CD40LG and B-cell chronic lymphocytic leukemia: The molecular identity of the receptor, however, was obscure until 2009, when the functional cloning strategy (i.e., IgM binding) was employed for the cDNA libraries of two human cell types that are known to bind the Fc portion of IgM molecules, namely, phorbol myristate acetate (PMA)-activated 697 pre-B cell line and chronic lymphocytic leukemia (CLL) B cells [9].