OASL and infection: RTD-1 treatment upregulated expression of oligoadenylate synthetase family genes, OAS1, OAS2, OAS3, and OASL, which are activated by double-stranded RNA and stimulate the antiviral activity of RNase L37,38 and are involved in response to multiple viruses including SARS-CoV-2.39–41 Consistent with this, RTD-1 inhibited the infection of Calu-3 2B4 cells with SARS-CoV-2 (Fig. 9).