Monoclonal Antibodies against Zika Virus NS1 Protein Confer Protection via FcγReceptor-Dependent and -Independent Pathways

Abstract

Zika virus (ZIKV) infection during pregnancy causes congenital defects such as fetal microcephaly. Monoclonal antibodies (MAbs) against the nonstructural protein 1 (NS1) have the potential to suppress ZIKV pathogenicity without enhancement of disease, but the pathways through which they confer protection remain obscure. Here, we report two types of NS1-targeted human MAbs that inhibit ZIKV infection through distinct mechanisms. MAbs 3G2 and 4B8 show a better efficacy than MAb 4F10 in suppressing ZIKV infection in C57BL/6 neonatal mice. Unlike MAb 4F10 that mainly triggers antibody-dependent cell-mediated cytotoxicity (ADCC), MAbs 3G2 and 4B8 not only trigger ADCC but inhibit ZIKV infection without Fcγ receptor-bearing effector cells, possibly at postentry stages. Destroying the Fc-mediated effector function of MAbs 3G2 and 4B8 reduces but does not abolish their protective effects, whereas destroying the effector function of MAb 4F10 eliminates the protective effects, suggesting that MAbs 3G2 and 4B8 engage both Fcγ receptor-dependent and -independent pathways. Further analysis reveals that MAbs 3G2 and 4B8 target the N-terminal region of NS1 protein, whereas MAb 4F10 targets the C-terminal region, implying that the protective efficacy of an NS1-targeted MAb may be associated with its epitope recognition. Our results illustrate that NS1-targeted MAbs have multifaceted protective effects and provide insights for the development of NS1-based vaccines and therapeutics. IMPORTANCE Zika virus (ZIKV) is a mosquito-borne flavivirus that has been linked to congenital microcephaly during recent epidemics. No licensed antiviral drug or vaccine is available. Monoclonal antibodies (MAbs) against the nonstructural protein 1 (NS1) inhibit ZIKV pathogenicity but do not enhance the disease as envelope protein-targeted MAbs do. However, the protection mechanisms are not fully understood. Here, we show that in the presence or absence of Fcγ receptor-bearing effector cells, NS1-targeted human MAbs 3G2 and 4B8 inhibit ZIKV infection. Compared to MAb 4F10 that has no inhibitory effects without effector cells, 3G2 and 4B8 confer better protection in ZIKV-infected neonatal mice. Destroying the Fc-mediated effector function reduces but does not abolish the protection of 3G2 and 4B8, suggesting that they engage both Fcγ receptor-dependent and -independent pathways. The protective efficacy of NS1-targeted MAbs may be associated with their epitope recognition. Our findings will help to develop NS1-based vaccines and therapeutics.

Flavivirus NS1 and Its Potential in Vaccine Development

“…An example of the first type is 4F10, which binds the C-terminal region, can trigger Fc-G receptor-mediated phagocytosis, and inhibits ZIKV infection through effector cells. MAbs 3G2 and 4B8 are examples of the second type, which bind the Nterminal region and can inhibit infection through ADCC without effector cell assistance through both Fc-G receptor-independent and -dependent mechanisms [59]. These results suggest that the protective efficacy of a mAb may be linked with its epitope recognition.…”

“…These results suggest that the protective efficacy of a mAb may be linked with its epitope recognition. Protection is hypothesized to occur through the inhibition of viral replication or the disruption of the production of infectious viral particles [59]. MAbs Z15 and Z17 were protective in non-pregnant mice, while mAbs Z17, ZIKV-292, and 749-A4 were protective in pregnant mice [60].…”

Requirement of Fc-Fc Gamma Receptor Interaction for Antibody-Based Protection against Emerging Virus Infections

“…Importantly, mAb treatment resulted in higher brain mass, decreased lymphocyte infiltration, and reduced neurological score [128]. All of the mAbs induced ADCC in vitro, but only the 4F10-LALA-PG variant showed reduced protection during in vivo challenge compared to the LALA-PG variants of 4B8 and 3G2 [128]. In vitro analysis showed 4B8 and 3G2 could reduce release of virions when added at late times post-infection, suggesting a potential alternative mechanism of protection [128].…”

“…Another study addressed the protective efficacy of human anti-ZIKV NS1 mAbs in neonate mice. Multiple administrations of mAbs targeting the N-terminal region (β-roll), 4B8 and 3G2, or the C-terminal region (β-ladder), 4F10, of NS1 significantly increased weight gain and survival and 4B8, and 3G2 reduced viral burden in the brain [128]. Importantly, mAb treatment resulted in higher brain mass, decreased lymphocyte infiltration, and reduced neurological score [128].…”

“…Multiple administrations of mAbs targeting the N-terminal region (β-roll), 4B8 and 3G2, or the C-terminal region (β-ladder), 4F10, of NS1 significantly increased weight gain and survival and 4B8, and 3G2 reduced viral burden in the brain [128]. Importantly, mAb treatment resulted in higher brain mass, decreased lymphocyte infiltration, and reduced neurological score [128]. All of the mAbs induced ADCC in vitro, but only the 4F10-LALA-PG variant showed reduced protection during in vivo challenge compared to the LALA-PG variants of 4B8 and 3G2 [128].…”