Regulation of the innate immune response in human neurons by ICP34.5 maintains herpes simplex virus 1 latency

Herpes simplex virus 1 (HSV-1) establishes latent infections in sensory neurons, from which HSV sporadically reactivates due to external stress and other stimuli. Latency and reactivation are studied through in vivo models in a variety of hosts, as well as in vitro models using primary neurons, and neurons derived from pluripotent stem cells (iPSCs). These systems behave disparately, but the reasons remain unknown. The interferon (IFN)-based neuronal innate immune response is critical in controlling HSV-1 replication and HSV-1 counters these responses in part through infected-cell protein 34.5 (ICP34.5). ICP34.5 also promotes neurovirulence by preventing host translational shutoff and interfering with host cell autophagy. Here we demonstrate in a human iPSC neuronal model that sustaining host translation is the key activity of ICP34.5 for enhancement of reactivation. Specifically, our data shows that ICP34.5 was key for maintenance of HSV-1 latency. While interaction of ICP34.5 with the autophagy regulator Beclin 1 was important for maintaining latency, this was not due to modulation of bulk autophagy. Our work from primary mouse neurons suggested that the major effect of ICP34.5 on latency maintenance occurs in an IRF3/7-dependent manner. Notably, the role of ICP34.5 in regulating latency and reactivation differs between neurons derived from human iPSCs (iNeurons) and primary mouse trigeminal (TG) neurons. This highlights the importance of selecting an appropriate neuronal model and validating experimental outcomes in multiple models.