The P.1 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant of concern (VOC) was first identified in Brazil and has since spread around the world, demonstrating increased transmissibility compared to the wildtype virus. This is due to several particular mutations that have also co-occurred in other highly transmissible VOCs. These mutations are generally centered on the receptor-binding domain (RBD) of the spike protein, including the N501Y, K417T, and E484K mutations, among others.
The therapeutic monoclonal antibody CT-P59 binds to the RBD of SARS-CoV-2, the site of these three major mutations, which may therefore reduce the potency of this antibody against the P.1 lineage. In a paper recently uploaded to the preprint server bioRxiv* by Ryu et al. (July 9, 2021), the neutralizing potency of this monoclonal antibody towards both wildtype and P.1 SARS-CoV-2 is investigated. The researchers found that the ability to bind with the virus is impeded by the mutations, resulting in reduced potency in vitro.
How was the study performed?
Vero E6 and HEK-293T cells expressing the ACE2 receptor were exposed to live P.1 SARS-CoV-2 virus and P.1 pseudovirus followed by administration of the CT-P59 monoclonal antibody, and the binding affinity to both wildtype and P.1 receptor binding domains assessed. ACE2 transgenic mice infected with P.1 SARS-CoV-2 were also exposed to the antibody, and viral load was assessed in the nasal cavity and lungs at various time points.
The group found that the dissociation constant of CT-P59 was reduced around 12-fold against the P.1 strain compared to wildtype. The antibody also showed a total of 138-fold reduced neutralization of P.1 live viruses. This was noted to be dependent on the particular mutation applied in the case of the pseudovirus, with D614G, E484K, and N501Y mutations resulting in less than 10-fold reductions individually, suggesting that the cumulative effect of the mutations results in a greater conformational change.
Therapeutic potency in vivo
Amongst the control group of mice infected with P.1 SARS-CoV-2, there was a 0% survival rate at eight days post-infection, while no death or significant weight loss was observed in those treated with the monoclonal antibody. With regards to body weight, the former group saw an average of 28.4% loss at seven days post-infection, while treatment with 5, 20, 40, or 80 mg/kg CT-P59 resulted in losses of 18.8, 16.6, 16.7 and 9.2%, respectively, with the mice recovering completely at ten days post-infection.
The control group also saw average viral loads in the lungs of 5.1 log (PFU+1)/mL at three days post-infection, declining to 2.4 at six days, while those administered with the antibody saw antibody titers reduce by a factor of 9.2, 5.5, 2.5 and 3.6 at day 3, at 5, 20, 40 and 80 mg/kg dosage, respectively. No virus was detected in the lungs at six days post-infection amongst those administered with the antibody at any dosage. Neither was the virus detected in the nasal cavity at either three or six days post-infection amongst this group.
The mutations to the spike protein in the P.1 strain of SARS-CoV-2 result in reduced neutralizing potency of the CT-P59 monoclonal antibody in vitro, likely due to slight conformational changes resulting from the mutations.
However, the therapeutic benefit of the monoclonal antibody is maintained in mice against this strain, and the group further suggests that a higher clinical dosage, 40 mg/kg, would likely overcome the observed reduced potency in vitro, while being still within the safe dosage range.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Ryu, Dong-Kyun, Bobin Kang, Sun-Je Woo, Min-Ho Lee, Aloys SL Tijsma, Hanmi Noh, Jong-In Kim, Ji-Min Seo, Cheolmin Kim, Minsoo Kim, Eunji Yang, Gippeum Lim, Seong-Gyu Kim, Su-Kyeong Eo, Jung-ah Choi, Sang-Seok Oh, Patricia M Nuijten, Manki Song, Hyo-Young Chung, Carel A van Baalen, Ki-Sung Kwon, Soo-Young Lee. (2021) Therapeutic efficacy of CT-P59 against P.1 variant of SARS-CoV-2. bioRxiv preprint server. doi: https://doi.org/10.1101/2021.07.08.451696,