Innate and Adaptive Immune Responses to SARS-CoV-2 in Humans: Relevance
to Acquired Immunity and Vaccine Responses
Abstract
The factors responsible for the spectrum of COVID-19 disease severity
and the genesis and nature of protective immunity against COVID-19
remain elusive. Multiple studies have investigated the immune responses
to COVID 19 in various populations, including those without evidence of
COVID 19 infection. Information regarding innate and adaptive immune
responses to the novel SARS-CoV-2 has evolved rapidly. Here, data are
accumulating defining disease phenotypes that aid in rational and
informed development of new therapeutic approaches for the treatment of
patients infected with SARS-CoV-2 and the development of novel vaccines.
In this article, we summarize data on important innate immune responses
including cytokines, specifically IL-6 and complement, and explore
potential treatments. We also examine adaptive immune responses and
derivative therapeutics such as monoclonal antibodies directed at spike
proteins. Finally, we explore data on real-time assessments of adaptive
immune responses which include CD4+/CD8+ T-cells, NKT-cells, memory
B-cells, and T-follicular cells with specificities for COVID-19 peptides
in infected individuals and normals. Data of two novel vaccines have
been released, both showing >95% efficacy in preventing
SARS-CoV-2 infection. Analysis of humoral and cellular responses to the
vaccines will determine the robustness and durability of protection. In
addition, long-term assessment of SARS-CoV-2 memory B and T-cell
mediated immune responses in patients recovering from an infection or
those with cross-reactive immunologic memory will help to define risk
for future SARS-CoV infections. Finally, patients recovering from
SARS-CoV-2 infection may experience prolonged immune activation likely
due to T-cell exhaustion. This will be an important new frontier for
study.