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, J.; Cheng, M. P.; Corsini, R.; Caya, C.; Mendoza, E. J.; Manguiat, K. J.; Wood, H.; Drebot, M.; Zaharatos, G.; Bazin, R.; Beaudoin-Bussieres, G.; Prevost, J.; Finzi, A.; Ndao, M.; Yansouni, C. P.

Background: SARS-CoV-2 surrogate neutralization assays that bypass 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 were used to compare cPass to plaque-reduction neutralization test (PRNT) and a pseudotyped lentiviral neutralization 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 had 100% sensitivity (95%CI 82-100) and 95% specificity (76-100). Sensitivity was also very high compared to the pseudotyped lentiviral neutralization assay, but specificity was lower, ranging from 17-70%. Highest agreement between cPass and ELISA was for anti-RBD IgG (r=0.851 at 0-6 weeks; r=0.798 at > 6 weeks). Anti-RBD IgG diagnostic accuracy for detection of neutralizing antibodies was essentially identical to that of cPass. Conclusions: The added value of cPass compared to an IgG anti-RBD ELISA was not supported by these results.