Fig. 2: A hyACE2 knock-in mouse supports SARS-CoV-2 infection.
a, Amino acid sequence of human (h)ACE2 and mouse (m)ACE2. In red are the eight residues involved in the interaction with the SARS-CoV-2 spike protein. b, Molecular modeling of the interaction between SARS-CoV-2 spike RBD (orange) and hACE2 or mACE2 (cyan). Crosses indicate the absence of interaction. Electrostatic and hydrophobic interactions in green and yellow dashed lines. c, Experimental setup. The 3T3 cells transduced with lentiviral vectors to express hACE2 (blue symbols), mACE2 (gray symbols) and a hybrid human/mouse (hy)ACE2 (green symbols) were infected with different concentrations of SARS-CoV-2. Nontransduced (WT) 3T3 cells as control. n = 3 biological replicates. d, Dose-dependent viral activity in 3T3 cells infected with SARS-CoV-2 D614G (left), B.1.617.2 (middle) or B.1.1.529 (right). Infection rates as a percentage of the virus-induced cytopathic effect 72 h after infection. Comparison with WT 3T3 cells. n = 3 biological replicates. e, Design of human/mouse hybrid Ace2 allele. f, Experimental setup. K18-hACE2 transgenic mice (n = 4) and hyACE2 knock-in mice (n = 5) were infected with 5 × 105 TCID50 of SARS-CoV-2 B.1.617.2 (Delta). PBS-exposed mice were used as controls (n = 2). Peripheral blood, lung and NT were analyzed 6 days after challenge. g, SARS-CoV-2 RNA in the NT (left) and lung (right). RNA values as copy number per ng of total RNA and the LOD as a dashed line. h, Respiratory frequency (left) and Rpef (right) were assessed by WBP 5 days postinfection (average over a 15-min data collection period). i, Anti-S1 RBD IgG levels in the plasma. j,k, Absolute number of total CD8+ T cells (j, left) and CD4+ T cells (k, left) and of cytokine-producing CD8+ cells (j, right) and CD4+ cells (k, right) in the lung on in vitro stimulation with a pool of SARS-CoV-2 peptides. Data are expressed as mean ± s.e.m. and are representative of at least two independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001; Kruskal–Wallis test followed by uncorrected Dunn’s test; each comparison stands alone (g–i, j and k (left)). Two-way ANOVA, Tukey’s multiple comparison (j and k (right)); two-way ANOVA, Fisher’s LSD test (each comparison stands alone; d).
