Lessons learned from an unusual presentation of CD3+, CD56 - T-cell large granular lymphocyte leukemia

The WHO classification subdivides large granular lymphocytic leukemias (LGLLs) into two subtypes, T and natural killer (NK) LGLLs, with distinct immunophenotypes and clinical presentations.1 Although arising from a common progenitor cell, NK cells are bone marrow–derived innate immune cells capable of cytokine production and cytotoxicity, and T cells are thymic-derived, antigen-specific lymphocytes that express a T-cell receptor (TCR).2 Natural killer T (NKT) cells, a subset of T cells, express NK-associated antigens such as CD16, CD56, and CD57, in addition to a CD1d-restricted, semi-invariant TCR.3 The point at which NKT cells branch from other TCR rearranged cells is not clearly defined. However, this is believed to be mediated through CD1d thymic-dependant signaling in CD4 CD8 double-positive thymocyte precursors.4,5 NK LGLL has a CD3−, CD8+, CD16+, CD56+ phenotype, with variable expression of CD57. It presents in teenagers and young adults with “B” symptoms, lymphadenopathy, hepatosplenomegaly, lymphocytosis, anemia, and thrombocytopenia and typically follows an aggressive clinical course.6 T-cell LGLLs are CD3+, CD8+, CD16+ with a clonal TCR rearrangement and defective Fas (CD95) -mediated apoptosis.7,8 Median age of onset is 55 years, presenting with splenomegaly, neutropenia, and recurrent infections. It is associated with rheumatoid arthritis and follows an indolent and protracted clinical course.9 We describe the case of a teenage patient with T-cell LGLL, who despite having a CD56 immunophenotype, initially showed an aggressive clinical course more in keeping with an NKT leukemia. We discuss the reasoning behind his conservative management and the observed changes in lymphocyte count and serum cytokine/chemokine levels over an 18-month period. There have been no reported cases of an initially aggressive presentation with subsequent spontaneous regression.