The development of synthetic vaccines

Sequence analysis of the 47-kilodalton major integral membrane immunogen of Treponema pallidum

The complete primary amino acid sequence for the 47-kilodalton (kDa) major integral membrane immunogen of Treponema pallidum subsp. pallidum was obtained by using a combined strategy of DNA sequencing (of the cloned gene in Escherichia coli) and N-terminal amino acid sequencing of the native (T. pallidum subsp. pallidum-derived) antigen. An open reading frame believed to encode the 47-kDa antigen comprised 367 amino acid codons, which gave rise to a calculated molecular weight for the corresponding antigen of 40,701. Of the 367 amino acids, 113 (31%) were sequenced by N-terminal amino acid sequencing of trypsin and hydroxylamine cleavage fragments of the native molecule isolated from T. pallidum subsp. pallidum; amino acid sequence data had a 100% correlation with that of the amino acid sequence predicted from DNA sequencing of the cloned gene in E. coli. Although no consensus sequences for the initiation of transcription or translation were readily identifiable immediately 5' to the putative methionine start codon, a 63-base-pair PstI fragment located 159 nucleotides upstream was required for expression of the 47-kDa antigen in E. coli. The 47-kDa antigen sequence did not reveal a typical leader sequence. The overall G+C content for the DNA corresponding to the structural gene was 53%. Hydrophilicity analysis identified at least one major hydrophilic domain of the protein near the N terminus of the molecule which potentially represents an immunodominant epitope. No repetitive primary sequence epitopes were found. The combined data provide the molecular basis for further structural and functional studies regarding the role of the antigen in the immunopathogenesis of treponemal disease.

Immunisation of volunteers with a synthetic peptide vaccine for enterotoxigenic Escherichia coli

A completely synthetically produced peptide vaccine, consisting of the 18-aminoacid Escherichia coli heat-stable toxin and the 26-aminoacid epitope of the heat-labile toxin B subunit, was given orally to thirteen volunteers. It raised antitoxin titres to both toxin components four-fold in serum samples and seven-fold in jejunal aspirates over preimmunisation control titres. Jejunal aspirates taken after immunisation from vaccinees, but not controls, neutralised the secretory activity of both toxins in appropriate biological assays. These findings show that synthetically produced vaccines are immunogenic in human beings. The peptide used is a promising vaccine for diarrhoeal disease caused by enterotoxigenic strains of E coli.

The safety of egg-containing vaccines for egg-allergic patients

Forty-two patients with a history of egg sensitivity were evaluated for receiving avian-grown vaccines. After giving a history and undergoing physical examination, each patient was skin-tested with egg antigens and six egg-propagated vaccines, given an oral egg challenge, and finally, when possible, given a vaccine challenge. Thirty-seven of the 42 patients (88%) were ultimately given one or more of the vaccines with no reactions or only minimal ones to both egg protein and vaccine; they had mild reactions consisting of pruritus, headache, and apprehension. Immunization was withheld from three patients who had a history of severe reactions after egg ingestion and strongly positive skin reactivity to both egg and vaccine. A history of egg intolerance should not, by itself, disqualify a patient from receiving one of these vaccines. However, a history of exquisite sensitivity to egg protein indicates that a severe vaccine reaction is likely. An intradermal skin test utilizing 0.02 ml of a 1:100 dilution of the vaccine and resulting in a wheal of greater than 5 mm was found to be the test that most reliably predicted those patients who should not receive the vaccine.

Variation of influenza A, B, and C viruses

Influenza is caused by highly variable RNA viruses belonging to the orthomyxovirus group. These viruses are capable of constantly changing the genes coding for their surface proteins as well as for their nonsurface proteins. The mechanisms responsible for these changes in type A influenza viruses include recombination (reassortment) of genes among strains, deletions and insertions in genes, and, frequently, point mutations. In addition, old strains may reappear in the population. Influenza viruses of types B and C appear to vary to a lesser degree. The mechanisms responsible for changes in these viruses are not well characterized.