CTLA4 and B-cell chronic lymphocytic leukemia: Furthermore, the rate of CTLA-4 expression seems to determine proliferation activity and apoptosis of CLL cells; CTLA-4 blockade in high CTLA-4 expressors induces pro-survival signals in CLL cells, indicating that the systemic administration of a CTLA-4 blocking antibody as immunotherapy might be an unfavourable strategy for these patients.