We exploited the powerful adjuvant properties of
cholera holotoxin (CT) to create a mucosally administered
subunit vaccine against respiratory syncytial virus (RSV). A genetically detoxified mutant CT with an E to H substitution at
amino acid 29 of the CT-A1 subunit (CT-E29H) was compared to wild type CT for toxicity and potential use as an intranasal (IN) adjuvant for the natural fusion (F)
protein of RSV. When compared to CT the results demonstrated that: (1)
CT-E29H binding to
GM1 ganglioside was equivalent, (2) ADP-ribosylation of
agmatine was 11.7%, and (3) toxicity was attenuated in both Y-1 adrenal (1.2%) and patent mouse gut weight assays. IN vaccination with F
protein formulated with
CT-E29H induced serum anti-CT and anti-F
protein antibodies that were comparable to those obtained after vaccination with equivalent doses of CT. Vaccinations containing
CT-E29H at doses of 0.1 microg were statistically equivalent to 1.0 microg in enhancing responses to F
protein.
Antigen-specific mucosal
IgA and anti-RSV
neutralizing antibodies were detected in nasal washes and sera, respectively, of mice that had received F
protein and 0.1 or 1.0 microg of
CT-E29H. Anti-F
protein IgA was not detected in the nasal washes from mice IN vaccinated with 0.01 microg
CT-E29H or IM with F
protein adsorbed to AlOH adjuvant. In addition, the formulation of purified F
protein and
CT-E29H (0.1 and 1.0 microg) facilitated protection of both mouse lung and nose from live RSV challenge. Collectively, the data have important implications for
vaccine strategies that use genetically detoxified mutant
cholera holotoxins for the mucosal delivery of highly purified RSV
antigens.