UM-729 is a new pyrimidoindole and enhances the self-renewal of human hematopoietic stem cells in vitro. UM729 has no effect on AhR target genes but has been shown to collaborate with AHR antagonists in preventing differentiation of acute myeloid leukemia (AML) cells in culture. In addition, UM729 has been reported to expand normal hematopoietic stem cells in a AhR-independent fashion.