Memory T cell responses targeting the SARS coronavirus persist up to 11 years post-infection

Abstract

Severe acute respiratory syndrome (SARS) is a highly contagious infectious disease which first emerged in late 2002, caused by a then novel human coronavirus, SARS coronavirus (SARS-CoV). The virus is believed to have originated from bats and transmitted to human through intermediate animals such as civet cats. The re-emergence of SARS-CoV remains a valid concern due to the continual persistence of zoonotic SARS-CoVs and SARS-like CoVs (SL-CoVs) in bat reservoirs. In this study, the screening for the presence of SARS-specific T cells in a cohort of three SARS-recovered individuals at 9 and 11 years post-infection was carried out, and all memory T cell responses detected target the SARS-CoV structural proteins. Two CD8(+) T cell responses targeting the SARS-CoV membrane (M) and nucleocapsid (N) proteins were characterized by determining their HLA restriction and minimal T cell epitope regions. Furthermore, these responses were found to persist up to 11 years post-infection. An absence of cross-reactivity of these CD8(+) T cell responses against the newly-emerged Middle East respiratory syndrome coronavirus (MERS-CoV) was also demonstrated. The knowledge of the persistence of SARS-specific celullar immunity targeting the viral structural proteins in SARS-recovered individuals is important in the design and development of SARS vaccines, which are currently unavailable.

Keywords: Epitope; Immunity; SARS-CoV; T cell.

Copyright © 2016 Elsevier Ltd. All rights reserved.

Figures

Fig. 1

IFNγ ELISpot results for SARS-specific memory T cell screening. PBMCs from (A) a healthy individual and (B) SARS-recovered individual (SARS subject 1) were expanded in vitro using a mixture of SARS-CoV peptides, followed by IFNγ ELISpot assay using SARS peptide matrix pools of the structural (top panels) and accessory proteins (lower panels). Each bar represents the IFNγ-producing response to an individual peptide matrix pool (numeric or alphabetic) in SFU per 5 × 104 cells. The threshold for a positive response was set as two times above the mean SFU of unstimulated cells (Neg), as indicated by the dotted line in the right panels. Cells stimulated with PMA/ionomycin were included as positive control (Pos).

Fig. 2

ICS and flow cytometry analysis of unstimulated and M29-stimulated T cells after restimulation using M29 peptide. The percentages of CD8+ IFNγ+ and CD8+CD107a+ T cells shown represent the percentage of the T cells in total T cell population (after gating the CD3+ cells) present in the short-term T cell line obtained by restimulation using M29 peptide from SARS subject 1 at 9 years post-infection.

Fig. 3

ICS and flow cytometry analysis of restimulated T cells from SARS subject 1 at 11 years post-infection. Percentages of CD8+IFNγ+ responses (left panels) and CD8+CD107a+ responses (right panels) of (A) unstimulated, (B) M29147–155-stimulated, (C) N53266–275-stimulated T cells are as indicated in the upper right quadrant of each dot plot. Percentage CD8+ IFNγ+ cells shown represent the percentage of IFNγ-producing cells in the total T cell population (after gating the CD3+ cells) which were in vitro expanded in the presence of M29147–155 and N53266–275 peptides.

Fig. 4

Cross-reactivity of SARS-specific M29 and N53 CD8+ T cells. Sequence alignments of (A) M29 and (B) N53 regions of human SARS-CoV (HKU39849), civet SARS-CoV (SZ3), bat SL-CoVs (Rp3, Rf1 and Rs3367) and MERS-CoV. (C) Percentages of CD8+IFNγ+ T cell responses induced by SARS-CoV and MERS-CoV M29 (left) and N53 (right) minimal peptides. Percentage CD8+ IFNγ+ cells shown represents the percentage of IFNγ-producing cells in the total T cell population (after gating the CD3+ cells) present in the short-term T cell line obtained by restimulation using SARS-CoV M29 and N53 minimal peptides (M29147–155 and N53266–275) from SARS subject 1 at 9 years post-infection.