SARS-CoV-2 emerging variants: Antigens, antibodies, ELISA kits, and more

With the continuous spread of SARS-CoV-2 and subsequent diseases, emerging variants of the virus have been identified across the globe. The persistent challenges posed by SARS-CoV-2 to the international public health system have created more concern among scientists, drug and vaccine developers and the general population.

For simpler and more practical analysis of the variants, the World Health Organization (WHO) has designated certain “Variants of Interests (VOIs)” and “Variants of Concerns (VOCs)” due to their capacity to remarkably alter the characteristics of the virus.

WHO recently renamed the primarily circulating variants by Greek alphabets, i.e. Alpha (α) for B.1.1.7 (U.K. variant), Beta (β) for B.1.351 (South Africa), Gamma (γ) for P.1 (Brazil), Delta (γ) for B.1.617.2 (India), etc.

From the outbreak of the SARS-CoV-2 Delta in India in April 2021, the highly contagious Delta variant has swiftly spread all over the world and replaced Alpha to be the most widespread variant. The Lambda (C.37) variant gained highlight during this summer as the WHO denoted its rapid spread in South American countries, including Ecuador, Argentina, Peru and Brazil. According to WHO reports, “lambda has been associated with substantive rates of community transmission in multiple countries, with rising prevalence over time concurrent with increased COVID-19 incidence” and that additional investigations would be carried out into the variant. Furthermore, some new variants were successively identified around the world, such as C.1.2 (South Africa) and Mu (Columbia).

To restrict the spread of the SARS-CoV-2 variants, surveillance is required to investigate the way in which certain variants may influence the transmissibility of the virus, the associated disease severity, or the effectiveness of vaccines, therapeutic medicines and diagnostic tools.

Table 1. Source: ACROBiosystems

ACROBiosystems has been observing the most up-to-date genomic data of the virus and pursuing SARS-CoV-2 variant-related product development in full swing. The company now presents a complete solution to assist the research and development on the variant: a collection of antibodies, recombinant antigens, magnetic beads and ELISA kits has now been launched by ACROBiosystems.

Applications

• Diagnostic tools development
• Academic research
• Vaccine development
• Therapeutic drug screening

Relevant recommendations

• SARS-CoV-2 Lambda | C.37 (South America)
• SARS-CoV-2 Delta | B.1.617.2 (India)
• SARS-CoV-2 "Delta Plus" | AY.1 | B.1.617.2.1 (India)
• SARS-CoV-2 C.1.2 (South Africa)
• SARS-CoV-2 Mu | B.1.621 (Columbia)
• SARS-CoV-2 Kappa | B.1.617.1 (India)
• SARS-CoV-2 Alpha | B.1.1.7 (U.K)
• SARS-CoV-2 Beta | B.1.351 (South Africa)
• SARS-CoV-2 Gamma | P.1 (Brazil)
• SARS-CoV-2 Epsilon | B.1.427/B.1.429 (California)
• SARS-CoV-2 Critical Spike Single Mutation
• SARS-CoV-2 High-Frequency Nucleocapsid Mutations

Recombinant antigens

Image Credit: ACROBiosystems

• Offer recombinant antigens of VOCs with crucial mutations, enveloping K417N/T, E484K, N501Y and D614G on the spike protein; R203G, G204R on the nucleocapsid protein, etc.
• Multiple tags (His, Avi, Fc, mFc) are now available in large volumes
• Increased purity, high bioactivity, and increased stability verified by SEC-MALS&ELISA

> Featured products: Super stable spike trimer mutants

• Viral lineage information retrieved from GISAID/PANGOLIN/Nextstrain database
• Suitable for inhibitor screening assays and serological antibody titer tests
• Stable pre-fusion conformation secured by 6P & 2A mutations
• Cover mutations of VOCs (Alpha/Beta/Delta/Gamma variants): Alpha (Cat. No. SPN-C52H6), Beta (Cat. No. SPN-C52Hk), Gamma (Cat. No. SPN-C52Hg), Delta (Cat. No. SPN-C52He), Lambda (Cat. No. SPN-C52Hs)
• High trimer purity (>90%) verified by SEC-MALS

Antibodies

Image Credit: ACROBiosystems

• A wide spectrum of neutralizing antibodies with the ability to neutralize all the VOCs in the pseudovirus neutralization assay
• Anti-nucleocapsid antibody pair with the ability to recognize nucleocapsid protein of all the existing N variants
• ELISA verified high specificity and binding activity

> Featured products 1: Broad-spectrum neutralizing antibody verified by pseudovirus assay

• Cat. No. S1N-M122 with the ability to neutralize all the VOCs in pseudovirus neutralization assay, which is apt to be a positive control in the inhibitor screening tests.

> Featured products 2: Anti-nucleocapsid antibody pair verified by colloidal gold-based assay

• Cat. No. NUN-M223/NUN-S95 is capable of recognizing all the prevalent nucleocapsid protein variants verified by the colloidal gold-based essay, which makes it an optimum ingredient for the development of antigen detection tools.

ELISA kits

Image Credit: ACROBiosystems

• ELISA kits are available in variant-specific series
• High sensitivity and specificity with highly reproducible outcomes
• Deliver high throughput with the ability to perform 90+ samples simultaneously
• Ability to detect anti-mutant-neutralizing antibodies based on competitive ELISA

> Featured products: Variants-specific ELISA kits

Variant-specific ELISA kits can be utilized to verify vaccine effectiveness against viral variants by measuring anti-mutant-neutralizing antibody titers.

