<i>HLA</i> Polymorphisms Are Associated with Treatment-Free Remission Following Discontinuation of Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia

Treatment-free remission (TFR) is one of the therapeutic goals for patients with chronic phase chronic myeloid leukemia (CML-CP). Although previous reports indicated that antitumor immunity contributes to TFR, its determinants are still unclear. We previously reported that allelic polymorphisms of killer immunoglobulin-like receptors (<i>KIR</i>) and human leukocyte antigens (<i>HLA</i>) are associated with achievement of deep molecular response (DMR) in patients with CML-CP. Here, we examined the association between TFR and polymorphisms of <i>KIRs</i> and <i>HLAs</i> in patients who discontinued tyrosine kinase inhibitors (TKI). Seventy-six patients were enrolled, and their <i>KIR</i> and <i>HLA</i> polymorphisms and natural killer (NK) cell activation status were investigated as previously described. Overall, 33 patients discontinued TKIs, and 21 of 33 achieved TFR [63.6%; 95% confidence interval (CI), 44.9%-77.5%] at 1 year. Multivariate analysis revealed that male sex (HR, 0.157; 95% CI, 0.031-0.804; <i>P</i> = 0.003) and <i>HLA-A*02:01, *11:01</i>, or <i>*24:02</i> (HR, 6.386; 95% CI, 1.701-23.980; <i>P</i> = 0.006) were associated with TFR. Patients who achieved DMR and discontinued TKIs exhibited higher NK cell activation status than those who did not. By contrast, there were no significant differences in NK cell activation status between the patients who achieved TFR and those who experienced molecular relapse. These results suggest NK cell activation status contributes to achievement of DMR, whereas T-cell-mediated immunity contributes to TFR in patients with CML-CP.