Bacillus anthracis secretes two toxins into the extracellular medium during growth. The two toxins consist of three distinct proteins which combine in a pairwise fashion. Protective antigen (PA) can combine with lethal factor (LF) or edema factor (EF). PA combined with LF makes lethal toxin while PA combined with EF makes edema toxin. Part of each toxin is directly transported to the cytosol of living cells where it exerts its effect (see Arora, N., K.R. Klimpel, Y. Singh, and S.H. Leppla, 1992, J Biol Chem 267:15542-15548). We propose to take advantage of the efficient delivery of proteins to the cytosol to intracellularly inoculate living cells. Nearly all cell types have the ability to process proteins found in the cytosol and combine them with MHC class I molecules. The combination of the processed protein with the MHC class I molecule presented on the surface of the living cell results in the stimulation of a population of T-cells which recognize the processed protein antigen. Once stimulated, this population of T-cells can expand and become primed to rapidly respond to and eliminate cells which bear an identical combination of MHC class I and processed antigen. By making fusions between LF and different polypeptide antigens we will be able to vaccinate a host against many pathogens. Our initial work will focus on priming a response against several known antigenic proteins expressed by HIV-1, including gp120, gp41 p24, Nef, Tat and Rev.
