Donor-Derived T-Cell Large Granular Lymphocytic Leukemia in a Patient With Peripheral T-Cell Lymphoma.

T-cell large granular lymphocytic (T-LGL) leukemia after hematopoietic stem cell transplantation (SCT) is rare and its natural history and clinical outcome have not been well described. We report the clinical, morphologic, immunophenotypic, and molecular features of a case of donor-derived T-LGL leukemia in a 16-year-old man who received allogeneic SCT for peripheral T-cell lymphoma not otherwise specified (PTCL-NOS). The patient presented with persistent neutropenia and splenomegaly 9 months after SCT when the chimerism study showed a 100% donor pattern. A splenectomy revealed T-LGL leukemia. Flow cytometric analysis showed an aberrant T-cell population positive for CD3, CD5 (dim, subset), CD7, CD8, CD16 (subset), CD57, CD94 (dim, partial), and T-cell receptor (TCR) αβ, and negative for CD4, CD26, CD56, and TCRγδ. Molecular studies showed monoclonal TCRβ and TCRγ gene rearrangements. Both the immunophenotype and molecular profile of the T-LGL leukemia were different from the pre-SCT PTCL. Sequencing analysis for STAT3 exon 21 did not reveal any mutation in both pre-SCT and post-SCT specimens. The patient did not receive any treatment for T-LGL leukemia; however, his count progressively increased after splenectomy, despite the presence of persistent T-LGL leukemia in the bone marrow. There was no evidence of recurrent PTCL. We propose an algorithm to diagnose this rare post-SCT neoplasm.