No prophylactic vaccine has provided robust protection against HIV-1. Vaccine-induced broadly neutralizing antibodies (bnAbs) have not been achieved in humans and most animals, however cows vaccinated with HIV-1 envelope trimers produce bnAbs with unusually long third heavy complementarity determining regions (CDRH3). Alongside neutralization, Fc-mediated effector functions including antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (ADP) may be critical for in vivo bnAb antiviral activity. Here, we aimed to augment the Fc-dependent effector functions of a chimeric human-bovine bnAb, NC-Cow1, which binds the CD4 binding site (CD4bs) and exhibits broader and more potent neutralization than most human CD4bs bnAbs by using an exceptionally long 60aa CDRH3. The bovine variable region of NC-Cow1 was paired with a human IgG1 Fc region mutated to create three variants: G236R/L328R (GRLR) that abrogates Fc-gamma receptor (FcgammaR) binding, and two variants that enhance binding: G236A/S239D/I332E (GASDIE) and G236A/S239D/A330L/I332E (GASDALIE). Both GASDIE and GASDALIE improved binding to human FcgammaRIIA and FcgammaRIIIA, enhanced human NK cell activation and mediated higher levels of ADCC and ADP activity compared to the wild-type human IgG1 Fc. GASDALIE mediated higher phagocytic activity compared to GASDIE. As expected, GRLR eliminated binding to FcgammaRs and did not mediate ADCC or ADP. We demonstrated that mutations in the human Fc region of bovine chimeric antibodies with ultra-long CDRH3 regions could enhance antibody effector functions while maintaining envelope binding and neutralization. This study will have significant implications in the development of multifunctional anti-HIV antibodies, which may be important to prevent HIV-1 transmission in an antibody-based topical microbicide.IMPORTANCEDespite successful antiviral chemotherapy, HIV is still a lifelong persistent virus and no vaccine yet prevents HIV transmission. Topical microbicides offer an important alternative method to prevent sexual transmission of HIV-1. With the production of highly potent anti-HIV-1 bnAbs and multifunctional antibodies, monoclonal antibodies are now important prophylactic agents. Recently discovered anti-HIV-1 bovine bnAbs (with higher potency and breadth than most human bnAbs) could be novel candidates as potent topical microbicides. Our study is significant as it demonstrates the compatibility of combining bovine-derived neutralization with human-derived antibody-effector functions. This study is a new approach to antibody engineering that strengthens the feasibility of using high potency bovine variable region bnAbs with augmented Fc function and promotes them as a strong candidate for antibody-mediated therapies.
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