Both CD4+ and CD8+ T cells respond to antigens fused to anthrax lethal toxin.
The lethal toxin produced by Bacillus anthracis is a bipartite toxin in which the first protein, protective antigen (PA), transports the second protein, lethal factor, across the host cell membrane. We have previously shown that CD8(+) T-cell epitopes fused to a nontoxic derivative of lethal factor (LFn) are delivered into the host cell cytosol in a PA-dependent manner. Delivery of these antigens targets them to the intracellular major histocompatibility complex (MHC) class I processing and presentation pathway and leads to the stimulation of antigen-specific CD8(+) T cells in vivo. In this report, we describe the generation and characterization of LFn fusion proteins that include not only a CD8(+) T-cell epitope but also a CD4(+) T-cell epitope. We first show that these fusion proteins induce antigen-specific CD4(+) T-cell responses following incubation with dendritic cells in vitro or injection into mice. Stimulation of CD4(+) T cells by LFn fusion proteins does not require PA but is enhanced by PA in vitro. We also show that a single LFn fusion protein and PA can deliver antigen to both the MHC class II and the MHC class I pathways, resulting in the simultaneous induction of antigen-specific CD4(+) T cells and antigen-specific CD8(+) T cells in the same mouse. These results suggest that this toxin delivery system is capable of stimulating protective immune responses where effective immunization requires stimulation of both classes of T cells.
Shaw
Christine A
CA
Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115, USA.
Starnbach
Michael N
MN
D000818:Animals; D000942:Antigens, Bacterial / Q000276:immunology / Q000378:metabolism*; D001408:Bacillus anthracis / Q000276:immunology / Q000378:metabolism; D001427:Bacterial Toxins / Q000276:immunology / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D003713:Dendritic Cells; D000939:Epitopes / Q000378:metabolism; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D007371:Interferon-gamma / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D011994:Recombinant Proteins; D013047:Specific Pathogen-Free Organisms
D000942:Antigens, Bacterial; D001427:Bacterial Toxins; D000939:Epitopes; D011994:Recombinant Proteins; C030325:anthrax toxin; D007371:Interferon-gamma