Two-phase releasing immune-stimulating composite orchestrates protection against microbial infections.

Sepsis, a syndrome of acute organ dysfunction induced by various infections, could lead to a very high mortality in hospitals despite the development of advanced medical technologies. Herein, a type of two-phase releasing immune-stimulating composite is developed by mixing alginate (ALG) with muramyl dipeptide (MDP) and the nanoparticle formulation of monophosphoryl lipid A (MPLA), the latter two are immunomodulatory agents with different release rates from the formed ALG hydrogel. The obtained two phase-releasing composite could provide instantaneous sepsis protection by the rapid release of MDP to enhance the phagocytic and bactericidal function of macrophages. Later on, such composite could further offer long-term sepsis protection by the sustained release of MPLA to continuously activate the immune system, via up-regulating the production of various pro-inflammatory cytokines, promoting the polarization of macrophages, and increasing the percent of natural killer (NK) cells in the lesion after sepsis challenge. Mice survived from sepsis challenge after such treatment could resist a second infection. Notably, treatment with our composite could increase the mouse survival rate in a cecal ligation and puncture (CLP) induced polymicrobial sepsis model. This work provides an easy-translatable immune-stimulating formulation for effective protection against sepsis under various triggering causes. Our strategy may be promising for long-term broad prevention against various infections, and could potentially be used to protect medical workers under a new pandemic before a reliable vaccine is available.