Hannah Clayton

 Background: The Severe Acute Respiratory Syndrome Coronavirus – 2 (SARS-CoV-2), also known as covid-19, caused the global pandemic that began in 2019. Covid-19 is transmitted via respiratory droplets and attacks ciliated cells and type II pneumocytes in lung tissue. It has had a case fatality rate of approximately 2% with risk factors including older age, diabetes, hypertension, chronic lung disease, and immunocompromised patients. Symptoms of Covid-19 occur 4-5 days after infection and include symptoms such as cough, fatigue, shortness of breath, and fever. Covid-19 is commonly diagnosed with nasopharyngeal swabs and PCR tests.₁ The SARS-CoV-2 virus is highly variable and mutates quickly which makes treatment for the virus difficult.₂ Current treatments include vaccinations and antibody treatments. Nanobodies are another option for treatment and can be designed to target specific receptors that can block spike protein binding on multiple variants and strains.₃

Objective: In this narrative review, we explored different mechanisms for nanobodies that can neutralize common domains in the SARS-CoV-2 virus.

Search Methods: An online search in the PubMed database was conduced from 2019-2023 using the following keywords: “coronavirus”, “therapy”, “nanobody”.

Results: Five different mechanisms and nanobodies were investigated. The first was the Ty1 nanobody was isolated from infected alpacas and neutralized the spike proteins of SARS-CoV-2 and prevented them from binding the angiotensin converting enzyme 2 (ACE2) receptor.₅ The ACE2 receptor is where the SARS-CoV-2 spike proteins bind in humans.₄ The Ty1 nanobody had a half maximal inhibitory concentration (IC₅₀) of 0.77 µg/ml and can be produced by bacteria in quantities of up to 30 mg/L demonstrating that nanobodies can be mass produced. The second nanobody investigated was the 3-2A2-4 nanobody which binds to a highly conserved epitope between various strains of covid-19.₆ Nanobody 3-2A2-4 binds to an alternate site that blocks the ACE2 receptor and had a IC₅₀ of 0.106 µg/ml against authentic SARS-CoV-2 virus and its variants. The third nanobody, ARBD-2-5-Fc, is a fused nanobody that has an IC50 of 0.0293 nM against authentic virus Omicron BA.1.₇ This nanobody neutralized the virus in wild mice at doses as low as 1 mg/kg. The fourth study looked at the WNBFc nanobodies which were previously identified nanobodies that were bound to the Fc domain of IgG1 molecule to prevent clearance.₈ Two of the tested nanobodies were able to reduce viral loads in mice. The final study explored the Bn03 nanobody that has an IC50 of 0.11-0.76 mg/ml against pseudoviruses of the wildtype and five variants.₂ This nanobody was also aerosolized for drug delivery and lowered the viral load in mice.

Conclusions: These studies have shown that nanobodies can be isolated, combined, and engineered to target specific epitopes that can block the ACE2 receptor. The nanobodies were shown to reduce the viral load in mice and can be delivered in aerosolized form. This treatment can be quickly developed for a multitude of variants but with a rapidly mutating virus it can still pose a challenge to treat SARS-CoV-2.

Works Cited:

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