An Improved Inactivated Influenza Vaccine with Enhanced Cross Protection

Abstract

Current inactivated influenza vaccines are strain-specific and poorly effective against variant or mismatched viruses. They are standardized based on their hemagglutinin (HA) or ability to induce strain-specific hemagglutination inhibition (HAI) antibodies. The HA is known to undergo major conformational changes when exposed to the low pH environment of endosomes (pH 5.0 and 37°C), which are required for membrane fusion during virus cell entry. In an effort to improve these vaccines, influenza antigens treated under various low pH conditions were evaluated for increased cross-reactive antibody response and cross protection. It was found that a full range of structural and antigenic changes in HA could be induced by varying low pH treatment conditions from the mild (low pH at ≤25°C) to the strong (low pH at ≥37°C) as determined by analysis of potency, HA morphology, protease sensitivity, and reactivity with an anti-HA2 domain (CD) antibody. Inactivated antigens of both H1N1 and H3N2 strains treated at mild low pH conditions (0–25°C) exhibited only moderate HA structural and antigenic changes and markedly increased antibody response against HA2, the highly conserved part of HA, and cross protection against heterologous challenge in mice by up to 30% in survival. By contrast, antigen treated with low pH at 37°C showed more extensive structural and antigenic changes, and induced much less of an increase in antibody response against HA2, but a greater increase with response against HA1, and did not provide any increased cross protection. These results suggest that the increased response against HA2 obtained with the mild low pH treatment is associated with the increased cross protection. These antigens treated at the mild low pH conditions remained capable of inducing a high level of strain-specific HAI antibodies. Thus, they could readily be formulated as an inactivated influenza vaccine which not only provides the same strain-specific protection but also an increased cross protection against heterologous viruses. Such a vaccine could be particularly beneficial in cases of vaccine mismatch.

Passive inhalation of dry powder influenza vaccine formulations completely protects chickens against H5N1 lethal viral challenge

“…In real life situations, where passive inhalation would be performed in large rooms, a portion of the aerosolized vaccine formulation would also end up in food and water. However, previous studies have shown that HA of the influenza vaccine undergoes conformational changes at acidic pH and is thus susceptible to proteolytic cleavage in the acidic environment [41,42]. Consequently, little-no neutralizing antibodies are induced by acidic pH treated influenza vaccine [41,42].…”

“…However, previous studies have shown that HA of the influenza vaccine undergoes conformational changes at acidic pH and is thus susceptible to proteolytic cleavage in the acidic environment [41,42]. Consequently, little-no neutralizing antibodies are induced by acidic pH treated influenza vaccine [41,42]. Therefore, it is speculated that the acidic environment in the stomach of chickens would not really add up to the lung induced mucosal immunity.…”

Characterization of Inactivated Influenza Vaccines Used in the Russian National Immunization Program

“…We used negative-stain transmission electron microscopy (TEM) and dynamic light scattering (DLS) to evaluate the microstructure of IIVs. In interpreting the TEM images obtained, we used the results of previous electron microscopy studies of the influenza virus [37,38], whole inactivated virus vaccines [39], and purified recombinant HA [40,41], as well as TEM images of influenza virions we derived from the virus-containing allantoic fluid ( Figure S21).…”

Targeting Hemagglutinin: Approaches for Broad Protection against the Influenza A Virus

“…To elicit HA stalk-specific immune responses, several approaches were developed. For instance, mild low-temperature treatment (at ≤25 °C) could moderately change the structure of HA, thus inducing an enhanced stalk specific antibody response which results in cross-protection in mice [168]. Heterologous prime-boost immunization could also elicit HA stalk-specific antibodies [169,170].…”