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Critical role of diagnostic SARS-CoV-2 T cell assays for immunodeficient patients
  1. Rohan Ameratunga1,2,
  2. See-Tarn Woon1,
  3. Richard Steele3,
  4. Klaus Lehnert4,
  5. Euphemia Leung5,
  6. Anna E S Brooks6
  1. 1 Department of Virology and Immunology, Auckland City Hospital, Auckland, New Zealand
  2. 2 Department of Clinical Immunology, Auckland City Hospital, Auckland, New Zealand
  3. 3 Department of Clinical Immunology, Wellington Hospital, Wellington, New Zealand
  4. 4 Centre for brain Research, University of Auckland, Auckland, New Zealand
  5. 5 Cancer Research, Faculty of Medical and health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand
  6. 6 School of Biological Sciences, The University of Auckland, Auckland, New Zealand
  1. Correspondence to Dr Rohan Ameratunga, Auckland City Hospital, Auckland 1023, New Zealand; rohana{at}


After almost 3 years of intense study, the immunological basis of COVID-19 is better understood. Patients who suffer severe disease have a chaotic, destructive immune response. Many patients with severe COVID-19 produce high titres of non-neutralising antibodies, which are unable to sterilise the infection. In contrast, there is increasing evidence that a rapid, balanced cellular immune response is required to eliminate the virus and mitigate disease severity. In the longer term, memory T cell responses, following infection or vaccination, play a critical role in protection against SARS-CoV-2.

Given the pivotal role of cellular immunity in the response to COVID-19, diagnostic T cell assays for SARS-CoV-2 may be of particular value for immunodeficient patients. A diagnostic SARS-CoV-2 T cell assay would be of utility for immunocompromised patients who are unable to produce antibodies or have passively acquired antibodies from subcutaneous or intravenous immunoglobulin (SCIG/IVIG) replacement. In many antibody-deficient patients, cellular responses are preserved. SARS-CoV-2 T cell assays may identify breakthrough infections if reverse transcriptase quantitative PCR (RT-qPCR) or rapid antigen tests (RATs) are not undertaken during the window of viral shedding. In addition to utility in patients with immunodeficiency, memory T cell responses could also identify chronically symptomatic patients with long COVID-19 who were infected early in the pandemic. These individuals may have been infected before the availability of reliable RT-qPCR and RAT tests and their antibodies may have waned. T cell responses to SARS-CoV-2 have greater durability than antibodies and can also distinguish patients with infection from vaccinated individuals.

  • COVID-19
  • Cell Proliferation
  • Immunoglobulins

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  • Handling editor Tahir S Pillay.

  • Contributors Planning: RA. Conception: RA. Writing: RA. Editing: S-TW, AESB, EL, RS, KL.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.