Sublingual Immunization with M2-Based Vaccine Induces Broad Protective Immunity against Influenza

Abstract

BackgroundThe ectodomain of matrix protein 2 (M2e) of influenza A virus is a rationale target antigen candidate for the development of a universal vaccine against influenza as M2e undergoes little sequence variation amongst human influenza A strains. Vaccine-induced M2e-specific antibodies (Abs) have been shown to display significant cross-protective activity in animal models. M2e-based vaccine constructs have been shown to be more protective when administered by the intranasal (i.n.) route than after parenteral injection. However, i.n. administration of vaccines poses rare but serious safety issues associated with retrograde passage of inhaled antigens and adjuvants through the olfactory epithelium. In this study, we examined whether the sublingual (s.l.) route could serve as a safe and effective alternative mucosal delivery route for administering a prototype M2e-based vaccine. The mechanism whereby s.l. immunization with M2e vaccine candidate induces broad protection against infection with different influenza virus subtypes was explored.Methods and ResultsA recombinant M2 protein with three tandem copies of the M2e (3M2eC) was expressed in Escherichia coli. Parenteral immunizations of mice with 3M2eC induced high levels of M2e-specific serum Abs but failed to provide complete protection against lethal challenge with influenza virus. In contrast, s.l. immunization with 3M2eC was superior for inducing protection in mice. In the latter animals, protection was associated with specific Ab responses in the lungs.ConclusionsThe results demonstrate that s.l. immunization with 3M2eC vaccine induced airway mucosal immune responses along with broad cross-protective immunity to influenza. These findings may contribute to the understanding of the M2-based vaccine approach to control epidemic and pandemic influenza infections.

Viroporins: structure, function and potential as antiviral targets

“…M2 is a 97 aa protein with a single TMD which forms disulphidelinked tetramers in membranes (Holsinger & Lamb, 1991;Sugrue & Hay, 1991). The N-terminal 25 aa are located on the surface of the plasma/virion membrane and are highly conserved; considerable efforts have been focused on this region as a pan-influenza vaccine strategy (Neirynck et al, 1999;Shim et al, 2011). The TMD (aa 25-46) is followed by an amphipathic helix (aa 47-62) and the remaining cytosolic domain.…”

Cross-Reactive Influenza-Specific Antibody-Dependent Cellular Cytotoxicity Antibodies in the Absence of Neutralizing Antibodies

“…Indeed, other surface influenza proteins, including the NA and M2 protein, are also likely to be targets for ADCC (49). Vaccination studies performed using influenza M2 protein suggest a protective role mediated by nonneutralizing Abs (50)(51)(52). The M2-specific Abs were shown to protect against both homologous and heterologous influenza virus challenge in the mouse model.…”

Programming of Influenza Vaccine Broadness and Persistence by Mucoadhesive Polymer-Based Adjuvant Systems

“…Previous studies have shown that the i.n. mucosal route is superior to systemic administration for inducing cross-protective immunity in mice (7,30,48). Other studies have focused on chemical and genetic conjugates (carrier molecules or virus particles) or a combination of DNA and recombinant or live influenza vaccines to improve cross-protection (49)(50)(51)(52)(53).…”

“…These results are consistent with previous studies that demonstrated that i.n. vaccination with 3M2eC plus CT induced Abs that could improve mortality but not morbidity (7). In contrast, mice that received sM2HA2 with CA-PMQ showed negligible signs of disease and only a slight and transient loss of weight.…”

“…Influenza matrix protein 2 (M2), particularly the ectodomain (M2e), is well conserved across influenza (7) strains and is considered an attractive target for inducing crossprotection against influenza A subtypes. Similarly, the stalk domain, especially the fusion peptide (HA2) of hemagglutinin (HA), is another potent conserved region (8) that can induce a specific Ab response with cross-protection within a given subtype and even among various subtypes of influenza A virus (9).…”