BACTERIAL GHOSTS - NONLIVING CANDIDATE VACCINES

Expression of cloned PhiX174 gene E in bacteria results in lysis of ba cteria. It is unique among phage lysis systems as it introduces a tran smembrane tunnel structure through the cell envelope complex of Gram-n egative bacteria. The resulting bacterial ghosts have intact envelope structures devoid of cytoplasmic contents. E-mediated lysis has been a chieved in a variety of Gram-negative bacteria including Escherichia c oli, Salmonella typhimurium, Vibrio cholerae, Klebsiella pneumoniae, a nd Actinobacillus pleuropneumoniae. Such ghosts, derived from human or animal pathogens, have been proposed as non-living candidate vaccines and represent an alternative to heat or chemically inactivated bacter ia. In 'recombinant ghosts', foreign proteins (e.g., viral proteins) a re inserted into the inner membrane via specific N-, or C-, or N- and C-terminal anchor sequences prior to lysis. Relevant advantages of (re combinant) bacterial ghosts as immunogens include: (i) inactivation pr ocedures that denature relevant immunogenic determinants are not emplo yed in the production of ghosts used as vaccines or as carriers of rel evant antigens; (ii) the recombinant proteins are inserted into a high ly immune stimulatory environment; (iii) there is no size limitation o f the foreign protein moieties: multiple antigenic determinants can be presented simultaneously; (iv) bacterial ghosts can be produced inexp ensively in large quantities; (v) (recombinant) ghosts are stable for long periods of time and do not require the cold chain storage system. Intraperitoneal, subcutaneous or intramuscular applications of recomb inant ghosts in experimental animals induced specific humoral and cell ular immune responses against bacterial and viral components. Initial aerosol vaccinations of swine with ghosts from Actinobacillus pleuropn eumoniae showed that protective immunity can be established by this ro ute of application and that the well-preserved surface structures of g hosts obtained by E-mediated lysis are able to target the mucosal immu ne system.