Therapeutic Immune Monitoring of Chronic Myeloid Leukemia Patients Treated with Tyrosine Kinase Inhibitors: Focus on CD4⁺ CD25⁺ t Cells

Background and Objectives: In clinical, conventional Tyrosine Kinase Inhibitors (TKIs) including imatinib, dasatinib, and nilotinib are remarkably effective forms of therapy for certain types of solid cancers as well as Ph+ leukemias. In addition to the BCR-ABL target oncoprotein, they also inhibit certain off-target kinases (Eph, c-KIT, TEC, SRC). Some TKIs affect immune reconstitution as well as the proliferation, function, and activation of T cells. Certain TKIs have been known to have an especially strong effect on CD4+CD25+ T cells, also known as regulatory T Cells (Tregs). There is currently a gap in the clinical data available about on this area of study.

Patients and methods: In this study, we collected 108 Peripheral Blood (PB) samples from patients in the Chronic Phase (CP) of Chronic Myeloid Leukemia (CML) at the time of diagnosis (n=31) and also the TKIs treatment. Groups consisted of individuals treated with TKIs like imatinib (n=12), dasatinib (n=11) and nilotinib (n=8), as well as healthy controls (n=15). We evaluated the quantity and function of Tregs from patients in the CML-CP at the time of diagnosis and during treatment with TKIs.

Results: It was found that at diagnosis, patients with CML had a similar proportion and absolute number of lymphocytes compared to healthy donors. After TKIs treatment, proportions and absolute numbers of total T cellsACD4⁺ T cells and Tregs decreased at different degree. Moreover, thedecrease would be more and more significant as time goes on.Our results indicated that although these three TKIs show similar inhibitory effects in the proportion and number of Tregs in vivo, they have differential effects on the functions of Tregs in vitro. The proliferation, suppression, and expression of suppressive cytokines (IL-4,IL-10 and TGF-β) as well as suppression-associated molecules (FoxP3, GITR, and CTLA-4) of Tregs decreased in groups treated with imatinib and dasatinib. The decrease was not significant in the nilotinib-treated group.

Conclusions: The results showed that imatinib and dasatinib have stronger inhibitory roles than nilotinib when it comes to regulating the number and functions of Tregs. These findings can be used to argue in favor of calls for personalized treatment and follow-up of CML patients during TKIs treatment, particularly for those patients who received combination therapy with allo-transplantation and post-transplant TKIs.