As regard proliferation activity after ex vivo stimulation, we assume that the observed lack of significant differences between studied groups of CLL patients may be caused by a gradual decline of CTLA-4 expression in the high CTLA-4 expressors following ex vivo stimulation to the level found in the low CTLA-4 expressors. The gene discussed is CTLA4; the disease is B-cell chronic lymphocytic leukemia.