Case 5: T-Lymphoblastic Leukemia/Lymphoma
Clinical Vignette
This 12-year-old male presents with anemia, thrombocytopenia, lymphocytosis, and blast in peripheral blood. A peripheral blood sample is submitted for flow cytometric immunophenotyping using ClearLLab 10C Panels.
Flow Cytometric Immunophenotyping
T Cell Tube
Figure T03. This Side Scatter vs Forward Scatter dot plot shows events in the Singlets gate. This plot is intended to exclude cell debris, which usually has decreased forward scatter with increased side scatter. Early apoptotic cells also have mildly increased side scatter while late apoptotic and necrotic cells have variably decreased side scatter. Viable cells are included in the Cells gate.
Figure T04. This CD45 vs Side Scatter dot plot shows events in the Cells gate. This plot is intended to highlight various subsets of white blood cells, which are gated as CD45 positive. The CD45 negative population usually includes red blood cells, platelet aggregates, or non-hematopoietic cells.
Figure T06. This CD3 vs Side Scatter dot plot shows all viable cells. The CD3+ gate identifies cells with surface CD3 expression. CD3 is highly specific for T cells, being expressed only on the surface of mature T cells and later stage immature T cells. These cells typically have low to moderate side scatter. The aberrant population (purple) expresses surface CD3 at a level lower than that seen on normal T cells (aqua).
Figure T07. This TCRγδ vs Side Scatter dot plot shows all viable cells. TCRγδ is a subtype of T cell receptor and expressed on a small subset of cytotoxic T cells. These cells typically have low side scatter. The aberrant population (purple) expresses variable TCRγδ at a level lower than that seen on normal gamma/delta T cells (few aqua events, lower middle).
Figure T09. This CD2 vs Side Scatter dot plot shows all viable cells. CD2 is an antigen expression by nearly all immature and mature T cells (aqua). CD2 is also expressed on NK cells (red) and at a low level on monocytes (green). The aberrant population (purple) expresses CD2.
Figure T10. This CD56 vs Side Scatter dot plot shows all viable cells. CD56 is normally expressed on a major subset of NK cells (red), T cells with natural killer activity (NK/T cells), and many gamma/delta T cells (aqua). CD56 is also partially expressed on monocytes (green) in both reactive and neoplastic conditions. The aberrant population (purple) is negative for CD56.
Figure T11. This CD5 vs Side Scatter dot plot shows all viable cells. CD5 is expressed on most immature and mature T cells (aqua), and at a low level on a subset of mature B cells. Very early immature T cells and gamma/delta T cells typically have little to no CD5 expression. A small subset of NK cells expresses CD5. The aberrant population (purple) expresses CD5 at a level lower than that seen on normal T cells (aqua).
Figure T12. This CD34 vs Side Scatter dot plot shows all viable cells. CD34 is a marker of early hematopoietic progenitors. It is expressed on hematopoietic stem cells, early myeloid progenitors (myeloblasts), and immature B and T cells (lymphoblasts). The aberrant population (purple) is negative for CD34.
Flow Cytometry Result Interpretation
Flow cytometric immunophenotyping identifies a phenotypically distinct population of cells with expression of CD2, intermediate surface CD3, variable CD4, intermediate CD5, bright CD7, intermediate CD8, variable CD10, intermediate CD38, dim CD45, and variable TCRγδ without CD34, CD56, CD117, or other B cell or myeloid antigens.
The immunophenotype of the population is consistent with abnormal immature T cells, i.e. T-lymphoblasts. Compared with normal peripheral blood, the presence of an immature T cell population in the peripheral blood is aberrant, with co-expression of CD4 and CD8, mildly decreased CD5, and dim CD45. This finding supports a diagnosis of T-lymphoblastic leukemia/ lymphoma. Additional testing for TdT and CD1a could be performed to confirm the immaturity of the T cells.