Medroxyprogesterone acetate inhibits CD8⁺ T cell viral-specific effector function and induces herpes simplex virus type 1 reactivation

Clinical research suggests hormonal contraceptive use is associated with increased frequencies of HSV reactivation and shedding. We examined the effects of medroxyprogesterone acetate (MPA), the compound most commonly used for injectable hormonal contraception, on HSV type 1 (HSV-1) reactivation and CD8⁺ T cell function in murine trigeminal ganglia (TG). In ex vivo TG cultures, MPA dramatically inhibited canonical CD8⁺ T cell effector functions, including IFN-γ production and lytic granule release, and increased HSV-1 reactivation from latency. In vivo, MPA treatment of latently infected ovariectomized mice inhibited IFN-γproduction and lytic granule release by TG resident CD8⁺ T cells stimulated directly ex vivo. RNA specific for the essential immediate early viral gene ICP4 as well as viral genome DNA copy number were increased in mice that received MPA during latency, suggesting that treatment increased in vivo reactivation. The increase in HSV-1 copy number appeared to be the result of a two-tine effect, as MPA induced higher reactivation frequencies from latently infected explanted TG neurons in the presence or absence of CD45⁺ cells. Our data suggest hormonal contraceptives that contain MPA may promote increased frequency of HSV reactivation from latency through the combinatory effects of inhibiting protective CD8⁺ T cell responses and by a leukocyteindependent effect on infected neurons.