Study highlights role of IgG antibodies that bind to the receptor binding domain (RBD) of the SARS-CoV-2, and not the IgG antibodies that bind to the whole viral protein mix, as an excellent surrogate measurement to estimate neutralising antibodies
While intensive efforts continue to focus on development of an effective vaccine, anti-viral or other therapeutic entity, plasma therapy is currently being widely explored as an interim strategy to treat COVID-19.
A recent study by ICMR while raising the lack of benefits from plasma therapy, has highlighted the urgent need for prior measurement of neutralising antibody titres in donors and participants, which may better aid in delineating the role of plasma therapy in management of COVID-19.
Neutralising antibodies, typically of IgG subclass that can potentially block viral infection, are key components for the success of plasma therapy and titers of >320 are generally considered most suitable for successful plasma therapy. Currently, however, mere presence of IgG antibody, regardless of its neutralising ability, is used as a selection criterion for donor convalescent plasma because assessment of neutralising antibodies in routine clinical samples remains a challenge.
Thus, it is important to note that we have insufficient knowledge to understand whether all donors had sufficient titers of neutralising antibodies to donate plasma, and whether these titers reflected in all recipients that received the transfusion.
In this direction, a new ICMR funded study led by Drs Anmol Chandele and Kaja Murali Krishna of ICGEB-Emory Vaccine Center at the International Centre for Genetic Engineering and Biotechnology, in collaboration with ICMR-National Institute of Malaria Research, Department of Biotechnology and the Emory Vaccine Center, Atlanta gives new hope to improve plasma therapy regimen in India1.
This study finds that nearly half of the COVID-19 recovered individuals examined did not have appreciable levels of neutralising antibodies despite having SARS-CoV-2 specific IgG. More importantly, this study finds that it was IgG antibodies that bind to the receptor binding domain (RBD) of the SARS-CoV-2, and not the IgG antibodies that bind to the whole viral protein mix, served as an excellent surrogate measurement to estimate neutralising antibodies. They report that RBD binding IgG titers of more than 1:3000 indicate neutralising antibody levels of more 1:320, a titer which is likely to increase chances of success with plasma therapy.
It is important to note that many Indian government agencies and institutions are already making efforts to bring these RBD-based IgG assays more widely available, and thus this study is very relevant and timely to scientifically validate these efforts. It is notable that the Translational Health Sciences and Technology Institute (THSTI), which is another institute within the Delhi NCR biocluster, has made available an in-house RBD IgG ELISA assay that was recently used for a sero-survey in Pune and very recently RBD IgG assay facility is has been inaugurated in Nagpur.
These basic research efforts currently pursued at the ICGEB-Emory Vaccine Center to understand human immunology of COVID-19 infections in India, gives renewed hope to tailor and improve plasma therapy in India.
References:
- https://www.biorxiv.org/content/10.1101/2020.08.31.276675v1