The coronavirus 2019 (COVID-19) pandemic has caused over 254 million confirmed cases and more than 5.1 million deaths worldwide as of 17th November 2021. Approximately 20% of people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remain asymptomatic throughout the infection. The remaining 80% exhibit only mild or moderate disease, and approximately 15% develop severe disease requiring hospitalization, oxygen support, and other interventions. The case-fatality rates (CFR) of COVID-19 vary substantially in different regions, ranging from below 1% to up-to-20%.
The current control measure against SARS-CoV-2 is vaccination. Effective messenger RNA (mRNA) vaccines and viral vector vaccines have been developed against the Wuhan-Hu-1 reference sequence and are being administered on a global level. At this point, all current vaccines target the virus spike protein to produce neutralizing antibodies against this protein to block virus entry into cells. In addition, DNA vaccines that elicit strong cellular responses have also been explored.
As an additional therapeutic measure, neutralizing antibodies, alone or in cocktails, are being researched for their neutralizing capabilities. Three SARS-CoV-2-neutralizing monoclonal antibodies (mAb) products: REGEN-COV (casirivimab plus imdevimab), bamlanivimab plus etesevimab, and Sotrovimab have been approved for the treatment of mild to moderate COVID-19 in outpatients under Emergency Use Authorizations (EUAs) by the FDA.
These mAbs have been developed through isolated memory B cells from either convalescent patients or immunized mice that contain humanized immunoglobulin genes. Although vaccination and antibody cocktail prophylaxis/therapy seem promising, the emergence of SARS-CoV-2 variants with increased transmissibility, virulence, and antibody resistance has raised concerns about the success of halting the pandemic.
Canadian public health researchers recently published a study in the journal Antiviral Research wherein they described generating a panel of murine hybridomas recognizing SARS-CoV-2 spike protein or nucleoprotein, capable of neutralizing the SARS-CoV-2 variants of concern, proving their therapeutic potential.
Study details and methodology
Researchers immunized four mice and boosted them with formalin-inactivated SARS-CoV-2, and used their spleens for fusion and hybridoma selection.
A panel of forty-four clones were detected based on ELISA screening against purified inactivated SARS-CoV-2, recombinant spike protein (rSP), recombinant nucleoprotein (rNP), and in parallel with negative screening with Bovine Serum Albumin.
Researchers obtained a lead panel of six spike protein-specific mAbs (F459G1, F461G8, F461G11, F461G14, F461G15, and F461G16) after multiple sets of analytical and purification procedures like on ELISA, Western immunoblot, and isotyping, for subcloning and producing these mAbs on a large scale for testing antibody sequence, antigen specificity, antigen affinity, surrogate virus neutralization test, and neutralization of multiple SARS-CoV-2 variants. The amino acid sequences of these mAbs were determined by mass spectrometry.
All six mAbs showed strong binding capacity with spike proteins. Two mAbs, F461G8 and F461G11, had endpoint titers at 156 ng/mL. At the same time, the other four mAbs, F459G1, F461G14, F461G15, and F461G16 showed stronger binding with the endpoints at 19.5 ng/mL, 4.9 ng/mL, 4.9 ng/mL, and 3.1 ng/mL, respectively.
Both F461G8 and F461G14 showed a substantial reduction of neutralization potency to most of the tested variants. Specifically, F461G8 reduced the potency of variants P.1 and B.1.351 by up to thirty-two folds, and the potency to variant B.1.1.7 and B.1.617.2 was reduced by two-fold and eight-fold, respectively.
F461G14 showed neutralizing activity at more than thirty-two- to sixty-four--fold reduction to variants P.1, B.1.1.7, and B.1.351, respectively. F459G1 showed sixteen-, four- and eight-fold reduced neutralizing activity to P.1, B.1.1.7, and B.1.351, respectively. In contrast, F461G11, F461G15, and F461G16 showed minor or no change of neutralization to variants P.1, B1.1.7, and B.1.351. Moreover, the three mAb clones exhibited increased neutralizing four to eight-fold, variants B.1.617.2, compared to the reference isolate (hCoV-19/Canada/ON_ON-VIDO-01-2/2020, EPI_ISL_425177).
This study successfully demonstrated the neutralization potential of three mAbs, F461G11, F461G15, and F461G16, against the four variants of concern (VOC): B.1.1.7 (alpha), B.1.351 (beta), P.1 (gamma), and B.1.617.2 (delta).
While global vaccination campaigns are on and breakthrough infections occurring despite double doses, when the world is facing shortages in vaccine supplies, these mAbs appear as a ray of hope amidst all calamities. These mAbs are promising candidates for COVID-19 therapy, and understanding their interactions with virus spike protein should support public health agencies globally to plan their COVID-19 combat strategies accordingly.