Role of T cells: Understanding Exposure & Immunity to COVID-19

Role of T cells: Understanding Exposure & Immunity to COVID-19

The T cell immune response

The adaptive immune response, and in particular the T-cell response, plays a crucial role in clearing viral infections, including influenza viruses and SARS-CoV.1,2,3 Therefore, understanding the T-cell response to SARS-CoV-2 may help characterize how differences in the T-cell response early in COVID-19 could predict disease trajectory and help triage patient populations.

T cells are the first responders of the adaptive immune system and activate the antibody response. T cells, or T lymphocytes, are critical components of the adaptive immune system. Various types of T cells exist, including cytotoxic, helper, regulatory, and memory T cells. T cells play an essential role in the immune response to pathogens, including direct killing of infected cells, stimulation of antibody production by B cells, and encoding of immune memory. The T cell response itself is highly specific because there are trillions of T cells with receptors that have evolved to detect harmful pathogens making them an excellent clinical marker.

T Detect T Cell

T cells vs. antibodies

Studies show that T cell immune responses, which occur prior to the antibody response, can be detected approximately one week after the onset of COVID-19 symptoms.4,5,6 In one study, SARS-CoV-2 specific CD4+ and CD8+ T cells were detected in 100% and 80% of patients, respectively.7 CD4+ and CD8+ T-cell responses have been observed in patients with both mild and severe COVID-19 disease, and this T-cell response has been shown to be both robust and diverse.8,9 Notably, a higher proportion of CD8+ T-cells are seen in patients with mild symptoms, suggesting a possible protective effect from the cytotoxic CD8+ response.8,9 T cells generate immune responses to various regions of the SARS-CoV-2 virus, providing a more comprehensive understanding of the immune response in COVID-19.10

We observe that with the SARS-CoV-2 virus, as with many other pathogens, the T cell response provides a key link to understanding exposure and immunity when it comes to COVID-19.

Why T cells?

  • T cells responses arise earlier than antibodies and last through clearance into convalescence.11
  • T cells play a critical role in supporting the development of antibodies by B cells and can serve as the first signs of an immune response to SARS-CoV-2 infection.12
  • T cells specific to SARS-CoV-2 were observed up to several months after the primary infection.13
  • T cells develop responses to various parts of a virus; this makes T cell tests highly specific and robust compared to antibody tests, which might not capture the entire immune response.14,15
  • Early studies show T cell immune response correlates with disease severity.16
T Detect Virus Cell

Solving a big data problem to study the T cell

Trillions of T cells means millions of sequences. What makes the task of studying T cells daunting is that T cells have been historically notoriously hard to study.

Our bodies have hundreds of millions of different T cells in order to be prepared to respond to millions of different types of threats. Most researchers have continued to rely on techniques to either measure the immune response solely based on antibody levels, or sometimes measuring T cells using techniques that are expensive, bespoke and low throughput.

Learn more about Adaptive’s platform that enables the identification of specific T cells

For Patients

The T-Detect COVID Test can detect past infection months after exposure.

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For Physicians

The T-Detect COVID Test may capture COVID-19 infections missed by serology tests.

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For Employers

The T-Detect COVID Test can help your employees get the answers they need.

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For Researchers

Learn how you can use the T-Detect COVID Test for research purposes.

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In vitro diagnostic for prescription use only. This test has not been cleared or approved by the FDA. The T-Detect COVID Assay is available for use as a CLIA-validated laboratory developed test (LDT). T-Detect COVID is not indicated for use in patients under age 18.


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  2. Oh H-LJ, et al. Emerg Microbes Infect. 2012;1(1):1-6. doi:10.1038/emi.2012.26.
  3. Tang F, et al. J Immunol. 2011;186(12):7264- 7268. doi:10.4049/jimmunol.0903490.
  4. Cox RJ, et al. Nat Rev Immunol. 2020;20(10):581-582. doi:10.1038/ s41577-020-00436-4.
  5. Tay MZ, et al. Nat Rev Immunol. 2020;20(6):363-374. doi:10.1038/ s41577-020-0311-8.
  6. Gallais F, et al. medRxiv. Published online June 6, 2020. 2020.06.21.20132449; doi:10.1101/2020. 06.21.20132449.
  7. Weiskopf D, et al. Sci Immunol. 2020; 5(48):eabd2071. doi:10.1126/sciimmunol. abd2071.
  8. Swadling L, et al. Nat Immunol. 2020;21:1307–1308. doi:10.1038/s41590- 020-0798-y.
  9. Peng Y, et al. Nat Immunol. 2020;21(11):1336-1345. doi:10.1038/ s41590-020-0782-6
  10. Grifoni A, et al. Cell. 2020;181(7):1489- 1501.e15. doi:10.1016/j.cell.2020.05.015.
  11. Funk CD, et al. Front Pharmacol. 2020;11. doi:10.3389/fphar.2020.00937.
  12. Sekine T, et al. Cell. 2020;183(1):158-168.e14. doi:10.1016/j.cell.2020.08.017. ​
  13. Zuo J, et al. Robust SARS-CoV-2-specific T-cell immunity is maintained at 6 months following primary infection. bioRxiv. 2020.
  14. Gutierrez L, et al. Deciphering the TCR Repertoire to Solve the COVID-19 Mystery. Trends Pharmacol Sci. 2020.
  15. Poland GA, et al. SARS-CoV-2 immunity: review and applications to phase 3 vaccine candidates. Lancet. 2020.
  16. Gittelman RM, et al. Diagnosis and tracking of past SARS-CoV-2 infection in a large study of Vo’, Italy through T-cell receptor sequencing. medRxiv. 2020.