ROTAVIRUS VACCINE ADMINISTERED PARENTERALLY INDUCES PROTECTIVE IMMUNITY

We performed experiments to determine whether parenteral immunization with SA11 rotavirus can induce active protective immunity in a rabbit model of rotavirus infection. After one or two intramuscular injection s of 1 ml of live or formalin-inactivated SA11 virus, we evaluated the mucosal and serologic immune response and protection from challenge w ith a high dose of live, virulent rabbit (Ala) rotavirus. Inactivated SA11 virus preparations, evaluated by enzyme-linked immunosorbent assa y (ELISA) with a panel of VP4- and VP7-specific neutralizing and nonne utralizing monoclonal antibodies, did not show a loss of epitopes from the inactivation procedure compared with live virus. Administration o f two doses of vaccine, one at zero days postvaccination (DPV) and a b ooster shot at 49 DPV, followed by challenge at 71 DPV with 3.5 x 10(5 ) PFU of Ala virus resulted in protection from challenge. None of the two-dose virus-vaccinated rabbits shed virus after challenge, while vi rus shedding was detected in all control rabbits (P = 0.001, Fisher's exact two-tailed test). Differences in total serum immunoglobulin (Ig) antirotavirus ELISA titers (P < 0.05, Wilcoxon's rank sum test) were observed between groups vaccinated with virus in aluminum phosphate or Freund's adjuvant but not between groups vaccinated with live or inac tivated virus in either adjuvant. All rabbits given two doses of vacci ne had detectable antirotavirus intestinal antibody of the IgG, but no t IgA, isotype. After challenge, fourfold or greater increases in inte stinal IgG antibody responses were observed in three rabbits, whereas all controls and all but one virus-vaccinated rabbit had an intestinal IgA antibody response. In contrast, vaccination of rabbits with one d ose of SA11 followed by challenge at 21 DPV did not protect from chall enge; no difference in the mean number of days of virus shedding betwe en any of the vaccinated groups and controls was observed. A serologic , but not a mucosal, antibody response was observed after the one-dose vaccination regimen. Differences in serologic antibody titers were no t observed between any of the one-dose virus-vaccinated groups. These data indicate that parenteral vaccination with two, but not one, doses of rotavirus in either Freund's adjuvant or aluminum phosphate can in duce active protection from challenge. The observed protection may hav e been mediated by IgG antirotavirus antibody in the intestine. In the majority of rabbits, the presence of intestinal IgG did not interfere with the induction of IgA antirotavirus antibody. These results are t he first to show the ability to use parenteral immunization with inact ivated rotavirus to induce active protective immunity. They support th e further development of rotavirus subunit vaccines or evaluation of c ombined parenteral-oral vaccination regimens.