Broadly neutralizing anti-influenza antibodies require Fc receptor engagement for in vivo protection

Abstract

In vivo protection by antimicrobial neutralizing Abs can require the contribution of effector functions mediated by Fc-Fcγ receptor (Fc-FcγR) interactions for optimal efficacy. In influenza, broadly neutralizing anti-hemagglutinin (anti-HA) stalk mAbs require Fc-FcγR interactions to mediate in vivo protection, but strain-specific anti-HA head mAbs do not. Whether this rule applies only to anti-stalk Abs or is applicable to any broadly neutralizing Ab (bNAb) against influenza is unknown. Here, we characterized the contribution of Fc-FcγR interactions during in vivo protection for a panel of 13 anti-HA mAbs, including bNAbs and non-neutralizing Abs, against both the stalk and head domains. All classes of broadly binding anti-HA mAbs required Fc-FcγR interactions to provide protection in vivo, including those mAbs that bind the HA head and those that do not neutralize virus in vitro. Further, a broadly neutralizing anti-neuraminidase (anti-NA) mAb also required FcγRs to provide protection in vivo, but a strain-specific anti-NA mAb did not. Thus, these findings suggest that the breadth of reactivity of anti-influenza Abs, regardless of their epitope, necessitates interactions with FcγRs on effector cell populations to mediate in vivo protection. These findings will guide the design of antiviral Ab therapeutics and inform vaccine design to elicit Abs with optimal binding properties and effector functions.

Figure 3. Broadly neutralizing anti-NA mAb requires Fc-FcγR interactions to mediate protection in vivo, but strain-specific anti-NA mAb does not.

(A) Broadly neutralizing anti-HA stalk mAb FI6 (red circles), strain-specific anti-HA head mAb 4C04 (blue squares), strain-specific anti-NA mAb 3C02 (green circles), and broadly neutralizing anti-NA mAb 3C05 (green squares) neutralization of Neth09 virus. Values represent the mean ±SEM of duplicate samples. (B and C) Mice were given the indicated doses of IgG2a (red circles) or DA265-mutant (blue squares) 3C02 (B) or 3C05 (C) mAb or PBS (black triangles) before Neth09 viral infection. Values represent the mean ± SEM percentage of weight change compared with day-0 values (left panels) and percentage of survival (right panels). n = 4–5 mice per group. Significant differences between the IgG2a sample and DA265 sample are shown. **P < 0.01 by Student’s t test.

Figure 2. Broadly neutralizing anti-HA head mAbs and pan-H1, non-neutralizing anti-HA head mAbs require Fc-FcγR interactions for protection in vivo.

WT mice were given the indicated doses of IgG2a (red circles) or DA265-mutant (blue squares) 4G05 (A), 1F05 (B), 1A01 (C), 1A05 (D), or 4G01 (E) mAb or PBS (black triangles) before Neth09 viral infection. Values represent the mean ± SEM percentage of weight change compared with day-0 values (left panels) and percentage of survival (right panels). n = 5–7 mice per group. Significant differences between the IgG2a and DA265 samples are shown. *P < 0.05 and **P < 0.01, by 2-tailed Student’s t test.

Figure 1. Broadly binding and neutralizing anti-HA stalk mAbs require Fc-FcγR interactions for protection in vivo.

(A) Broadly neutralizing anti-stalk (red lines), strain-specific anti-head (blue lines), broadly neutralizing anti-head (green lines), and non-neutralizing anti-head (purple lines) mAb binding to Neth09-infected cells by flow cytometric analysis and (B) neutralization of Neth09 virus (mean ± SEM) in duplicate samples. (C and D) WT mice were given the indicated doses of IgG2a (red circles) or DA265-mutant (blue squares) FI6 mAb (C), 2G02 mAb (D), or PBS (black triangles) before Neth09 virus infection. Values represent the mean ± SEM percentage of weight change compared with day-0 values (left panels) and percentage of survival (right panels). n = 4–5 mice per group. Significant differences between the IgG2a and DA265 samples are shown. *P < 0.05 and **P < 0.01, by 2-tailed Student’s t test.