CD40 and B-cell chronic lymphocytic leukemia: The most important cellular elements in CLL microenvironment are mesenchymal stromal cells, nurse-like cells and T cells [76] and the interaction between leukemic B cells and cells from microenvironment is mediated by different receptors e.g., chemokine receptors, BCR, CD38, CD40 and TLRs (toll like receptors) [77].