Herpes simplex virus type 1 dUTPase mutants are attenuated for neurovirulence, neuroinvasiveness, and reactivation from latency

Herpes simplex virus type 1 (HSV-1) encodes a dUTPase which has been shown to be dispensable for normal viral replication in cultured cells (S. J. Caradonna and Y. Cheng, J. Biol. Chem. 256:9834-9837, 1981; F. B. Fisher and V. G. Preston, Virology 148:190-197, 1986). However, the importance of this enzyme in vivo has not been determined. In this report, HSV-1 strain 17 syn⁺ and two isogenic engineered dUTPase-negative mutants were characterized in the mouse model. Both mutants replicated with wild-type kinetics and achieved wild-type titers in cultured cells. The mutants were 10-fold less neurovirulent than 17 syn⁺ following intracranial inoculation and more than 1,000-fold less virulent following footpad inoculation. The dUTPase^- mutants replicated with wild-type kinetics in the footpad and entered and replicated efficiently in the peripheral nervous system of the mouse. However, their replication in the central nervous system was significantly reduced. The dUTPase^- strains established latent infections but displayed a greatly reduced reactivation frequency in vivo. Neurovirulence, neuroinvasiveness, and reactivation frequency were all restored by recombination with wild-type dUTPase sequences. These results have important implications with regard to anti-herpesvirus therapeutic strategies.