By Varun C. Anipindi
While scientists are striving to identify the specific protection mechanisms against SARS-CoV-2, a recent publication in Cell Reports Medicine followed a group of 254 COVID-19-recovered individuals who were infected during the first surge of COVID-19 in Seattle and Atlanta. With aims to unravel the spectrum of immunity to COVID-19 infection, authors report that these individuals mounted robust humoral and cell-mediated immune responses that can be detected for over 8 months post-infection.
- Individuals who have recovered from SARS-CoV-2 mount robust antibody and cell-mediated immune responses that can be detected over 8 months post-infection.
- Higher level of anti-spike IgG antibodies in serum are correlated with increased functional ability to block re-infections.
- SARS-CoV-2 infection induces polyfunctional T cell responses targeting structural proteins as well as the nucleocapsid protein.
- SARS-CoV-2 infection may also boost antibodies against SARS-CoV-1 and other common coronaviruses.
The researchers first demonstrated robust IgG and IgA antibody responses against SARS-CoV-2 spike in COVID-19 convalescent individuals that stabilized over time (half-life of 8 months), suggesting the establishment of robust long-lived memory B cells. These antibodies were capable at potentially neutralizing SARS-CoV-2, and this neutralization capacity was positively corelated with the level of IgG antibodies against the spike and RBD proteins, thereby suggesting that higher levels of antibodies (as induced by vaccines) is important for preventing re-infections.
Next, researchers evaluated cell-mediated immunity against SARS-CoV-2 and found that 89% and 69% of all infected individuals mounted CD4+ and CD8+ T cell responses, respectively. CD4+ T cells exhibited a polyfunctional response profiled as ‘central’ memory (long-term, with a half-life of >6 months) and were able to target a broad variety of SARS-CoV-2 structural proteins. Conversely, CD8+ T cells largely exhibited a polyfunctional response profiled as ‘effector’ memory (short-term) and preferentially targeted the nucleocapsid protein.
Finally, researchers attempted to identify factors to relate immune responses to disease severity and found that age and disease severity were independently associated with the magnitude of antibody responses and CD4+ T cell responses, but not with CD8+ T cell responses.
In summary, this study provides valuable insights into the scope of immunity induced against SARS-CoV-2 in individuals who have recovered from infection. The immune response to SARS-CoV-2 is broad and comprised of both antibodies and T cells, which tend to persist as memory B cells and T cells that are detectable 8 months after the onset of symptoms. Overall, this is a valuable longitudinal cohort – the study group is being followed for 2+ years – to evaluate the spectrum and longevity of immune responses to SARS-CoV-2. This can be extremely helpful in guiding the development of vaccines, which may help further support the mitigation of the ongoing COVID-19 pandemic.
Cohen KW, Linderman SL, Moodie Z, Czartoski J, Lai L, Mantus G, et al., Longitudinal analysis shows durable and broad immune memory after SARS-CoV-2 infection with persisting antibody responses and memory B and T cells. Cell Reports Medicine 2021. https://doi.org/10.1016/j.xcrm.2021.100354