Role of IL-15 and IL-21 in viral immunity: applications for vaccines and therapies

Most people suffer from at least one viral infection in their life, some more virulent and aggressive than others. The aggressiveness and progression of viral diseases depends on the type of virus and quality of antiviral response generated during innate immunity and maintained during adaptive immunity. Two recently discovered cytokines (IL-15 and IL-21) appear to be key regulators in this process. IL-15 induces an antiviral state during innate immunity through the regulation of IFN-alpha/beta production and natural killer cell proliferation. During the memory phase, antigen-specific CD8(+) T cells are highly dependent on IL-15 signaling. IL-21 induces natural killer cell maturation and IFN-gamma production and acts to enhance the proliferation of memory CD8(+) T cells, its effects being more pronounced when combined with IL-15. We describe the mechanisms and potential uses of these cytokines in the design of antiviral vaccines and therapies.