Investigating human natural killer cell subsets and their responses to a Herpes Simplex Virus lipopeptide, a potential vaccine candidate

Abstract

Herpes Simplex Virus (HSV) type 1 and 2 cause lifelong, latent infection with recurrences. Serious complications can occur and no vaccine is available. Natural killer (NK) cells play a role in the interface between innate and adaptive immunity, and in the antiviral response. Nonetheless, NK cells have been largely overlooked in designing vaccine candidates. Previously, NK cells were activated by a TLR2 agonist, Pam2Cys, conjugated to an HSV gD peptide: Pam2Cys-30-5, and stimulated CD4+T cells in the absence of other antigen-presenting cells. Human NK cells are comprised of functionally diverse subsets. CD56dimCD16+ are the predominant subset in circulation, >95%, and CD56brightCD16-/dim are <5%. They have been characterised as highly cytolytic or as potent cytokine producers, respectively. The selective responses of CD56bright NK cells to the cytokines IL-15, IL-2 and IL-7 were compared to enrich this subset in culture. IL-7 selectively enhanced CD56bright survival and proliferation, and perforin expression was not increased. IL-7 CD56bright NK cells expressed similar immune function genes as CD56bright NK cells. CD56bright and CD56dim NK cell responses to Pam2Cys-30-5 were investigated. Both subsets were activated by Pam2Cys-30-5, indicated by expression of CD69 and cytokines. The CD56dim subset produced higher concentrations of cytokines, whilst significant upregulation of HLA-DR was exclusive to the CD56bright subset. CD16 was significantly downregulated on CD56dim NK cells, and both shedding and internalisation were detected as mechanisms. Soluble factors produced by both NK cell subsets induced increased expression of maturation markers CD83 and CD80 on monocyte-derived dendritic cells (MDDCs). Finally, normal foreskin and an initial penile herpes lesion biopsy were examined for NK cells. CLA was expressed on CD16- NK cells in normal foreskin, indicating a regular turnover of these cells. In infected tissue the majority of NK cells were CD16+. NK cells may play a role in innate control of initial genital HSV infection and should be considered in vaccine development. Furthermore, understanding the mechanism of NK cell responses to TLR2 agonists will provide insight into their use as vaccine adjuvants.