Daclizumab inhibits CD40L expression independently of cell division. Reconstituted PBMC cultures of pure, CFSE-labeled CD45RO⁺ or CD45RA⁺ CD4⁺ T cells were CD28 costimulated ± anti-CD25 Ab. On the left, a dot plot of such a CD28-costimulated culture of CD45RA⁺ cells at 48 hours is shown. The number of cell divisions (0, 1, 2) as measured by CFSE dilution is indicated. On the right, the distribution of divided cells and CD40L on those cells, in the presence (daclizumab) and absence (control) of anti-CD25 is shown.