New findings suggest that the SARS-CoV-2 virus damages an important immune-cell response.
The quality of CD8+ T cell response to two doses of the Pfizer-BioNTech Covid-19 vaccine was considerably lower in people with prior SARS-CoV-2 infection compared to people without prior infection, the US study found.
In addition, the level of this T cell was substantially lower in unvaccinated people with Covid-19 than in vaccinated people who had never been infected. Importantly, people who recover from SARS-CoV-2 infection and then get vaccinated are more protected than people who are unvaccinated.
The study was co-funded by the National Institute of Allergy and Infectious Diseases (NIAID) and led by Mark M Davis, Director of the Stanford Institute for Immunity, Transplantation and Infection and a professor of microbiology and immunology at Stanford University School of Medicine in California.
Lower CD8+ T cell response
Dr Davis and colleagues used a very sensitive tool to analyse how CD4+ T cells and CD8+ T cells respond to SARS-CoV-2 infection and vaccination.
The tool was designed to identify T cells that target any of dozens of specific regions on the virus’s spike protein as well as some other viral regions. The Pfizer-BioNTech vaccine uses parts of the SARS-CoV-2 spike protein to elicit an immune response without causing infection.
The researchers found that vaccination of people who had never been infected with SARS-CoV-2 induced robust CD4+ and CD8+ T-cell responses to the virus’ spike protein. In addition, these T cells produced multiple types of cytokines.
However, people who had been infected with SARS-CoV-2 prior to vaccination produced spike-specific CD8+ T cells at considerably lower levels and with less functionality. Moreover, the researchers observed substantially lower levels of spike-specific CD8+ T cells in unvaccinated people with Covid-19 than in vaccinated people who had never been infected.
Taken together, these findings suggest that SARS-CoV-2 infection damages the CD8+ T cell response. The effect is similar to that in earlier studies showing long-term damage to the immune system after infection with viruses such as hepatitis C or HIV.
The new findings highlight the need to develop vaccination strategies to specifically boost antiviral CD8+ T cell responses in people previously infected with SARS-CoV-2, the researchers conclude.