Nearly half the people who have recovered from COVID-19 may not have appreciable levels of neutralising antibodies needed to qualify as ideal plasma donors to other COVID-19 patients, according to a new study1.
The study, conducted on 42 patients who had recovered from COVID-19 at Indian government medical facilities in Haryana, Uttar Pradesh and Delhi, found that despite having the SARS-CoV-2 specific antibodies IgG, 21 of them did not have ‘appreciable levels’ of neutralising antibodies, 7 had sufficiently high levels and the rest 14 had intermediate levels.
Neutralising antibodies, typically of the IgG subclass, block viral infection and determine the success of convalescent plasma therapy, where plasma from a recovered patient is used to treat another patient. A titer test, showing the amount of antibodies within a person's blood, can point to the most suitable levels of neutralising antibodies. A titer score of over 320 is generally considered ideal for plasma therapy. In this study, only 7 of the 42 COVID-19 recovered people showed a neutralising titer score above 320.
The study, published preprint (yet to be peer reviewed), also found that the IgG antibodies that bound to the receptor binding domain (RBD) of the SARS-CoV-2 are a better measure of the amount of neutralising antibodies than the IgG antibodies that bind to the entire viral protein mix.
Currently, the mere presence of IgG antibody, regardless of its neutralising ability, is used as a selection criterion for donor convalescent plasma. This is because assessment of neutralising antibodies in routine clinical samples remains a challenge due to several practical issues associated with biosafety requirements to handle live viruses.
The authors say choosing individuals with sufficiently high neutralising titers as plasma donors could increase the success of convalescent plasma therapy.
(The authors of this work are from: International Centre for Genetic Engineering and Biotechnology, Emory Vaccine Centre and ICMR-National Institute of Malaria Research, New Delhi, India.)
1. Nayak, K. et al. Characterization of neutralizing versus binding antibodies and memory B cells in COVID-19 recovered individuals from India. bioRxiv (2020) doi: 10.1101/2020.08.31.276675