Induction of cell-mediated immune responses to human immunodeficiency virus type 1 Gag protein by using Listeria monocytogenes as a live vaccine vector.

Cytolytic T cells, acting through cytokines or by direct lysis of infected target cells, have been shown to play a significant role in the control of viral infections and may be responsible for the prolonged asymptomatic phase following infection by HIV. Accordingly, methods that can generate strong cell-mediated immune responses may be useful in the development of prophylactic and therapeutic vaccines against HIV. Listeria monocytogenes is a Gram-positive intracellular microorganism that elicits strong cell-mediated immune responses against its own secreted proteins following infection. In this study we have modified the chromosome of L. monocytogenes so that it stably expresses and secretes the p55 HIV gag gene product and examined the cell-mediated immune response of BALB/c mice to infection with this recombinant organism. Infected animals were found to mount a specific, strong, long-lasting CD8+ cytolytic T cell response against a predominant epitope contained within the p24 fragment of the HIV Gag protein. This epitope previously has been shown to be recognized by CTLs obtained from some HIV-infected humans. Our results suggest that chromosomally modified strains of L. monocytogenes may provide valuable vaccine vectors for use against HIV.