Archive | 2021
Dynamic SARS-CoV-2 specific B cell and T cell responses following immunization of an inactivated COVID-19 vaccine
Abstract
\n OBJECTIVE\n The dynamic adaptive immune responses elicited by the inactivated virus vaccine, CoronaVac, remain elusive.\n \n METHODS\n In a prospective cohort of 100 SARS-CoV-2 naïve healthcare professionals who received two doses of CoronaVac, we analyzed SARS-CoV-2-specific humoral and cellular responses at four different timepoints, including before vaccination (T1), 2\xa0weeks after the first dose (T2), 2\xa0weeks after the booster dose (T3), and 8-10\xa0weeks post the booster dose (T4). SARS-CoV-2-specific antibodies, serum neutralizing activities, peripheral B cells, CD4+ and CD8+ T cells, and their memory subsets were simultaneously measured in this cohort.\n \n RESULTS\n SARS-CoV-2 Spike-specific IgG responses reached the peak (geometric mean titer [GMT] 54827, 30969-97065) after two doses and rapidly declined (GMT 502, 212-1190) at T4, whereas suboptimal IgA responses were detected (GMT 5, 2-9). Spike-specific circulating B cells (0.60%, 0.46-0.73% of total B cells) and memory B cells (1.18%, 0.92-1.44% of total memory B cells) were effectively induced at T3 and sustained over time (0.33%, 0.23-0.43%; 0.87%, 0.05-1.67%, respectively). SARS-CoV-2-specific circulating CD4+ T cells (0.57%, 0.47-0.66%) and CD8+ T cells (1.29%, 1.04-1.54%) were detected at T3. At T4, 0.78% (0.43-1.20%) of memory CD4+ T cells and 0.68% (0.29-1.30%) of memory CD8+ T cells were identified as SARS-CoV-2 specific, while 0.62% (0.51-0.75%) of CD4+ T cells and 0.47% (0.38-0.58%) of CD8+ T cells were SARS-CoV-2 specific terminally differentiated effector memory cells. Furthermore, age and interval between doses affected the magnitude of CoronaVac induced immune responses. SARS-CoV-2 memory CD4+ T cells was strongly associated with both RBD-specific memory B cells (r=0.87, p<0.0001) and SARS-CoV-2 specific memory CD8+ T cells (r=0.48, p<0.0001).\n \n CONCLUSIONS\n CoronaVac induced robust circulating and memory B cells and T cell responses. Our study offers new insight into the underlying immunobiology of inactivated virus vaccines in humans and may have implications for vaccine strategies in the future.\n