Vaccination with a Shigella DNA vaccine vector induces antigen-specific CD8+ T cells and antiviral protective immunity

A prototype Shigella human immunodeficiency virus type 1 (HIV-1) gp120 DNA vaccine vector was constructed and evaluated for immunogenicity in a murine model. For comparative purposes, mice were also vaccinated with a vaccinia virus-env (vaccinia-env) vector or the gp120 DNA vaccine alone. Enumeration of the CD8(+)-T-cell responses to gp120 after vaccination using a gamma interferon enzyme-linked spot assay revealed that a single intranasal dose of the Shigella HIV-1 gp120 DNA vaccine vector elicited a CD8(+) T-cell response to gp120, the magnitude of which was comparable to the sizes of the analogous responses to gp120 that developed in mice vaccinated intraperitoneally with the vaccinia-env vector or intramuscularly with the gp120 DNA vaccine. In addition, a single dose of the Shigella gp120 DNA vaccine vector afforded significant protection against a vaccinia-env challenge. Moreover, the number of vaccinia-env PFU recovered in mice vaccinated intranasally with the Shigella vector was about fivefold less than the number recovered from mice vaccinated intramuscularly with the gp120 DNA vaccine. Since the Shigella vector did not express detectable levels of gp120, this report confirms that Shigella vectors are capable of delivering passenger DNA vaccines to host cells and inducing robust CD8+ T-cell responses to antigens expressed by the DNA vaccines. Furthermore, to our knowledge, this is the first documentation of antiviral protective immunity following vaccination with a live Shigella DNA vaccine vector.