Flow cytometry profiling of cellular immune response in COVID-19 infected, recovered and vaccinated individuals

SARS-CoV-2 has infected over 753 million individuals and caused more than 6.8 million deaths globally to date. COVID-19 disease severity has been associated with SARS-CoV-2 induced hyper inflammation and the immune correlation with its pathogenesis remains unclear. Acute viral infection is characterised by vigorous coordinated innate and adaptive activation, including an early cellular response that correlates well with the amplitude of virus specific humoral response.

The present study covers a wide spectrum of cellular immune response against COVID-19, irrespective of infection and vaccination.

We analysed immune status of (a) COVID-19 hospitalised patients including deceased and recovered patients, and compared with home isolated and non-infected healthy individuals, and (b) infected home isolated individuals with vaccinated individuals, using flow cytometry. We performed flow cytometry analysis of PBMCs to determine non-specific cell-mediated immune response.

The immune response revealed extensive induction and activation of multiple immune lineages, including T and B cells, Th17 regulatory subsets and M₁, M₂ macrophages in deceased and hospitalised recovered patients, vaccinated and healthy individuals. Compromised immune cell expression was observed in deceased patients even in later stages, while expression was restored in hospitalised recovered patients and home isolated individuals.

The findings associated with recovery and convalescence define a new signature of cellular immune response that persists in individuals with SARS-CoV-2 infection and vaccination. The findings will help in providing a better understanding of COVID-19 disease and will aid in developing better therapeutic strategies for treatment.