Does the answer to Covid-19 lie back in 2003?
The COVID-19 pandemic is the biggest public-health crisis in a century, and the development of medical interventions to combat the SARS-CoV-2 coronavirus is a top priority. Writing in Nature, Pinto et al. provide evidence needed to take one of the crucial first steps for such efforts in the developing arena of antibody immunotherapy.
The level of protection provided by the immune system in response to SARS-CoV-2 exposure and infection is a hotly debated topic2. It is thought that one major arm of the immune response to such infection is the development of antibodies that recognize the virus. Of particular interest are antibodies that bind to a protein on the viral surface known as the spike protein. Coronaviruses derive their name from their distinctive, crown-like (coronal) viral silhouettes, which are due to these proteins.
Antibodies that recognize and bind to the viral ‘spike’ can block its ability to bind the ACE2 receptor protein on human cells. An interaction between the spike protein and ACE2 is part of a process that can enable coronaviruses to enter human cells. Thus, antibodies that could hinder spike-protein function would block infection; such antibodies are termed neutralizing antibodies. Much remains to be learnt about the immunological responses to SARS-CoV-2. Nevertheless, it is becoming clear that antibodies taken from the blood serum of people who have recovered from COVID-19 can be used for treatment by being transfused into other people who have the disease3.
Such ‘convalescent sera’ approaches are highly attractive, particularly as an immediate treatment option. That’s because more-conventional therapeutics, such as drugs or vaccines, are unlikely to be available for some time. A more high-tech approach to using convalescent sera is the manipulation of antibody-producing B cells taken from the blood of people who had COVID-19 or other coronavirus infections. Each B cell makes one unique antibody, and clonal populations of a B cell of interest can be used to generate an identical pool of a particular desired antibody known as a monoclonal antibody. To accelerate the process of therapeutic development, Pinto and colleagues ‘went back in time’, and turned to samples of B cells collected from a person who had been infected by the coronavirus SARS-CoV. This virus, which is similar to SARS-CoV-2, caused an outbreak in 2003 of a disease called severe acute respiratory syndrome (SARS). The hope with such an approach is that the resemblance between the two viruses might mean that some antibodies that recognize SARS-CoV also recognize and neutralize SARS-CoV-2.