Recently, SARS-CoV-2–specific T cells were detected in persons with a history of mild COVID-19 infection and in antibody-seronegative family members of COVID-19 patients ( 6 F. speculated that T-cell immunity could also be protective against infection with SARS-CoV-2 ( 5). described the importance of T cells for the recovery from a structurally related coronavirus, the Middle East respiratory syndrome (MERS) virus, in 2017 ( 4) Braun et al. We decided to follow up with these volunteers by repeating antibody tests and by assessing T-cell immunity by enzyme-linked immunospot (ELISpot) assay for interferon-γ (IFN-γ). When searching for potential CP donors with PCR-confirmed SARS-CoV-2 infection, we observed that 17% of those who volunteered had either borderline or negative results (ratio <1.1) to a SARS-CoV-2 IgG ELISA. One promising therapeutic option to treat severely ill patients with coronavirus disease (COVID-19) is the use of convalescent plasma (CP) of donors who recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection ( 1– 3). We concluded that, in convalescent patients with undetectable SARS-CoV-2 IgG, immunity may be mediated through T cells. We observed a similar frequency (80%) of T-cell immunity in convalescent donors with strong antibody responses but did not detect immunity in negative controls. Using interferon-γ ELISpot, we observed that 78% of PCR-positive volunteers with undetectable antibodies showed T cell immunity against SARS-CoV-2. We analyzed participants with PCR-confirmed infection who had strong antibody responses (ratio >3) as positive controls and participants without symptoms of SARS-CoV-2 infection and without household contact with infected patients as negative controls. Sixty days after onset of symptoms, 13/78 (17%) study participants had borderline or negative results to an ELISA detecting IgG against the S1 protein of SARS-CoV-2.
We investigated immune responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among a group of convalescent, potential blood donors in Germany who had PCR-confirmed SARS-CoV-2 infection.
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