T/NK Lymphocytosis in CML Ph+ Patients During Dasatinib Therapy.

Some authors reported that Natural Killer (NK) cells from CML patients are defective in NK cell activity and NK cell number decrease as the disease progresses to the advanced phase and probably the abnormal BCR/ABL gene causes abnormal NK cell differentiation.TK inhibitors reduce BCR/ABL transcription and could restore NK cell numbers and/or function.Moreover Dasatinib,by the blockade of SRC Kinases,could affect the development of NK cells as well as T-lymphocytes.Our aim was to verify the impact of Dasatinib treatment on T CD8+ and NK cells modulation.

We evaluated 24 patients with CML resistant/intollerant to Imatinib and treated with Dasatinib at a starting dose of 70 mg/BID or 100 mg/QD.Blood count were monitored; lymphocytosis has been definited by an increased number of peripheral blood lymphocyte counts ≥ 3.0×10(e)⁹/L and by the predominance of LGLs in peripheral blood smear. Immunophenotyping was done with flow-cytometry using antibodies against the following antigens: CD2, CD3, CD4, CD5, CD7, CD8, CD16, and CD56.

With a median of 19 mo. of Dasatinib therapy (range 3–43), 15/24 cases (62.5%) developed peripheral blood lymphocytosis. Median onset of lymphocytosis was 3 months after the initiation of Dasatinib therapy (range 1–12) and duration was 14 months (range 6–40).Lymphocytosis was CD3+/CD8+/Cytotoxic T Cell in 9 patients (60%) and CD3-/CD16+/CD56+/NK Cell in 6 patients (40%).In all 15 patients no symptoms or signs suggestive of LGL leukemia or viral infections were documented.There was no significant difference in terms of the frequency of severe adverse events, including pleural effusion between patients with and without lymphocytosis. 11(73%) of the 15 patients who developed lymphocytosis achieved MMolR and 4/11 presented Bcr/Abl mutation at the time of imatinib treatment (F317L, E255K, F359V, E255K),whereas only 3(33%) of the 9 patients without lymphocytosis achieved MMolR and 1/3 presented Bcr/Abl mutation (F359V). Moreover molecular response was earlier in the group of patients with lymphocytosis (8vs12 mo.).

The development of lymphocytosis in our patients seems to be associated to an improved response to dasatinib in terms of molecular response and time to response. The assessment of higher frequency lymphocytosis requires further analysis; a larger patients'cohort should be needed to explore the biological role of lymphocytosis and the impact on the long term outcome in patients treated with dasatinib.

No relevant conflicts of interest to declare.