Many have embraced antibodies and the possibility of immunity to COVID-19 as the key to reopening society and the economy. Serology testing – also known as antibody testing – can indicate whether someone is producing an immune response to the virus.

But we still do not know whether the presence of antibodies in recovered patients holds promise for long-lasting immunity. Insight from immunological studies on recovered SARS patients infected in 2003 showed that antibody levels wane after just a few years. A different immune response caused by T cells provides long term protection, even 11 years post-infection.

Based on this data, it is likely that T cell responses play a substantial role in developing protective immunity against SARS-CoV-2, the virus that causes COVID-19. There are two main types of T cells: helper and killer T cells. When they recognize a virus, helper T cells signal to activate other types of immune cells, while killer T cells release molecules that destroy the virus. 

In a new study published in the journal Cell, researchers at the La Jolla Institute for Immunology identified viral protein pieces in SARS-CoV-2 that are already known to induce T cell immune responses. They then exposed the immune cells from ten recovered COVID-19 patients to these protein pieces and measured the T cell immune responses.

All of the patients had helper T cells that recognized the main SARS-CoV-2 spike protein, and about 70% of them also had killer T cells that recognized the spike and membrane proteins. The main target of the 100+ vaccines for COVID-19 in development is the antibody response to the spike protein, but this new understanding of the T cell response could provide new and potentially better targets.

The mission to make a vaccine against COVID-19 is possibly the most urgent public health problem in the world today. The encouraging results in both the similarities in immune response to SARS and SARS-CoV-2 and the identification of strong T cell responses in recovered COVID-19 patients promote further research in designing vaccines to induce T cell responses.