RR:C19 Evidence Scale rating by reviewer:
Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.
SARS-CoV-2 has infected more than 500 million people and 6.2 million have died as a result of COVID-19. Several effective vaccines have been developed and distributed globally; however, due to the high mutation rate of SARS-CoV-2, different variants have emerged. Some of these variants (VOCs) account for higher transmissibility and can evade neutralization by vaccine-induced and therapeutic (mAb) antibodies. In the present study entitled “Broadly neutralizing antibodies against Omicron variants of SARS-CoV-2 derived from mRNA-lipid nanoparticle-immunized mice”, Ruei-Min Lu and colleagues describe an innovative method to discover anti-SARS-CoV-2 broadly neutralizing mAbs with potential applications in clinical settings. The authors used mRNA encoding SARS-CoV-2 Kappa (B.1.617.1) variant spike and RBD, encapsulated in lipid nanoparticles (LNP), to immunize mice and produce sp-Ab secreting hybridoma clones. Since the target protein is directly expressed in the animal, this approach does not require the manufacture of proteins and allows the protein to be expressed in its natural conformation, favoring an efficient stimulation of humoral immunity. Using this platform, the authors generated anti-RBD mAbs that neutralized the five current SARS-CoV-2 VOCs. Moreover, candidate mAbs were bioengineered (K-RBD-chimeric Abs) and a humanized mAb candidate (K-RBD-humanized Ab-62) neutralized Omicron sublineages BA.1 and BA.2 with IC50 values 7.0 and 9.5 ng/ml, respectively. This broadly neutralizing antibody, with a higher spectrum, compared to currently mAbs with emergency use authorization, may be a promising tool for controlling current SARS-CoV-2 variants. In general, the work is methodologically correct and conclusions are supported by the results presented in the manuscript.
The major limitations of this study are:
The lack of in vivo testing of these novel mAbs candidates in animal models for SARS-CoV-2.
The lack of a deeper analysis of candidate mAbs interaction with SARS-CoV-2 spike/RBD. Although the authors acknowledge that they plan to analyze the binding interface by cryo-EM, this particular analysis is necessary to explain why Omicron mutations (K417N, S477N, and E484A) do not impact the neutralizing activity of these candidate mAbs as they observed for K417A, Y453A, Q474A, and F486A. Additionally, ACE2 competition assay (complementary approach) could have been used to show the degree of RBD recognition by these candidate mAbs.
Methods should be described in more detail, particularly for some complex procedures (i.e., mRNA construct, LNP formulation, chimeric mAb construction, and mAb humanization) to allow replication of the experiments; references could be added if such procedures were previously described in detail.
Discuss why the hybridoma method was selected over a single B-cell RT-qPCR (human donor) and why the SARS-CoV-2 Kappa (B.1.617.1) variant was selected as an immunization candidate. These limitations should be stated and discussed thoroughly in the discussion section.
Line 149: What was the timing of immunization?
Line 156: ELISA isotyping KIT
Line 255 and 259: This should say mAb 91