Microenvironmental Interactions in Chronic Lymphocytic Leukemia: The Master Role of CD49d

Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease characterized by the accumulation/expansion of a clonal population of neoplastic cells with the morphologic appearance of small mature B lymphocytes in blood, bone marrow, and lymphoid organs. A combination of genetic lesions is primarily responsible for the first step(s) of neoplastic transformation, along with microenvironmental signals, which concurrently operate by enhancing proliferation and/or inhibiting apoptosis. In this context, CD49d is known to play a pivotal role in mediating both cell-cell and cell-matrix interactions in CLL-involved tissues, eventually delivering pro-survival signals and protecting CLL cells from drug-induced damages. In the present review, we address, in detail, CD49d activities in the CLL microenvironment, CD49d functional and physical interactions with other microenvironmental receptors (including CD38 and B-cell receptor), and the relationship of CD49d expression with specific cytogenetic features in CLL.