Construction and characterization of genetically inactivated pertussis toxin

Pertussis toxin has been shown to be an important virulence factor and an antigen which will probably be essential to a pertussis vaccine. Inactivation of the pertussis toxin was required due to the pharmacological properties associated with this toxin. However, chemical inactivation has the potential of altering important epitopes or of failing to inactivate the toxin. Cloning and sequencing of the pertussis toxin operon has permitted the introduction of specific mutations in the S1 gene which have been shown to have a profound effect on the subsequent enzyme activity. Various mutations were constructed, re-assembled into the pertussis toxin operon and returned to the Bordetella pertussis chromosome for expression. Pertussis toxin, with lysine substituted for arginine at position 9 in the S1 subunit (PTA-K9) was assembled and expressed to wild type levels. Substitution of codons for aspartic acid, glycine and glutamine, for that of glutamic acid at position 129 were incorporated into the PTA-K9 construction. Virulence of these constructed B. pertussis strains and ADP-ribosylation by their toxoids were greatly reduced relative to that found with the wild type. Additionally, PTA-K9 was found to have reduced leukocytosis promotion and histamine sensitization activities. Finally, PTA-K9 was shown to be a protective immunogen in both intracerebral and aeorosol challenge assays.