PTEN and acute myeloid leukemia: Because phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is the major negative regulator of AKT phosphorylation, we also examined its levels in WT and B7-H4-null AML cells, and showed that PTEN was markedly downregulated in B7-H4-null leukemia cells (Figure 5c, first panel).