High levels of sIL7R are associated with a high risk of developing multiple sclerosis (MS)(18), and there is genetic and functional epistasis for MS risk between these IL7R alleles and alleles in DDX39B (15) In a recent study, we established that DDX39B activates FOXP3 intron splicing and regulates the expression of FOXP3(16), a lineage-defining transcription factor that is essential for T regulatory cell function (19–21). Here, IL7R is linked to myeloid sarcoma.