Lytic granule‐mediated, noncytolytic CD8+ T cell inhibition of HSV‐1 reactivation from neuronal latency

The purpose of our studies is to identify and characterize the mechanisms employed by HSV‐specific CD8 + T cells (HSV‐CD8) to block HSV‐1 reactivation from latency in sensory ganglia, potentially limiting recurrent herpetic disease. HSV‐CD8 can secrete IFN‐γ to inhibit reactivation in some, but not all neurons, suggesting involvement of additional effector mechanisms. We now show that the lytic granule components perforin (Pfn) and granzyme B (GrB) are necessary for optimal protection from HSV‐1 reactivation in sensory neurons both in vivo and in ex vivo trigeminal ganglia (TG) cultures. We further establish that HSV‐CD8 exhibit vectorial release of lytic granules into immune synapses formed with both susceptible fibroblasts and latently infected neurons in ex vivo TG cultures. Importantly, while lytic granule release activates the caspase system of fibroblasts leading to morphologic signs of apoptosis, similar lytic granule release does not induce caspase activation or morphologic signs of apoptosis in neurons. Together our findings establish that directed lytic granule release by HSV‐CD8 is required to block neuronal HSV‐1 reactivation, that lytic granules block HSV‐1 reactivation in neurons without activating caspases or inducing apoptosis, and that GrB is one (but apparently not the only) lytic granule component required to block HSV‐1 reactivation. Supported by NIH, Eye & Ear Foundation, & RPB.