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In addition to the classical immunological functions such as neutralization, antibody-dependent cellular cytotoxicity, and complement activation, IgG antibodies possess a little-recognized and under-utilized effector function at mucosal surfaces: trapping pathogens in mucus. IgG can potently immobilize pathogens that otherwise readily diffuse or actively swim through mucus by forming multiple low-affinity bonds between the array of pathogen-bound antibodies and the mucin mesh. Trapping in mucus can exclude pathogens from contacting target cells, and facilitate their rapid elimination by natural mucus clearance mechanisms. Despite the fact that most infections are transmitted at mucosal surfaces, this muco-trapping effector function has only been revealed within the past decade, with the evidence to date suggesting that it is a universal effector function of IgG-Fc capable of immobilizing both viral and highly motile bacterial pathogens in all major mucosal secretions. This review provides an overview of the current evidence for Fc-mucin crosslinking as an effector function for antibodies in mucus, the mechanism by which the accumulation of weak Fc-mucin bonds by IgG bound to the surface of a pathogen can result in immobilization of antibody-pathogen complexes, and how trapping in mucus can contribute to protection against foreign pathogens. 

Nonhormonal products for on-demand contraception are a global health technology gap; this unmet need motivated us to pursue the use of sperm-binding monoclonal antibodies to enable effective on-demand contraception. Here, using the cGMP-compliant Nicotiana -expression system, we produced an ultrapotent sperm-binding IgG antibody possessing 6 Fab arms per molecule that bind a well-established contraceptive antigen target, CD52g. We term this hexavalent antibody “Fab-IgG-Fab” (FIF). The Nicotiana -produced FIF had at least 10-fold greater sperm-agglutination potency and kinetics than the parent IgG, while preserving Fc-mediated trapping of individual spermatozoa in mucus. We formulated the Nicotiana -produced FIF into a polyvinyl alcohol–based water-soluble contraceptive film and evaluated its potency in reducing progressively motile sperm in the sheep vagina. Two minutes after vaginal instillation of human semen, no progressively motile sperm were recovered from the vaginas of sheep receiving FIF Film. Our work supports the potential of multivalent contraceptive antibodies to provide safe, effective, on-demand nonhormonal contraception. 

Respiratory syncytial virus (RSV) causes substantial morbidity and mortality in infants, the immunocompromised, and the elderly. RSV infects the airway epithelium via the apical membrane and almost exclusively sheds progeny virions back into the airway mucus (AM), making RSV difficult to target by systemically administered therapies. An inhalable “muco‐trapping” variant of motavizumab (Mota‐MT), a potent neutralizing mAb against RSV F is engineered. Mota‐MT traps RSV in AM via polyvalent Fc‐mucin bonds, reducing the fraction of fast‐moving RSV particles in both fresh pediatric and adult AM by ≈20–30‐fold in a Fc‐glycan dependent manner, and facilitates clearance from the airways of mice within minutes. Intranasal dosing of Mota‐MT eliminated viral load in cotton rats within 2 days. Daily nebulized delivery of Mota‐MT to RSV‐infected neonatal lambs, beginning 3 days after infection when viral load is at its maximum, led to a 10 000‐fold and 100 000‐fold reduction in viral load in bronchoalveolar lavage and lung tissues relative to placebo control, respectively. Mota‐MT‐treated lambs exhibited reduced bronchiolitis, neutrophil infiltration, and airway remodeling than lambs receiving placebo or intramuscular palivizumab. The findings underscore inhaled delivery of muco‐trapping mAbs as a promising strategy for the treatment of RSV and other acute respiratory infections.