Heterosubtypic Antibodies to Influenza A Virus Have Limited Activity against Cell-Bound Virus but Are Not Impaired by Strain-Specific Serum Antibodies

Abstract

The majority of influenza virus-specific antibodies elicited by vaccination or natural infection are effective only against the eliciting or closely related viruses. Rare stem-specific heterosubtypic monoclonal antibodies (hMAbs) can neutralize multiple strains and subtypes by preventing hemagglutinin (HA)-mediated fusion of the viral membrane with the endosomal membrane. The epitopes recognized by these hMAbs are therefore considered promising targets for the development of pan-influenza virus vaccines. Here, we report the isolation of a novel human HA stem-reactive monoclonal antibody, hMAb 1.12, with exceptionally broad neutralizing activity encompassing viruses from 15 distinct HA subtypes. Using MAb 1.12 and two other monoclonal antibodies, we demonstrate that neutralization by hMAbs is virtually irreversible but becomes severely impaired following virus attachment to cells. In contrast, no interference by human anti-influenza virus serum antibodies was found, indicating that apically binding antibodies do not impair access to the membrane-proximal heterosubtypic epitopes. Our findings therefore encourage development of new vaccine concepts aiming at the induction of stem-specific heterosubtypic antibodies, as we provide support for their effectiveness in individuals previously exposed to influenza virus. IMPORTANCEThe influenza A virus hemagglutinin (HA) can easily accommodate changes in its antigenic structures to escape preexisting immunity. This variability restricts the breadth and long-term efficacy of influenza vaccines. Only a few heterosubtypic antibodies (hMAbs), i.e., antibodies that can neutralize more than one subtype of influenza A virus, have been identified. The molecular interactions between these heterosubtypic antibodies and hemagglutinin are well characterized, yet little is known about the functional properties of these antibodies. Using a new, extraordinarily broad hMAb, we show that virus neutralization by hMAbs is virtually irreversible and that efficient neutralization is possible only if stem-specific hMAbs bind to HA before the virus attaches to the cell surface. No interference between strain-specific human serum immunoglobulin and hMAbs was found, indicating that preexisting humoral immunity to influenza virus does not limit the efficacy of stem-reactive heterosubtypic antibodies. This knowledge supports the development of a pan-influenza virus vaccine. H emagglutinin (HA), the major surface antigen of influenza A virus, exists in 18 subtypes and is responsible for virus entry into the host cell. Influenza virus vaccines are usually effective against seasonal influenza (1-3), but currently available vaccines elicit antibodies of limited breadth that neutralize only the inoculated and closely related seasonal strains. This strain-specific (or homotypic) nature of the antibody response implies that seasonal vaccines have to be regularly reformulated to reflect antigenic changes acquired by drifting. Furthermore, vaccines have to precisely match the antigenic outfit of the ...

Broadly Neutralizing Anti-Influenza Virus Antibodies: Enhancement of Neutralizing Potency in Polyclonal Mixtures and IgA Backbones

“…Previous work has indicated that HA stalk-binding antibodies appear to be capable of accessing their epitope on virions (43), and thus their inferior potency is likely due to their inability to inhibit HA bind- ing to cell surface receptors: the robust means of neutralization achieved by HA head-binding antibodies (37). A recent study has also suggested that stalk-binding monoclonal antibodies have limited activity against cell-bound viruses, which would further limit their neutralization potency (44). Despite this inferior capacity to neutralize virus, passive transfer experiments in mice have demonstrated a strong propensity for these antibodies to activate antibody-dependent cellular cytotoxicity (ADCC), which correlates with enhanced protection in vivo (13).…”

Recombinant Influenza Vaccines: Saviors to Overcome Immunodominance

“…HA stem antibodies protect by (i) preventing viral entry by blocking the fusion of host cell membrane and viral membrane (29), (ii) reducing viral egress by blocking neuraminidase activity through steric hindrance (30)(31)(32), and (iii) FcR-mediated induction of antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis and reactive oxygen species production (33)(34)(35). Several human-derived broadly neutralizing anti-stem antibodies have been identified against either influenza group 1 (36)(37)(38)(39) or group 2 (38,(40)(41)(42) or both groups (40,(43)(44)(45)(46)(47)(48)(49)(50) or even against both influenza A and B subtypes (51). The identification of these antibodies was an incentive to develop vaccines, which are discussed below.…”

A broadly neutralizing anti-influenza antibody reveals ongoing capacity of haemagglutinin-specific memory B cells to evolve

“…In fact, the stem region has become a main target for development of novel treatments using either antibody-based vaccine design or passive immunotherapy. So far, several bnAbs capable of neutralizing multiple serotypes of influenza A virus within group 1 and/or group 2 have been isolated from immunized mice, phage libraries, memory B or plasma cells of immune donors 12 13 14 15 16 17 18 19 20 21 . Most bnAbs, such as F10 (ref.…”