Shifting the Immune Memory Paradigm: Trained Immunity in Viral Infections

Trained immunity is defined as the de facto memory characteristics induced in innate immune cells after exposure to microbial stimuli after infections or certain types of vaccines. Through epigenetic and metabolic reprogramming of innate immune cells after exposure to these stimuli, trained immunity induces an enhanced nonspecific protection by improving the inflammatory response upon restimulation with the same or different pathogens. Recent studies have increasingly shown that trained immunity can, on the one hand, be induced by exposure to viruses; on the other hand, when induced, it can also provide protection against heterologous viral infections. In this review we explore current knowledge on trained immunity and its relevance for viral infections, as well as its possible future uses.