Broadly neutralizing antibodies consistently trap HIV-1 in fresh cervicovaginal mucus from select individuals.

In addition to direct neutralization and other classical effector functions, IgG possesses a little recognized and thus under-utilized effector function at mucosal surfaces: Fc-mucin bonds enable IgG to trap viruses in mucus. Due to the paucity of envelope glycoproteins that limits the number of IgG that can bind HIV, it remains poorly understood whether IgG-mucin interactions can effectively immobilize HIV in human cervicovaginal mucus (CVM). Here, we obtained 54 fresh, undiluted CVM specimens from 17 different women, and employed high-resolution multiple particle tracking to quantify the mobility of fluorescent HIV virus-like-particles in CVM treated with various HIV-specific IgG. We observed consistent and effective trapping of HIV by broadly neutralizing antibodies (VRC01, PGT121, and 2F5) in a subset of women. While trapping efficacy was not affected by the menstrual cycle, it was positively correlated with appreciable L. Crispatus populations in the microbiome, and negatively correlated with appreciable L. Iners or G. Vaginalis populations. Our work demonstrates for the first time that IgG-mucin crosslinking is capable of reinforcing the mucosal barrier against HIV, and motivates further investigation of passive immunization against vaginal transmission of STIs. STATEMENT OF SIGNIFICANCE: HIV transmission in women primarily occurs vaginally, yet the 3-way interactions between mucins and HIV virions mediated by HIV-binding antibodies in cervicovaginal mucus (CVM) is not well understood. While IgG-Fc possess weak affinity to mucins that trap virus/IgG complexes in mucus, the effectiveness against HIV remains unclear, due to the low number of virion-bound IgG. Here, we discovered that IgG can trap HIV consistently in CVM from select individuals regardless of their birth control status or menstrual cycle phase. IgG-mediated trapping of HIV was moderately associated with microbiome composition. These results suggest that IgG-mucin interactions could potentially reduce HIV transmission and highlight the importance of mucosal secretions in antibody-mediated prevention of HIV and other sexually transmitted infections.