SPI1 and leukemia: Similar to the leukemia that develops in NRAS(G12D) only mice (Fig. 4), recipient mice that received ΔβCat-TCF7-SPI1 only had an enlarged thymus, limited splenic invasion, and a more mature CD4+/CD8+ immunophenotype with similar disease latency (median DFS = 67.5 days) (Fig. 5b–d).