CTLA4 and B-cell chronic lymphocytic leukemia: In the low CTLA-4 expressors, no significant impact of cell culture in medium alone or ex vivo stimulation on the surface expression of the CTLA-4 molecule was found, and the median proportions of sCTLA-4+ CLL cells were comparable to those observed in healthy individuals at each time point tested (Table 2, Figs. 1 and 2).