Since the novel coronavirus emerged at the end of 2019, scientists around the world, including immunologist Dan Barouch, The William Bosworth Castle Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, have been developing vaccines to protect against COVID-19 and to put an end to the pandemic. As of November 2020, three pharmaceutical companies released early data showing high rates of protection in phase III human trials for their vaccines, but questions remain about how the body develops and maintains immunity after vaccination or infection.
In a new paper in the journal Nature, Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess, and colleagues shed light on the role of antibodies and immune cells in protection against SARS-CoV-2, the virus that causes COVID-19, in rhesus macaques. “In this study, we define the role of antibodies versus T cells in protection against COVID-19 in monkeys. We report that a relatively low antibody titer [the concentration of antibodies in the blood] is needed for protection,” said Barouch. “Such knowledge will be important in the development of next-generation vaccines, antibody-based therapeutics and public health strategies for COVID-19.”
Building on previous findings that SARS-CoV-2 infection protects rhesus monkeys from re-exposure, Barouch and colleagues purified and collected antibodies from animals that had recovered from infection. They administered the antibodies at various concentrations to 12 uninfected macaques and observed that protection against SARS-CoV-2 challenge was dose-dependent. Animals that received higher amounts of antibodies were protected more completely, while animals that received lower amounts of antibodies were less protected. Similarly, when the researchers administered various concentrations of the purified antibodies to six macaques with active SARS-CoV-2 infection, those given higher doses demonstrated more rapid viral control.
In a second set of experiments, Barouch and colleagues evaluated the role of specific immune cells, CD8+ T cells, in contributing to protection against SARS-CoV-2 infection by removing these cells from animals that had recovered from the virus. Removal of these immune cells left the animals vulnerable to infection after re-exposure to SARS-CoV-2.
“Our data define the role of antibodies and T cells in protection against COVID-19 in monkeys. Antibodies alone can protect, including at relatively low levels, but T cells are also helpful if antibody levels are insufficient,” said Barouch, who is also a steering committee member of the Ragon Institute of MGH, MIT and Harvard. “Such correlates of protection are important given the recent successful vaccine results from human trials and the likelihood that these and other vaccines will become widely available in the spring. As a result, future vaccines may need to be licensed based on immune correlates rather than clinical efficacy.”