Bjørn Haneberg

The live oral polio vaccine was the first mucosal vaccine accepted for general use. Since then, similar vaccines have been developed against typhoid fever, cholera and rotavirus infection, and a nasal vaccine against influenza has recently been registered in the USA. The only non-living mucosal vaccine on the market today is an oral cholera vaccine consisting of inactivated Vibrio cholerae and the B subunit of cholera toxin. Several groups of scientists are at present working on the development of other mucosal vaccines based on inactivated microbes or parts of them. Results from animal trials at the Norwegian Institute of Public Health, suggest that non-living nasal vaccines can provide protective immunity and may be combined with the same types of vaccines for injection. Clinical trials with nasal vaccines consisting of beta-propiolactone inactivated influenza particles, showed that it was possible to achieve serum concentrations of antibodies at levels providing protection against influenza. IgA antibodies, which were formed in nasal secretions, were specifically aimed at influenza and ought to hinder the spread of the disease. By optimizing the immunization regimes so that the immunological memory is better exploited, and by adding adjuvants to the formulations, it is probable that non-living mucosal vaccines can be realistic alternatives to several of the vaccines now given by injection.

Mice immunized intranasally with a formalin‐inactivated A/PR/8/34 (H1N1) influenza whole virus vaccine adjuvanted with cholera toxin, outer membrane vesicles from group B meningococci or formalin‐inactivated whole cell Bordetella pertussis were protected against replication of the homologous virus in the nasal cavity. Only some mice were protected against clinical illness measured as weight loss and lowered body temperature. All mice immunized subcutaneously with one‐tenth the intranasal vaccine dose without adjuvant were protected against clinical illness but not against local mucosal viral replication. Replicating virus was primarily found in animals with low concentrations of immunoglobulin (Ig)‐A antibodies in saliva regardless of concentrations of IgG antibodies in serum. Clinical illness was seen only in those with low serum antibodies regardless of antibody levels in saliva. Nonreplicating nasal vaccines may not be sufficiently protective unless they also have a substantial influence on systemic immunity.

Inhalation of antigens may stimulate the immune system by way of the upper as well as the lower airways. We have shown that at least 1,000 times more live pneumococci were recovered from pulmonary tissue after being presented as drops of a liquid suspension onto the nares of anesthetized mice compared to the number of bacteria recovered from animals that were not anesthetized in the course of the challenge. Mice that were similarly immunized intranasally by inhalation of three different nonreplicating particulate vaccine formulations, i.e., a meningococcal outer membrane vesicle (OMV) vaccine, a formalin-inactivated whole-virus influenza (INV) vaccine, and the INV vaccine with OMVs as a mucosal adjuvant, during general intravenous anesthesia developed concentrations of vaccine-specific serum immunoglobulin G (IgG) antibodies that were four to nine times higher than in mice that were fully awake during immunizations. The concentrations of IgA antibodies in serum were also higher in anesthetized than in nonanesthetized mice and correlated positively with the corresponding levels of serum IgG antibodies in the anesthetized but not in the nonanesthetized mice. In saliva and feces, however, the concentrations of IgA antibodies were equally high whether or not the animals were dormant during immunizations. The results indicate that intrapulmonary antigen presentation, as a part of an intranasal immunization strategy, is of importance for systemic but not for mucosal antibody responses. A major portion of IgA antibodies in serum may thus be derived from nonmucosal sites.