Dynamics of CD4 T Cell and Antibody Responses in COVID-19 Patients With Different Disease Severity

Abstract

Disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ranges from mild illness to severe respiratory disease and death. In this study, we determined the kinetics of viral loads, antibody responses (IgM, IgG, neutralization) and SARS-CoV-2-specific CD4 T cells by quantifying these parameters in 435 serial respiratory and blood samples collected from a cohort of 29 COVID-19 patients with either moderate or severe disease during the whole period of hospitalization or until death. Remarkably, there was no significant difference in the kinetics and plateau levels of neutralizing antibodies among the groups with different disease severity. In contrast, the dynamics of specific CD4 T cell responses differed considerably, but all patients with moderate or severe disease developed robust SARS-CoV-2-specific responses. Of note, none of the patients had detectable cross-reactive CD4 T cells in the first week after symptom onset, which have been described in 20-50% of unexposed individuals. Our data thus provide novel insights into the kinetics of antibody and CD4 T cell responses as well as viral loads that are key to understanding the role of adaptive immunity in combating the virus during acute infection and provide leads for the timing of immune therapies for COVID-19.

Keywords: COVID-19 patients; SARS-CoV-2; SARS-CoV-2-specific T cells; SARS-CoV-2-specific antibodies; adaptive immunity.

Figure 1

SARS-CoV-2 viral load in COVID-19 patients with different disease severity. (A) Viral load from nasopharyngeal swabs (green) and endotracheal aspirates (orange). Data points are mean; error bars indicate SD; slopes represent best fit. (B) Viral load from nasopharyngeal swabs from all patients (n = 29). Data points indicate viral load in individual samples; slopes represent viral RNA decline in patient groups, as assessed by Generalized Estimation Equations (GEE) applying an unstructured correlation matrix. Group one, moderate (blue); group two, severe (red), and group three, deceased (black).

Figure 2

Titers of neutralizing antibodies and correlation with viral load and IgM and IgG titers against the spike protein. (A–C) Neutralizing antibody titers in moderate (n = 13), severe (n = 9), and deceased (n = 7) patients. (D) Correlation between neutralizing antibody titers and virus RNA loads was assessed using Pearson correlation. (E,F) IgM and IgG ELISA titers against the spike protein in 29 patients. Each line represents an individual patient. (G–I) Correlation between neutralizing antibody titers and anti-S IgM and IgG ELISA titers, anti-S IgM ELISA titers and anti-S IgG ELISA titers, as assessed by Pearson correlation.

Figure 3

Extent of SARS-CoV-2-specific CD4 T cell responses over time. (A) Extent of CD4 T cell responses to the four SARS-CoV-2 structural proteins, as determined by IFN-γ ELISpot assays (n = 21); data are presented as box and whiskers plots, with bounds from 25th to 75th percentile,plots, with bounds from 25th to 75th percentile, median line, and whiskers ranging from minimum to maximum of total IFN-γ spots. Significance was determined by Kruskal Wallis test, *P < 0.05, **P < 0.01, ***P < 0.001. Area below cut off in IFN-γ ELISpot assay (<50 spots per 106 PBMCs) is shaded gray. (B) Percentage of spots contributed by S1, S2, M, N, and E. (C) Kinetics of CD4 T cell responses in patients with moderate or severe disease and in deceased patients; group one, moderate (blue circles); group two, severe (red squares) and group three, deceased (black triangles). (D) Kinetics of CD4 T cell responses in patients with corticosteroid therapy (n = 5); group two, severe (red squares) and group three, deceased (black triangles). Dotted gray lines indicate 500 spots (i.e., 10 times the cut-off of the ELISpot assay). Area below cut off in IFN-γ ELISpot assay (<50 spots per 10⁶ PBMCs) is shaded gray. (E–P) CD4 T cell responses (gray columns), neutralizing antibody titers (green lines), and virus loads in nasopharyngeal swabs (red lines) or endotracheal aspirates (dotted red line) in individual patients. Arrows indicate time points of ELISpot assays with no detectable CD4 T cell reactivity; red star indicates discharge, negative PCR result was not obtained; nt, not tested; LOD, limit of detection. (Q–S) Correlations between virus-specific CD4 T cell levels and vRNA loads, anti-S IgG, or IgM ELISA titers were assessed using Pearson correlation.