Oral Salmonella typhimurium vaccine expressing circumsporozoite protein protects against malaria.

Immunization with radiation-attenuated malaria sporozoites induces potent cellular immune responses, but the target antigens are unknown and have not previously been elicited by subunit vaccines prepared from the circumsporozoite (CS) protein. A method is described here for inducing protective cell-mediated immunity to sporozoites by immunization with attenuated Salmonella typhimurium transformed with the Plasmodium berghei CS gene. These transformants constitutively express CS antigens and, when used to immunize mice orally, colonize the liver, induce antigen-specific cell-mediated immunity, and protect mice against sporozoite challenge in the absence of antisporozoite antibodies. These data indicate that the CS protein contains T cell epitopes capable of inducing protective cell-mediated immunity, and emphasize the importance of proper antigen presentation in generating this response. Analogous, orally administered vaccines against human malaria might be feasible.

Development of vaccines based on formulations containing nonionic block copolymers.

In summary, data indicate that nonionic block copolymers in several different delivery formats can effectively enhance antibody responses to a variety of viral, parasite, or bacterial antigens. Polymers have historically been evaluated as polymers alone in aqueous buffer, in oil-in-water and water-in-oil emulsions. Several of those formulations can induce protective antibodies in preerythrocytic or erythrocytic malaria vaccine models or in pneumococcal vaccine models. In those models, protective immunity is associated with the development of IgG2a subclass antibodies. These results tend to indicate that copolymer adjuvant can influence isotype development, possibly by stimulating the appropriate T-cell subsets. Although there are some data suggesting that microfluidized vaccines containing the L121 nonionic block copolymer can induce CTL, equivalent experimental results with larger block polymers, which are effective in induction of greater proportions of IgG2a, have not yet been obtained. Several of the basic formulations with an appropriate copolymer may be suitable for clinical evaluation in conjunction with either current or future subunit antigens. Other formulations containing copolymers may also be suitable for mucosal administration.

Fragmentation of colicins A and E1 by cell surface proteases.

Interaction of either colicin A or E1 with the surface of Escherichia coli cells resulted in extensive cleavage of the colicins into many peptide fragments in the molecular weight range of 10,000 to 30,000 released into the supernatants of colicin-cell mixtures. The protease inhibitor P-aminobenzamidine inhibited the cleavage of colicin A and enhanced colicin killing activity, suggesting that proteolysis is not required for the killing action of colicin. Fragments derived from the supernatants of the mixtures were inactive against sensitive cells. Proteolytic activity against both colicins was localized primarily in the outer membrane fraction of the cell envelope. At least two distinct protease activities appear to be present. Examination of the patterns of cleavage and inactivation of the colicins by a series of resistant mutants indicates that specific colicin receptors play no essential role in colicin proteolysis. In addition, evidence is presented that adsorption of colicin to specific receptors is a reversible process.

Properties of Escherichia coli mutants altered in calcium/proton antiport activity.

Mutants sensitive to growth inhibition by CaCl2 were found to have alterations in calcium uptake in everted membrane vesicles. These mutations map at different loci on the Escherichia coli chromosomes. A mutation at the calA locus results in vesicles which have two- to threefold higher levels of uptake activity than vesicles from wild-type cells. The calA mutation is phenotypically expressed as increased sensitivity to CaCl2 in a strain also harboring a mutation in the corA locus, which is involved in Mg2+ transport. The calA locus maps very close to purA and cycA at about min 97. The calB mutation results both in sensitivity to CaCl2 at pH 5.6 and in vesicles with diminished calcium transport capability. The CalB phenotype is also expressed only in a corA genetic background; the calB locus appears to map very near, yet separately from, the calA locus. When the cor+ allele is present, calA and calB mutations still result in a defect in calcium transport in vesicles. In addition, both calC and calD mutations result in vesicles with impaired calcium transport activity. calC is cotransducible with kdp and nagA, whereas calD is cotransducible with proC.

Isolation and genetic characterizations of Bacillus megaterium cobalamin biosynthesis-deficient mutants.

Ethanolamine is deaminated by the action of ethanolamine ammonia-lyase (EC 4.3.1.7), an adenosylcobalamin-dependent enzyme. Consequently, to grow on ethanolamine as a sole nitrogen source, Bacillus megaterium requires vitamin B12. Identification of B. megaterium mutants deficient for growth on ethanolamine as the sole nitrogen source yielded a total of 34 vitamin B12 auxotrophs. The vitamin B12 auxotrophs were divided into two major phenotypic groups: Cob mutants, which could use cobinamide or vitamin B12 to grow on ethanolamine, and Cbl mutants, which could be supplemented only by vitamin B12. The Cob mutants were resolved into six classes and the Cbl mutants were resolved into three, based on the spectrum of cobalt-labeled corrinoid compounds which they accumulated. Although some radiolabeled cobalamin was detected in the wild type, little or none was evident in the auxotrophs. The results indicate that Cob mutants contain lesions in biosynthetic steps before the synthesis of combinamide, while Cbl mutants are defective in the conversion of cobinamide to cobalamin. Analysis of phage-mediated transduction experiments revealed tight genetic linkage within the Cob class and within the Cbl class. Similar transduction analysis indicated the Cob and Cbl classes are weakly linked. In addition, cross-feeding experiments in which extracts prepared from mutants were examined for their effect on growth of various other mutants allowed a partial ordering of mutations within the cobalamin biosynthetic pathway.