Table 2. Source: ACROBiosystems

Pre-coupled magnetic beads

Image Credit: ACROBiosystems

• Delivers high-outcome and low non-specific binding
• Produced by coupling biotinylated proteins to streptavidin-conjugated magnetic beads
• The system is pre-coupled and ready to use for capturing target proteins from the sample
• Available in uniform size and large surface-to-volume ratio

> Featured products 1: Antigen-coupled beads (MBS-K029, MBS-K030, MBS-K031)

• Designed for immunocapture/bio panning/flow cytometry
• Pre-coupled with Spike protein, Spike RBD, Spike S1, Spike RBD, etc.

> Featured products 2: Antibody-coupled beads (MBS-K014)

• Created by coupling anti-SARS-CoV-2 antibody that can bind WT and variants with increased affinity

> Featured products 3: ACE2-coupled beads (MBS-K013)

• Suitable for antigen detection

Products targeting circulating variants

Table 3. Source: ACROBiosystems

Table 4. Source: ACROBiosystems

Table 5. Source: ACROBiosystems

Table 6. Source: ACROBiosystems

Table 7. Source: ACROBiosystems

Application and sample data

> Scientific research: verify binding ability between spike mutants and ACE2

According to the verification done by SPR array, the binding affinity between SARS-CoV-2 RBD mutants and human ACE2 is usually 10 times higher (Alpha: KD = 1.24E-09; Beta: 3.27E-09; Gamma: 2.23E-09M) than the binding affinity between WT RBD and ACE2 (KD = 1.03E-08M).

The increased binding affinity of the RBD mutants with ACE2 may be underlying the increased infectivity of the Alpha/Beta/Gamma variants by facilitating viral entry into human cells.

SARS-CoV-2 WT/variant Spike RBD (Upper left: WT, Cat.No. SPD-C52H3; upper right: Alpha, Cat. No. SPD-C52Hn; lower left: Beta, Cat. No. SPD-C52Hp; lower right: Gamma, Cat. No. SPD-C52Hr) captured on Protein A Biosensor can bind human ACE2 (Cat. No. AC2-H52H8) with differential affinity as determined in SPR assay. Image Credit: ACROBiosystems

> Vaccine evaluation during research: Detect neutralization against SARS-CoV-2 variants

a. Anti-SARS-CoV-2 variant neutralizing antibody titer serologic assay kit

Measurement of antibody titer in 56 post-vaccination (Inactivated vaccine) serum samples by Anti-SARS-CoV-2 Variant Neutralizing Antibody Titer Serologic Assay Kits. The neutralizing ability of the vaccinated sera against the Alpha variant (Cat. No. RAS-N028) is slightly compromised as compared to the wild type (Cat. No. RAS-N022); neutralization against the Beta variant (Cat. No. RAS-N031) and Gamma variant (Cat. No. RAS-N034) decreased significantly. Image Credit: ACROBiosystems

b. Broad-spectrum neutralizing antibody (positive control)

According to the verification done by pseudovirus assays, the wide-spectrum neutralizing antibody can potently neutralize all the SARS-CoV-2 VOCs at a comparable level with the WT.

Neutralization of SARS-CoV-2 WT RBD and Alpha, Beta, Gamma, Kappa variant by a broadly neutralizing antibody (Cat. No. S1N-M122). Image Credit: ACROBiosystems

> Therapeutic drug development: screen for highly potent small molecule drugs/broad-spectrum neutralizing antibodies

a. Inhibitor screening kit

The verification done in the P3-level laboratory affirmed the ability of the selected antibodies to inhibit SARS-CoV-2 infection of Vero cells. The data explained the high sensitivity of the kit.

Inhibitor screening ELISA assay by SARS-CoV-2 Inhibitor Screening Kit (Cat. No. EP-105). Image Credit: ACROBiosystems

b. Antigen-pre-coupled magnetic beads

The capture of Anti-S1 Antibody by SARS-CoV-2 Spike Trimer (B.1.1.7) Coupled Magnetic Beads (Cat.No. MBS-K029). Immobilized 24 μg Spike protein/1 mg beads can bind the Anti-S1 Antibody with an EC50 of 0.5848 μg/mL (QC tested). Image Credit: ACROBiosystems

> Diagnostic tools development: verify if S/N antibody pair can recognize S/N variants

a. Anti-spike antibody pair

Detection of Spike RBD variants (Cat.No. SPD-C52Hn; SRD-C52H3; SPD-C52Hp) by anti-spike antibody pair (Cat. No. S1N-M12A1, S1N-M13A1) in Sandwich ELISA. Image Credit: ACROBiosystems

b. Anti-nucleocapsid antibody pair

Anti-SARS-CoV-2 Nucleocapsid Antibody, Human IgG1 (Cat. No. NUN-S95) (Detection antibody) can bind multiple nucleocapsid protein variants with a high affinity comparable with the WT N protein (Cat. No. NUN-C5227). Image Credit: ACROBiosystems

Anti-SARS-CoV-2 Nucleocapsid Antibody, Chimeric mAb, Human IgG1 (AM223) (Cat. No. NUN-M223) (Capture antibody) can bind multiple nucleocapsid protein variants with a high affinity comparable with the WT N protein (Cat. No. NUN-C5227). Image Credit: ACROBiosystems