Mucosal and Systemic Responses to Severe Acute Respiratory Syndrome Coronavirus 2 Vaccination Determined by Severity of Primary Infection

Abstract

With much of the world infected with or vaccinated against severe acute respiratory syndrome coronavirus 2 (commonly abbreviated SARS-CoV-2; abbreviated here SARS2), understanding the immune responses to the SARS2 spike (S) protein in different situations is crucial to controlling the pandemic. We studied the clinical, systemic, mucosal, and cellular responses to two doses of SARS2 mRNA vaccines in 62 individuals with and without prior SARS2 infection that were divided into three groups based on antibody serostatus prior to vaccination and/or degree of disease symptoms among those with prior SARS2 infection: antibody negative (naive), low symptomatic, and symptomatic. Antibody negative were subjects who were antibody negative (i.e., those with no prior infection). Low symptomatic subjects were those who were antibody negative and had minimal or no symptoms at time of SARS2 infection. Symptomatic subjects were those who were antibody positive and symptomatic at time of SARS2 infection. All three groups were then studied when they received their SARS2 mRNA vaccines. In the previously SARS2-infected (based on antibody test) low symptomatic and symptomatic groups, reactogenic symptoms related to a recall response were elicited after the first vaccination. Anti-S trimer IgA and IgG titers, and neutralizing antibody titers, peaked after the 1st vaccination in the previously SARS2-infected groups and were significantly higher than for the SARS2 antibody-negative group in the plasma and nasal samples at most time points. Nasal and plasma IgA antibody responses were significantly higher in the low symptomatic group than in the symptomatic group at most time points. After the first vaccination, differences in cellular immunity were not evident between groups, but the activation-induced cell marker (AIM⁺) CD4⁺ cell response correlated with durability of IgG humoral immunity against the SARS2 S protein. In those SARS2-infected subjects, severity of infection dictated plasma and nasal IgA responses in primary infection as well as response to vaccination (peak responses and durability), which could have implications for continued protection against reinfection. Lingering differences between the SARS2-infected and SARS2-naive up to 10 months postvaccination could explain the decreased reinfection rates in the SARS2-infected vaccinees recently reported and suggests that additional strategies (such as boosting of the SARS2-naive vaccinees) are needed to narrow the differences observed between these groups. IMPORTANCE This study on SARS2 vaccination in those with and without previous exposure to the virus demonstrates that severity of infection dictates IgA responses in primary infection as well as response to vaccination (peak responses and durability), which could have implications for continued protection against reinfection.

Keywords: IgA; IgG; SARS-CoV-2; mucosal immunity; systemic response; vaccination.

FIG 1

Reactogenicity after first and second vaccination. Percent reported symptoms after the first (A) and second (B) vaccinations is shown on the y axis. Ab-negative (Ab-), low symptomatic (L), and symptomatic (S) groups are shown in orange, blue, and white, respectively. LAD, lymphadenopathy. Each symptom was assessed by 2-tailed Fisher’s exact test between the Ab-negative and the low symptomatic or symptomatic group, with P values of <0.05 being considered significant and shown with asterisks.

FIG 2

Nasal and systemic IgG ELISA responses to SARS2 S trimer. (A) IgG endpoint titers were measured at baseline, 14 days after the 1st vaccination, 14 days after the 2nd vaccination, and 10 months after the 2nd vaccination. Horizontal red lines represent median values. (B) IgG endpoint titers measured at all time points until 10 months after the second vaccination. Dotted lines represent decay slopes for each cohort between months 3 and 10. The limit of detection >(LOD) for the nasal IgG ELISA is 1:500, and that for the plasma IgG ELISA is 1:50 (dotted black lines). Ab-negative, low symptomatic, and symptomatic groups are shown in orange, blue, and black, respectively. The y axis represents reciprocal endpoint titer to SARS2 S trimer in a logarithmic scale. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.

FIG 3

Nasal and systemic IgM and IgA ELISA responses to SARS2 S trimer. (A) IgM endpoint titers were measured at baseline, 14 days after the 1st vaccination, and 14 days after the 2nd vaccination. Horizontal red lines represent median values. (B) IgA endpoint titers were measured at baseline, 14 days after the 1st vaccination, 14 days after the 2nd vaccination, and 10 months after the 2nd vaccination. Horizontal red lines represent median values. (C) IgA endpoint titers measured at all time points until 10 months after the second vaccination. The low symptomatic group had a smaller slope of decline for IgA binding titers (−0.045 log titer/month) than the symptomatic group (−0.082 log titer/month) but not the antibody-negative group (−0.028 log titer/month) (P = 0.04 and P = 0.59, respectively). Dotted lines represent decay slopes for each cohort between months 3 and 10. The LOD for the nasal IgM ELISA is 1:500, that for nasal IgA is 1:500, that for plasma IgM is 1:20, and that for plasma IgA is 1:100 (dotted black lines). Ab-negative, low symptomatic, and symptomatic groups are shown in orange, blue, and black, respectively. The y axis represents reciprocal endpoint titer to SARS2 S trimer in a logarithmic scale. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.

FIG 4

Live virus neutralization in plasma against WA-1 (A) and B.1.617.2 (Delta) (B) measured at baseline, at 14 days after 1st vaccination, and prior to and 14 days after the 2nd vaccination. ID₉₉ is defined as highest dilution at which 99% cells were protected. Horizontal red lines represent median values. The lowest dilution tested was 1:40 (dotted black line). *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.

FIG 5

SARS2 S-specific CD4⁺ and CD8⁺ T cells following vaccination in unexposed and previously infected individuals. (A) Representative gating strategy of AIM⁺ (surface CD40L⁺ OX40⁺) CD4⁺ T cells stimulated with S peptide pool or left unstimulated (DMSO). (B) AIM⁺ S-specific CD4⁺ T cells of total CD4⁺ T cells. LOD, 0.007%. (C) Representative gating strategy of AIM⁺ (CD40L⁺ OX40⁺) circulating T follicular helper (cT_FH) cells (blue, CXCR5⁺) overlaid on total CD4⁺ T cells (gray). (D) AIM⁺ S-specific cT_FH cells of total CD4⁺ T cells. LOD, 0.01%. (E) Representative gating strategy of CD40L⁺ IFN-γ⁺ CD4⁺ T cells. (F) Spike-specific CD40L⁺ IFN-γ⁺ CD4⁺ T cells of total CD4⁺ T cells. LOD, 0.007%. (G) Spike-specific CD40L⁺ CD4⁺ T cells producing IFN-γ, IL-2, or TNF-α of total CD4⁺ T cells. LOD, 0.007%. (H) Representative gating strategy of CD69⁺ IFN-γ⁺ CD8⁺ T cells. (I) Spike-specific CD69⁺ IFN-γ⁺ CD8⁺ T cells of total CD8⁺ T cells. LOD, 0.007%. (J) Spike-specific CD69⁺ CD8⁺ T cells producing IFN-γ, IL-2, or TNF-α of total CD8⁺ T cells. LOD, 0.007%. All data are background subtracted. Horizontal red lines represent median values. *, P ≤ 0.05; **, P ≤ 0.01; ***, P ≤ 0.001; ****, P ≤ 0.0001.