Phenotypic and functional changes of T cell subsets after CoronaVac vaccination.

BACKGROUND: The pandemic coronavirus disease 2019 (COVID-19) is a major global public health concern and several protective vaccines, or preventive/therapeutic approaches have been developed. Sinovac-CoronaVac, an inactivated whole virus vaccine, can protect against severe COVID-19 disease and hospitalization, but less is known whether it elicits long-term T cell responses and provides prolonged protection. METHODS: This is a longitudinal surveillance study of SARS-CoV-2 receptor binding domain (RBD)-specific IgG levels, neutralizing antibody levels (NAb), T cell subsets and activation, and memory B cells of 335 participants who received two doses of CoronaVac. SARS-CoV-2 RBD-specific IgG levels were measured by enzyme-linked immunosorbent assay (ELISA), while NAb were measured against two strains of SARS-CoV-2, the Wuhan and Delta variants. Activated T cells and subsets were identified by flow cytometry. Memory B and T cells were evaluated by enzyme-linked immune absorbent spot (ELISpot). FINDINGS: Two doses of CoronaVac elicited serum anti-RBD antibody response, elevated B cells with NAb capacity and CD4+ T cell-, but not CD8+ T cell-responses. Among the CD4+ T cells, CoronaVac activated mainly Th2 (CD4+ T) cells. Serum antibody levels significantly declined three months after the second dose. INTERPRETATION: CoronaVac mainly activated B cells but T cells, especially Th1 cells, were poorly activated. Activated T cells were mainly Th2 biased, demonstrating development of effector B cells but not long-lasting memory plasma cells. Taken together, these results suggest that protection with CoronaVac is short-lived and that a third booster dose of vaccine may improve protection.

Anti-Inflammatory Effects and Decreased Formation of Neutrophil Extracellular Traps by Enoxaparin in COVID-19 Patients.

Neutrophil Extracellular Traps (NETs) are a contributing factor of vascular thrombosis and alveolar damage in COVID-19 patients. As enoxaparin is currently used to inhibit vascular thrombosis, this study aimed to investigate whether enoxaparin also reduced inflammation and NETs in COVID-19 patients. Patients with COVID-19 infection were classified into three groups: mild, moderate, and severe (n = 10 for all groups). Plasma was collected from patients and healthy donors (n = 10). Neutrophils isolated from healthy controls were incubated with COVID-19 or healthy plasma, and with or without enoxaparin pretreatment in vitro. Neutrophils and plasma isolated from patients treated with enoxaparin were also investigated. The levels of inflammatory cytokines and NET products such as dsDNA, NE, MPO-DNA and Histone-DNA complexes in plasma and supernatants were measured using immunofluorescence staining and ELISA kits. The expression of inflammatory signaling genes by neutrophils (RELA, SYK, ERK and PKC) was measured using real-time qPCR. The levels of NET products were elevated in the plasma of COVID-19 patients, particularly in the severe group (p < 0.01). Moreover, plasma from the severe group enhanced NET formation (p < 0.01) from neutrophils in vitro. Enoxaparin pretreatment in vitro decreased plasma-induced NETs in a dose-dependent manner and down-regulated the expression of inflammatory genes (p < 0.05). Patients treated with prophylactic enoxaparin showed lower inflammatory cytokine levels and expression of inflammatory genes (p < 0.05). Increased NETs were associated with the severity of COVID-19 infection, particularly in patients with severe pneumonia, and could be used as biomarkers to assess disease severity. Enoxaparin pretreatment inhibited NETs and reduced the expression of inflammatory cytokines, and these effects mostly persisted in patients treated with prophylactic enoxaparin.