[Single-cell analysis of immune-lineage features in T-cell large granular lymphocytic leukemia].

<b>Objective:</b> To investigate alterations in the immune lineage of T-cell large granular lymphocytic leukemia (T-LGLL) at the single-cell transcriptome level and to elucidate its pathogenic mechanisms. <b>Methods:</b> Peripheral blood samples were collected from 5 T-LGLL patients before and after treatment (from June 2019 to December 2020) and 3 healthy controls at the Institute of Hematology & Blood Diseases Hospital, CAMS & PUMC. Single-cell transcriptome sequencing libraries were prepared and sequenced using 10× Genomics technology. Differentially expressed genes in immune cells were compared between patients and healthy donors, followed by pathway enrichment analyses. <b>Results:</b> Profiling 67,237 immune cells revealed that, in T-LGLL: 1) Effector CD8+ T cells exhibited increased numbers, enhanced cytotoxicity, and greater proliferative capacity. Following effective immunosuppressive therapy, both the proliferative capacity and effector functions of these cells significantly decreased (<i>P</i><0.05). 2) The proportion of regulatory T (Treg) cells was reduced, accompanied by increased apoptosis. After effective immunosuppressive therapy leading to remission, Treg cell proportions increased, and apoptotic pathways were downregulated (<i>P</i><0.05). 3) Antigen-presenting cells (APCs) showed enhanced functionality. Monocytes and dendritic cells were enriched in antigen synthesis and presentation pathways, while B cells displayed increased antigen-binding capacity and were enriched in pathways related to T-cell activation (<i>P</i><0.05). 4) Natural killer (NK) cells exhibited attenuated cytotoxic function but demonstrated an enhanced regulatory capacity over T cells (<i>P</i><0.05) . <b>Conclusions:</b> T-LGLL patients present a characteristic immunological profile marked by an imbalance in immune homeostasis. This profile includes abnormal activation and expansion of effector CD8(+) T cells, and a reduction in Treg cell numbers accompanied by functional impairment. Furthermore, APCs and NK cells were found to positively regulate T-lymphocyte activation, differentiation, and proliferation.