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Background Respiratory tract infections (RTIs) are a leading cause of hospitalization and death in people age ≥65 years. RTIs are caused by multiple viruses, most of which lack effective treatments. An immunotherapy that enhances pan-antiviral innate immunity may reduce RTI incidence in older adults. Inhibition of targets downstream of target of rapamycin complex 1 (TORC1) was reported to upregulate pan-antiviral gene expression and protect mice from a viral RTI (York AG et al. Cell 2015). We evaluated whether TORC1 inhibition increased antiviral gene expression and decreased RTI incidence in older adults. Methods A randomized, double-blind, placebo, controlled study was conducted to determine whether the TORC1 inhibitor RTB101 alone or in combination with the TORC1 inhibitor everolimus reduced the incidence of laboratory-confirmed RTIs. The study enrolled 652 older adults at increased risk of RTI-related morbidity and mortality (defined as age ≥85 years, or age ≥65 years with asthma, COPD, type 2 diabetes mellitus, or current smokers). Subjects were treated for 16 weeks during winter cold and flu season with oral RTB101 5 mg or 10 mg once daily (QD), RTB101 10 mg twice daily, RTB101 10 mg + everolimus 0.1 mg QD, or matched placebo. The primary endpoint was the percentage of subjects with ≥1 laboratory-confirmed RTI through Week 16. Results RTB101 was well tolerated. In the intent-to-treat analysis, RTB101 10 mg QD was observed to: reduce the percentage of subjects with laboratory-confirmed RTIs by 30.6% compared with placebo (P = 0.025); reduce the incidence of RTIs caused by multiple different viruses; and upregulate interferon-stimulated pan-antiviral gene expression in whole blood (P = 0.00001 vs. placebo, Figure 1). Furthermore, RTB101 10 mg QD was observed to reduce the time to alleviation of moderate to severe RTI symptoms by 5 days, and to reduce the rate of all-cause hospitalization (rate ratio 0.439, 90% CI 0.196–0.983, P = 0.047). Conclusion RTB101 10 mg QD was associated with a significant reduction in laboratory-confirmed RTIs due to multiple viral pathogens that lack effective medicines for treatment or prevention. RTB101 was observed to upregulate interferon-stimulated pan-antiviral gene expression, which may underlie the reduction in RTI incidence. Disclosures Joan Mannick, MD, resTORbio (Employee, Shareholder), Amelia Tomlinson, PhD, resTORbio (Employee), Sarb Shergill, PhD, resTORbio (Employee), Grace Teo, PhD, resTORbio (Employee), Lloyd Klickstein, MD, PhD, resTORbio (Employee).