Hypogammaglobulinemia, characterized by reduced serum immunoglobulin G (IgG), immunoglobulin A (IgA), or immunoglobulin M (IgM) levels, is commonly observed in chronic lymphocytic leukemia (CLL) with an incidence ranging from 20% to 70% (16). Here, CD40LG is linked to B-cell chronic lymphocytic leukemia.