CD33 and acute myeloid leukemia: YCU-AML1 cells proliferated in co-culture system with OP9 stromal cells with GM-CSF supplementation, which resembles the culture condition of OCI-AML20, previously reported AML cell line harboring inv(3) and monosomy 7 (Fig. 8A).13 Cultured YCU-AML1 cells maintained high CD34, CD38, CD13 and CD33 positivity as the original case (Fig. 8B).