Synthetic Genes at the Forefront of Antibody Drug Discovery (ADD)

Antibody-drug discovery (ADD) is an arduous process that often starts with the extensive screening of antibody libraries to identify optimal candidates, namely those having high-affinity antigen binding and other desirable functional properties. For example, during the COVID-19 pandemic, discovering potent neutralizing anti-SARS-CoV-2 antibodies has been prioritized. From the early stages of the pandemic, neutralizing antibodies were proposed to correlate with protection from infection (Addetia et al. 2020). Over time, more evidence upheld this view; thus, efforts to identify and characterize anti-SARS-CoV-2 neutralizing antibodies of potential clinical value continue to this date (Quiros-Roldan et al. 2021). While the now available SARS-CoV-2 vaccines represent the first line of defense for most people, monoclonal antibodies can serve as prophylactic or therapeutic bio drugs for a fraction of the population that remain unprotected due to comorbidities or inability to respond to vaccines.

The first FDA-approved monoclonal antibody drug for infectious diseases was granted back in 1998 to palivizumab to prevent lower respiratory tract complications following respiratory syncytial virus (RSV) infections in high-risk infants. Most recently, and during earlier stages of the COVID-19 pandemic, in 2020, the monoclonal antibody mixture Inmazeb (i.e., atoltivimab, maftivimab, and odesivimab-ebgn) received FDA approval for use in adult and pediatric patients to neutralize Ebola viral attachment and cell entry. Following up on the heels of these successful precedents, scientists have taken advantage of the rich diversity of patient-derived monoclonal antibodies to identify potential candidates for COVID-19 prevention or treatment.

Identifying Anti-SARS-CoV-2 Neutralizing Antibodies

Throughout the pandemic, scientists, such as those in Dr. David D. Ho’s team at Columbia University, have been busy evaluating neutralizing titers from SARS-CoV-2 infected patients (Liu et al. 2020). Peripheral-blood-derived B cells isolated from clinical study participants having high-neutralizing antibody titers enabled Dr. Ho’s team to identify several monoclonal antibodies with potential for clinical use.

The advantage of this strategy for antibody discovery lies in the direct access to an individual’s antibody repertoire, which may be rapidly obtained through VDJ mRNA sequencing at the single B cell level. However, significant challenges remain, such as the hurdles imposed by large numbers of antibody sequences that painstakingly need to be optimally synthesized and seamlessly cloned for monoclonal antibody production in support of functionality assays, lead optimization, preclinical studies, and towards potential clinical evaluation.

With sequences for over 200 antibodies at hand, Dr. Ho’s group expedited their “gene to antibody” workflow by relying on GenScript’s codon-optimized antibody gene synthesis, cloning, and plasmid preparation services. As a result, Dr. Ho’s team found that synthetic, codon-optimized, and cloned antibody sequences, efficiently expressed functional antibodies in transfected Expi293 cells. Additionally, antibody products successfully supported a battery of in vitro and in vivo assays, including antigen-binding and neutralization, epitope mapping, cryo-electron microscopy analysis, and protection from in vivo SARS-CoV-2 infection challenge studies in a preclinical model. Overall, this approach enabled the team to identify nine highly neutralizing antibodies with potential as drug candidates targeting the Spike protein at the receptor-binding domain (RBD), N-terminal domain (NTD), and quaternary Spike epitopes.

Anti-SARS-COV-2 Spike Monoclonal Antibodies “(B) Interaction between the S protein and the host cell receptor ACE2. Most therapeutic mAb target the RBD of the S protein at positions required for the interaction with ACE2 (Bamlanivimab, Etesevimab, Casirivimab, Imdevimab, Cilgavimab, Tixagevimab, Regdanvimab) while Sotrovimab targets the RBD, but does not compete with human ACE2 receptor binding. mAbs binding the NTD have been demonstrated to neutralize SARS-CoV-2, and these could be developed for therapeutic purposes (Created with BioRender.com).” Retrieved with modifications from Quiros-Roldan et al. 2021, creativecommons.org/licenses/by/4.0/

Expediting ADD for SARS-CoV-2 Variants

The SARS-CoV-2 pandemic has been an extremely dynamic process. The rapid accumulation of mutations has given rise to many SARS-CoV-2 variants, which have imposed different challenges to our vaccine or infection-derived immunity. Therefore, developing new variant-specific antibody drugs continues to be critical for treating and protecting susceptible individuals.

The Omicron variant (B.1.1.529), with its high transmissibility and many Spike protein mutations, raised concerns about the efficacy of pre-existing anti-SARS-CoV-2 monoclonal antibody drugs. Not surprisingly, Dr. Ho’s studies found the neutralizing potency of various monoclonal antibodies, including those authorized for clinical use (e.g., bamlanivimab, casirivimab, and imdevimab, among others) diminished or even abolished against the Omicron variant (Liu et al. 2021).

As we move into another phase of the global COVID-19 pandemic, with the continued evolution of Omicron sublineages, the need to expedite the discovery and development of new effective monoclonal antibody drugs remains (Iketani et al. 2022). Hence, strategies that accelerate gene to antibody product workflows in the ADD pipeline would enable greater agility in developing therapy solutions in response to the fast viral evolution.

Reference

• Addetia, A. et al. Neutralizing antibodies correlate with protection from SARS-CoV-2 in humans during a fishery vessel outbreak with a high attack rate. J. Clin. Microbiol. (2020) doi:10.1128/JCM.02107-20..
• Iketani, S. et al. Antibody evasion properties of SARS-CoV-2 Omicron sublineages. Nature (2022). https://doi.org/10.1038/s41586-022-04594-4.
• Liu, L. et al. Potent neutralizing antibodies against multiple epitopes on SARS-CoV-2 spike. Nature (2020) doi:10.1038/s41586-020-2571-7..
• Liu, L. et al. Striking antibody evasion manifested by the Omicron variant of SARS-CoV-2. Nature 602, 676–681 (2022). https://doi.org/10.1038/s41586-021-04388-0.
• Quiros-Roldan E. et al. Monoclonal Antibodies against SARS-CoV-2: Current Scenario and Future Perspectives. Pharmaceuticals. 2021; 14(12):1272. https://doi.org/10.3390/ph14121272.