CYP24A1 and B-cell chronic lymphocytic leukemia: On the contrary, the presence of stromal cells in the culture system resulted in a significant increase in CYP24A1+ CLL cells at 24 h (n = 9, FD: 2, p < 0.05), which was further enhanced when calcitriol was added to the medium (FD: 1.2, p < 0.05) (Figure 5D), indicating that calcitriol action is maintained in the co-culture system.