STAT3 mutations in natural killer cells are associated with cytopenia in patients with chronic lymphoproliferative disorder of natural killer cells

Chronic lymphoproliferative disorder of natural killer (NK) cells (CLPD-NK) is a rare disease with an indolent clinical course, which is characterized by persistent increase in large granular lymphocytes of NK-cell type. A somatic mutation in signal transducer and activator transcription 3 (STAT3) has been reported in patients with CLPD-NK; however, the details of the mutational profiles and their clinical significance remain unclear. We performed mutation analyses of the STAT3, STAT5B, and TNF-alpha-induced protein 3 (TNFAIP3) genes for mononuclear cell-derived DNA in 17 CLPD-NK patients using allele-specific polymerase chain reaction and amplicon sequencing. Mutations in STAT3 and TNFAIP3 were found in 29% (5/17) and 6% (1/17) of cases, respectively. All patients were negative for STAT5B mutations. In all three STAT3-mutation (+) patients studied, STAT3 mutations were restricted to sorted NK cells. STAT3 mutation (+) patients had a lower hemoglobin level (6.6 g/dL vs. 13.9 g/dL, P = 0.0044) and showed a trend toward reduced neutrophil counts (1.22 × 10⁹/L vs. 3.10 × 10⁹/L, P = 0.070) compared with the STAT3 mutation (−) patients. No mutations in these genes were found in patients with neuropathy. These results suggest that heterogeneity of CLPD-NK and STAT3-mutated NK cells may play a significant role in cytopenia in CLPD-NK patients.