Comprehensive Characterization of Innate and Adaptive Immune Profiles in the Pediatric COVID-19 Convalescent Phase.

Background: Knowledge of the effect of SARS-CoV-2 on the innate and adaptive immune responses of children is currently lacking. We investigated the immune profile of recovered pediatric patients 3 to 11 weeks after acute COVID-19.

Methods: Children who were previously healthy or had a preexisting chronic disease and had a positive reverse transcription polymerase chain reaction/serology were enrolled (n=23). The control group was composed of 25 patients without COVID-19 paired by age, sex and baseline chronic conditions. We performed immunophenotyping, hematologic and inflammatory markers analysis, cytokines and T-cell receptor excision circle (TREC) quantifications.

Results: Most COVID-19 convalescent pediatric patients (COVID-19 CPP) had chronic conditions (73.9%), as well as 80% of the controls. Five children developed multisystem inflammatory syndrome in children. COVID-19 CPP had higher lymphocyte numbers than controls due to an increase in CD4+ T cells. Naive, effector memory (EM) reexpressing CD45RA T cells and follicular CD4+ T cells, as well as TRECs and HLA-DR+ and CD38+CD4+ activated T lymphocytes, were increased in those patients. EM2 and EM3 CD4+ T cells, EM2 CD8+ T cells and memory B cells were elevated in the COVID-19 CPP group. Numbers of neutrophils, monocytes and natural killer cells were equivalent but with increased activation in the recovered patients.

Conclusions: In the short-term following infection, COVID-19-recovered patients show persistent activation profiles in phagocytes, T-cell subtypes and natural killer cells. Meanwhile, increased production of lymphocytes, TRECs and naive T cells suggests immune response recovery, even in immunosuppressed patients and children with comorbidities. The clinical implications of these findings should be further studied.