Abstract: EP728

Type: e-Poster

Background

Chronic myeloid leukemia (CML) is caused by spontaneous generation of a mutated tyrosine kinase with constitutive activation (BCR-ABL). After several years of treatment with tyrosine kinase inhibitors (TKIs), patients with sustained, deep molecular response (DMR) may interrupt treatment but approximately 50% experience relapse at some point after withdrawal. In addition to their direct effect on the BCR-ABL+ cancerous clone, TKIs are also immunomodulatory drugs that induce a potent antileukemic, cytotoxic response during treatment. It is unknown why this response, based on Natural Killer (NK) and CD8+ T cells, is only conserved in some patients after discontinuation, whereas others relapse and have to restart treatment.

Aims

To analyze phenotypic and genotypic markers that may be used as predictors of relapse in patients with CML during treatment-free remission (TFR).

Methods

We recruited 93 samples for analysis divided in 5 groups. 'On-TKI': 45 patients with CML on treatment with TKIs for  at least 9 months (imatinib (11), nilotinib (9), dasatinib (20), bosutinib (5)); 'Off-TKI': 17 patients on successful TFR for at least 7 months; 'Relapse': 7 patients who relapsed during TFR: 3 samples prior to TKI reintroduction and 4 samples who had already restarted TKIs; 'New diagnosis': 4 patients still untreated with recent CML diagnosis; and 20 healthy donors as basal controls. PBMCs were subjected to phenotypic analysis by flow cytometry. Genotyping of HLA-E and KIR genes was performed using real-time qPCR.

Results

1) Patients’ results are shown in Table 1. 2) Treatment with TKIs induced an increase of 8.6±1.2% ((p<0.001) in CD56+ Natural Killer (NK) cells regarding healthy controls. This increase was sustained in patients “Off TKI” during successful TFR but it was reduced 9.5±1.4% in patients “Off TKI” on relapse. This cell population was not recovered in these patients even after restarting TKI treatment. 3) A population of NK cells with cytotoxic phenotype CD3-CD56+CD16+ was increased 8.1±2.8% in “Off TKI” patients during TFR, regarding patients “On TKI”. This population was reduced 12±3.8% in patients “Off TKI” who relapsed but increased 18.8±6.7% once treatment was restarted. 4) Populations of cytotoxic cells CD8+TCRgd+ and CD8-TCRgd+ were respectively increased 19±3.9% (p<0.0001) and 6.1±1.0% (p<0.05) in “Off TKI” patients regarding healthy controls but they were reduced 17.95±1.3% and 7.8±0.1%, respectively, in “Off TKI” patients who relapsed. 5) Analysis of HLA-E alleles showed that 60% of patients “Off TKI” were heterozygous for HLA-E, whereas only 15.4% of patients on relapse were heterozygous, being predominant (61.5%) homozygous HLA‐E*0103/0103 genotype in this group. 7) KIR genes encoding for inhibitory molecules KIR2DL2 and KIR2DL5 and activating molecules KIR2DS2 and KIR2DS3 were present in >71% of patients who relapsed after treatment interruption, regarding <50% in “Off TKI”. Consequently, 86% of patients who relapsed showed KIR haplotypes BX.

Conclusion

We identified several biomarkers as potential predictors of relapse in CML patients during TFR: CD56+<4%; CD3-CD56+CD16+<7%; CD8+TCRgd+<7%; CD8-TCRgd+<4%; CD86+>20%; homozygosis for HLA-E*0103; and KIR haplotypes BX. These biomarkers need to be validated in a larger, longitudinal cohort of patients.

Session topic: 07. Chronic myeloid leukemia - Biology & Translational Research

Keyword(s): Chronic myeloid leukemia, Treatment-free remission, Tyrosine kinase inhibitor