterized by chronic expansion of clonal, mature cytotoxic T cells in the peripheral blood and bone marrow [1]. CD4+ T-LGLL has been reported more frequently associated with secondary neoplasms such as monoclonal B-cell lymphocytosis and plasma cell disorders [2, 3]. Up to 55% of CD4+ T-LGLL patients have been shown to harbor STAT5B mutations [4, 5]. In CD8+ T-LGLL, the most common mutated gene is STAT3 [6], whereas STAT5B mutations are rare and often associated with an aggressive disease form [7–9]. All reported STAT5B mutations in CD4+ T-LGLL are point mutations within the SH2 or transactivation domains of STAT5B. N642H and Y665F are the most common STAT5B mutations, and they both have been shown to increase STAT5B protein activity [4, 10, 11]

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