Modulating the Expression of Multiple Surface Receptors on Epithelial Cells and Promoting Lung Macrophage Anti-viral Functions by OM-85 Inhibits Severe Acute Respiratory Syndrome Coronavirus 2 Infection

The emergence of a new virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Wuhan, China, in December 2019 triggered a global pandemic, forcing much of the world to adopt lockdown strategies and leading to extraordinary threats to the global healthcare system. The clinical manifestations of the disease, referred to as COVID-19, range from mild, self-limiting flu-like respiratory illness to life-threatening multi-organ failure and death. The rapid progress in our understanding of COVID-19 pathogenesis has led the development of effective vaccines, monoclonal antibodies, and anti-viral agents. However, a major cause of concern is the continuous and rapid emergence of new mutations that can progressively decrease sensitivity to the existing anti-COVID-19 tools. Safe, affordable, and widely available treatments are therefore urgently needed to reduce the frequency and/or severity of SARS-CoV-2 infection. OM-85 is a standardised lysate of bacterial strains widely used for the prophylaxis of airway recurrent infections in adults and children with an excellent safety profile. In experimental animal models and in clinical trials this compound was shown to possess anti-viral activities through immunomodulatory responses, but also by inhibiting infection. The positive results reported in models of common respiratory virus infection has recently encouraged researchers from three independent groups to evaluate whether OM-85 could also affect SARS-CoV-2 infection. The results of these studies are summarised in this review.