3.1 In vivo infection of Human ACE2 (hACE2) expressing mice with SARSr-CoV S protein
variants
In Year 5, we continued with in vivo infection experiments of diverse bat SARSr-CoVs on
transgenic mice expressing human ACE2. Mice were infected with 4 strains of SARSr-CoVs
with different S protein, including the full-length recombinant virus of SARSr-CoV WIV1 and
three chimeric viruses with the backbone of WIV1 and S proteins of SHC014, WIV16 and
Rs4231, respectively. Pathogenicity of the 4 SARSr-CoVs was evaluated by recording the
survival rate of challenged mice in a 2-week course. All of the 4 SARSr-CoVs caused lethal
infection in hACE2 transgenic mice, but the mortality rate vary among 4 groups of infected mice
(Fig. 13a). 14 days post infection, 5 out of 7 mice infected with WIV1 remained alive (71.4%),
while only 2 of 8 mice infected with rWIV1-SHC014 S survived (25%). The survival rate of mice
infected with rWIV1-WIV16S and rWIV1-4231S were 50%. Viral replication was confirmed by
quantitative PCR in spleen, lung, intestine and brain of infected mice. In brain, rWIV1, rWIV1-
WIV16S and rWIV1-4231S cannot be detected 2 days or 4 days post infection. However,
rWIV1-SHC014 was detected at all time points and showed an increasing viral titer after
infection. The viral load reached more than 10e9 genome copies/g at the dead point (Fig. 13b).
We also conducted histopathological section examination in infected mice. Tissue lesion and
lymphocytes infiltration can be observed in lung, which is more significant in mice infected with
rWIV1-SHC014 S (Fig. 13d) than those infected with rWIV1 (Fig. 13c). These results suggest
that the pathogenicity of SHC014 is higher than other tested bat SARSr-CoVs in transgenic
mice that express hACE2.
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