Detection of Emerging Ibrutinib Resistance by Flow Cytometry in Patients with Chronic Lymphocytic Leukaemia

Abstract Background: Although ibrutinib is effective drug in the treatment of chronic lymphocytic leukaemia (CLL), during the treatment acquired resistance may occur, making its detection an important issue. We aimed to find phenotypic markers on CLL cells which expression may correlate with the appearance of ibrutinib resistance. Methods: We examined 28 (treatment naïve, ibrutinib sensitive, clinically ibrutinib resistant) peripheral blood (PB) samples. The surface markers` expression (CD69, CD184, CD86, CD185, CD27) were assessed by flow cytometry. Furthermore, the BTKC481S resistance mutation was tested using digital droplet PCR. We also investigated the change of the phenotype of CLL cells during ibrutinib treatment in one patient with acquired ibrutinib resistance. Results: The expression of CD27 (p=0.016), CD69 (p=0.015) and CD86 (p=0.015) was higher in the clinically resistant cohort than in the ibrutinib sensitive cohort. Besides, we found that high CD86 and CD27 expressions accompanied by BTKC481S mutation. Our prospective study showed that the increase of the expression of CD27, CD69, and CD86 was ahead of clinical resistance with three months. Conclusion: Our study suggests that the flow cytometric measurements of certain markers may reveal and predict the development of ibrutinib resistance, and this method may in the future become a part of the follow-up on patients treated with ibrutinib.