Analysis of SARS-CoV-2 Antibodies in COVID-19 Convalescent Plasma using a Coronavirus Antigen Microarray

Rafael R. de Assis; Aarti Jain; Rie Nakajima; Algis Jasinskas; Jiin Felgner; Joshua M. Obiero; Oluwasanmi Adenaiye; Sheldon Tai; Filbert Hong; Philip Norris; Mars Stone; Graham Simmons; Anil Bagri; Martin Schreiber; Andreas Buser; Andreas Holbro; Manuel Battegay; Donald K. Milton; Huw Davies; Laurence M. Corash; Michael P. Busch; Philip L. Felgner; Saahir Khan

This study reveals several insights into the antibody response to SARS-CoV-2 infection. The antibody profiles of naïve individuals include high IgG reactivity to common cold coronaviruses with low-level cross-reactivity with S2 domains from SARS-CoV-2 and other epidemic coronaviruses, which is not surprising given the high degree of sequence homology and previously observed serologic cross-reactivity 15 between S2 domains of betacoronaviruses, a group that includes SARS-CoV-2, SARS-CoV, MERS, and common cold coronaviruses HKU1 and OC43. However, naïve individuals do not show crossreactivity to other SARS-CoV-2 antigens. Even for the nucleocapsid protein, which also has high sequence homology between betacoronaviruses, cross-reactivity is only seen between SARS-CoV-2 and SARS-CoV and not with MERS-CoV or common cold coronaviruses. In addition, the quantitative difference between high antibody reactivity to SARS-CoV-2 S2 in the positive group and low-level antibody cross-reactivity in the negative group is large enough that these antigens still discriminate these groups with high significance. This study also informs antigen selection and design for population surveillance and clinical diagnostic assays and vaccine development. The observation that naïve individuals with antibodies to common cold coronaviruses do not show cross-reactivity to SARS-CoV-2 nucleocapsid protein dispels concerns that the high sequence homology of this protein across betacoronaviruses would impair its performance as a diagnostic or vaccine antigen. The low-level antibody cross-reactivity of naïve individuals for SARS-CoV-2 spike protein containing S2 domain may not preclude its use as a diagnostic antigen given large quantitative difference in antibody reactivity between positive and negative groups, but this cross-reactivity may influence response to vaccination with spike protein antigens containing the S2 domain. The coronavirus antigen microarray can be useful both as an epidemiologic tool and as a research tool. The high throughput detection of SARS-CoV-2-specific antibody profiles that reliably distinguish COVID-19 cases from negative controls can be applied to large-scale population surveillance studies for a more accurate estimation of the true prevalence of disease than can be achieved with symptom-based PCR testing. In addition, detection of these antibodies in SARS-CoV-2 convalescent plasma donations can provide validation prior to clinical use for passive immunization. The variation in the SARS-CoV-2 antibody profiles among acute and convalescent donors suggests that epitope characterization of convalescent donor plasma will be informative for evaluation of passive immune therapy efficacy in COVID-19 patients. The central role of inflammation in the pathogenesis of severe COVID-19 16 can be more closely studied by analyzing both strain-specific and cross-reactive antibody responses, particularly to test hypotheses regarding antibody-dependent enhancement with critical implications for vaccine development 17 .