Commercial immunoassays for detection of anti-SARS-CoV-2 spike and RBD antibodies: urgent call for validation against new and highly mutated variants

Abstract

Measuring the level of protection conferred by anti-SARS-CoV-2 (trimeric) spike or RBD (receptor binding domain) antibodies (especially total and IgG) is a suitable and reliable approach for predicting biological protection against the risk of infection and severe coronavirus disease 2019 (COVID-19) illness. Nonetheless, SARS-CoV-2 has undergone a broad process of recombination since the identification of the prototype lineage in 2019, introducing a huge number of mutations in its genome and generating a vast array of variants of interest (VoI) and concern (VoC). Many of such variants developed several mutations in spike protein and RBD, with the new Omicron (B.1.1.529) clade displaying over 30 changes, 15 of which concentrated in the RBD. Besides their impact on virus biology, as well as on the risk of detection failure with some molecular techniques (i.e., S gene dropout), recent evidence suggests that these mutations may also jeopardize the reliability of currently available commercial immunoassays for detecting anti-SARS-CoV-2 antibodies. The antigen (either spike or RBD) and epitopes of the prototype SARS-CoV-2 coated in some immunoassays may no longer reflect the sequence of circulating variants. On the other hand, anti-SARS-CoV-2 antibodies elicited by highly mutated SARS-CoV-2 variants may no longer be efficiently recognized by the currently available commercial immunoassays. Therefore, beside the compelling need to regularly re-evaluate and revalidate all commercially available immunoassays against live virus neutralization assays based on emerging VoCs or VoIs, diagnostic companies may also consider to redevelop their methods, replacing former SARS-CoV-2 antigens and epitopes with those of the new variants.

Emergence of SARS-CoV-2 Omicron (B.1.1.529) variant, salient features, high global health concerns and strategies to counter it amid ongoing COVID-19 pandemic

“…Due to variations in the targeted area, S gene dropouts have been reported, and hence reliability of currently used detection systems is also under question. The immunoassays based on coated antigens with prototype SARS-CoV-2 virus may not necessarily detect the antibodies against currently circulating variants and hence there is a compelling need of regular re-evaluation and revalidation of live virus neutralization assays based on emerging VOIs and VOCs ( Lippi et al, 2021 ).…”

Omicron (B.1.1.529 variant of SARS‐CoV‐2); an emerging threat: Current global scenario

“… 33 , 34 There is also a need to design and validate potent commercial immunoassays for detecting anti‐SARS‐CoV‐2 spike and RBD antibodies against the newly emerging and highly mutated variants such as Omicron. 35 A recent study also suggests that the Omicron variant of SARS‐CoV‐2 encodes 37 amino acid substitutions in the spike protein, out of which 15 are in RBD region and the Omicron RBD binds to human ACE2 with increased affinity. 36 Still vaccine inequity and hesitancy are the influential factors for the emergence of such novel variants and their transmission.…”

Differential avidity determination of IgG directed towards the receptor‐binding domain (RBD) of SARS‐CoV‐2 wild‐type and its variants in one assay: Rational tool for the assessment of protective immunity

“…This might point to problems for the detection of SARS‐CoV‐2 omicron infection with test systems based on RBD from WT, and vice versa. The resolution of such diagnostic problems requires the modification and validation of test systems to cope with new and highly mutated variants, as originally suggested by Lippi et al 41 …”