The leading cause of hospitalization and death in children with trisomy 21 (TS21), also known as Down syndrome (DS), is lower respiratory tract infection (LRTI). Children with DS have nine times higher risk of hospitalization and mortality due to LRTIs caused by respiratory syncytial virus (RSV). Understanding the mechanisms driving the high susceptibility to severe viral LRTI in DS is needed to develop novel therapeutic strategies to treat this condition. As chromosome 21(HSA21) encodes four of the six known Interferon (IFN) receptors, TS21 results in triplication of these receptor genes leading to IFN hyperactivation in DS. With the central role of IFNs on antiviral defense, it remains puzzling how IFN hyperactivation contributes to severe viral LRTIs in DS. Through preliminary studies we show that, compared to euploid controls, airway epithelial cells (AECs) from children with DS exhibit IFN-induced dysregulation of NRF2, a transcription factor essential for the antioxidant response required to limit RSV replication. The AECs of children with DS also show dysregulated expression of BACH1 and its inhibitor miR-155, both of which are located on HSA21, and regulate NRF2- dependent AEC antioxidant responses during viral infection. Thus, our results identify a novel mechanism of impaired airway antiviral responses in TS21, and provide an unexpected molecular nexus between two widely recognized cellular pathologies in DS - dysregulated IFN activation (interferonopathy) and oxidative imbalance. Our central hypothesis is that hyperactivation of IFN in the airway epithelium of children with DS dysregulates BACH1 signaling, leading to reduced antiviral and NRF2-driven antioxidant responses and greater severity of viral respiratory infection. Our study will address the historical exclusion of DS children from research related to airway antiviral immunity, and thus will have a transformative potential to improve their health and survival. To elucidate the mechanisms of pathogenesis of severe viral respiratory infections in DS and develop innovative precision medicine approaches for this vulnerable population, we propose three aims: AIM 1: Define the role of IFN-induced BACH1 dysregulation during viral respiratory infection in the airway epithelium of children with DS. AIM 2: Investigate how interferonopathy and altered miR-155 expression dysregulates antioxidative and antiviral responses in the airway epithelium of children with DS. AIM 3: Establish the association of dysregulated antioxidative and antiviral responses in DS with greater disease severity during respiratory viral infection. The result of this human-based transformative study will define a previously unrecognized targetable mechanism causing dysregulated anti-oxidative and antiviral responses in TS21. This ground-breaking knowledge will greatly move forward our understanding of the pathobiology of severe viral LRTI in DS and will provide the essential molecular foundation for the development of new diagnostic tools and highly innovative therapies.

Public Health Relevance Statement: We will elucidate the mechanism mediating the dysregulation of airway antiviral and antioxidative responses in Down Syndrome (DS). This may provide the foundation to develop novel approaches to prevent severe respiratory infections caused by RSV and other viruses (e.g. SARS-CoV-2) in children and adults with DS.