CTLA4 and B-cell chronic lymphocytic leukemia: Furthermore, based on the fact that CTLA-4 gene polymorphisms may influence the CTLA-4 expression level in CLL cells [22, 37], we cannot exclude that the strong divergence of CTLA-4 expression observed among the patients might result, at least in part, from the presence of specific alleles predisposing to overexpression of the CTLA-4 molecule.