Cloning of multiple genes involved with cobalamin (Vitamin B12) biosynthesis in Bacillus megaterium.

An effective shotgun cloning procedure was developed for Bacillus megaterium by amplifying gene libraries in Bacillus subtilis. This technique was useful in isolating at least 11 genes from B. megaterium which are involved with cobalamin (vitamin B12) biosynthesis. Amplified plasmid banks were transformed into protoplasts of both a series of Cob mutants blocked before the biosynthesis of cobinamide and Cbl mutants blocked in the conversion of cobinamide into cobalamin. Amplification of gene libraries overcame the cloning barriers inherent in the relatively low protoplast transformation frequency of B. megaterium. A family of plasmids was isolated by complementation of seven different Cob and Cbl mutants. Each plasmid capable of complementing a Cob or Cbl mutant was transformed into each one of the series of Cob and Cbl mutants; many of the plasmids isolated by complementation of one mutation carried genetic activity for complementation of other mutations. By these criteria, four different complementation groups were resolved. At least six genes involved in the biosynthesis of cobinamide are carried on a fragment of DNA approximately 2.7 kilobase pairs in length; other genes involved in the biosynthesis of cobinamide were located in two other complementation groups. The physical and genetic data permitted an ordering of genes within several of the complementation groups. The presence of complementing plasmids in mutants blocked in cobalamin synthesis resulted in restoration of cobalamin biosynthesis.

Cation/proton antiport systems in Escherichia coli. Properties of the potassium/proton antiporter.

The potassium/proton antiport system of Escherichia coli has been characterized by the effect of monovalent cations on the pH gradient formed by oxidation of lactate in everted membrane vesicles. Substrates of the system include K+, Na+, Li+, Rb+, and Tl+. The antiporter could also be assayed by uptake of 204Tl+ into everted vesicles. The antiporter exhibits a basic pH optimum and catalyzes electroneutral proton/cation exchange. Antiporter activity is trypsin-sensitive, but trypsin inactivation is prevented by prior formation of an electrochemical proton gradient. Two other proton/cation exchangers, the Na+/H+ and Ca2+/H+ antiporters, were unaffected by the trypsin treatment. Regulation of cytosolic pH by K+/H+ exchange is postulated, where proton return to the cytosol by the K+/H+ antiporter prevents alkalinization of the cytosol during proton extrusion associated with the formation of a protonmotive force or during growth at alkaline pH.

Energy transduction in Escherichia coli: new mutation affecting the Fo portion of the ATP synthetase complex.

A mutation affecting the intrinsic membrane portion (BFo) of the ATP synthetase complex is described. The phenotype is different from previously reported BFo mutants. This mutation results in the ability of membranes lacking the extrinsic membrane portion (BF1) of the ATP synthetase complex to maintain a transmembrane pH gradient. Unlike other BFo mutants, this strain, NR71, is capable of utilizing ATP hydrolysis for the formation of a transmembrane pH gradient.

Targeting polymerised liposome vaccine carriers to intestinal M cells.

Due to their transcytotic capability, intestinal M cells may represent an efficient potential route for oral vaccine delivery. We previously demonstrated that the lectin Ulex europaeus agglutinin 1 (UEA1, specific for alpha-L-fucose residues) selectively binds to mouse Peyer's patch M cells and targets 0.5 microm polystyrene microparticles to these cells. Using a gut loop model we now demonstrate that covalently-membrane-bound UEA1 similarly targets polymerised liposomes (Orasomes, approximately 200 nm diameter), potential biocompatable oral vaccine delivery vehicles, to mouse M cells. Targeting was inhibited by alpha-L-fucose while the co-entrapped adjuvant, monophosphoryl Lipid A (MPL), failed to exert any detrimental effect on UEA1-mediated M cell targeting. Lectin-mediated M cell targeting may thus permit the efficacy of mucosal vaccines to be enhanced if cellular relationship between particle binding and immune outcome can be established.

Phase I clinical trials of aroA aroD and aroA aroD htrA attenuated S. typhi vaccines; effect of formulation on safety and immunogenicity.

PBCC211, an aroA aroD derivative of S. typhi strain CDC10-80, was tested in phase I trials as a single dose typhoid fever vaccine. Three different vaccine preparations, reconstituted lyophilized bacteria, freshly grown bacteria or lyophilized bacteria reconstituted from sachets, were orally administered to a total of 86 adult volunteers. An aroA aroD htrA strain, PBCC222, was also tested in 38 volunteers. Formulation impacted on the determination of a safe and immunogenic dose; reconstituted lyophilized cultures required higher doses than the broth cultures to stimulate seroconversion. In general, doses which seroconverted the majority of group members produced undesirable symptoms regardless of attenuation or formulation. The inability to separate the presence of symptoms from achieving significant immunogenicity in these aroA aroD or aroA aroD htrA strains precludes their use as single dose typhoid vaccines in the formulations tested. Multiple doses of these strains at a lower, safe level may be effective as vectors for foreign antigens.