LTA1 is a safe, intranasal enterotoxin-based adjuvant that improves vaccine protection against influenza in young, old and B-cell-depleted (μMT) mice

Abstract

Enterotoxin-based adjuvants including cholera toxin and heat-labile toxin (LT) are powerful manipulators of mucosal immunity; however, past clinical trials identified unacceptable neurological toxicity when LT or mutant AB5 adjuvant proteins were added to intranasal vaccines. Here, we examined the isolated enzymatic A1 domain of LT (LTA1) for intranasal safety and efficacy in combination with influenza (flu) vaccination. LTA1-treated mice exhibited no neurotoxicity, as measured by olfactory system testing and H&E staining of nasal tissue in contrast with cholera toxin. In vaccination studies, intranasal LTA1 enhanced immune responses to inactivated virus antigen and subsequent protection against H1N1 flu challenge in mice (8-week or 24-months). In addition, lung H1N1 viral titers post-challenge correlated to serum antibody responses; however, enhanced protection was also observed in μMT mice lacking B-cells while activation and recruitment of CD4 T-cells into the lung was apparent. Thus, we report that LTA1 protein is a novel, safe and effective enterotoxin adjuvant that improves protection of an intranasal flu vaccination by a mechanism that does not appear to require B-cells.

Chemically Synthesized Alcaligenes Lipid A Shows a Potent and Safe Nasal Vaccine Adjuvant Activity for the Induction of Streptococcus pneumoniae-Specific IgA and Th17 Mediated Protective Immunity

“…Notably, low numbers of neutrophils were noted in mice receiving nasal immunization with PspA, together with Alcaligenes lipid A under uninfected conditions (Figure 7), suggesting that the recruitment of neutrophils seem to be mediated by antigen-specific immune responses, but not non-specific activation by lipid A, which was different phenotype from CT. We found that CT induced the accumulation of neutrophils in the nose under uninfected conditions, indicating that CT induced non-specific inflammation upon nasal administration. Consistent with this finding, it has been shown that CT induces inflammatory responses, including neutrophil infiltration into subepithelial tissues of nasopharynx cavity [59,60], and E. coli lipid A enhanced inflammatory cytokines, such as TNFα and IL-1β [61]. These findings suggest that Alcaligenes lipid A possesses higher levels of safety as a nasal vaccine adjuvant, compared with the classical mucosal adjuvant: CT and immuno-stimulatory component: E. coli lipid A.…”

Intranasal immunization with outer membrane vesicle pertussis vaccine confers broad protection through mucosal IgA and Th17 responses

“…The cause of this neurotoxic effects were thought to be the combination of binding of de B subunit of LT to surface gangliosides (especially GM1) and inflammation associated with the A subunit. However, the use of the enzymatic A1 domain was shown to be safe and effective 52 .…”

Adjuvantation of Influenza Vaccines to Induce Cross-Protective Immunity

“…In an earlier study, Tamura et al found that the CT B subunit (CTB) could significantly increase IN TIV-induced cross-protection against a drifted virus in murine models, while subcutaneous delivery of the same vaccine failed to induce similar levels of cross-protection [ 149 ]. An LT-adjuvanted influenza vaccine was approved for IN delivery in Switzerland (Nasalflu, Berna Biotech) during the 2000-2001 flu season [ 174 ]. However, it was pulled off the market due to the 19-fold increased risks of Bell’s palsy or facial paralysis in vaccine recipients [ 174 ].…”

“…An LT-adjuvanted influenza vaccine was approved for IN delivery in Switzerland (Nasalflu, Berna Biotech) during the 2000-2001 flu season [ 174 ]. However, it was pulled off the market due to the 19-fold increased risks of Bell’s palsy or facial paralysis in vaccine recipients [ 174 ]. Therefore, different LT mutants were developed to reduce the enterotoxicity of LT-based adjuvants, such as single-mutant LT (R192G) and double-mutant LT (R192G/L211A) [ 175 , 176 ].…”