Chronic lymphocytic leukemia (CLL) has been considered as an accumulative disease deriving from defects in apoptosis, but recent studies showed that CLL is a dynamic process in which monoclonal B cells proliferate within pseudofollicular proliferation centers. Microenvironmental interactions are essential for the survival and proliferation of CLL cells. The cell traffic between blood and secondary lymphoid tissues is controlled by tissue-specific chemokines and their specific receptors on B lymphocytes. Interstitial cell migration and adhesion events, predisposed by activational stimuli, determine CLL cell localization. Stimulation through the B cell receptor plays an important role in the expansion of the malignant clone in CLL. B cell receptors become activated either in an antigen-dependent or in an antigen-independent fashion in the secondary lymphatic tissues. However, low expression of the BCR correlates with reduced induction of protein tyrosine kinase activity and defective intracellular calcium mobilization and tyrosine phosphorylation. In contrast to normal B cells, leukemic cells are poor antigen presenting cells. This is due to the fact that leukemic cells have a reduced expression of costimulatory molecules and defects in the formation of immunological synapse with T cells. Increased surface expression of the costimulatory molecules on CLL cells correlates with their proliferation. At present, conventional treatments are not directed to interactions between CLL cells and their microenvironment, which is probably one of the reasons why, despite the significant progress in treatment, the disease still remains incurable. In this regard, identifying key biomarkers of intercellular interactions of neoplastic CLL population in comparison with clinical laboratory abnormalities in CLL enable clarification of essential processes in the development of the disease, and can be the basis for stratifying patient groups in order to optimize therapeutic approaches, which will make them relevant and promising.
Part of the book: Leukemias
Acute myeloid leukemia (AML) is a clonal, malignant disease of hematopoietic tissues that is characterized by accumulation of abnormal blast cells, principally in the marrow and impaired production of normal blood cells. The unsatisfactory clinical outcomes of AML patients urged the development of new therapy strategies, one of which includes the implementation of new nucleoside analogs. Clofarabine has offered new promising perspectives within induction and consolidation therapies. This chapter will evaluate the efficacy and tolerability of clofarabine as a single agent and in combination therapy, including hematopoietic stem cell transplantation, for AML patients.
Part of the book: Leukemias