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.