T-cell large granular lymphocyte leukemias have multiple phenotypic abnormalities involving pan-T-cell antigens and receptors for MHC molecules.

T-cell large granular lymphocyte (T-LGL) leukemias represent monoclonal T-cell expansions that express CD16, CD56, or CD57 and cause cytopenias. The identification of T-LGL leukemias can be difficult because reactive T-LGL cells also can express CD16, CD56, and CD57, and many leukemia cases show only mild lymphocytoses. In this study, 23 T-LGL leukemia cases were analyzed by 3- and 4-color flow cytometry to identify markers that could aid in discriminating leukemic from normal T-LGL. In most cases (18/23), abnormalities (bright, dim, or negative expression) of 2 or more pan-T-cell antigens were identified, with all cases showing abnormal CD5 levels. Abnormal expression of CD94 was identified in 22 of 23 cases, and 15 of 21 cases also showed abnormal expression of class 1 MHC receptor molecules identified by antibodies against CD158a, CD158b, CD158e, CD158i, CD158k, and CD94. These studies help define abnormal phenotypic features typical of T-LGL leukemia that may have important diagnostic value.