SARS-CoV-2-reactive interferon-γ-producing CD8+ T cells in patients hospitalized with Coronavirus viral disease-2019

There is limited information on SARS-CoV-2 T-cell immune responses in patients with Covid-19. Both CD4+ and CD8+ T cells may be instrumental in the resolution of and protection from SARS-CoV-2 infection. Here, we tested 25 hospitalized patients with either microbiologically documented Covid-19 (n=19) or highly suspected of having the disease (n=6) for the presence of SARS-CoV-2-reactive- CD69+-expressing interferon-gamma;-producing-(IFN-gamma;) CD8+ T cells by a flow-cytometry for intracelular cytokine staining assay. Two sets of overlapping peptides encompassing the SARS-CoV-2 Spike glycoprotein N-terminal 1-643 amino acid sequence and the entire sequence of SARS-CoV-2 M protein were used simultaneously as antigenic stimulus. Ten patients (40%) had detectable responses, displaying frequencies ranging from 0.15 to 2.7% (median of 0.57 cells/microlitre; range, 0.43-9.98 cells/microlitre). The detection rate of SARS-CoV-2-reactive IFN-gamma; CD8+ T cells in patients admitted to intensive care was comparable (P=0.28) to that in patients hospitalized in other medical wards. No correlation was found between SARS-CoV-2-reactive IFN-gamma; CD8+ T-cell counts and SARS-CoV-2 S-specific antibody levels. Likewise, no correlation was observed between either SARS-CoV-2-reactive IFN-gamma; CD8+ T cells or S-specific IgG-antibody titers and blood cell count or levels of inflammatory biomarkers. In summary, in this descriptive, preliminary study we showed that SARS-CoV-2-reactive IFN-gamma; CD8+ T cells can be detected in a non-negligible percentage of patients with moderate to severe forms of Covid-19. Further studies are warranted to determine whether quantitation of these T-cell subsets may provide prognostic information on the clinical course of Covid-19.