Impaired Cellular Immunity to SARS-CoV-2 in Severe COVID-19 Patients

Abstract

The high infection rate and rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) make it a world-wide pandemic. Individuals infected by the virus exhibited different degrees of symptoms, and most convalescent individuals have been shown to develop both cellular and humoral immune responses. However, virus-specific adaptive immune responses in severe patients during acute phase have not been thoroughly studied. Here, we found that in a group of COVID-19 patients with acute respiratory distress syndrome (ARDS) during hospitalization, most of them mounted SARS-CoV-2-specific antibody responses, including neutralizing antibodies. However, compared to healthy controls, the percentages and absolute numbers of both NK cells and CD8⁺ T cells were significantly reduced, with decreased IFNγ expression in CD4⁺ T cells in peripheral blood from severe patients. Most notably, their peripheral blood lymphocytes failed in producing IFNγ against viral proteins. Thus, severe COVID-19 patients at acute infection stage developed SARS-CoV-2-specific antibody responses but were impaired in cellular immunity, which emphasizes on the role of cellular immunity in COVID-19.

Keywords: SARS-CoV-2; T cells; acute respiratory distress syndrome; adaptive immunity; interferon gamma; neutralization antibody.

Figure 1

Presence of SARS-CoV-2 NP- and S-RBD-specific antibodies in severe COVID-19 patients. (A) Titration of individual serum samples. (B) Data from the same experiments as (A) were presented as area under curve (AUC). (C) IgG isotypes of 10 COVID-19 patients to recombinant NP and S-RBD. (D) Serum ELISA titers to NP and S-RBD in sera from convalescent individuals (n=14), severe patients (n=10) and HD (n=10). The experiment was performed in duplicates. NP, nucleocapsid protein. S-RBD, receptor binding domain of spike protein. HD, healthy donor; Pt, patient; AUC, area under curve. HD#1-9, the sera were collected before SARS-CoV-2 outbreak. *P<0.05, 0.05<**P<0.001. ns, not significant.

Figure 2

Measurement of neutralizing antibodies in severe patients. (A) Neutralizing antibody titers of 10 severe COVID-19 patients. (B) Comparison of NAT50 between convalescent subjects (n=14) and severe patients (n=10). Date are presented as Mean ± SEM. (C) Pie plot showing NAT50 range in severe and convalescent patients. HD, healthy donor; Pt, patient; NAT50, neutralizing antibody titers. ns, not significant.

Figure 3

Phenotypic analysis of blood lymphocytes in severe COVID-19 patients. (A) Phenotypic analysis of PBMCs from one representative COVID-19 patient. (B) Summarized data on the frequencies of different immune cell subsets in COVID-19 patients and the ratio of CD4:CD8 T cells. (C) Summarized data on the absolute numbers of different immune cell subsets in COVID-19 patients. HD, healthy donors (HD#10-14); Pt, patients (n=7). Data are presented as Mean ± SEM. *P<0.05, 0.05<**P<0.001, ***P<0.001. ns, not significant.

Figure 4

SARS-CoV-2-specific T cell responses in COVID-19 patients. (A) Intracellular cytokine staining of CD3⁺CD56^-CD8^- T cells. (B) Summarized data on the frequencies of cytokine-producing CD3⁺CD56^-CD8^- T cells as indicated. (C) Summarized data on the frequencies of polyfunctional CD3⁺CD56^-CD8^- T cells as indicated. (D) Representative FACS plots showing polyfunctional CD3⁺CD56^-CD8^- T cells. (E) IFNγ ELISpot analysis of PBMCs from severe COVID-19 patients (n=7) and convalescent individuals (n=7) to anti-CD3 antibody. (F) IFNγ ELISpot analysis of PBMCs from severe COVID-19 patients (n=7) and convalescent individuals (n=14) to and viral proteins. The experiment with patients was performed in duplicates. (G) The ratios of IFNγ-producing T cells in response to NP or anti-CD3 stimulation in both convalescent (n=14) and severe (n=7) patients. (H) Correlation between NAT50 and the percentage of TNFα⁺ CD4⁺ T cells. Date are presented as Mean ± SEM. *P<0.05, 0.05<**P<0.001. ns, not significant.