Immune features of COVID-19 convalescent individuals revealed by a single-cell RNA sequencing

It remains unclear whether immune responses following natural infection can be sustained or potentially prove critical for long-term immune protection against SARS-CoV-2 reinfection. Here, we systematically mapped the phenotypic landscape of SARS-CoV-2-specific immune responses in peripheral blood samples of convalescent patients with COVID-19 by single-cell RNA sequencing. The relative percentage of the CD8 + effector memory subset was increased in both convalescent moderate and severe cases, but NKT-CD160 and marginal zone B clusters were decreased. Innate immune responses were attenuated reflected by decreased expression of genes involved in interferon-gamma, leukocyte migration and neutrophil mediated immune response in convalescent COVID-19 patients. Functions of T cell were strengthened in convalescent COVID-19 patients by clear endorsement of increased expression of genes involved in biological processes of regulation of T cell activation, differentiation and cell–cell adhesion. In addition, T cell mediated immune responses were enhanced with remarkable clonal expansions of TCR and increased transition of CD4 + effector memory and CD8 + effector-GNLY in severe subjects. B cell immune responses displayed complicated and dual functions during convalescence of COVID-19, providing a novel mechanism that B cell activation was observed especially in moderate while humoral immune response was weakened. Interestingly, HLA class I genes displayed downregulation while HLA class II genes upregulation in both T and B cell subsets in convalescent individuals. Our results showed that innate immunity was declined but SARS-CoV-2-specific T cell responses were retained even strengthened whereas complicated and dual functions of B cells, including declined humoral immunity were presented at several months following infections.