Clearance of attenuated rabies virus from brain tissues is required for long-term protection against CNS challenge with a pathogenic variant.

Rabies virus is a neurotropic lyssavirus which is 100% fatal in its pathogenic form when reaching unprotected CNS tissues. Death can be prevented by mechanisms delivering appropriate immune effectors across the blood-brain barrier which normally remains intact during pathogenic rabies virus infection. One therapeutic approach is to superinfect CNS tissues with attenuated rabies virus which induces blood-brain barrier permeability and immune cell entry. Current thinking is that peripheral rabies immunization is sufficient to protect against a challenge with pathogenic rabies virus. While this is undoubtedly the case if the virus is confined to the periphery, what happens if the virus reaches the CNS is less well-understood. In the current study, we find that peripheral immunization does not fully protect mice long-term against an intranasal challenge with pathogenic rabies virus. Protection is significantly better in mice that have cleared attenuated virus from the CNS and is associated with a more robust CNS recall response evidently due to the presence in CNS tissues of elevated numbers of lymphocytes phenotypically resembling long-term resident immune cells. Adoptive transfer of cells from rabies-immune mice fails to protect against CNS challenge with pathogenic rabies virus further supporting the concept that long-term resident immune cell populations must be established in brain tissues to protect against a subsequent CNS challenge with pathogenic rabies virus.