1019 - Chemokine receptor and adhesion molecule profile on B-cell chronic lymphocytic leukemia (B-CLL) lymphocytes in different lymphoid compartments and changes during BTK inhibitor therapy

B-cell chronic lymphocytic leukemia (B-CLL) is a lymphoproliferative disorder characterized by circulation of B lymphocytes between bone marrow, peripheral blood, and lymphoid organs. Homing, proliferation, and apoptosis of lymphocytes is a consequence of the interaction with tumor microenvironment. Bruton's tyrosine kinase (BTK) inhibitors (ibrutinib, acalabrutinib, etc.) in addition to inhibition B-cell receptor signaling also significantly influence interactions with the microenvironment. Along reduction of tumor mass ibrutinib may induce a significant redistribution of B lymphocytes from lymphoid organs to the peripheral blood.
We have designed the study to evaluate relationship of chemokine receptor and adhesion molecules profile on B-CLL lymphocytes in different lymphoid compartments with tumor mass distribution and redistribution in B-CLL patients treated with BTK inhibitors. Patients with B-CLL who started BTK inhibitor monotherapy (ibrutinib or acalabrutinib) were included in this prospective, longitudinal, observational study. Both untreated and previously treated patients were included. Patients receiving other active agents for CLL (steroids, anti-CD20 antibodies, bcl2 antagonist or chemotherapy) or other malignancy were excluded from the study. Patients were followed for six months after BTK inhibitor treatment start. Time points are the beginning of the treatment, the third and the sixth month after start of BTK inhibitor treatment. Methods include complete blood count, computed tomography (CT) of the neck, the thorax, the abdomen and the pelvis and flow cytometry with determination of expression levels of CXCR3, CXCR4, CXCR5, CCR7, CD38 and CD49d on malignant CD5+/CD19+ lymphocytes from peripheral blood (PB), bone marrow (BM) and lymph nodes (LN) at the start and from peripheral blood during follow-up.
We have evaluated 25 patients (10 female, 15 male) who completed follow-up, median age was 73 years. Ibrutinib have received 20 patients and acalabrutinib 5 patients. Median TTM at the beginning of treatment was 10.4 and at the end of six month of treatment 4.0. Median of TD at the beginning of the treatment was 0.62 and 1 at the end of sixth months of treatment. Redistribution lymphocytosis during first 6 months was observed in 76% patients. Profile of CXCR4 showed higher expression in PB compared to BM and LN contrary to CXCR3, CCR7 and CD38 showing higher expression in LN (p < 0.05). CXCR5 showed lower expression in LN (p < 0.05). There was no significant difference between compartments for CD49d. There were changes in expression pattern of analyzed molecules (higher CXCR4 and lower CXCR3, CXCR5, CCR7) on PB lymphocytes during BTK inhibitor treatment in patients with significant tumor redistribution (differences are smaller and less significant than between compartments before treatment). When analyzed relationship with lymphoid compartment involvement CXCR4 in PB and BM and CXCR3 in BM were positively associated with TTM and lymphocytosis, CXCR3, CXCR4 and CCR7 in LN were negatively associated with LN size, and CXCR4 in BM was positively associated with spleen size (p < 0.05). After 6-months no significant relationships were observed due to significant reduction of tumor mass.
BTK inhibitors induce the significant redistribution of B-CLL lymphocytes from lymphoid organs and BM to PB in the first months of the treatment. Tumor distribution is related to different chemokine receptor and adhesion molecule patterns observed by significant intraclonal heterogeneity between B-CLL lymphocytes in lymphoid compartments. Changes of surface molecules CXCR3, CXCR4, CXCR5, CCR7, CD38 and CD49d expression during ibrutinib treatment and consequent impact on interactions with microenvironment may play an important role in the disease pathogenesis, drug resistance and may reveal new treatment strategies. Current study is ongoing evaluating other molecules involved in interactions within microenvironment and with development of model for tumor distribution and redistribution.