T cells: The unsung heroes of the immune system

T cells are white blood cells that contribute both brains and brawn to help make the immune system our body’s most powerful tool to fight disease. T cells are the first responders in the adaptive immune system—the system that takes over when the body’s innate immunity isn’t enough to fight off an invader.

Although they’re often underappreciated, T cells play a key role in not only our defense against infections and cancers, but also in our ability to understand how to treat or prevent them in the future.

How T cells work

When you’re exposed to a pathogen or germ—such as a virus or harmful bacteria—T cells jump into action immediately. They kill infected cells and stimulate B cells to produce antibodies, which circulate in the blood to look for remaining traces of the virus and bind to them so T cells can destroy them.1

This process kicks in when someone is infected with a pathogen such as SARS-CoV-2 (the virus that causes COVID-19) or even the common cold.2,3,4

There are three types of T cells at work within the immune response:1

  • Killer T cells (CD8): The front-line army of the immune system, these killer cells find and destroy “enemy” cells that are replicating pathogens in our bodies. By recognizing antigens (foreign substances in the body that trigger an immune response), killer T cells find infected cells and terminate them.
  • Helper T cells (CD4): These cells act like coaches or commanders, using chemical messages to help B cells and killer T cells create more of themselves to fight the infection harder. B cells mature and become plasma cells, which make antibodies.
  • Memory T cells (CD4 and CD8): Memory cells remain long-term, even after an infection is no longer in the body. These cells help the body recognize and fight off germs more easily the next time, making it more difficult to get reinfected with certain diseases.

Some viruses—including the flu, the common cold or even SARS-CoV-2 (the virus that causes COVID-19)—must be fought off repeatedly because they change and mutate over time.

T cells versus antibodies: how are they different?

T cells and antibodies are both critical in the immune system’s fight, but there are a few differences between the two.

  • T cells start first and stay longer: Killer T cells kick off the immune response, activating B cells to produce antibodies. They spring into action shortly after a new infection, often before symptoms begin—and in some infections we know they stay in the body longer, while antibodies tend to wane more quickly.1
  • T cells target a broader response: T cells develop highly targeted responses to various parts of a pathogen, each playing a very specialized role in the body’s overall immune response. Their receptors are extraordinarily specific and diverse, able to recognize and differentiate between the millions of antigens our bodies are continuously exposed to.
  • T cells may have activity that continues even in patients whose antibody response is compromised: Studies have shown that patients deficient in antibodies still have robust T-cell activity, which may help us further understand how to treat these critical populations.5-9

How can T cells help inform better healthcare decisions?

Studying T-cell responses provides a wealth of information. Not only can they help detect and diagnose disease, they may also help measure disease severity.

T cells may also give us key insights into vulnerable immunocompromised population groups that may not make sufficient antibodies. Studying the full adaptive immune response—both antibodies and T cells—may be the only way to answer critical questions for these populations.

T-cell testing may also add a critical dimension to how individual or population immunity is measured. With COVID-19, it has been shown to perform as well or better than antibody testing in a clinical study.10, 12

T cells can provide insight into which specific parts of a pathogen induce an immune response, and this could contribute to the next generation of vaccines or therapeutics.11

The T-Detect test

The T-Detect test from Adaptive Biotechnologies uses the power of T cells to provide information about a person’s adaptive immune response. T-Detect COVID, the first-ever T-cell-based clinical test to receive FDA emergency use authorization (EUA), can determine whether a person has had a recent or prior adaptive immune response to SARS-CoV-2.

COVID-19 is the first of many potential diseases Adaptive hope to detect by looking at the T-cell response. It’s our goal to use future versions of T-Detect to help diagnose many different illnesses using the immune system’s natural abilities.


T Detect Patient Action Home

For Patients

In a study, T-cell responses were detected up to 15 months after initial COVID-19 infection with 86% sensitivity.12

Learn More
T Detect Physicians Action

For Physicians

T-Detect COVID can capture past COVID-19 infections that may be missed by serology testing.

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  1. Alberts B, et al. Helper T Cells and Lymphocyte Activation. Molecular Biology of the Cell. 4th edition. 2002. https://www.ncbi.nlm.nih.gov/books/NBK26827/.
  2. Hufford MM, et al. Curr Top Microbiol Immunol. 2015;386:423-455. doi:https://doi.org/10.1007/82_2014_397.
  3. Callister SM, et al. Clin Infect Dis. 2016;62(10):1235-1241. https://doi.org/doi:10.1093/cid/ciw112.
  4. Moss P. Nat Immunol. 2022;(2):186-193. https://doi.org/doi:10.1038/s41590-021-01122-w.
  5. Kinoshita H., Durkee-Shock J., Jensen-Wachspress M., et al. Robust Antibody and T Cell Responses to SARS-CoV-2 in Patients with Antibody Deficiency. J Clin Immunol, 41: 1146–1153. 2021. https://doi.org/10.1007/s10875-021-01046-y.
  6. Apostolidis S., Kakara M., Painter M., et al. Cellular and humoral immune responses following SARS-CoV-2 mRNA vaccination in patients with multiple sclerosis on anti-CD20 therapy. Nat Med. September 14, 2021. doi:https://doi.org/10.1038/s41591-021-01507-2.
  7. Bange E.M., Han N.A., Wileyto P., et al. CD8+ T cells contribute to survival in patients with COVID-19 and hematologic cancer. Nat Med. May 20, 2021. doi:https://doi.org/10.1038/s41591-021-01386-7.
  8. Kearns P., Sibert S., Willicombe M., et al. Examining the immunological effects of COVID-19 vaccination in patients with conditions potentially leading to diminished immune response capacity – the OCTAVE trial. Preprint with Lancet. August 23, 2021. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3910058.
  9. Katz J.D., Bouley A.J., Jungquist R.M., et al. Humoral and T-cell response to SARS-CoV-2 vaccination in multiple sclerosis patients treated with ocrelizumab. Multiple Sclerosis and Related Disorders. November 2021.
  10. Dalai S, et al. Clinical validation of a novel T-cell receptor sequencing assay for identification of recent or prior SARS-CoV-2 infection. Clin Infect Dis. 2022. doi:10.1093/cid/ciac353.
  11. Dan J.M., et al. Immunological memory to SARS-CoV-2 assessed for greater than six months after infection. bioRxiv. doi: https://doi.org/10.1101/2020.11.15.383323.
  12. Gittelman RM, et al. Longitudinal analysis of T cell receptor repertoires reveals shared patterns of antigen-specific response to SARS-CoV-2 infection. JCI Insight. 2022. doi:10.1172/jci.insight.151849.

T-Detect COVID is not FDA cleared or approved. It is authorized for emergency use under an Emergency Use Authorization (EUA). 

T-Detect is not indicated for use in patients under age 18.