Dasatinib, a 2nd-generation tyrosine kinase inhibitor (TKI), can specifically induce large granular lymphocytes (LGL) in some patients with Philadelphia chromosome (Ph)-positive leukemia. To investigate the properties of the induced LGLs, we performed prospective and longitudinal analyses. From Feb 2011 to Jan 2013, a total of 17 patients with Ph-positive leukemia who were previously untreated or refractory to imatinib were enrolled. T cell receptor (TCR)-γ/δ gene rearrangements and phenotypic profiles of lymphocytes were examined before and during administration of dasatinib. LGL lymphocytosis was observed in half of the dasatinib-treated cases (LGL+ group), showing a relation to increased achievement of complete cytogenetic response within 6 months. The phenotypes of the increased lymphocytes were revealed to be mostly natural killer cells. In the LGL+ group, clonal TCR-γ gene rearrangements were frequently detected at diagnosis (six of nine cases) and persisted during therapy, compared with only two of eight in the LGL- group. The proportion of regulatory T cells to CD4+ T cells at diagnosis was lower in the LGL+ compared with the LGL- group (median 4.2 vs. 6.6 %), and this disparity was sustained throughout the therapeutic period. These results demonstrate that immunological condition at diagnosis may affect LGL lymphocytosis in some dasatinib-treated patients.
Keywords: Clonality; Dasatinib; LGL; Regulatory T cell.