The MicroRNA-Let-7b-mediated Attenuated Strain Of Influenza A (H1N1) Virus In A Mouse Modell

Background Influenza virus can cause respiratory diseases caused by an influenza virus. Influenza is worldwide pandemic. The H1N1 influenza virus threatens the public health mostly because of its high susceptibility and fast spread. Vaccine is the most effective approach to prevent severe diseases and deaths caused by pandemic influenza. However, because of the restrictions, LAVIs can only offer the suboptimal protection. The microRNA (miRNA) mediated gene silencing may better solve this problem. Previously, we had generated the reassortant LAIVs for the A/Nanjing/108/2009 H1N1 by incorporating let-7b response elements (MREs) into the open-reading frame of the viral PB1 genes which is attenuated in HBE cells. Focusing on the attenuation of influenza viruses in animal studies is the first step in the course of developing safe and effective vaccines. The study aims at demonstrating that the let-7b mediated attenuated viruses (miRT-H1N1) are physiologically safe in mice.Methods Both of the pathogenicity and the median lethal dose (LD50) of miRT-H1N1 virus were investigated with the help of the infected mouse model. In different infectious stages, the replicative abilities of miRT-H1N1 virus, wild type (wt)-H1N1 viruses and scramble (scb1)-H1N1 viruses in lungs of the infected mice were compared. The degree of lesions and the expression levels of IL-6, TNF-α and IFN-β in lungs of mice infected with different viruses were observed.Results In miRT-H1N1 virus-infected mice,100% survival rate was achieved. And much lower pathogenicity was characterized by non-significant weight loss. The miRT-H1N1 virus was not fatal for mice even with the administration of the highest dose(LD50>107 TCID50). The viral load in lungs of miRT-H1N1 mice was significantly lower than that of the wild-type virus infected mice. And we discovered weaker pulmonary lesions and lower levels of selected pro-inflammatory cytokines in lungs of the miRT-H1N1 viruses infected mice.Conclusions The virulence of miRT-H1N1 virus reduced significantly in lungs of mice, suggesting that the miRT-H1N1 virus was safe to mice. Our study indicated that the miRNA-mediated gene silencing is an alternative approach to attenuate the toxicity of wt influenza viruses for the development of vaccine.