Some Insights On SARS-CoV-2 Immunity

The COVID-19 epidemic is ignited by the global spreading of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1], which has been the center of scientific research for an effective treatment since the beginning of the outbreak. SARS-CoV-2 is a betacoronavirus, which as a RNA virus has a high mutation rate, correlating to its strengthened virulence [2].The very latest study on the SARS-CoV-2 reinfection case released by HKU undermined the viability of the herd immunity constructed by natural infection and vaccination [2], showing that the virus will likely be circling within human populations. And, on the other hand, this report made us reconsider the necessary approaches during vaccine design and against SARS-CoV-2, including vaccination for recovered patients [3].

The reinfection case was supported with genetic evidence which differentiated it from the prolonged first episode infection [1], and this may imply that future vaccines may not provide a very lasting immunity against SARS-CoV-2. In contrast, as denoted by Le Bert et al. [3], serological samples from patients who recovered from SARS-CoV-2 and SARS (SARS-CoV) years ago, and those who were never exposed to SARS and SARS-CoV-2, displayed the presence of SARS-CoV2-specific T cells. The T cell response mounted differed in two patient groups, where the ORF1-specific T cell responses were greater in the patients with no infection history, while the structural protein specific T cell responses were preferentially detected in patients who recovered from either SARS [3]. The action of cross-reactive T cells can be explained by the fact that, different strains of coronaviruses share sometimes highly conserved genetic and structural components (see Figure.1), for instance, the ORF1 region which encodes non-structural proteins (NSPs), accounting for two thirds of the virus genome [2]. In addition, structural proteins, in the above study the N proteins, also have a considerable degree of homology among betacoronaviruses [3]. Accordingly, it is supposed that patients who were never exposed to the SARS-CoV-2 acquired the pre-existing from previous infection with homolog commoncold coronaviruses like HCoV-OC43, HCoV-HKU1, HCoV-NL63 and HCoV-229E [5]; this might explain the fiercely varied severity seen in the patient population [3,5]. Through the understanding of the underlying mechanisms that determine the severity of the SARS-CoV-2 infection is vital for the control of the disease, as people with distinct levels of pre-existing T cell memory may mount immune response of different strength and speed [5]; it may also shed light on the design of novel vaccines for SARS-CoV-2.

Figure.1. Sequence Map of SARS-CoV-2 (Taken from Le Bert et al., SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls., 2020, Fig.1)

Bibliography:

1.  To KK, Hung IF, Ip JD, et al. COVID-19 re-infection by a phylogenetically distinct SARS-coronavirus-2 strain confirmed by whole genome sequencing [published online ahead of print, 2020 Aug 25]. Clin Infect Dis. 2020;ciaa1275. doi:10.1093/cid/ciaa1275

2.  Abdullahi IN, Emeribe AU, Ajayi OA, Oderinde BS, Amadu DO, Osuji AI. Implications of SARS-CoV-2 genetic diversity and mutations on pathogenicity of the COVID-19 and biomedical interventions [published online ahead of print, 32020 Jul 10]. J Taibah Univ Med Sci. 2020;10.1016/j.jtumed.2020.06.005. doi:10.1016/j.jtumed.2020.06.005

3.  Le Bert N, Tan AT, Kunasegaran K, et al. SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls. Nature. 2020;584(7821):457-462. doi:10.1038/s41586-020-2550-z

4.  Mateus J, Grifoni A, Tarke A, et al. Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans [published online ahead of print, 2020 Aug 4]. Science. 2020;eabd3871. doi:10.1126/science.abd3871

5. Sette A, Crotty S. Pre-existing immunity to SARS-CoV-2: the knowns and unknowns [published correction appears in Nat Rev Immunol. 2020 Aug 17;:]. Nat Rev Immunol. 2020;20(8):457-458. doi:10.1038/s41577-020-0389-z