Kosmaczewska et al. were the first to conduct studies on the surface and cytoplasmic expression of CTLA-4 in CD19+/CD5+ CLL B cells in relation to clinical parameters and polymorphism of genes encoding proteins regulating the cell cycle, showing the relationship of this molecule with the inhibition of the CLL cell cycle [29]. Here, CD19 is linked to B-cell chronic lymphocytic leukemia.