Interleukin-6 in CLL: accelerator or brake?

Old and New Facts and Speculations on the Role of the B Cell Receptor in the Origin of Chronic Lymphocytic Leukemia

The engagement of the B cell receptor (BcR) on the surface of leukemic cells represents a key event in chronic lymphocytic leukemia (CLL) since it can lead to the maintenance and expansion of the neoplastic clone. This notion was initially suggested by observations of the CLL BcR repertoire and of correlations existing between certain BcR features and the clinical outcomes of single patients. Based on these observations, tyrosine kinase inhibitors (TKIs), which block BcR signaling, have been introduced in therapy with the aim of inhibiting CLL cell clonal expansion and of controlling the disease. Indeed, the impressive results obtained with these compounds provided further proof of the role of BcR in CLL. In this article, the key steps that led to the determination of the role of BcR are reviewed, including the features of the CLL cell repertoire and the fine mechanisms causing BcR engagement and cell signaling. Furthermore, we discuss the biological effects of the engagement, which can lead to cell survival/proliferation or apoptosis depending on certain intrinsic cell characteristics and on signals that the micro-environment can deliver to the leukemic cells. In addition, consideration is given to alternative mechanisms promoting cell proliferation in the absence of BcR signaling, which can explain in part the incomplete effectiveness of TKI therapies. The role of the BcR in determining clonal evolution and disease progression is also described. Finally, we discuss possible models to explain the selection of a special BcR set during leukemogenesis. The BcR may deliver activation signals to the cells, which lead to their uncontrolled growth, with the possible collaboration of other still-undefined events which are capable of deregulating the normal physiological response of B cells to BcR-delivered stimuli.

Leukemia stem cells promote chemoresistance by inducing downregulation of lumican in mesenchymal stem cells

Leukemia stem cells (LSCs) are responsible for therapeutic failure and relapse of acute lymphoblastic leukemia. As a result of the interplay between LSCs and bone marrow mesenchymal stem cells (BM-MSCs), cancer cells may escape from chemotherapy and immune surveillance, thereby promoting leukemia progress and relapse. The present study identified that the crosstalk between LSCs and BM-MSCs may contribute to changes of immune phenotypes and expression of hematopoietic factors in BM-MSCs. Furthermore, Illumina Genome Analyzer/Hiseq 2000 identified 7 differentially expressed genes between BM-MSCs^LSC and BM-MSCs. The Illumina sequencing results were further validated by reverse transcription-quantitative polymerase chain reaction. Following LSC simulation, 2 genes were significantly upregulated, whereas the remaining 2 genes were significantly downregulated in MSCs. The most remarkable changes were identified in the expression levels of lumican (LUM) gene. These results were confirmed by western blot analysis. In addition, decreased LUM expression led to decreased apoptosis, and promoted chemoresistance to VP-16 in Nalm-6 cells. These results suggest that downregulation of LUM expression in BM-MSCs contribute to the anti-apoptotic properties and resistance to chemotherapy in LSCs.

Cirmtuzumab blocks Wnt5a/ROR1 stimulation of NF-κB to repress autocrine STAT3 activation in chronic lymphocytic leukemia

Coculture of nurse-like cells (NLCs) with chronic lymphocytic leukemia (CLL) cells induced leukemia cell phosphorylation of STAT3 (pSTAT3), which could be blocked by anti-Wnt5a antibodies or the anti-ROR1 monoclonal antibody, cirmtuzumab. Time-course studies revealed Wnt5a could induce activation of NF-κB within 30 minutes, but required more than 3 hours to induce pSTAT3. Culture of isolated CLL cells for 24 hours revealed Wnt5a-induced expression of interleukin 6 (IL-6), IL-8, CCL2, CCL3, CCL4, and CXCL1, which in turn could induce pSTAT3 in unstimulated CLL cells within 30 minutes. We found that Wnt5a could induce CLL cell expression of NF-κB target genes, including IL-6, and that this effect could be blocked by cirmtuzumab or drugs that inhibit NF-κB. Examination of CLL cells and plasma collected from patients treated with cirmtuzumab revealed reduced levels of phosphorylated p65 and diminished expression of NF-κB and STAT3 target genes in CLL cells, as well as lower plasma levels of IL-6, in the samples after therapy. Collectively, these studies indicate that Wnt5a/ROR1-dependent signaling contributes to CLL cell activation of NF-κB, which in turn causes autocrine IL-6-induced activation of pSTAT3. As such, this study demonstrates that cirmtuzumab can inhibit leukemia cell activation of both NF-κB and STAT3 in patients with CLL.