Immunization with chemically detoxified pertussis toxin can prevent severe whooping cough with an efficacy similar to that of the cellular pertussis vaccine, which normally gives unwanted side effects. To avoid the reversion to toxicity and the loss of immunogenicity that may follow chemical treatment of pertussis toxin, inactive toxins were constructed by genetic manipulation. A number of genetically engineered alleles of the pertussis toxin genes, constructed by replacing either one or two key amino acids within the enzymatically active S1 subunit, were introduced into the chromosome of strains of Bordetella pertussis, B. parapertussis, and B. bronchiseptica. These strains produce mutant pertussis toxin molecules that are nontoxic and immunogenic and that protect mice from the intracerebral challenge with virulent Bordetella pertussis. Such molecules are ideal for the development of new and safer vaccines against whooping cough.

The introduction of two amino acid substitutions within the enzymatically active subunit Si of pertussis toxin (PT) abolishes its ADP-ribosyltransferase activity and toxicity on CHO cells (Pizza et al., Science 246:497-500, 1989). These genetically inactivated molecules are also devoid of other in vivo adverse reactions typical of PT, such as induction of leukocytosis, potentiation of anaphylaxis, stimulation of insulin secretion, and histamine sensitivity. However, the mutant PT molecules are indistinguishable from wild-type PT in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and maintain all the physical and chemical properties of PT, including affinity for toxin-neutralizing poly-and monoclonal antibodies. Either alone or stabilized with formaldehyde, PT mutants are able to induce high levels of neutralizing antibodies and to protect mice in a dose-dependent fashion against intracerebral challenge with virulent B. pertussis. These results clearly show that these genetically inactivated PT molecules are nontoxic but still immunogenic and justify their development as a component of a new, safer aceliular vaccine against whooping cough.

The diagnosis of infection caused by Mycobacterium tuberculosis is of increased public health concern following increases in the number of cases in developed countries and major increases in developing countries associated with the spread of human immunodeficiency virus (HIV) infection. The specificity of purified protein derivative skin testing for the detection of infection is compromised by exposure to environmental mycobacteria. Examination of sputum detects the most infectious patients, but not those with extrapulmonary disease. The 38-kDa antigen of M. tuberculosis contains two M. tuberculosis-specific B-cell epitopes. We overexpressed the gene for this antigen in Escherichia coli and evaluated the recombinant product in in vitro assays of T-cell function and as a target for the antibody response in humans. The sensitivity and specificity of the antigen as a skin test reagent were also assessed in outbred guinea pigs. We found that 69% of healthy sensitized humans recognize the antigen in vitro, as manifested by both cell proliferation and the production of gamma interferon. Untreated patients initially have a lower frequency of response (38%); this recovers to 72% during therapy. A total of 292 patients (20 with HIV coinfection) and 58 controls were examined for production of antibody to the 38-kDa antigen by using a commercially available kit. The sensitivity of the test in comparison with that of culture was 72.6%, and the specificity was 94.9%. The antigen was also tested for its ability to induce skin reactions in outbred guinea pigs sensitized by various mycobacterial species. The antigen provoked significant skin reactions in M. tuberculosis-, M. bovis BCG-, and M. intracellulare-sensitized animals. The significance of these findings and the usefulness of this antigen in immunodiagnosis are discussed.

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