CYP24A1 and B-cell chronic lymphocytic leukemia: To this purpose, we cultured CLL cells with calcitriol for 24 h and measured by flow cytometry the expression of CYP24A1. We found that the percentage of CYP24A1+ CLL cells dramatically increased in the presence of calcitriol compared to non-treated cells (n = 16 cases: FD: 3.3, p < 0.0001; Figure 1H), indicating that the VDR is functional in CLL.