Dasatinib-induced anti-leukemia cellular immunity through a novel subset of CD57 positive helper/cytotoxic CD4 T cells in chronic myelogenous leukemia patients

Dasatinib induces lymphocytosis of large granular lymphocytes (LGLs) in a proportion of patients with chronic myelogenous leukemia (CML), and is associated with better clinical outcomes. LGLs consist of cytotoxic T lymphocytes and natural killer cells; however, the context and phenotypic/functional features of each type of LGL are unknown. To better define features of these LGLs, we investigated lymphocytosis in CML patients treated with dasatinib. D57-positive and CD4-positive type I T-helper (Th) cells (CD57+ Th cells) rarely occur in CML patients without lymphocytosis and in healthy individuals; however, a substantial increase in the proportion of CD57+ Th cells was observed in CML patients treated with dasatinib. In addition, these cells showed appreciable levels of cytocidal activity via cytotoxic degranulation. Analysis of T-cell receptor α and β sequences showed a skewed T-cell repertoire in the CD57+ Th cells. Furthermore, patients with LGLs and CD57+ Th lymphocytosis achieved stronger molecular responses than did those without lymphocytosis. While further studies are warranted, our observations suggest that dasatinib induces the expansion of CD57+ Th-LGLs, which may play a crucial role in the dasatinib-induced response against Philadelphia chromosome-positive leukemia.