An oral versus intranasal prime/boost regimen using attenuated human rotavirus or VP2 and VP6 virus-like particles with immunostimulating complexes influences protection and antibody-secreting cell responses to rotavirus in a neonatal gnotobiotic pig model

Abstract

We determined the impact of mucosal prime/boost regimens and vaccine type (attenuated Wa human rotavirus [AttHRV] or nonreplicating Wa 2/6 rotavirus-like particles [VLP]) on protection and antibody-secreting cell (ASC) responses to HRV in a neonatal gnotobiotic pig disease model. Comparisons of delivery routes for AttHRV and evaluation of nonreplicating VLP vaccines are important as alternative vaccine approaches to overcome risks associated with live oral vaccines. Groups of neonatal gnotobiotic pigs were vaccinated using combinations of oral (PO) and intranasal (IN) inoculation routes as follows: (i) 3 oral doses of AttHRV (AttHRV3xPO); (ii) AttHRV3xIN; (iii) AttHRVPO, then 2/6VLP2xIN; (iv) AttHRVIN, then 2/6VLP2xIN; and (v) mock-inoculated controls. Subsets of pigs from each group were challenged with virulent Wa HRV [P1A(8) G1] (4 weeks post-primary inoculation) to assess protection. The AttHRVPO+2/6VLP2xIN pigs had the highest protection rates against virus shedding and diarrhea (71% each); however, these rates did not differ statistically among the vaccine groups, except for the AttHRVIN+2/6VLPIN group, which had a significantly lower protection rate (17%) against diarrhea. The isotype, magnitude, and tissue distribution of ASCs were analyzed by enzyme-linked immunospot assay. The highest mean numbers of virus-specific IgG and IgA ASCs were observed pre- and postchallenge in both intestinal and systemic lymphoid tissues of the AttHRVPO+2/6VLPIN group. Thus, the AttHRVPO+2/6VLPIN vaccine regimen using immunostimulating complexes (ISCOM) and multiple mucosal inductive sites, followed by AttHRV3xPO or IN regimens, were the most effective vaccine regimens, suggesting that either AttHRVPO+2/6VLPIN or AttHRV3xIN may be an alternative approach to AttHRV3xPO for inducing protective immunity against rotavirus diarrhea.

FIG. 1.

Prechallenge antibody-secreting cell responses in gnotobiotic pigs primed with AttHRVPO and boosted IN with various doses (25, 100, 250 μg) of 2/6VLP in a dose-response study. Different letters denote statistically significant differences at P < 0.05 in the same tissue for the same isotype, among vaccine groups. Statistical symbols: A, statistically different from B and C; B, statistically different from C at P < 0.05.

FIG. 2.

Prechallenge antibody-secreting cell responses in gnotobiotic pigs primed or boosted with various rotavirus vaccines by different routes. Different letters denote statistically significant differences at P < 0.05 in the same tissue for the same isotype, among vaccine groups. Statistical symbols: A, statistically different from B and C; B, statistically different from C at P < 0.05. No ASC were detected in controls at the cell concentrations tested (not shown).

FIG. 3.

Postchallenge antibody-secreting cell responses in gnotobiotic pigs primed or boosted with various rotavirus vaccines or by different routes. Different letters denote statistically significant differences at P < 0.05 in the same tissue for the same isotype, among vaccine groups. Statistical symbols: A, statistically different from B and C; B, statistically different from C at P < 0.05. Graphs in this figure are depicted using different scales.