Identifying a safe and efficacious mucosal adjuvant is crucial for the development of
subunit vaccines against rotavirus and other mucosal pathogens. Moreover, recognition of determinants of protective immunity to
rotavirus infection is essential to the design of the means to prevent or control this viral
gastrointestinal disease. We have studied the kinetics of systemic and mucosal antibody responses elicited upon mucosal immunization of mice with rotavirus recombinant virus-like particles (rVLPs) alone or combined with a detoxified version of
cholera toxin,
CT-E29H.
CT-E29H has been shown to maintain the adjuvant effect of parental
cholera holotoxin. Both inbred BALB/c and outbred CD-1 mice were immunized with rotavirus VP2/6-rVLPs (2/6-VLPs) combined with
CT-E29H, orally or intranasally (i.n.), and the comparative efficacy of different formulations was then determined. Rotavirus-specific serum and fecal
IgA,
IgM, and
IgG antibodies were determined by
enzyme-linked
immunoadsorbent assay (ELISA) weekly (or every other week) following vaccination. Animals then were challenged with a murine rotavirus strain,
EDIM. The degree to which vaccinated animals were protected from the wild-type rotavirus challenge was reflected in the levels of
viral antigen shed in stools (percent reduction in
antigen shedding, PRAS). BALB/c mice immunized by either route produced rotavirus-specific serum
IgA,
IgM and
IgG, as well as fecal
IgA and
IgG, but not
IgM; however, the intranasal immunization induced stronger systemic
IgG and
IgM responses than did oral immunization. Similar levels of prechallenge rotavirus-specific fecal and serum
IgA were detected in both the orally and the i.n. immunized groups. Two immunizations with 2-6VLPs and
CT-E29H were sufficient to protect BALB/c mice, regardless of the route of administration. PRAS was 99.6, 98.8, and 98.8% for oral, i.n. and the oral + i.n. groups, respectively; in contrast vaccination with 2/6-VLPs alone was not protective (PRAS = 39%), indicating the critical role of
CT-E29H in inducing protective levels of immune responses. Two of four outbred CD-1 mice that were immunized orally with 2/6-VLPs-CT-E29H showed no humoral responses (PRAS, 65%), but four of four i.n. immunized CD-1 mice displayed humoral responses (PRAS, 97.9%). Serum anti-VP6 and VP2
antibodies were detected in all immunoresponsive mice. The combined results in two strains of mice indicate that CTE29H is an effective mucosal adjuvant capable of inducing protective immune responses and suggest that
intranasal administration is the preferred route of immunization.