JAK3 and rheumatoid arthritis: Inhibition of JAK3 with tofacitinib (approved by the Food and Drug Administration [FDA] for the treatment of rheumatoid arthritis) in HOX9A–JAK3-mutated mice resulted in a reduction in spleen weight and in white cell count after 20 days.90 Given the increased expression of PIM1 in HOX9A–JAK3-mutated mice, the use of a PIM1 inhibitor in combination with inhibition of JAK–STAT might be of value.