Immunogenicity and Efficacy of a Trivalent HSV-2 gC2, gD2, gE2 Nucleoside-Modified mRNA-LNP Vaccine Against HSV-1 Eye Infection and Neuroinvasion in Mice

Background/Objectives: Eye infection with herpes simplex virus type 1 (HSV-1) can result in keratitis, a leading cause of corneal blindness. We evaluated whether an experimental vaccine containing HSV-2 immunogens to prevent genital herpes also protects against HSV-1 eye infection and neuroinvasion. Methods: Mice were immunized twice, one month apart, with PBS or a nucleoside-modified lipid nanoparticle vaccine containing mRNA encoding for gC2, gD2, and gE2. One month later, 106 plaque forming units (PFU) (10 lethal dose 50, LD50) of the HSV-1 McKrae strain were added to the intact cornea of each eye. Results: The vaccine prevented death and markedly reduced eyelid and attached conjunctival inflammation (blepharoconjunctivitis) and weight loss compared with the PBS group. Tissues from the ocular conjunctiva and eye bulb, olfactory bulb/peduncle, trigeminal ganglia, and brain (brainstem, cerebrum, and cerebellum) were harvested 5 days post-infection from 5 mice each in the PBS and vaccine groups, and from another 10 mice in the vaccine group 7 weeks post-infection. At 5 days, HSV-1 was not detected in any tissue in the vaccine group, while viral titers were positive in 16 of 25 (64%), and HSV-1 DNA was detected in 22 of 25 (88%) individual tissues in the PBS group. Histopathological and immunohistochemical analysis at 5 days post-infection confirmed that the vaccine protected against inflammation; however, some animals experienced breakthrough blepharoconjunctivitis. At 7 weeks, 3 of 10 (30%) mice in the vaccine group had HSV-1 DNA detected in the eyes or trigeminal ganglia tissues, but no animal had HSV-1 DNA detected in brain tissues. The vaccine produced cross-reactive HSV-1 neutralizing antibodies and gD1 IgG binding antibodies, but low or undetectable cross-reactive binding antibodies to gC1 and gE1. Conclusions: Despite occasional mild, localized breakthrough infections, the vaccine provided disease-modifying immunity and was neuroprotective. The results suggest that a single herpes vaccine effective against genital HSV-2 may be neuroprotective against HSV-1 following eye infection.