CD4+CD25+T Cells Regulate Vaccine-Generated Primary and Memory CD8+T-Cell Responses against Herpes Simplex Virus Type 1

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Abstract
It has become evident that naturally occurring CD25+ regulatory T cells (Treg cells) not only influence self-antigen specific immune response but also dampen foreign antigen specific immunity. This report extends our previous findings by demonstrating that immunity to certain herpes simplex virus (HSV) vaccines is significantly elevated and more effective if Treg cell response is curtailed during either primary or recall immunization. The data presented here show that removal of CD25+ Treg cells prior to SSIEFARL-CpG or gB-DNA immunization significantly enhanced the resultant CD8+ T-cell response to the immunodominant SSIEFARL peptide. The enhanced CD8+ T-cell reactivity in Treg cell-depleted animals was between two- and threefold and evident in both acute and memory stages. Interestingly, removal of CD25+ Treg cells during the memory recall response to plasmid immunization resulted in a twofold increase in CD8+ T-cell memory pool. Moreover, in the challenge experiments, memory CD8+ T cells generated with plasmid DNA in the absence of Treg cells cleared the virus more effectively compared with control groups. We conclude that CD25+ Treg cells quantitatively as well as qualitatively affect the memory CD8+ T-cell response generated by gB-DNA vaccination against HSV. However, it remains to be seen if all types of vaccines against HSV are similarly affected by CD25+ Treg cells and if it is possible to devise means of limiting Treg cell activity to enhance vaccine efficacy.