The COVID-19 pandemic is caused by the SARS-CoV-2 virus, a new member of the coronavirus group. The virus can cause asymptomatic infection or mild flu-like symptoms. Pneumonia and respiratory failure requiring mechanical ventilation represent more severe illness.
In recent studies, cell-mediated immunity to the COVID-19 coronavirus has been found in healthy individuals who have never been exposed to the virus. Immunity in unexposed individuals may result from prior exposure to human coronaviruses which cause up to 15% of flu-like illness in adults and are similar to SARS-CoV-2. Antibodies to the virus develop after COVID-19 infection. Antibodies may fail to develop in some or may be short-lived in others.
A majority of the US population has now received at least one dose of the COVID-19 vaccine. Vaccination also leads to antibody formation in most healthy immunocompetent individuals. However, antibody is detected in roughly half of most immunocompromised individuals, who have been vaccinated. Immunocompromised individuals are those who are receiving immunosuppressive drugs for organ transplants, autoimmune diseases or other illnesses, or those who are immune deficient. While additional vaccine doses have led to antibody formation in some of these individuals, such ‘booster” doses have yet to become the standard of care.
Assessing immunity to the COVID-19 coronavirus is an important goal as people return to school, work, and entertainment. Individuals 60 years or older, those with underlying chronic conditions like diabetes and cardiovascular disease, and immunocompromised individuals may be especially vulnerable during this period.
PlexCOVID-19 is a lab-developed blood test that measures cellular immunity to SARS-CoV-2. Severe forms of COVID-19 infection may be associated with decreased cell-mediated immunity to SARS-CoV-2. COVID-19 vaccination can enhance cell-mediated immunity in healthy immunocompetent and some immunocompromised individuals.
Knowledge about cell-mediated immunity to SARS-CoV-2 can be combined with available clinical data and laboratory data to assess patient immune status toward the COVID-19 coronavirus. Available laboratory data may include previous antibody test results or cell mediated immunity results.
PlexCOVID-19 measures functional cell-mediated immunity to the COVID-19 coronavirus. T-cells and B-cells, which express the inflammatory marker, CD154 are measured after stimulation with the spike antigens of this virus. Three different spike antigens are used in this test: S1 is specific for SARS-CoV-2, S2, is present in SARS-CoV-2 and human coronaviruses, and the complete spike antigen, S is a combination of S1 and S2. Simultaneously, T-cells and B-cells are stimulated with mitogen to measure general cell based immune responsiveness.
The PlexCOVID-19 test measures the cellular immune response of T-cells and B-cells and determines whether this response is in the low, intermediate or high range of responses observed in healthy immunocompetent individuals without COVID-19 infection, or healthy immunocompetent individuals who have received COVID-19 vaccination.
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Assay Category |
Lab-developed test, antigen-specific T-cell and B-cell function. |
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Intended Use |
To measure cell-mediated immunity to the SARS-CoV-2 virus. |
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Methodology |
Stimulation of peripheral blood leukocytes with the spike protein antigen of SARS-CoV-2 and flow cytometry. Mitogen-stimulation of peripheral blood leukocytes serves as a positive control. |
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Test Report |
Available within 30 hours of receiving the blood sample. |
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Test Readout |
Frequency (%) of SARS-CoV-2-specific T-cells and B-cells that express CD154, an inflammatory marker. This readout is compared with reference ranges from healthy or vaccinated individuals. The patient’s results are ranked compared to these reference ranges. This rank or quartile, ranges from low or quartile 1, to high or quartile 4, with the middle 50% divided into quartile 2 and quartile 3. |
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Reference Range |
The test reports frequencies of the different T-cells and B-cells that react to the three spike antigens. A quartile is assigned to each frequency by comparing with frequencies observed in healthy or vaccinated individuals. |
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Test Interpretation |
Frequencies of spike antigen reactive T-cells and B-cells and their ranking as quartiles can be used to assess the cellular immune status toward the COVID-19 coronavirus. |
Purpose
Knowledge about cell-mediated immunity to SARS-CoV-2 can be combined with available clinical data to assess whether COVID-19 infection or vaccination has altered cellular immune status to the COVID-19 coronavirus.
