A bispecific bispecific T cell engagement strategy targeting SARS-CoV-2 spikes to control SARS-CoV-2 infection

In a recent study published in the Communications Biology Journal, researchers have described a novel strategy to control severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections where a bispecific T-cell engager is used to target the SARS-CoV-2 spike protein .

Study: A bispecific T cell engagement strategy targeting spikes provides dual-layer protection against SARS-CoV-2 infection in vivo. Image Credit: Tsuguliev/Shutterstock.com

Background

Although the rapid development of vaccines and monoclonal antibodies has succeeded in limiting the severity and mortality during the coronavirus disease 2019 (COVID-19) pandemic, the emergence of new variants with immune evasive mutations continues to spark periodic concerns.

Antiviral technology comprised of small molecules that target viral entry and replication of SARS-CoV-2 is being investigated, and some of them, such as Paxlovid, have been approved for clinical use. Neutralizing antibodies were also quite effective against SARS-CoV-2 in early clinical use.

Many of these antibody therapies target the angiotensin-converting enzyme-2 (ACE-2) receptor, the primary receptor for SARS-CoV-2 entry.

However, new spike protein mutations continue to challenge the effectiveness of neutralizing antibodies and new approaches, in addition to existing small molecule inhibitors and neutralizing antibodies, are needed to combat emerging variants of SARS-CoV-2.

Bispecific antibodies that target two epitopes and bispecific fusion proteins with an ACE-2 soluble arm and an antibody arm have also been developed to improve neutralization efficiency while simultaneously targeting evasive immune mutations.

About the study

The researchers developed a bispecific T-cell engager (S-BiTE) that targets the SARS-CoV-2 spike protein in the current study.

This fusion protein includes an extracellular ACE-2 domain to block viral entry and an anti-CD3ε single-chain variable fragment (scFv) (3ε differentiation cluster) to eliminate virus-producing cells by activating T cells.

The extracellular ligand ACE-2 was used to identify cells expressing the SARS-CoV-2 spike protein, similar to live Cells infected with SARS-CoV-2. The monovalent extracellular domain of ACE-2 shows high affinity for the receptor binding domain of the SARS-CoV-2 spike-Fc fusion protein (RBD).

Compared to the bivalent parental anti-CD3 antibody, the monovalent anti-CD3ε scFv has reduced affinity for CD3ε, which ensures that T cells will not bind and be activated if the SARS-CoV-2 spike protein is absent.

A T-cell activation assay using co-cultured cells expressing the SARS-CoV-2 spike protein was performed in vitro to test the T cell activating capacity of S-BiTE. The cytotoxicity of S-BiTE was also compared to that of ACE-2-human immunoglobulin g (IgG1) Fc fusion proteins.

Additionally, a pseudotyped SARS-CoV-2 production system was used to test the efficacy of S-BiTE in preventing viral release. The cytotoxicity of S-BiTE was also tested live.

Additionally, the safety profile of S-BiTE was tested using mouse models to ensure that it did not cause unwanted T-cell depletion or activation.

MSCs were engineered to stably express S-BiTE, and the preferential biodistribution of MSCs in the lungs also indicated its potential use in the treatment of SARS-CoV-2-induced pneumonia.

The efficacy of S-BiTE in eliminating cells expressing the spike protein was further tested using live virus-infected cells and against the Delta variant spike protein.

Results

The results reported that S-BiTE competed with membrane receptors and blocked free SARS-CoV-2 entry into permissive cells while activating strong T cell-mediated cytotoxicity to eliminate SARS-CoV-2 infected cells. virus.

Furthermore, S-BiTE was also effective against the original SARS-CoV-2 strain and the Delta variant, indicating its potential efficacy and use against emerging immunoevasive SARS-CoV-2 variants.

Treatment of a humanized mouse model infected with SARS-CoV-2 with S-BiTE significantly reduced the viral load more effectively than neutralizing antibodies alone.

Use of humanized mouse models to test the safety profile also reported no significant differences in immune cell subtypes, depletion or unwanted activation of T cells, or any infiltration of major tissues. with immune cells.

The first of two significant advantages of using S-BiTE over standard neutralizing antibody therapies uses ACE-2 as the targeting moiety, which will be effective against nearly all variants of SARS-CoV-2.

The second advantage comes from the use of anti-CD3ε to activate T cells to eliminate virus-infected cells, which is significantly more effective than antibody-mediated cytotoxicity.

conclusion

Overall, the results reported that S-BiTE prevented viral entry by competing with membrane ACE-2 receptors and activating T-cell cytotoxicity, effectively eliminating SARS-CoV-infected cells. 2.

S-BiTE technology can be further optimized by selecting target moieties and enhancing safety and neutralization capabilities to improve efficacy against emerging SARS-CoV-2 variants.