The need for and challenges of comparing SARS?CoV?2 antibody assays

Since its appearance in Wuhan, China, late December 2019, the novel coronavirus SARS-CoV-2 has rapidly spread, causing over 1.2 million deaths worldwide as of early November 2020.1 Currently, no targeted therapy is available for associated disease COVID-19, but several options are being investigated, including COVID-19 convalescent plasma (CCP). Its use relies on principle passive immunity. One largest experiences comes from Mayo Clinic expanded access program (EAP) United States.2 The goal was to increase CCP availability adults phase pandemic. Starting March 2020, donors were qualified by PCR-based evidence infection and a sufficient recovery time interval; antibody testing not widely available. Several different assays have since obtained regulatory approval States.3 Retrospective analysis EAP data showed that CPP transfusion safe. Higher levels with improved mortality when population subset (3082 patients) analysed. safety suggestion dose-response contributed Food Drug Administration issuing an emergency authorization (EUA) August 23, 2020. Of note, expert panel did comment limitations EAP.4 In European Union (EU), treatments occurred predominantly randomised clinical trials except specific compassionate programmes.5 challenge determining stems complexity responses. For instance, some patients, T-cell response may dominate explaining why recovered few antibodies.6 Antibodies prevent viral entry into host cells called neutralising antibodies considered most effective. gold standard method determination plaque reduction (PRNT) infected cell cultures requires live virus. These must be performed high containment biosafety level 3 (BSL 3) laboratories. Alternative using pseudovirus still require BSL 2 facilities. Despite deployed EU countries selecting ongoing trials, such nor easy scale up, especially if future needs increase. contrast, immunoassays more accessible compatible 1 laboratories vary their sensitivity anti-SARS-CoV-2 immunoglobulins (IgG and/or IgM). Immunoassays directly detect inhibition (recombinant) proteins receptors commercially (eg, AcroBiosystems, Newark, DE) or under development good correlation virus neutralisation suggested.7, 8 Most arbitrarily define bottom threshold based titre measurements assays. 1:320 means only inhibits 50% activity at dilution vitro will included trials. This however differ trial design donor because robust scientific rationally justify strict cut-off titre. addition, titres depending assay performance precise efficacy proven. Depending used protocol followed, each programme can establish own policy.9 States, EUA specifically calls assayed Ortho Vitros IgG SARS-CoV-2.10 Because many blood collection centres already implemented other assays, it very difficult logistically them change platforms. Furthermore, reliance single poses risks case supply chain constraints critical reagent shortages. Therefore, correlations established between various tests so amended include Harvala colleagues described comparison (micro)neutralisation assay, reporter (RVPN) four enzyme-linked (ELISAs) targeting spike protein.11 determine optimal immunoassay values corresponding adequate levels. A 1:100 selected arbitrarily.9 this study, 43% samples 52 April 2020 exceeded 1:100, which implications given physicians favour transfusing higher units. Blood need encourage return also recruitment decrease time.12 All ELISAs detected strongest EUROimmun IgG. Selecting signal 9.1 successfully excluded 26 below threshold. Lower cut-offs increased risk false positives, is, possibility contains insufficient antibodies. However, reading identified 65% above threshold,11 illustrating delicate balance accepting units low discarding sufficiently positive negative predictive depend seroprevalence, locations,13 whether screening provide proof past infection. findings mirror recent reports.14, 15 Luchsinger found had modest varying accuracy predicting activity. Goodhue suggested two-step scheme undergo reflex testing. Thus, either met. To support wider CCP, equivalent reports shown complicated differences responses binding vs Novel quick reliable measure presence wide dynamic range developed. authors declare competing interests.