Programmed cell death 1‐expressing CD56‐negative natural killer (NK) cell expansion is a hallmark of chronic NK cell activation during dasatinib treatment

Dasatinib treatment markedly increases the number of large granular lymphocytes including natural killer (NK) cells in a proportion of Ph(+) leukemia patients, which associates with a better prognosis. In‐depth immune profiling of NK cells can predict therapeutic response in these patients. In the present study, we showed that CD56‐negative (CD56(neg)) NK cells increased exclusively in cytomegalovirus‐seropositive (CMV(+)) patients treated with dasatinib. The increase longitudinally paralleled with progressive differentiation of CD56(dim) NK cells during dasatinib therapy driven by CMV reactivation as shown by principal component analysis on 19 NK cell markers. The CD56(neg) NK cells showed downregulation of NK‐activating receptors, upregulation of PD‐1, and lower cytotoxicity and cytokine production, indicating that these cells are anergic and dysfunctional as seen in chronic infections with HIV‐1 or hepatitis C virus. Moreover, cytolytic activity of CD56(dim) and CD56(neg) NK cells against leukemia cells was partially restored by nivolumab in proportion to the frequency of PD‐1(+) NK cells. The proportion of patients who achieved deep molecular responses at 2 years was significantly higher in dasatinib‐treated patients with ≥3% CD56(neg) NK cells than in those with fewer CD56(neg) NK cells (54.5% vs 15.8%, P = .0419). These findings suggest that CD56(neg) NK cells may be an exhausted population induced by chronic activation through CMV reactivation during dasatinib therapy. Expansion of CD56(neg) NK cells is a hallmark of chronic NK cell activation in patients treated with dasatinib and may predict a better clinical outcome. Furthermore, PD‐1 blockade may enhance anti‐leukemia responses of such NK cells.