A surprising finding in the RV immune correlates

A surprising finding in the RV144 immune correlates analysis was that monomeric anti-Env IgA in plasma may mitigate otherwise protective IgG responses (Haynes et al., 2012, Tomaras et al., 2013). Both IgA and IgG antibody isotypes are key mediators of defense against pathogen invasion. Although IgG is more abundant in the lower female genital tract and male foreskin epidermis, IgA is the main Ab isotype in most mucosal compartments (Lemos et al., 2016, Mestecky et al., 2009). The two human subclasses of IgA, IgA1 and IgA2, can each exist as dimeric (dIgA) and multimeric forms comprising two or more monomeric IgAs covalently linked by a J-chain; multimerization enhances IgA avidity and its aggregation potential (Stieh et al., 2014, Woof and Russell, 2011). Compared to IgA1, IgA2 is the more prevalent subclass in the female genital tract and colon (Woof and Russell, 2011), and its shorter hinge region and additional disulfide bonds create a more compact, rigid structure with enhanced resistance to degradation by proteases present in the mucosa. The polymeric IgA receptor (pIgR) provides unidirectional transport of dIgA to the apical epithelial surface, where it complexes with secretory component (SC), resulting in secretory IgA (sIgA). Moreover, the glycosylation of IgA SC facilitates the interaction with mucus (Woof and Russell, 2011). Transport and maintenance of IgG in the GI and GU tracts are regulated by the neonatal Fc receptor (FcRn) on epithelial cells, which binds IgG at low pH and releases it at neutral pH (Pyzik et al., 2015, Tzaban et al., 2009). In the lower female genital tract, the acidic pH of the lumen favors retention of IgG at this site. In the gut, FcRn enables transport of IgG to the lumen where it can bind to its cognate antigen and then return as immune complexes for presentation to dendritic LY335979 (Pyzik et al., 2015, Tzaban et al., 2009). Thus, FcRn may paradoxically also enable transcytosis of infectious HIV-1 virions carried in tow by IgG (Gupta et al., 2013). In summary, differences in the structure, transport and Fc-mediated effector functions can influence the role of IgG and IgA Abs in mucosal HIV-1 infection. Despite its importance in mucosal host defense, the role of IgA in mucosal protection against HIV-1 transmission is less defined than that of IgG. To address this, we generated a mAb panel of IgG1 and various IgA isoforms, with particular emphasis on the more stable IgA2 subclass; these include a bnAb directed against the HIV-1 gp120 CD4 binding site (CD4bs) neutralizing epitopes, and nnAbs directed at gp120 C1 and V2 epitopes and the gp41 immunodominant domain (Bonsignori et al., 2011, Wu et al., 2011, Liu et al., 2013, Liao et al., 2013, Bonsignori et al., 2012). Moreover, we have expressed the CD4bs bnAb, CH31, as IgG1, and as monomeric, dimeric and secretory IgA2 (Zhang et al., 2016). We similarly expressed the IgG1, monomeric and dimeric IgA2 isoforms of the non-neutralizing gp41-specific mAb, 7b2 (Zhang et al., 2016, Santra et al., 2015). Using these mAbs, the impact of various IgA forms on the functional capacity of neutralizing and non-neutralizing mAbs was investigated in various assays and models of HIV-1 transmission. This panel has been extensively characterized in a variety of in vitro assays supporting their potential to exert various antiviral functions in vivo, such as phagocytosis (Tay et al., 2016), virus capture (Liu et al., 2013, Liu et al., 2014), virus aggregation (Stieh et al., 2014, R. Shattock, personal communication), blocking of virus binding to galactosyl ceramide (GalCer) (Dennison et al., 2014), ADCC (Tomaras et al., 2013, Pollara et al., 2014, Bonsignori et al., 2012) and neutralization (Santra et al., 2015). Here, we have evaluated the protective capacity of these mAbs ex vivo in a human vaginal tissue explant model and in vivo in an NHP intrarectal model of HIV-1 infection to identify key Ab properties associated with early mucosal protection that may guide the development of effective prevention strategies.