A flow cytometry-based proliferation assay for clinical evaluation of T-cell memory against SARS-CoV-2

In general, the method of choice for evaluating immunity against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is detection of antibodies against the virus in patient sera. However, this is not feasible in patients who do not produce antibodies, either due to a primary immunodeficiency or secondary to treatment with immunosuppressive drugs. Assessment of the antiviral T cell response is an alternative to serological tests, but most T cell assays are labor-intensive and unsuitable for a clinical routine laboratory. We developed a flow cytometry-based assay for T cell proliferative responses against SARS-CoV-2, based on the detection of blast transformation of activated cells. The assay was validated on previously SARS-CoV-2 infected individuals and healthy seronegative blood donors, displaying 74% sensitivity and 96% specificity for previous infection with SARS-CoV-2. The usefulness of the assay was demonstrated in a patient with common variable immunodeficiency with a history of COVID-19. The described T-cell assay is a clinically relevant complement to serology in the evaluation of cellular immunity against SARS-CoV-2, which can be emulated by any routine lab with flow cytometric competence.