diagnostics Communication Use of Lateral Flow Immunoassay to Characterize SARS-CoV-2 RBD-Specific Antibodies and Their Ability to React with the UK, SA and BR P.1 Variant RBDs Enqing Tan 1, Erica Frew 1, Jeff Cooper 2, John Humphrey 2, Matthew Holden 1, Amanda Restell Mand 1, Jun Li 2, Shaya Anderson 2, Ming Bi 2, Julia Hatler 2, Anthony Person 2, Frank Mortari 3, Kevin Gould 4,* and Shelly Barry 1,* 1 Diagnostic Reagents Division, Bio-Techne Corporation, Devens Site, Devens, MA 01434, USA; [email protected] (E.T.); [email protected] (E.F.); [email protected] (M.H.); [email protected] (A.R.M.) 2 Reagent Solutions Division, Bio-Techne Corporation, Minneapolis Site, Minneapolis, MN 55413, USA; [email protected] (J.C.); [email protected] (J.H.); [email protected] (J.L.); [email protected] (S.A.); [email protected] (M.B.); [email protected] (J.H.); [email protected] (A.P.) 3 Corporate Development, Bio-Techne Corporation, Minneapolis Site, Minneapolis, MN 55413, USA; [email protected] 4 Diagnostic Reagents Division, Bio-Techne Corporation, San Marcos Site, San Marcos, CA 92078, USA * Correspondence: [email protected] (K.G.); [email protected] (S.B.) Abstract: Identifying anti-spike antibodies that exhibit strong neutralizing activity against current dominant circulating variants, and antibodies that are escaped by these variants, has important Citation: Tan, E.; Frew, E.; Cooper, J.; implications in the development of therapeutic and diagnostic solutions and in improving under- Humphrey, J.; Holden, M.; Mand, standing of the humoral response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) A.R.; Li, J.; Anderson, S.; Bi, M.; infection. We characterized seven anti-SARS-CoV-2 receptor binding domain (RBD) antibodies for Hatler, J.; et al. Use of Lateral Flow binding activity, pairing capability, and neutralization activity to SARS-CoV-2 and three variant Immunoassay to Characterize RBDs via lateral flow immunoassays. The results allowed us to group these antibodies into three SARS-CoV-2 RBD-Specific Antibodies distinct epitope bins. Our studies showed that two antibodies had broadly potent neutralizing and Their Ability to React with the activity against SARS-CoV-2 and these variant RBDs and that one antibody did not neutralize the UK, SA and BR P.1 Variant RBDs. South African (SA) and Brazilian P.1 (BR P.1) RBDs. The antibody escaped by the SA and BR P.1 Diagnostics 2021, 11, 1190. https:// doi.org/10.3390/diagnostics11071190 RBDs retained binding activity to SA and BR P.1 RBDs but was unable to induce neutralization. We demonstrated that lateral flow immunoassay could be a rapid and effective tool for antibody Academic Editor: Sandeep K. Vashist characterization, including epitope classification and antibody neutralization kinetics. The potential contributions of the mutations (N501Y, E484K, and K417N/T) contained in these variants’ RBDs to Received: 1 June 2021 the antibody pairing capability, neutralization activity, and therapeutic antibody targeting strategy Accepted: 25 June 2021 are discussed. Published: 30 June 2021 Keywords: COVID-19; SARS-CoV-2 variant; lateral flow immunoassay; spike protein; receptor Publisher’s Note: MDPI stays neutral binding domain (RBD); neutralizing antibody; therapeutic antibody cocktail; epitope binning; rapid with regard to jurisdictional claims in neutralization test; ACE2 published maps and institutional affil- iations. 1. Introduction The continued emergence of SARS-CoV-2 variants has raised concerns and challenges Copyright: © 2021 by the authors. for the control, prevention, and management of the coronavirus disease (COVID-19) [1]. Licensee MDPI, Basel, Switzerland. Currently, the circulating variants of greatest concern include the United Kingdom variant This article is an open access article (B.1.1.7 lineage, UK) [2,3], the SA variant (B.1.351 lineage) [4], the BR P.1 (B.1.1.28.1 lin- distributed under the terms and eage) [5], the Brazilian variant P.2 (B.1.1.28.2 lineage, BR P.2) [6], the Denmark mink variant conditions of the Creative Commons (B.1.1.298 lineage, DM) [7], the California variants (B.1.429/427 lineage, CA) [8], the New Attribution (CC BY) license (https:// York variants (B.1.526/525 lineage, NY) [9], and the more recent Indian variant (B.1.617 creativecommons.org/licenses/by/ lineage, IN) [10]. In the absence of an effective strategy to curb the spread of SARS-CoV-2 4.0/). Diagnostics 2021, 11, 1190. https://doi.org/10.3390/diagnostics11071190 https://www.mdpi.com/journal/diagnostics Diagnostics 2021, 11, x FOR PEER REVIEW 2 of 17 Diagnostics 2021, 11, 1190 2 of 16 SARS-CoV-2 virus infection, and due to more individuals harboring the virus, it is inevi- tablevirus that infection, more variants and due are to more likely individuals to emerge. harboring the virus, it is inevitable that more variantsThe areSARS likely-CoV to-2 emerge. virus infects mammalian cells by attaching transmembrane spike proteinsThe (S SARS-CoV-2 protein) to virusthe angiotensin infects mammalian-converting cells enzyme by attaching 2 receptors transmembrane (ACE2) found spike on theproteins surface (S protein)of the human to the target angiotensin-converting cells [11,12]. Hence, enzyme inhibiting 2 receptors the binding (ACE2) of foundSARS- onCoV the- 2surface spike protein of the human to ACE2 target has cellsbeen [ 11the,12 primary]. Hence, strategy inhibiting behind the binding most SARS of SARS-CoV-2-CoV-2 vaccines spike [13,14protein], therapeutic to ACE2 has antibodies been theprimary [15,16], and strategy therapeutic behind mostsoluble SARS-CoV-2 ACE2 molecul vaccineses [17]. [13 It,14 is], evidenttherapeutic that antibodiesthe receptor [15 binding,16], and domain therapeutic (RBD) soluble of the ACE2viral spike molecules protein [17 plays]. It is a evidentcritical rolethat in the the receptor binding binding of SARS domain-CoV-2 (RBD) to ACE2. of the viral spike protein plays a critical role in the bindingAs of of 14 SARS-CoV-2 May 2021, tothere ACE2. are two therapeutic neutralizing antibody cocktails in use for theAs treatment of 14 May of 2021, COVID there-19 are patients two therapeutic that have neutralizing received emergency antibody cocktailsuse authorization in use for fromthe treatment the FDA of[15,16 COVID-19]. Regeneron’s patients REGN that have-COV2 received is a combination emergency of use two authorization anti-SARS-CoV from- 2the RBD FDA monoclo [15,16].nal Regeneron’s antibodies REGN-COV2(REGN10933 isand a combination REGN10987), of twoand anti-SARS-CoV-2Eli Lily’s cocktail RBDis a combinationmonoclonal antibodiesof two anti (REGN10933-SARS-CoV-2 andRBD REGN10987), monoclonal andantibodies Eli Lily’s (LY cocktail-CoV555 is and a combi- LY- CoV016).nation of The two emergence anti-SARS-CoV-2 of SARS RBD-CoV monoclonal-2 variants antibodies has unfortunately (LY-CoV555 caused and monoclonal LY-CoV016). antibodyThe emergence therapies of SARS-CoV-2and spike protein variants-based has vaccines unfortunately to be less caused effective monoclonal than was antibody deter- minedtherapies in the and original spike protein-based clinical studies vaccines [18,19]. to In be fact, less effectivedue to the than sustained was determined increase in in COVIDthe original-19 viral clinical variants studies that [ 18are,19 resistant]. In fact, to duethe LY to- theCoV555 sustained antibody, increase the FDA in COVID-19 recently revokedviral variants the e thatmergency are resistant use authorization to the LY-CoV555 for this antibody, monoclonal the FDA antibody recently (LY revoked-CoV555) the monotherapyemergency use [20]. authorization for this monoclonal antibody (LY-CoV555) monotherapy [20]. SARSSARS-CoV-2-CoV-2 variants variants contain contain numerous numerous mutations mutations or or deletions deletions along along the the entire entire viral viral spikespike protein, protein, but but this this report report focuses focuses on on the the key key mutations mutations in in the the RBD RBD that that have have a a direct direct impactimpact on on RBD RBD-ACE2-ACE2 interaction interaction and and the the escape escape mechanism mechanism of ofthe the virus virus from from neutraliz- neutral- ingizing antibodies antibodies.. Figure Figure 1 summarizes1 summarizes currently currently circulating circulating SARS SARS-CoV-2-CoV-2 variants variants and their and respectivetheir respective mutations mutations within within the spike the RBD, spike which RBD, whichinclude include the following the following:: N501Y N501Yin the UK,in the SA, UK, and SA, BR and-P.1 variants BR-P.1 variants [2,3]; E484K/Q [2,3]; E484K/Q in the SA, in BR the P.1, SA, BR BR P.2, P.1, NY BR, and P.2, IN NY, variants and IN [4variants–6,9,10] [;4 K417N/T–6,9,10]; K417N/Tin the SA inand the BR SA P.1 and variants BR P.1 [5,6]; variants L452R [5,6 in]; L452Rthe CA in and the IN CA variants and IN [8,10];variants S477N [8,10 ];in S477Nsome NY in some variants NY variants[9]; and Y453F [9]; and in Y453F the Denmark in the Denmark mink variant mink variant[7]. These [7]. mutationsThese mutations cause a cause higher a higherrate of viral rate ofinfectivity, viral infectivity, enhanced enhanced disease diseaseseverity, severity, and escape and es-of thecape antibody of the antibody’s’s neutralization neutralization action, action,resulting resulting in reduced in reduced vaccine vaccine efficacy efficacy [2,4,7,18] [2,4,7. ,18By]. completelyBy completely mapping mapping the SARS the SARS-CoV-2-CoV-2 RBD RBD mutations, mutations, Starr Starr et al. etwas al. able was to able demonstrate to demon- thatstrate the that RBD the containing RBD containing the E484K the E484K mutation mutation escapes escapes the LY the-CoV555 LY-CoV555 antibody, antibody, while while the RBDthe RBD containing containing the K417N/T the K417N/T mutations mutations escapes escapes the LY the-CoV016 LY-CoV016 antibody antibody [21].