Rotaviruses (RV) are the leading cause of infectious diarrhea in infants and young children in developed and developing countries. Live oral human RV (HRV) vaccines have reduced efficacy in developing countries, in part due to the suppressive effects of maternal antibodies (Ab). Maternal Ab may also interfere with other infant vaccines (measles, respiratory syncytial virus, etc.). We have previously documented suppression by maternal Ab of cellular and humoral immune responses to live HRV in intestinal tissues of gnotobiotic (Gn) pigs. It is unresolved whether suppression is due to reduction in antigenic mass through interference with viral replication, or due to immune regulatory effects of passive antibodies, or both. The mechanism(s) of suppression and means to overcome them will be investigated, using as a model HRV and the following approaches: 1) Intranasal (IN) delivery of non-replicating rotavirus-like-particles (VLP) will be used to analyze the effects of maternal Ab and T cell responses and cytotoxic activity in mucosal tissues, in a Gn pig model of HRV disease. Immune stimulating complexes (ISCOMs), (reputed to induce active immunity in the face of maternal Ab) and mutant heat-labile toxin of E. coli will be used as adjuvants. 2) Microencapsulation will be used to deliver live HRV directly to intestinal cells, without binding by maternal Ab. 3) Sequential IN VLP/oral live microencapsulated HRV vaccination will be examined as a combined prime/boost strategy to further evade the suppressive effects of maternal Ab. 4) The potential of IgA regulatory cytokines to enhance mucosal IgA responses in the face of maternal Ab will be investigated by incorporating recombinant cytokine(s) into the optimal vaccine delineated in 1), 2) or 3). 5) The effect of non-neutralizing antibodies to VP2/6 on virus neutralizing antibody responses induced by VP4 and VP7 on live Wa HRV and 2/6/4/7-VLP will be assessed using passive Ab to 2/6-VLP. Immune responses to Wa HRV will be monitored in serum and intestinal secretions by virus neutralization and viral protein-specific ELISA assays, and by quantifying RV antibody secreting cells (total and protein specific) in tonsillar, intestinal, and systemic tissues by ELISPOT. T cell responses will be assessed by a lymphoproliferative assay and analysis of cytokine responses by ELISA, ELISPOT, and RT-PCR. Clarification of the mechanisms of suppression by maternal Ab and means to overcome them will lead to more efficacious vaccines for both RV and other pathogens infecting neonates.
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