Immunological Synapse in the Biology of Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative disease manifested by accumulation of tumor B-cells with characteristic immunophenotype (CD19+CD5+CD23+) in bone marrow, peripheral blood and secondary lymphoid organs. The clinical course of CLL is heterogeneous. This is the most prevalent leukemia among older-aged patients. Despite the use of novel drugs refractory forms of disease remain. The latest discoveries in immunology enabled understanding of some mechanisms of tumor evasion from immune surveillance. The interaction of immune system cells occurs due to the development of immunological synapse that predominantly depends on the family of CD28/В7 molecules, the so-called immune checkpoints able to control the activating and inhibiting mechanisms of cells. The acquisition of tumor phenotype is a multistage process, in which cells obtain unique biological properties including the ability of being invisible to the immune system. As opposed to solid tumors in lymphoproliferative diseases tumor B-cells are able to express major histocompatibility complex class II and CD80 and CD86 co-stimulatory molecules. It proves their ability to present antigens to T-cells. Co-inhibitory molecules on the surface of tumor cells is a factor contributing to the inhibition of immune response. The present paper reviews current conceptions of biological properties and immunological interactions of CLL cells with the microenvironmental cells.