Figure 1.

Replication of SARS-CoV-2 in a lung tumor xenograft mouse model. (A) Schematic diagram of the experimental procedure. Calu-3 cells were subcutaneously implanted into the right flank of NRGA mice (n = 3 per group). After the tumor volume reached 100 mm³, the tumors were inoculated with 1 × 10⁶ pfu of parental SARS-CoV-2, and the virus titers in the tumors were analyzed at 3, 15, and 30 dpi. (B) Body weight of each infection group (left panel). Tumor volume of each infection group (middle panel). Tumor weight of each infection group (right panel). (C) Replication of SARS-CoV-2 in lung tumors. Tumor tissues were collected at 3, 15, and 30 dpi. Viral titers in the supernatants of tumor homogenates were determined by plaque assay (left panel). Serum, tumor, lung, and brain were collected at 30 dpi, and viral titers were determined by qRT-PCR analysis for the SARS-CoV-2 RdRP gene (right panel). (D) Sera were collected at 30 dpi from NRGA mice (n=3) intratumorally infected with 1 × 10⁶ pfu of parental SARS-CoV-2 and at 14 dpi from C57BL/6J (n=3) intraperitoneally infected with 1 × 10⁶ pfu of parental SARS-CoV-2. The parental SARS-CoV-2 S protein RBD-specific IgG titers in the sera were determined by ELISA. (E) Expression of SARS-CoV-2 N protein in tumor tissues. The expression levels of SARS-CoV-2 N protein in mock-infected and SARS-CoV-2-infected tumor homogenates were determined by western blot. Expression of β-actin was used as a control. (F) Expression of SARS-CoV-2 N protein and S protein in tumor tissues. Mice (n=2) were sacrificed at 30 dpi. Paraformaldehyde-fixed, paraffin-embedded tumor tissues were sliced to 5 µm thickness, and H&E staining and immunohistochemical staining were performed to detect SARS-CoV-2 S protein and N protein and hACE2. Scale bars, 25 µm. dpi, days post-infection; Anti-N mAb, anti-SARS-CoV-2 N protein monoclonal antibody; Anti-S Ab, anti-SARS-CoV-2 S protein polyclonal antibody.