Reduced Expression of CD62L Is Associated with Increased ADAM17 Activity and Predicts Molecular Response to Nilotinib Therapy in Patients with Early Chronic Phase Chronic Myelogenous Leukemia (CML-CP)

Background: In CML, immunological surveillance in the MRD-situation might be of particular relevance for long-term control or even elimination of CML-repopulating stem cells. Little is known about potential immune-modulatory effects of nilotinib in vivo. A comprehensive monitoring program to characterize nilotinib-induced immunological changes was set up as a substudy to the ENEST1st study (NCT01061177), which is focused on examining the role of first-line nilotinib therapy in CML-CP.

Aims: The identification of immunological changes induced by nilotinib and definition of immunological surrogates for response prediction in newly diagnosed CML-CP patients.

Methods: Peripheral blood was taken prior to treatment initiation and after 6 and12 months (mo) from 50 patients treated on the ENEST1st study. Whole blood was phenotyped by 9-color flow cytometry employing 6 panels of antibodies to determine various leukocyte populations and expression of differentiation and activation markers. Soluble factors in plasma were measured by ELISA. Changes in immune parameters were correlated to clinical endpoints.

Results: 55% of the patients included in this substudy achieved MMR at 6 mo, 75% at 12 mo and 79% at 24 mo of therapy. MR^4.5 was achieved by 5%, 18%, 24% of patients at 6, 12 and 24 mo of therapy, respectively. Expression of L-selectin (CD62L), a known lymph node homing marker, was very low on T cells at baseline (median 5.7%) and the proportion of CD62L-expressing cells among CD4⁺ and CD8⁺ T cells negatively correlated with SOKAL score and spleen size. During treatment, CD62L expression on both T cell subsets significantly increased (median 72.3%) to normal levels at mo 6. Moreover, higher proportions of CD62L⁺ cells among both CD4⁺ and CD8⁺ T cells at baseline were negatively associated with lower BCR-ABL1 mRNA burden at 3, 6, 9, 15 and 18 mo. Cumulative response rates for MMR and MR4 were significantly higher in patients with high proportions (cutoff: >25%) of CD62L expressing T cells when compared to patients with low proportions of CD62L⁺ cells. A detailed characterization of other T cell differentiation marker, such as CD45RA, CD45R0, CD28, CD27 and CD95, did not reveal a reduction of cells usually expressing high CD62L levels, such as naïve T cells. CD62L expression levels on granulocytes were also low at baseline and increased to normal levels during nilotinib therapy. Low levels of CD62L expression were associated with elevated plasma levels of soluble CD62L before treatment initiation. Washing whole blood from treatment naïve patient several times before staining partially restored immunoreactivity for CD62L, and plasma taken at baseline but not after treatment initiation reduced CD62L signal on normal T cells, indicating that interference by increased levels of soluble CD62L with assessment of surface CD62L at least in part contributes to low CD62L expression. Importantly, ADAM17 (TACE, CD156b), the metalloproteinase responsible for CD62L shedding was increased on granulocytes and monocytes but not on T cells of CML patients when compared to normal controls suggesting that reduced levels on CD62L on T cells were mediated by ADAM17 on myeloid cells.

Conclusion: We here show for the first time the prognostic impact of reduced CD62L expression levels at baseline for later molecular response to nilotinib in early CML-CP. Decreased expression of CD62L is at least in part due to increased CD62L-cleavage, probably by ADAM17, which is aberrantly expressed on the clonal myeloid cells. One may speculate that decreasing CD62L expression on T cells may interfere with immune surveillance of CML cells and that ADAM17 might be a target for adjunctive therapy. Larger prospective studies are needed to confirm the prognostic relevance of increased soluble CD62L and reduced T cell CD62L expression levels for molecular response in TKI-treated CML-CP.