The VLA-4 integrin is constitutively active in circulating chronic lymphocytic leukemia cells via BCR autonomous signaling: a novel anchor-independent mechanism exploiting soluble blood-borne ligands.

In chronic lymphocytic leukemia (CLL), survival of neoplastic cells depends on microenvironmental signals at lymphoid sites where the crosstalk between the integrin VLA-4 (CD49d/CD29), expressed in ~40% of CLL, and the B-cell receptor (BCR) occurs. Here, BCR engagement inside-out activates VLA-4, thus enhancing VLA-4-mediated adhesion of CLL cells, which in turn obtain pro-survival signals from the surrounding microenvironment. We report that the BCR is also able to effectively inside-out activate the VLA-4 integrin in circulating CD49d-expressing CLL cells through an autonomous antigen-independent BCR signaling.

Early reappearance of intraclonal proliferative subpopulations in ibrutinib-resistant chronic lymphocytic leukemia.

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib represents an effective strategy for treatment of chronic lymphocytic leukemia (CLL), nevertheless about 30% of patients eventually undergo disease progression. Here we investigated by flow cytometry the long-term modulation of the CLL CXCR4/CD5 proliferative fraction (PF), its correlation with therapeutic outcome and emergence of ibrutinib resistance. By longitudinal tracking, the PF, initially suppressed by ibrutinib, reappeared upon early disease progression, without association with lymphocyte count or serum beta-2-microglobulin.