Introduction
The severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) infection that led to the coronavirus disease in 2019 (COVID-19) is still a hazard to the general public’s health. Since the beginning of the pandemic, there have been more than 5.3 million recorded deaths and over 275 million confirmed cases (WHO weekly epidemiologic update). The predominant symptom of COVID-19 is a respiratory illness with symptoms ranging from asymptomatic or moderate infection to severe symptoms necessitating intensive care unit (ICU) hospitalization [1].
To control and eradicate viral infections, a unique adaptive immune response must be developed. More specifically, virus-specific T and B cells are stimulated, grow, and eventually develop into effector cells in response to infection. Neutralizing antibodies and memory B and T cells, which are specific to the viral antigen survive long after the infection has been eradicated. This memory immune response, which is activated during vaccination, is crucial in the prevention of reinfection. To comprehend the emergence and persistence of such protective immunity, it is crucial to characterize in detail the extent of specific adaptive immune responses in convalescent COVID-19 patients with varying degrees of severity. For foreseeing and controlling potential future waves of infections in the general population, a deeper understanding of the mechanisms driving the development of protective immunological memory in recovered individuals is of paramount importance for public health.
The early response to SARS-CoV-2 infection in severely ill COVID-19 patients is marked by significant immunological dysfunctions linked to a systemic inflammatory response and the emergence of altered innate and adaptive immune responses [1, 2]. More particular, T cell response is significantly altered in critically ill COVID-19 patients, and the most severe COVID-19 patients have been reported as having severe lymphopenia, phenotypic, and functional T cell alterations [3]. Therefore, it is still uncertain whether these critically ill patients can develop a strong and long-lasting SARS-CoV-2 specific T cell response despite the presence of significant immunological changes during the stay in the hospital.
Considering this, the objective of the current investigation was to monitor the immunological response, including memory T cells specific to SARS-CoV-2, in samples obtained 1 month and 6–8 months after infection from a cohort of convalescent critically ill COVID-19 patients.