Proliferation of large granular lymphocytes (LGL) and T-cell LGL (T-LGL) in peripheral blood along with demonstration of clonality are the hallmarks of a heterogeneous group of disorders, including T-LGL leukemia or T-LGL lymphocytosis. They are often associated with neutropenia and responsive to immunosuppression. The true nature of this entity is not well understood. Some cases are reported as reactive phenomena with very limited experience in pediatric population.
Hematology/Oncology Flow Cytometry Laboratory database has been reviewed retrospectively. Patients with identifiable distinct CD5-dim T-cell population and positive clonal T-cell receptor rearrangement were included in the analysis. Clinical and laboratory data were then reviewed.
Sixteen cases of children and young adults with increased peripheral blood clonal T-LGL population characterized by dim CD5 expression with wide range of underlying immune dysregulation/stimulation disorders were reviewed. Extended follow up with repeat testing suggested the reactive nature of persistent clonal T-LGL proliferations in this group.
Our observations indicate that clonal T-LGL proliferations in children and young adults are reactive in nature and some can be persistent with an indolent course with unknown consequentiality. Clonal T-LGL cells could be targeting the most prominent immunogenic stressor(s) involved as a control mechanism.

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