Abstract
Herpes simplex virus 1 (HSV-1) causes lifelong recurrent infections. Following primary infection of the oral or genital mucosa, HSV-1 travels retrogradely through axons and establishes latency in the cell body of ganglionic neurons of the peripheral nervous system. Periodic reactivation in neurons and anterograde transport of virions back to peripheral regions cause oral or genital ulcerations. Many host and viral factors implicated in retrograde and anterograde transport of HSV-1 have been identified. In particular, studies reported that introducing five amino acid substitutions in the R2 region of the viral tegument protein UL37 was sufficient to completely eliminate retrograde transport of HSV-1 strain F. Here, we introduced the same R2 mutations in the highly neurovirulent HSV-1 strain 17+. We show that this R2(17) virus is highly attenuated in mice and acts as a potent vaccine that protects mice against acute HSV-1 infection. However, we report that the R2(17) virus has residual retrograde transport. We show that R2(17) can establish latency in mouse models of ocular and vaginal infection and reactivate. These results contradict published evidence and show that the R2 mutation is not sufficient to fully prevent retrograde transport of HSV-1. IMPORTANCE: Herpes simplex virus 1 (HSV-1) is a ubiquitous pathogen without a cure or vaccine. HSV-1 travels through nerves between the oral and genital mucosa and the peripheral nervous system, where it establishes lifelong latency. Studies reported that introducing five amino acid substitutions in the R2 region of the viral tegument protein UL37 was sufficient to completely eliminate the retrograde transport of HSV-1 strain F from the mucosa to the nervous system. Here, we present contradictory findings. We report that an HSV-1 virus from strain 17+ with the same R2 mutation has residual retrograde transport. This shows that the R2 mutation is not sufficient to fully prevent the retrograde transport of HSV-1 in all settings. This finding may be particularly relevant for assessing the safety of prospective live-attenuated vaccines that include the R2 mutation.