Rotavirus Molecular Epidemiology Survey And Liposome Dna Vaccine Research

Human Rotavirus(HRV) has been recognized as the major etiology agent causing acute gastroenteritis in infants and young children worldwide . Rotavirus infects the enterocytes of the small intestines and results in severe dehydrating diarrhea, which can lead to death. Infection with group A rotaviruses cause an estimated 870,000 deaths each year in developing countries. Because of the widespread nature of rotavirus disease, development of vaccine is considered as the key to its control. As the basement of vaccine developing, understanding of the epidemiological features of individual rotavirus serotypes prevailing worldwide, especially in developing countries, is very important.In the present study, VP7 type(G serotype) of rotaviruses from infants and young children with acute gastroenteritis in Chongqing, China from 1998 to 2000 has been studied by RT-PCR and nucleotide sequencing. During theepidemic season of 1998 to 1999, serotype G1 was found to be largely predominant and accounted for 88%(44/50) of fifty rotavirus-positive fecal samples. While in the next season of 1999 to 2000, serotype G3 increased significantly-up to 78.95%(30/38). Mix-type(G1+G3 ) was found also in the two successive seasons. The results of nucleotide sequence analysis agreed with those of the RT-PCR typing assay. It supplied somewhat foundation for the development and evaluation of vaccine in Chongqing.A live, tetravalent reassortant, orally deliverable rotavirus vaccine has recently been licensed in the United States, but it has been less effective in many developing countries where the need for vaccine is the greatest. Killed rotavirus vaccines and subunit vaccines may be possible, but these types of vaccines do not provide endogenously synthesized proteins , and unless adjuvants are used, generally do not elicit cytotoxic T lymphocyte(CTL) responses that present to be important in controlling rotavirus infection. DNA vaccine, as the third generation of vaccine, can effectively induce systemic and cellular immunities, especially CTL response. For DNA-based immunization, the mammalian expression plasmid pcDNA3.1/VP7 was constructed by subcloning the entire genomic sequences containing VP7 from pcDNA1/VP7 into pcDNA3.1. In this study BALB/c mice were immunized by intramuscular and intranasal routes with 3 doses of pcDNA/VP7 at two-week intervals. Titers of serum IgG and IgA in blood specimens collected4 weeks after immunization were measured by ELISA. Serum rotavirus IgG titers in naked DNA and liposome-mediated DNA vaccine immunized mice were significantly higher than that of the unimmunized controls. Interestingly, only those mice administrated with liposome-mediated DNA vaccine by intramuscular route generated serum rotavirus IgA while no measurable serum rotavirus IgA was induced by naked plasmid or by intranasal immunized DNA-liposome complex. These results indicate that liposome as the vector and adjuvant can mediate rotavirus DNA vaccine by intramuscular injection to induce serum rotavirus-specific IgA, which may provide partial protection against rotavirus infection.