Nutlin-3-dependent p53 phosphorylation at Ser15 has also been observed in normal CD19+ B-cells, peripheral blood mononuclear cells (PBMCs), bone marrow mononuclear cells (BMMCs) and B-CLL cells to a level similar to that noted in response to fludarabine treatment, and in excess of that resulting from treatment with the protease inhibitor clasto-latacystin [25]. This evidence concerns the gene CD19 and B-cell chronic lymphocytic leukemia.