Alcaligenes lipid A: a unique TLR4 agonist mucosal adjuvant inducing secretory IgA and Th17 responses

The COVID-19 pandemic has underscored the importance of infectious disease control. In this context, intensive efforts are underway to develop novel vaccine modalities that will enable the production of effective and safe vaccines in preparation for future pandemics caused by emerging and re-emerging infectious diseases. To maximize the performance of these new modalities, adjuvants tailored to the characteristics of each platform are indispensable. In particular, the ability to elicit appropriate immune responses with minimal amounts of antigen is a critical determinant of both vaccine efficacy and safety in the development of mucosal vaccines that confer protection against infection by inducing immune responses in mucosal tissues - the primary sites of pathogen entry. Consequently, the development of superior adjuvants is a key factor for the practical implementation of mucosal vaccines. In this article, we focus on adjuvant development aimed at the creation of mucosal vaccines and introduce our efforts to apply Alcaligenes-derived lipid A to mucosal vaccine platforms.