Live biotherapeutic throat spray for respiratory virus inhibition and interferon pathway induction
Respiratory viruses such as influenza viruses, respiratory syncytial virus (RSV), and coronaviruses initiate infection at the mucosal surfaces of the upper respiratory tract (URT), where the resident respiratory microbiome has an important gatekeeper function. In contrast to gut-targeting administration of beneficial bacteria against respiratory viral disease, topical URT administration of probiotics is currently underexplored, especially for the prevention and/or treatment of viral infections. Here, we report the selection and formulation of a broad-acting throat spray with live lactobacilli which induce interferon regulatory pathways and are able to inhibit respiratory viruses. Rational selection of Lactobacillaceae strains was based on safety, applicability, and potential antiviral and immunostimulatory efficacy in the URT. Three strains, Lacticaseibacillus casei AMBR2, Lacticaseibacillus rhamnosus GG and Lactiplantibacillus plantarum WCFS1 significantly reduced the cytopathogenic effects of RSV, influenza A/H1N1 and B viruses, and HCoV-229E coronavirus in co-culture models with bacteria, virus and host cells. Subsequently, these strains were formulated in a throat spray and human monocytes were employed to confirm the formulation process did not reduce the interferon regulatory pathway-inducing capacity. Administration of the throat spray in healthy volunteers revealed that the lactobacilli were capable of temporary colonization of the throat in a metabolically active form.