Antigen Delivery Systems: Past, Present, and Future

The traditional global vaccine market consisted of the whole-cell vaccines and subunit vaccines.Whole-cell vaccines include inactivated vaccines and live attenuated vaccines, while subunit vaccines include recombinant protein subunit vaccines, polysaccharide vaccines, and conjugate vaccines.COVID-19, an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was declared a pandemic in March 2020.The urgent demand 370The COVID-19 pandemic has increased demand for safe and effective vaccines.Research to develop vaccines against diseases including Middle East respiratory syndrome, Ebolavirus, human immunodeficiency virus, and various cancers would also contribute to global well-being.For successful vaccine development, the advancement of technologies such as antigen (Ag) screening, Ag delivery systems and adjuvants, and manufacturing processes is essential.Ag delivery systems are required not only to deliver a sufficient amount of Ag for vaccination, but also to enhance immune response.In addition, Ag types and their delivery systems determine the manufacturing processes of the vaccine product.Here, we analyze the characteristics of various Ag delivery systems: plasmids, viral vectors, bacterial vectors, nanoparticles, self-assembled particles, natural and artificial cells, and extracellular vesicles.This review provides insight into the current vaccine landscape and highlights promising avenues of research for the development and improvement of Ag delivery systems.