Rationale
Antibody immunity to the highly contagious COVID-19 coronavirus can wane over time after infection or vaccination. Antibodies also fail to develop in half of all immunocompromised individuals who have been vaccinated. As booster vaccination programs are evaluated for healthy and vulnerable populations, there is interest in knowing whether cellular immunity to the COVID-19 coronavirus is present or not. This information is being sought especially for individuals who have failed to make antibodies to the COVID-19 coronavirus.
Cellular immunity can be measured in T-cells and B-cells that circulate in blood. This immunity can be directed toward any and all protein antigens present in the COVID-19 coronavirus. Among these antigens, the spike antigen of the virus is of interest because antibodies can develop to this antigen after natural COVID-19 infection or vaccination. The spike antigen includes an S1 component which is unique to the COVID-19 coronavirus, and S2 which is also shared with the human coronaviruses which can cause flu-like symptoms. Cellular immunity can be measured by stimulating circulating T-cells and B-cells with S1, S2 and the complete spike antigen, S, which is a combination of S1 and S2.
Intended Use
To assess the risk of COVID-19 infection and the severity of this infection.
Procedure
- PlexCOVID-19 measures functional cell-mediated immunity to the SARS-CoV-2 virus.
- A whole blood sample of 3 mL from children and 5 mL from adults is used. The blood must be in sodium heparin (green-top) tubes. Samples must be shipped at ambient temperature overnight to Plexision’s reference laboratory.
- SARS-CoV-2-specific T-cells that express the inflammatory marker, CD154, are measured after stimulation with the spike protein antigen of this virus.
- Simultaneously, stimulation of these cells with mitogen measures general T-cell and B-cell responsiveness.
- Results are reported within 24 hours after blood samples reach the laboratory.
- Results are reported as the frequencies (%) of T-cells (CD3, CD4 and CD8) and B-cells that respond to the S1, S2 and S antigens of the COVID-19 coronavirus. Each frequency is assigned a rank called the quartile, ranging from quartile 1 (low) through quartile 4 (high). These quartiles have been established in a healthy population of individuals without COVID-19 infection, and after vaccination.
Performance
Cellular immunity to the COVID-19 coronavirus can be combined with clinical information to assess immune status after natural infection and vaccination.
Benefits
The development of antibodies toward the COVID-19 coronavirus and the duration of this response has been variable. Knowledge about cellular immunity to the virus can be used assess immune status, especially for immunocompromised patients, many of whom fail to make antibodies after vaccination.
Sample & Shipping
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Sample Type |
A whole blood sample is collected in a sodium heparin (green-top) tube. |
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Volume |
3 mL for children and 5 mL for adults. |
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Transport Conditions |
Ship priority overnight, at room temperature. The sample must get to Plexision within 30 hours of the phlebotomy. |
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Specimen Stability |
30 hours at room temperature from the time of the phlebotomy. |
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Sample Discard Criteria |
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How to order
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Test Brochure | Contact us for more info. |
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Ordering Tests |
Please complete this form, print, and fax it to 412-224-2776. |
PlexCOVID-19 is a blood test that helps your healthcare provider determine cellular immunity to the COVID-19 coronavirus.
The PlexCOVID-19 test measures T-cell and B-cell immunity to the COVID-19 coronavirus. Patients requiring a complete assessment of immune status to the COVID-19 coronavirus will benefit from knowing whether cellular immunity is present in addition to antibody immunity. Some of these patients include those in whom antibodies to the COVID-19 coronavirus have failed to develop after natural infection or vaccination
The PlexCOVID-19 test must be ordered by your healthcare provider. The test requires half to one teaspoon of a blood sample. This sample is shipped overnight to Plexision’s laboratory for analysis. Results are sent to your healthcare provider within 24 hours of your sample arriving at the laboratory. Your healthcare provider will then help you understand the results.
Test results are ready 24 hours after the laboratory receives the blood sample.
The PlexCOVID-19 test measures the level of cell-mediated immunity toward the SARS-CoV-2 coronavirus. This immunity is measured by with white blood cell called the T-lymphocyte or T-cell and the B-lymphocyte or B-cell, which respond to stimulation by the spike antigen. When combined with patient variables, these measurements can be used to assess cellular immune status to the COVID-19 coronavirus. The frequencies of T-cells and B-cells that respond to the COVID-19 coronavirus are assigned a range from low to high. These ranges are determined by comparing test results with reference ranges established in healthy individuals without COVID-19 infection and healthy individuals who have been vaccinated.
