Mucosal application of plasmid-encoded IL-15 sustains a highly protective anti-Herpes simplex virus immunity

In a DNA immunization against Herpes simplex virus (HSV), we examined the ability of plasmid-encoded interleukin-15 (pIL-15) to induce and maintain the mucosal B and T cell immune response. pIL-15 generated memory CD8(+) T cell responses that were threefold higher and mainly maintained in the spleen, but high levels of immunoglobulin A antibodies were induced and maintained long-term in the vaginal mucosa. Both of these enhanced components of the immune responses were recalled rapidly upon challenge with a lethal dose of HSV McKrae, affording protection in mice immunized with codelivery of pIL-15. Our results show for the first time that intranasal administration of pIL-15 along with plasmid-encoded glycoprotein B of HSV leads to enhancement of primary and memory CD8(+) T cell responses as well as humoral immune response. Therefore, a mucosal immunization strategy that incorporates a potent cytokine such as IL-15 as an adjuvant might induce protective mucosal immune responses that constitute the initial barrier at mucosal portals of pathogen entry.