Vaccine for COVID-19: Role of adjuvants

In the emergency that the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has globally spread, vaccine is one of the most indispensable defense lines to repulse the resulting Coronavirus Disease 2019 (COVID-19) pandemic. The effective immunization frequently requires appropriate adjuvants which play a key role to activate the dendritic cell maturation. Indeed, the antigen presentation of dendritic cells indisputably needs the collaboration of co-stimulatory molecules which are only expressed by mature dendritic cells to trigger T cell response. In this review, we collectively summarized well-known adjuvants used for vaccination as well as their characteristics and immunostimulatory effects on both of humoral and cell-mediated immune response. Besides, the applicability of adjuvants in COVID-19 vaccination and accompanying challenges were also discussed. Generally, despite of certain successes of available licensed adjuvants in the vaccination, new generations of novel adjuvants would absolutely be required to produce effective vaccines for other inevitable pathogenic organisms in the future.