Abstract The Delta variant originally from India is rapidly spreading across the world and causes to resurge infections of SARS-CoV-2. We previously reported that CT-P59 presented its in vivo potency against Beta and Gamma variants, despite its reduced activity in cell experiments. Yet, it remains uncertain to exert the antiviral effect of CT-P59 on the Delta and its associated variants (L452R). To tackle this question, we carried out cell tests and animal study. CT-P59 showed reduced antiviral activity but enabled neutralization against Delta, Epsilon, and Kappa variants in cells. In line with in vitro results, the mouse challenge experiment with the Delta variant substantiated in vivo potency of CT-P59 showing symptom remission and virus abrogation in the respiratory tract. Collectively, cell and animal studies showed that CT-P59 is effective against the Delta variant infection, hinting that CT-P59 has therapeutic potency for patients infected with Delta and its associated variants. Highlights CT-P59 exerts the antiviral effect on authentic Delta, Epsilon and Kappa variants in cell-based experiments. CT-P59 showed neutralizing potency against variants including Delta, Epsilon, Kappa, L452R, T478K and P681H pseudovirus variants. The administration of clinically relevant dose of CT-P59 showed in vivo protection against Delta variants in animal challenge experiment.

The in vitro and in vivo potency of CT-P59 against Delta and its associated variants of SARS-CoV-2