A 10 Year Long-Lived Cellular and Humoral MERS-CoV Immunity Cross-Recognizing the Wild-Type and Variants of SARS-CoV-2: A Potential One-Way MERS-CoV Cross-Protection Toward a Pan-Coronavirus Vaccine

Abstract

MERS is a respiratory disease caused by MERS-CoV. Multiple outbreaks have been reported, and the virus co-circulates with SARS-CoV-2. The long-term (> 6 years) cellular and humoral immune responses to MERS-CoV and their potential cross-reactivity to SARS-CoV-2 and its variants are unknown. We comprehensively investigated long-lasting MERS-CoV-specific cellular and humoral immunity, and its cross-reactivity against SARS-CoV-2 and its variants, in individuals recovered from MERS-CoV infection 1-10 years prior. Two cohorts of MERS-CoV survivors (31 unvaccinated, 38 COVID-19 vaccinated) were assessed for MERS-CoV IgG, memory CD4⁺/CD8⁺ T cells, and neutralizing antibodies against MERS-CoV and SARS-CoV-2 variants. MERS-CoV IgG levels and T cell responses were higher in the 1-5 vs 6-10 year postinfection groups. Vaccinated MERS-CoV survivors had significantly elevated MERS-CoV IgG and neutralization compared to unvaccinated. Both groups demonstrated cross-reactive neutralization of SARS-CoV-2 variants. MERS-CoV survivors vaccinated against SARS-CoV-2 had higher anti-MERS IgG, cellular immunity, and neutralization than unvaccinated survivors. MERS-CoV immune responses can persist for a decade. COVID-19 vaccination boosted humoral and cellular immunity in MERS-CoV survivors, suggesting the benefits of vaccination for this population. These findings have implications for pan-coronavirus vaccine development.

Keywords: BA.5 variant; Delta variant; MERS‐CoV; SARS‐CoV‐2; cellular immunity; cross‐reactivity; humoral immunity; short‐term T cell line.

Figure 1

Data on the persistence of MERS‐CoV‐specific IgG concentration, a long‐lasting humoral response and MERS‐CoV‐specific IgG bind and cross‐recognize SARS‐CoV‐2. (a) Data on the persistence of MERS‐CoV spike‐specific IgG concentration (pg/mL). (b) MERS‐CoV spike‐specific IgG antibody levels were measured at 1–5 years and 6–10 years, respectively (pg/mL). (c) Functional blocking of ACE2 binding to SARS‐CoV‐2 RBD, due to limited samples only (n = 37) were included. (d) MERS‐CoV‐specific IgG binds and cross‐recognizes SARS‐CoV‐2 spike protein (optical density [OD]). We performed a pilot reverse experiment to measure MERS‐IgG binding to the spike protein of SARS‐CoV‐2 using an ELISA plate coated with SARS‐CoV‐2 spike protein. The results are presented as violin plots, where black lines indicate the median and green lines represent the upper and lower quartiles. Each red and blue dot represents one plasma sample.

Figure 2

MERS‐CoV‐specific and cross‐reactive SARS‐CoV‐2 T‐cell memory response. (a) The number of IFN‐γ secreting CD8⁺ T cells among 1–5 years and 6–10 years postinfection groups. (b) The number of TNF‐α secreting CD4⁺ T cells among 1–5 years and 6–10 years postinfection groups. (c) Cross‐reactive SARS‐CoV‐2 CD8⁺ T cells producing IFN‐γ. To study cross‐reactive SARS‐CoV‐2 and MERS‐CoV specific T‐cell responses among MERS‐CoV‐recovered individuals without COVID‐19 vaccination (n = 31), PBMCs were re‐stimulated with either the structural proteins of four MERS‐CoV (EMC strain) or SARS‐CoV peptide pool, and cultured in a 96‐well ELISpot plate for 20 h. This allowed the detection of CD8⁺ T cells producing IFN‐γ and CD4⁺ T cells producing TNF‐α, measured as Spot‐forming cells (SFCs) using TNF‐α and IFN‐γ ELIspots. All results are presented as violin plots, with black lines indicating the median and green lines representing the upper and lower quartiles. Each red and blue dot represents one sample.

Figure 3

Flow cytometry analysis of SARS‐CoV‐2 T‐cell lines (SARS‐CoV‐2‐TCL). (a) Percentage of TNF‐α positive memory CD4⁺ T cells specific to SARS‐CoV‐2 that cross‐reacted with MERS‐CoV. (b) Percentage of IFN‐γ positive memory CD8⁺ T cells specific to SARS‐CoV‐2 that cross‐reacted with MERS‐CoV.

Figure 4

Flow cytometry analysis of MERS‐CoV T‐cell lines (MERS‐CoV‐TCL). (a) Percentage of TNF‐α positive memory CD4⁺ T cells specific to MERS‐CoV that cross‐reacted with SARS‐CoV‐2. (b) Percentage of IFN‐γ positive memory CD8⁺ T cells specific to MERS‐CoV that cross‐reacted with SARS‐CoV‐2.

Figure 5

Correlations between MERS‐CoV‐specific IgG, CD8⁺ T cells producing IFN‐γ and CD4⁺ T cells producing TNF‐α and ACE2 binding to SARS‐CoV‐2 RBD. (a) Correlation between MERS‐CoV spike‐specific IgG and SARS‐CoV‐2 RBD/ACE blocking. (b) Correlation between MERS‐CoV‐specific IFN‐γ and MERS‐CoV spike‐specific IgG. (c) Correlation between MERS‐CoV‐specific TNF‐α and MERS‐CoV spike‐specific IgG. (d) Correlation between MERS‐CoV‐specific IFN‐γ and MERS‐CoV‐specific TNF‐α. (e) Correlation between SARS‐CoV‐2 cross‐reactive IFN‐γ and MERS‐CoV‐specific IFN‐γ. (f) Correlation between MERS‐CoV spike‐specific IgG and age. (g) Correlation between MERS‐CoV‐specific TNF‐α and age. (h) Correlation between MERS‐CoV‐specific IFN‐γ and age.

Figure 6

Neutralization titer of MERS‐CoV strains (HCoV‐EMC/2012, ChinaGD01, and Nigeria/NV1657) and SARS‐CoV‐2 strains (Wild type [WT], Delta variant, and BA.5 variant). Only 10 participants' samples were assayed (P1–P10 indicates participant numbers). FRNT 50 could not be performed for all participants due to the limited sample volume.