Vaccine

An isolated DNA molecule comprising a recombinant coding sequence encoding all of a Bordetella pertussis holotoxin or portion thereof wherein said holotoxin or portion thereof comprises either or both of a modified S2 subunit protein and a modified S3 subunit protein, wherein said modified subunit protein is specifically reactive against a wild-type pertussis toxin but is defective in pertussis toxin target cell receptor binding, and wherein:

• said modified S2 subunit comprises one or more amino acid sequence mutations selected from the group consisting of a deletion of one or more of Tyr.sup.102, Tyr.sup.103 and Asn.sup.105, an amino acid substitution of either or both of Tyr.sup.102 and Tyr.sup.103, and a substitution of a negatively-charged amino acid for Asn.sup.105, and
• said modified S3 subunit comprises one more amino acid sequence mutations selected from the group consisting of a deletion of one or more of Tyr.sup.102, Tyr.sup.103 and Lys.sup.105, an amino acid substitution of either or both of Tyr.sup.102 and Tyr.sup.103, and a substitution of a negatively-charged amino acid for Lys.sup.105.