Immunogenicity and protective efficacy of a DNA vaccine inducing optimal expression of the SARS-CoV-2 S gene in hACE2 mice.

The wide spread of coronavirus disease 2019 (COVID-19) has significantly threatened public health. Human herd immunity induced by vaccination is essential to fight the epidemic. Therefore, highly immunogenic and safe vaccines are necessary to control SARS-CoV-2, whose S protein is the antigenic determinant responsible for eliciting antibodies that prevent viral entry and fusion. In this study, we developed a SARS-CoV-2 DNA vaccine expressing the S protein, named pVAX-S-OP, which was optimized according to the human-origin codon preference and using polyinosinic-polycytidylic acid as an adjuvant. pVAX-S-OP induced specific antibodies and neutralizing antibodies in BALB/c and hACE2 transgenic mice. Furthermore, we observed 1.43-fold higher antibody titers in mice receiving pVAX-S-OP plus adjuvant than in those receiving pVAX-S-OP alone. Interferon gamma production in the pVAX-S-OP-immunized group was 1.58 times (CD3+CD4+IFN-gamma+) and 2.29 times (CD3+CD8+IFN-gamma+) lower than that in the pVAX-S-OP plus adjuvant group but higher than that in the control group. The pVAX-S-OP vaccine was also observed to stimulate a Th1-type immune response. When, hACE2 transgenic mice were challenged with SARS-CoV-2, qPCR detection of N and E genes showed that the viral RNA loads in pVAX-S-OP-immunized mice lung tissues were 104 times and 106 times lower than those of the PBS control group, which shows that the vaccine could reduce the amount of live virus in the lungs of hACE2 mice. In addition, pathological sections showed less lung damage in the pVAX-S-OP-immunized group. Taken together, our results demonstrated that pVAX-S-OP has significant immunogenicity, which provides support for developing SARS-CoV-2 DNA candidate vaccines.

In vitro and in vivo studies of the native isolates of nematophagous fungi from China against the larvae of trichostrongylides.

To screen potential nematophagous fungi candidates for the biological control of parasitic nematodes in livestock, in vitro and in vivo studies of the native isolates of nematophagous fungi against the larvae of trichostrongylides were conducted. The in vitro predatory activity of 16 native nematophagous fungal isolates on the larvae of trichostrongylides in sheep feces was assessed. In the ten isolates of Duddingtonia flagrans, the reduction percentage for the infective larvae (L3) of Trichostrongylus colubriformis ranged from 57.21 to 99.83%, and that of Haemonchus contortus ranged from 62.12 to 99.88%. The analysis of the same assay on five isolates of Arthrobotrys superba and one isolate of A. cookedickinson (Monacrosporium cystosporum) showed comparable results with those for D. flagrans. To determine the excretion time of fungal isolates in feces after oral administration, D. flagrans (SDH035) were studied in vivo in sheep and rabbits. Results showed that the tested fungal isolates existed in sheep feces from 12 to 72 h after fungal treatment, and the fungal excretion in rabbit feces occurred at 4 h, reached a peak at 10 h, and declined gradually 18 h after oral administration. All the native fungal isolates were assessed after passing through the gastrointestinal tract of sheep. Treatment with isolates of D. flagrans significantly reduced the number of developing larvae in the feces, and the efficacies ranged from 55.15 to 98.82%. One out of the five isolates of A. superba and A. cookedickinson (BS002) survived after passing through the gastrointestinal tract, and the L3 reduction rates were 83.79 and 81.33%, respectively. Results of the present study provide information about the in vitro predatory activity of nematophagous fungi from China on the L3 of trichostrongylides and their ability to pass through the gastrointestinal tract before administering them for biocontrol.