Ruxolitinib targets JAK-STAT signaling to modulate neutrophil activation in refractory macrophage activation syndrome.

Macrophage activation syndrome (MAS) is believed to be caused by inappropriate proliferation and activation of the mononuclear phagocytic system. Adult-onset Still disease (AOSD) is characterized by neutrophil activation and a cytokine storm, which can lead to the severe and potentially life-threatening complication of MAS. RNA sequencing revealed that neutrophils may play a distinct role and enhance the innate immunity of patients with AOSD with MAS (AOSD-MAS). In the CpG-induced secondary hemophagocytic lymphohistiocytosis (HLH) model, the depletion of neutrophils significantly reduced cytokine levels with effects comparable with monocyte depletion. Significant enrichment was observed in the type I/II interferon and JAK-STAT pathways in neutrophils from patients with AOSD-MAS. Treatment of 10 patients with refractory AOSD-MAS with ruxolitinib led to the resolution of inflammatory parameters and clinical symptoms. RNA sequencing and ex vivo assays confirmed that ruxolitinib suppressed aberrant NETosis and STAT3/STAT5 signaling. In vivo, PAD4 knockout further confirmed the pathogenic role of NETosis in a secondary HLH model. Moreover, the selective inhibition of STAT3 or STAT5 alleviated systemic inflammation. Ten functional variants were identified in genes related to the JAK-STAT pathway, however, their clinical relevance requires further validation. These findings suggest that ruxolitinib has the potential to facilitate disease remission in patients with refractory AOSD-MAS by broadly inhibiting JAK-STAT signaling and modulating neutrophil activation and NETosis.