SPI1 and acute lymphoblastic leukemia: These results suggest that PI3K activation can rescue the T cell developmental block in Spi1-null T cell progenitors (Champhekar et al., 2015; Spain et al., 1999), similar to the findings in our previous report on Pten;Rag-null mice (Guo et al., 2011).Therefore, SPI1 is essential for Pten-null LSC ‘stemness’ and T-ALL development.