3c). Growth kinetics in the mosquito cells was delayed as observed

RG7204 clinical trial by others [19] and [25], reaching equal titers compared to Vero cells at day 4 postinfection (Fig. 3d). Taken together, these data indicate that WNVsyn and the corresponding WNVwt isolate are indistinguishable with respect to replication and infectivity in both tested cell lines. In addition, virulence of WNVsyn and WNVwt were compared in cohorts of 7-week-old Balb/c mice. For this purpose mice were infected intranasally with virus dilutions corresponding to 2 × 105 to 2 × 102 TCID50 per animal. Survival was monitored for 21 days postinfection and LD50 values were calculated. Similar mortalities of infected mice induced by the two WNV viruses were observed (Table 2). The lethal dose 50 for WNVsyn and WNVwt was 3.6 and 3.4 log 10 TCID50, respectively. The experiment was repeated once and similar results were obtained. Following the demonstration that WNVsyn exhibits indistinguishable biological properties MLN8237 compared to the WNV wild-type isolate, the protective efficacy of experimental vaccines derived from both viruses was analyzed. For this purpose, groups of ten mice were immunized twice with

decreasing doses of formalin-inactivated, alum-adjuvanted whole virus vaccines derived from the viruses (see Section 2). Quantification by ELISA of vaccine preparations prior to formulation and adjuvantation confirmed the presence of equal amounts of antigen in the

respective dosage groups. Further, Western blotting confirmed equivalent amounts and protein patterns in the two antigen preparations (Fig. 4b). The predominant band in these preparations is the envelope antigen (E) migrating in the 60 kDa range, the fainter bands representing the pre-membrane (prM) and the dimeric membrane (M) proteins (see also [26]). PDK4 Two weeks after the second vaccination WNV-specific neutralizing antibodies were determined by a microneutralization assay. Serum analysis demonstrated high neutralizing antibody levels in both vaccine preparations (see Fig. 4a and Table 3). Mice were then challenged intranasally with a lethal dose (1 × 105 TCID50) of WNV wild-type virus. Vaccination with both preparations resulted in a high degree of protection in vaccinated mice. Complete protection was achieved using doses as low as 63 nanograms of the WNV antigens while 95% of the non-vaccinated controls died. The vaccines clearly induced a dose-dependent protection correlating with NT titers (Table 3). Modulators reverse genetics systems of positive-sense RNA viruses allow, for instance, for mutagenesis procedures and generation of chimeric viruses and thus are invaluable tools for live vaccine development and for studying the biology of those viruses (see e.g. Refs. [27] and [28]). Usually the starting material for the generation of seed viruses for vaccines or such reverse genetics systems are virus stocks derived from a biological source.