Now a T-cell-based clinical test for COVID-19
Our interest in the significance of T-cell immunity in fighting SARS-CoV-2 infection and in providing resistance to re-infection is only growing more. Now, we have the first clinical T-cell-based test for patients to confirm recent or prior COVID-19 infection.
So far, we have heavily relied upon SARS-CoV-2 antibodies to test if a person has been exposed to the virus.
Also, neutralizing antibody (nAb) response has been the key to establishing protection against the virus, not because it is the best mechanism, but simply because it is easier to measure them. 
Now, routine T-cell testing has entered a new era after the US Food and Drug Administration (FDA) gave Emergency Use Authorization (March 05, 2021) to "T-Detect" COVID-19 test (Adaptive Biotechnologies). 
It is a laboratory-based next-generation sequencing test that identifies T cells that recognize SARS-CoV-2 antigens.
The test aims to identify individuals with an adaptive T cell immune response to SARS-CoV-2 by analyzing DNA sequences from T cells, where a positive test indicates recent or previous SARS-CoV-2 infection. In contrast, a negative test result means that a patient is unlikely to have been infected with the virus. 
T-Detect COVID Test is a lab-based procedure with a seven- to ten-day turnaround time and meant for samples taken at least 15 days after symptom onset. A test can detect T cell response in the blood several days after initial infection.
The T-Detect COVID assay showed 97.1% sensitivity (positive percent agreement) and 100% specificity (negative percent agreement) compared to RT- PCR testing from 15 days or more after diagnosis. 
Thus, it is not meant to diagnose an active infection. Instead, it works as a complement to antibody tests to confirm recent or previous infections.
- A negative result does not preclude an ongoing or acute SARS-CoV-2 infection.
- The test should not be used to diagnose current SARS-CoV-2 infection.
- It is a valuable tool to determine if a person previously had COVID-19.
- The test results are meant to be used in combination with clinical findings, patient medical history, and other findings.
The test will be of great help for individuals who may have exhibited symptoms previously and suspect an exposure previously but have not tested positive for COVID-19 using an RT PCR or rapid antigen test.
Patients can now order T-Detect COVID online at www.t-detect.com by answering a few eligibility questions. 
Limitations of T cell response:
We still do not know how long after infection the T cell immune response remains and the level of protection it provides.
- Sheridan, C. COVID-19 testing turns to T cells. Nat Biotechnol 39, 533–534 (2021). https://doi.org/10.1038/s41587-021-00920-9
- Coronavirus (COVID-19) Update: FDA Authorizes Adaptive Biotechnologies T-Detect COVID Test. https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-adaptive-biotechnologies-t-detect-covid-test
- Sudeb C. Dalai, Jennifer N. Dines, Thomas M. Snyder, et al. Clinical Validation of a Novel T-cell Receptor Sequencing Assay for Identification of Recent or Prior SARS-CoV-2 Infection. medRxiv 2021.01.06.21249345; doi: https://doi.org/10.1101/2021.01.06.21249345
Adaptive Biotechnologies Launches T-Detect™ COVID, First Clinical T-Cell Based Test for Patients to Confirm Recent or Prior COVID-19 Infection. https://www.globenewswire.com/en/news-release/2021/02/23/2180346/0/en/Adaptive-Biotechnologies-Launches-T-Detect-COVID-First-Clinical-T-Cell-Based-Test-for-Patients-to-Confirm-Recent-or-Prior-COVID-19-Infection.html