IgG3 enhances neutralization potency and Fc effector function of an HIV V2-specific broadly neutralizing antibody

Abstract

Broadly neutralizing antibodies (bNAbs) protect against HIV infection in non-human primates and their efficacy may be enhanced through interaction with Fc receptors on immune cells. Antibody isotype is a modulator of this binding with the IgG3 subclass mediating potent Fc effector function and is associated with HIV vaccine efficacy and HIV control. BNAb functions are typically assessed independently of the constant region with which they are naturally expressed. To examine the role of natural isotype in the context of a bNAb lineage we studied CAP256, an HIV-infected individual that mounted a potent V2-specific bNAb response. CAP256 expressed persistently high levels of plasma IgG3 which we found mediated both broad neutralizing activity and potent Fc function. Sequencing of germline DNA and the constant regions of V2-directed bNAbs from this donor revealed the expression of a novel IGHG3 allele as well as IGHG3*17, an allele that produces IgG3 antibodies with increased plasma half-life. Both allelic variants were used to generate CAP256-VRC26.25 and CAP256-VRC26.29 IgG3 bNAbs and these were compared to IgG1 versions. IgG3 variants were shown to have significantly higher phagocytosis and trogocytosis compared to IgG1 versions, which corresponded to increased affinity for FcγRIIa. Neutralization potency was also significantly higher for IgG3 bNAbs, particularly against viruses lacking the N160 glycan. By exchanging hinge regions between subclass variants, we showed that hinge length modulated both neutralization potency and Fc function. This study showed that co-operation between the variable and natural IgG3 constant regions enhanced the polyfunctionality of antibodies, indicating the value of leveraging genetic variation which could be exploited for passive immunity.

Hinge length contributes to the phagocytic activity of HIV-specific IgG1 and IgG3 antibodies

“…These phenotypes were consistent at varying ratios of effector cells and target particles, whether cell lines or primary phagocytes were used as effectors, and whether fluorescent antigen beads or viral particles were used as targets. The direct relationship between hinge length and phagocytosis may also hold for other specificities, as Richardson et al now also demonstrate for CAP256 [89]. Collectively, this data points toward hinge modification as an additional tool for antibody engineering, and provides a new rationale to investigate IgG3 responses and allotypic variation in hinge length in the context of cohort studies.…”

“…We found that the neutralization activity of VRC01 and 447-52D were not altered by hinge length. However, Richardson et al find a modest but reproducible effect on the neutralization potency of CAP256 results from hinge modification [89]. Collectively, these data suggest that the impact of hinge composition varies across both different antibodies as well as across different viruses.…”

“…In contrast, as IgG2 and IgG4 antibodies have compromised effector function compared to IgG1 and IgG3, subclass switching has dramatic and generally predictable effects on the effector function of antiviral antibodies, as would be expected from their differing affinities for FcɣR [67]. Between IgG1 and IgG3, however, it has now been observed that the IgG3 subclass is associated with considerably enhanced phagocytic activity across multiple studies for multiple antibodies, including VRC01, 447-52D, CAP256, CH31, CH27, CH28, HG107, 7B2, 2158, and 1361 [12][13][14]89]. Here, these observations are extended to include two antibodies that recognize distinct viral epitopes and have differing phagocytic activities in their IgG1 forms.…”

Functional analysis of a monoclonal antibody reactive against anti-cluster A epitope obtained from a patient infected with HIV-1 CRF02_AG

“…IgG3 form of 1E5 showed better reactivity than the IgG1 form Recent reports described the superior nature of the IgG3 class over IgG1 not only for Fc-receptor-mediated functions, such as ADCC and ADCP, but also for neutralization capability (21,(23)(24)(25)(26)(27). To obtain 1E5 with superior activities, we constructed an IgG3 form of 1E5 in addition to the IgG1 form.…”

“…Recent reports have described the superior nature of the IgG3 class of antibodies over the IgG1 class, not only for Fc-receptor-mediated functions, such as ADCC and antibody-dependent cellular phagocytosis (ADCP) (21,(23)(24)(25)(26)(27), but also for their neutralization capability (26). The level of IgG3 correlated with anti-HIV-1 function in the RV-144 trial (28,29) and was involved in the control of disease in different cohorts (21,30).…”