Antibody responses to human rotavirus (HRV) in gnotobiotic pigs following a new prime/boost vaccine strategy using oral attenuated HRV priming and intranasal VP2/6 rotavirus-like particle (VLP) boosting with ISCOM.

Safer and more effective human rotavirus (HRV) vaccines are needed. We evaluated oral priming with attenuated WaHRV (AttHRV) followed by boosting with two intranasal (IN) doses of VP2/6 virus-like particles (2/6 VLP) with immunostimulating complexes (ISCOM) to determine if this regimen induces protection against diarrhoea and viral shedding in the gnotobiotic pig model. IgM, IgA and IgG antibody titres in serum and intestinal contents were quantified by enzyme-linked immunosorbent assay (ELISA) and serum neutralizing antibody titres were measured by a virus neutralization (VN) test. Seven groups of neonatal gnotobiotic pigs were vaccinated at post-inoculation days (PID) 0, 10 and 21 and challenged with virulent WaHRV at PID 28. The vaccine groups included: (1, 2) oral priming with AttHRV and boosting with two IN immunizations with 2/6 VLP-ISCOM (Att + 2/6 VLP-ISCOM) at VLP concentrations of 250 micro g or 25 micro g; (3, 4) three IN immunizations with 2/6 VLP-ISCOM at VLP concentrations of 250 micro g or 25 micro g (2/6 VLP-ISCOM); (5) three oral immunizations with AttHRV (3xAttHRV); (6) one oral immunization with AttHRV (1xAttHRV); (7) controls (ISCOM matrix and/or diluent). The pigs that received 3xAttHRV or Att + 2/6 VLP250-ISCOM had the highest protection rates against diarrhoea upon challenge at PID 28 with virulent WaHRV. The IgA antibody titres to HRV in intestinal contents were significantly higher in the Att + 2/6 VLP250-ISCOM group than in all other groups prechallenge (PID 28). Serum VN antibody titres were statistically similar after the first inoculation among the groups given AttHRV, but at PID 28 VN antibody titres were significantly higher for the 3xAttHRV and Att + 2/6 VLP250-ISCOM groups than for the 1xAttHRV group suggesting that boosting with 2/6 VLP also boosted VN antibody responses. In humans, intestinal IgA antibodies have been correlated with protection against symptomatic reinfection. Thus the vaccine regimen of one oral dose of AttHRV and two IN immunizations with 2/6 VLP250-ISCOM may be an alternative to multiple-dose live oral vaccines in humans.