A Nonfucosylated Variant of the anti-HIV-1 Monoclonal Antibody b12 Has Enhanced FcγRIIIa-Mediated Antiviral Activity In Vitro but Does Not Improve Protection against Mucosal SHIV Challenge in Macaques

Abstract

Eliciting neutralizing antibodies is thought to be a key activity of a vaccine against human immunodeficiency virus (HIV). However, a number of studies have suggested that in addition to neutralization, interaction of IgG with Fc gamma receptors (Fc␥R) may play an important role in antibody-mediated protection. We have previously obtained evidence that the protective activity of the broadly neutralizing human IgG1 anti-HIV monoclonal antibody (MAb) b12 in macaques is diminished in the absence of Fc␥R binding capacity. To investigate antibody-dependent cellular cytotoxicity (ADCC) as a contributor to Fc␥R-associated protection, we developed a nonfucosylated variant of b12 (NFb12). We showed that, compared to fully fucosylated (referred to as wild-type in the text) b12, NFb12 had higher affinity for human and rhesus macaque Fc␥RIIIa and was more efficient in inhibiting viral replication and more effective in killing HIV-infected cells in an ADCC assay. Despite these more potent in vitro antiviral activities, NFb12 did not enhance protection in vivo against repeated low-dose vaginal challenge in the simian-human immunodeficiency virus (SHIV)/macaque model compared to wild-type b12. No difference in protection, viral load, or infection susceptibility was observed between animals given NFb12 and those given fully fucosylated b12, indicating that Fc␥R-mediated activities distinct from Fc␥RIIIa-mediated ADCC may be important in the observed protection against SHIV challenge.

Towards HIV-1 remission: potential roles for broadly neutralizing antibodies

“…Overall, the evidence suggests that eliminating Fc-mediated function impairs the protective antiviral activity of bNAbs, but it is unclear whether enhancing ADCC activity improves protective efficacy. A nonfucosylated variant of b12 that had enhanced viral inhibitory and killing abilities in vitro failed to improve protection efficacy in vivo relative to WT b12 (44). Thus, definitive evidence for ADCC remains elusive.…”

Antibody functional assays as measures of Fc receptor-mediated immunity to HIV - new technologies and their impact on the HIV vaccine field.

“…The nonfucosylated variant of mAb b12 (NFb12), had increased FcγRIIIa binding and 10-fold improved potency in NKmediated ADCC and PBMC-mediated ADCVI assays, but, contrary to expectation, proved in vivo no more potent than wild-type Ab in protecting SHIV challenged rhesus macaques [127].…”

“…Some of these glycoforms of Fc interact poorly with FcγRIIIa (e.g. fucosylated [120][121][122][123]) and so are possibly non-inflammatory versions of IgG that may be most appropriate for protection against mucosal challenge, especially considering the lack of evidence for improved protection in SHIV challenge studies by the non-fucosyl-variant of the b12 bNAb [127].…”

Exploring the Potential of Monoclonal Antibody Therapeutics for HIV-1 Eradication

“…133 In a follow-up study, using an afucosylated form of b12, which should drive enhanced ADCC, demonstrated limited improvement in antibody protective efficacy in a vaginal challenge model. 134 However, FccRIIIa + NK cells are necessary for ADCC, which are limited at mucosal barriers, 135 including the vaginal walls. This most likely resulted in the limited protection of these antibodies in vivo.…”