Evaluation of a Commercial Culture-free Neutralization Antibody Detection Kit for Severe Acute Respiratory Syndrome-Related Coronavirus-2 and Comparison with an Anti-RBD ELISA Assay

Papenburg, Jesse; Cheng, Matthew P; Corsini, Rachel; Caya, Chelsea; Mendoza, Emelissa; Manguiat, Kathy; Robbin Lindsay, L; Wood, Heidi; Drebot, Michael A; Dibernardo, Antonia; Zaharatos, Gerasimos; Bazin, Reneé; Gasser, Romain; Benlarbi, Mehdi; Gendron-Lepage, Gabrielle; Beaudoin-Bussières, Guillaume; Prévost, Jérémie; Finzi, Andrés; Ndao, Momar; Yansouni, Cedric P

BACKGROUND: SARS-CoV-2 surrogate neutralization assays that obviate the need for viral culture offer substantial advantages regarding throughput and cost. The cPass SARS-CoV-2 Neutralization Antibody Detection Kit (Genscript) is the first such commercially available assay, detecting antibodies that block RBD/ACE-2 interaction. We aimed to evaluate cPass to inform its use and assess its added value compared to anti-RBD ELISA assays. METHODS: Serum reference panels comprising 205 specimens were used to compare cPass to plaque-reduction neutralization test (PRNT) and a pseudotyped lentiviral neutralization (PLV) assay for detection of neutralizing antibodies. We assessed the correlation of cPass with an ELISA detecting anti-RBD IgG, IgM, and IgA antibodies at a single timepoint and across intervals from onset of symptoms of SARS-CoV-2 infection. RESULTS: Compared to PRNT-50, cPass sensitivity ranged from 77% - 100% and specificity was 95% - 100%. Sensitivity was also high compared to the pseudotyped lentiviral neutralization assay (93% [95%CI 85-97]), but specificity was lower (58% [95%CI 48-67]). Highest agreement between cPass and ELISA was for anti-RBD IgG (r=0.823). Against the pseudotyped lentiviral neutralization assay, anti-RBD IgG sensitivity (99% [95%CI 94-100]) was very similar to that of cPass, but overall specificity was lower (37% [95%CI 28-47]). Against PRNT-50, results of cPass and anti-RBD IgG were nearly identical. CONCLUSIONS: The added value of cPass compared to an IgG anti-RBD ELISA was modest.