Rapid clearance of herpes simplex virus type 2 by CD8+ T cells requires high level expression of effector T cell functions

CD8⁺ T cells are important for resolution of HSV-2 lesions from the female genital epithelium. It is uncertain whether optimal clearance of viruses such as HSV-2 that cause a limited, non-systemic infection solely requires expression of effector functions by infiltrating CD8⁺ T lymphocytes, or if the clearance rate is reflective of the expression level of critical effector functions. To address this, CD8⁺ T cells from normal OT-I mice or OT-I mice deficient in IFNγ (IFNγ^-/-) or the IFNγ receptor (IFNγR^-/-) were activated in vitro in the presence of IFNγ or IL-4 to generate a series of effector populations (Tc1 and Tc2-like respectively) that secreted different levels of IFNγ and expressed different levels of HSV-specific cytolytic function. Compared with Tc1 cells, Tc2-like cells produced the type 2 cytokines IL-4 and IL-5, exhibited decreased IFNγ secretion, diminished proliferation in vitro, and decreased antigen-specific cytolysis in vivo. Clearance of an ovalbumin-expressing HSV-2 strain (HSV-2 tk^- OVA) by adoptively transferred Tc2-like cells was delayed relative to Tc1 cell recipients. Because donor Tc2-like cells proliferated in vivo and infiltrated the infected genital epithelium similar to Tc1 cells, the diminished virus clearance by Tc2-like effector cells correlated with reduced expression of critical effector functions. Together, these results suggest that high level expression of protective T cell functions by effector T cells is necessary for optimal clearance of HSV-2 from the genital epithelium. These results have important implications for vaccines designed to elicit CD8⁺ T cells against viruses such as HSV-2 that infect the genital tract.