In the PlexCOVID-19 test, cellular immunity to the COVID-19 coronavirus presents as responses to two different components of the spike antigen. The S1 spike antigen is specific for the COVID-19 coronavirus. The S2 spike antigen is present in the COVID-19 coronavirus and also in human coronaviruses that cause cause flu-like symptoms. Responses to these antigens can arise after natural COVID-19 infection or COVID-19 vaccination, because currently available vaccines use the spike antigen to build immunity.
Cellular immune responses to S1 can occur after COVID-19 infection and vaccination. Results must be combined with clinical history of infection or vaccination, or laboratory information which may also include results of previous antibody testing, to assess cellular status.
S2-reactive and S-reactive T-cells and B-cells indicate prior human coronavirus infection, previous COVID-19 infection, or COVID-19 vaccination. Results must be combined with clinical and laboratory information, which may include results of a previous antibody test, or T-cell immune responses measured before infection or vaccination, to assess cellular immune status.
The development of antibodies toward the COVID-19 coronavirus and the duration of this response has been variable. Knowledge about cellular immunity to the virus can be used as an additional measure to assess immune status, especially for immunocompromised patients, many of whom fail to make antibodies after vaccination.
The PlexCOVID-19 test must be ordered by your healthcare provider. The test requisition form is provided here. The completed form can be faxed to 412-224-2776. If there are any questions, please contact (855) PLE.XISION (753.9474) or 412-224-2504.
Plexision will bill your healthcare facility or your insurance plan as indicated on the requisition form. Plexision’s patient assistance plans will assist with the cost of PlexCOVID-19 if there is no insurance coverage.
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- Le Bert N, Tan AT, Kunasegaran K, et al. SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls. Nature 2020.
- Sekine T, Perez-Potti A, Rivera-Ballesteros O, et al. Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19. bioRxiv 2020:2020.06.29.174888.
- Weiskopf D, Schmitz KS, Raadsen MP, et al. Phenotype of SARS-CoV-2-specific T-cells in COVID-19 patients with acute respiratory distress syndrome. medRxiv 2020:2020.04.11.20062349.
- Kahn JS, McIntosh K. History and recent advances in coronavirus discovery. Pediatr Infect Dis J 2005;24:S223-7, discussion S6.
- Ng K, Faulkner N, Cornish G, et al. Pre-existing and de novo humoral immunity to SARS-CoV-2 in humans. bioRxiv 2020:2020.05.14.095414.
- Long QX, Tang XJ, Shi QL, et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med 2020.
- Ibarrondo FJ, Fulcher JA, Goodman-Meza D, et al. Rapid Decay of Anti-SARS-CoV-2 Antibodies in Persons with Mild Covid-19. N Engl J Med 2020.
- Sindhi R, Ashokkumar C, Spishock B, Saunders M, Mabasa A, Sethi P, Reddy A, Nibhanupudy B. T-cell and antibody immunity after COVID-19 mRNA vaccines in healthy and immunocompromised subjects-An exploratory studymedRxiv 2021.05.21.21257442; doi: https://doi.org/10.1101/2021.05.21.21257442.
- Ashokkumar C, Rohan V, Kroemer AH, Rao S, Mazariegos G, Higgs BW, Nadig S, Almeda J, Dhani H, Khan K, Yazigi N, Ekong U, Kaufman S, Betancourt-Garcia MM, Mukund K, Sethi P, Mehrotra S, Soltys K, Singh MS, Bond G, Khanna A, Ningappa M, Spishock B, Sindhi E, Atale N, Saunders M, Baliga P, Fishbein T, Subramaniam S, Sindhi R. Impaired T-cell and antibody immunity after COVID-19 infection in chronically immunosuppressed transplant recipients. bioRxiv. 2021 May 4:2021.05.03.442371. doi: 10.1101/2021.05.03.442371. Preprint.
Patent pending
PlexCOVID-19 is not FDA-approved