Janus kinase inhibitor ruxolitinib blocks thymic regeneration after acute thymus injury

Thymic epithelial cells (TECs) are crucial for the production of T-cells. Cancer therapies including cytotoxic drugs and ionizing radiations damage TECs resulting in abnormal T-cell production and function. Fortunately, TECs can regenerate after injury. The Janus kinase (JAK) pathway is important in supporting survival of TECs. JAK inhibitors are used to treat Cancer and immune disorders. The impact of JAK inhibitors on recovery of TECs is unknown. We induced acute thymus injury in mice by using ionizing radiation and evaluated the impact of ruxolitinib on thymus regeneration. We also tested if ruxolitinib affected proliferation of TECs in vitro. An increase was observed in the recovery of thymus cells after acute injury in association with up-regulation of TEC-related growth factors including keratinocyte growth factor (Kgf), epidermal growth factor (EGF), insulin-like growth factor 1 (Igf1) and receptor activator of NF-κB ligand (RANKL). Giving ruxolitinib decreased levels of receptors of these growth factors on TECs and blocked growth factor-induced recovery of thymus cells in damaged thymii. Ruxolitinib also blocked growth factors-induced proliferation of TECs in vitro. Thymus regeneration was inhibited when ruxolitinib was given immediately after thymus injury but not when it was given 1 week later. These data may have implications for how ruxolitinib is used in clinical practices.