Adaptive immunity to SARS-CoV-2 and COVID-19

Authors: Alessandro Sette1,2 and Shane Crotty1,2,∗


The adaptive immune system is important for control of most viral infections. The three fundamental components of the adaptive immune system are B cells (the source of antibodies), CD4+ T cells, and CD8+ T cells. The armamentarium of B cells, CD4+ T cells, and CD8+ T cells has differing roles in different viral infections and in vaccines, and thus it is critical to directly study adaptive immunity to SARS-CoV-2 to understand COVID-19. Knowledge is now available on relationships between antigen-specific immune responses and SARS-CoV-2 infection. Although more studies are needed, a picture has begun to emerge that reveals that CD4+ T cells, CD8+ T cells, and neutralizing antibodies all contribute to control of SARS-CoV-2 in both non-hospitalized and hospitalized cases of COVID-19. The specific functions and kinetics of these adaptive immune responses are discussed, as well as their interplay with innate immunity and implications for COVID-19 vaccines and immune memory against re-infection.


Coronavirus disease 2019 (COVID-19), caused by the novel human pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Hu et al., 2020), is a serious disease that has resulted in widespread global morbidity and mortality. Our understanding of SARS-CoV-2 and COVID-19 has rapidly evolved during 2020. As of December 2020, the United States has experienced >300,000 deaths, winter cases are rising exceptionally fast, and the first interim phase 3 vaccine trial results have been reported. The scientific advances in understanding SARS-CoV-2 and COVID-19 have been extraordinarily rapid and broad, by any metric, which is an amazing testament to the commitment, creativity, collaboration, and expertise of the international scientific community, both in academia and industry, under extremely challenging conditions. This article will review our current understanding of the immunology of COVID-19, with a primary focus on adaptive immunity.

The immune system is broadly divided into the innate immune system and the adaptive immune system. Although the adaptive and innate immune systems are linked in important and powerful ways, they each consist of different cell types with different jobs. The adaptive immune system consists of three major cell types: B cells, CD4+ T cells, and CD8+ T cells (Figure 1 ). B cells produce antibodies. CD4+ T cells possess a range of helper and effector functionalities. CD8+ T cells kill infected cells. Given that adaptive immune responses are important for the control and clearance of almost all viral infections that cause disease in humans, and adaptive immune responses and immune memory are central to the success of all vaccines, it is critical to understand adaptive responses to SARS-CoV-2.

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