SARS-CoV-2 specific T-cell immunity in COVID-19 convalescent patients and unexposed controls measured by ex vivo ELISpot assay

Clin Microbiol Infect. 2021 Jul;27(7):1029-1034. doi: 10.1016/j.cmi.2021.03.010. Epub 2021 Apr 2.


Objectives: SARS-CoV-2 T-cell response characterization represents a crucial issue for defining the role of immune protection against COVID-19. The aim of the study was to assess the SARS-CoV-2 T-cell response in a cohort of COVID-19 convalescent patients and in a group of unexposed subjects.

Methods: SARS-CoV-2 T-cell response was quantified from peripheral blood mononuclear cells (PBMCs) of 87 COVID-19 convalescent subjects (range 7-239 days after symptom onset) and 33 unexposed donors by ex vivo ELISpot assay. Follow-up of SARS-CoV-2 T-cell response was performed in ten subjects up to 12 months after symptom onset. The role of SARS-CoV-2 specific CD4 and CD8 T cells was characterized in a group of COVID-19 convalescent subjects. Moreover, neutralizing antibodies were determined in serum samples.

Results: In 14/33 (42.4%) unexposed donors and 85/87 (97.7%) COVID-19 convalescent subjects a positive result for at least one SARS-CoV-2 antigen was observed. A positive response was observed up to 12 months after COVID-19 infection (median 246 days after symptom onset; range 118-362 days). Of note, SARS-CoV-2 T-cell response seems to be mainly mediated by CD4 T cells. A weak positive correlation was observed between Spike-specific T-cell response and neutralizing antibody titre (p 0.0028; r2 = 0.2891) and positive SARS-CoV-2 T-cell response was observed in 8/9 (88.9%) COVID-19 convalescent subjects with undetectable SARS-CoV-2 neutralizing antibodies.

Discussion: Cross-reactive SARS-CoV-2 T-cell response in uninfected patients may be due to previous infections with other common coronaviruses. Our data suggest that long-term SARS-CoV-2 T-cell response might accompany a waning humoral response.

Keywords: ELISpot; Humoral response; Neutralizing antibodies; SARS-CoV-2; T-cell response.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Neutralizing / blood
  • Antibodies, Viral / blood
  • Antigens, Viral / immunology
  • CD4-Positive T-Lymphocytes / immunology*
  • CD8-Positive T-Lymphocytes / immunology*
  • COVID-19 / immunology*
  • Cohort Studies
  • Convalescence
  • Cross Reactions
  • Enzyme-Linked Immunospot Assay
  • Female
  • Follow-Up Studies
  • Humans
  • Immunity, Cellular
  • Immunologic Memory*
  • Male
  • Middle Aged
  • SARS-CoV-2 / immunology*
  • Young Adult


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Antigens, Viral