Intrafamilial Exposure to SARS-CoV-2 Associated with Cellular Immune Response without Seroconversion, France

Abstract

We investigated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibodies and T-cell responses against SARS-CoV-2 and human coronavirus (HCoV) 229E and OC43 in 11 SARS-CoV-2 serodiscordant couples in Strausbourg, France, in which 1 partner had evidence of mild coronavirus disease (COVID-19) and in 10 unexposed healthy controls. Patients with confirmed COVID-19 were considered index patients and their partners close contacts. All index patients displayed positive SARS-CoV-2-specific antibody and T-cell responses that lasted up to 102 days after symptom onset. All contacts remained seronegative for SARS-CoV-2; however, 6 reported COVID-19 symptoms within a median of 7 days after their partners, and 4 of those showed a positive SARS-CoV-2-specific T-cell response against 3 or 4 SARS-CoV-2 antigens that lasted up to 93 days after symptom onset. The 11 couples and controls displayed positive T-cell responses against HCoV-229E or HCoV-OC43. These data suggest that exposure to SARS-CoV-2 can induce virus-specific T-cell responses without seroconversion.

Trial registration: ClinicalTrials.gov NCT04405726.

Keywords: COVID-19; IgA; IgG; IgM; RT-PCR; SARS-CoV-2; antibodies; coronavirus disease; coronavirus symptoms; household exposure; interferon; intrafamilial contacts; serologic testing; severe acute respiratory syndrome coronavirus 2; viral-specific T-cell response.

Figure 1

SARS-CoV-2–specific T-cell response patterns in index patients, contacts, and unexposed healthy donors in study of intrafamilial exposure to SARS-CoV-2, France. A, B) Spot counts of SARS-CoV-2–specific T cells measured by interferon-gamma (IFN-γ) ELISPOT assay are shown for 11 couples, each including 1 confirmed coronavirus disease case (P) and 1 SARS-CoV-2 seronegative symptomatic (A) or asymptomatic (B) contact (C). C) Spot counts of IFN-γ–producing T cells in response to SARS-CoV-2 antigens are shown for the 5 out of the 10 controls (HD) tested who displayed detectable T-cell responses. All experiments were performed in duplicate. Data are shown as means and standard deviations of spots counts of IFN-γ–producing T cells per 1 million CD3+ cells. Each dot represents a single measured value. Blue dots correspond to T-cell responses detected in index patients, red dots correspond to those detected in contacts and gray dots to those found in healthy donors. The x-axis represents the SARS-CoV-2 antigens spanned by the peptide pools used in ELISPOT assays: the N-terminal and C-terminal regions of SARS-CoV-2 spike glycoprotein (S1 and S2, respectively); the N, M, and E proteins; and the accessory proteins 3A, 7A, 8, and 9B. C, contact; E, envelope small membrane protein; HD, healthy blood donor (control); M, membrane protein; N, nucleoprotein; P, index patient; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 2

Example of IFN-γ ELISPOT images corresponding to couple 2 (P2 and C2) in a study of intrafamilial exposure to SARS-CoV-2, France. T-cell–specific response was evaluated using peptide pools spanning SARS-CoV-2 structural protein (spike glycoprotein: N-terminal region = S1, C-terminal region = S2; N, M, and E proteins); SARS-CoV-2 accessory proteins (3A, 7A, 8, and 9B); and the N-terminal and C-terminal regions of the spike glycoprotein of common cold human coronaviruses 229 (ES1 and ES2) and OC43 (OS1 and OS2). All experiments were performed in duplicate with 4 wells of negative controls (cells with culture medium only) and 2 wells of positive controls (phytohemagglutinin) for each individual. P2 was reactive to all antigens tested except for SARS-CoV-2 proteins E and 8, whereas C2 was reactive to 1 SARS-CoV-2 protein only (S2) and to ES1, ES2, and OS2. C, contact; E, envelope small membrane protein; HCoV, human coronavirus; IFN-γ, interferon gamma; M, membrane protein; N, nucleoprotein; P, index patient; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 3

Frequency of specific T cells directed against spike glycoprotein antigens of the 2 common cold HCoVs 229E and OC43 in study of intrafamilial exposure to SARS-CoV-2, France. A) Index patients (n = 11); B) seronegative partners of index patients (n = 11); C) unexposed healthy controls (n = 10). Spot counts of common cold human coronaviruses-specific T cells were measured by interferon-gamma ELISPOT assay. All experiments were performed in duplicate. Data are shown as means and standard deviations of spot counts of interferon-gamma–producing T cells per 1 million CD3+ cells. T-cell secretion of IFN-γ was determined in response to peptide pools spanning the N-terminal and the C-terminal regions of the spike glycoprotein of HCoV 229E (ES1 and ES2 subpools) and HCoV OC43 (OS1 and OS2 subpools). Each color corresponds to 1 antigen subpool. C, contact; HCoV, human coronavirus; HD, healthy blood donor (control); P, index patient; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 4

Correlation of the T-cell responses against spike glycoprotein antigens of SARS-CoV-2 and HCoVs 229E and OC43 in study of intrafamilial exposure to SARS-CoV-2, France. Means of spot counts of interferon gamma–producing T cells per 1 million CD3+ cells in response to peptide pools spanning the N terminal (S1) and the C-terminal (S2) regions of spike glycoproteins of SARS-CoV-2 compared with HCoV-229E (A) and HCoV-OC43 (B) in 11 confirmed coronavirus disease cases (index patients), their seronegative partners (contacts), and 10 healthy blood donor controls. HCoV, human coronavirus; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.