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.

Shigella sonnei, an intestinal pathogen, produces a characteristic form I cell surface antigen now known to be plasmid encoded. We considered that the GalE Salmonella typhi Ty21a oral vaccine strain, highly effective against typhoid, might be modified so as to be protective also against shigellosis due to S. sonnei. The plasmid responsible for form I antigen synthesis was therefore conjugally transferred to the galE S. typhi strain. Serological studies revealed that the derivative strain produces the form I antigen in addition to the normal S. typhi somatic antigens. Testing in mice demonstrated that the derivative form I galE S. typhi strain is protective against both S. sonnei and S. typhi challenges. These data suggest that the galE S. Ty21a oral vaccine strain, which presumably stimulates the local immune system in the intestine, may also serve as a useful carrier for other antigenic determinants to protect against different intestinal infections.

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Two of seven sucrose-fermenting Salmonella strains obtained from clinical sources were found capable of conjugal transfer of the sucrose fermentation (Scr+) property to the Escherichia coli K-12 strain WR3026. The genetic elements conferring this Scr+ property, designated scr-53 and scr-94, were then conjugally transmissible from E. coli WR3026 Scr+ exconjugants to other strains of E. coli at frequencies of 5 x 10-I to 5 x 10-I for the scr-53 element and 10 6 to 10-s for the scr-94 element. In E. coli hosts, both of these elements were compatible with F-lac and with each of six previously characterized transmissible lac elements. No antibiotic resistance characteristics or colicin production were discovered to be associated with either scr-53 or scr-94. Neither scr element generated a male host response to the female-specific phage XII, but the scr-53 element rendered its E. coli host sensitive to the male-specific phage R-17. E. coli hosts containing scr-53 were susceptible to lysis by Plvir, and transduction of the scr-53 element was accomplished with this phage. The scr-53 element was isolated from E. coli WR3026, Scr+ transductants, and E. coli WR2036 Scr+ exconjugants as a covalently closed circular deoxyribonucleic acid molecule with a molecular weight (determined by electron microscopy) of approximately 52 x 106. Receipt of the scr-94 element rendered E. coli hosts of this element unsusceptible to lysis by Plvir, although adsorption of the phage by an E. coli WR3026 exconjugant containing scr-94 occurred as efficiently as it did on WR3026 itself. Repeated examination of E. coli strains harboring scr-94, as well as of the Salmonella strain which initially contained it, did not reveal the presence of circular deoxyribonucleic acid. The synthesis of the sucrose cleaving enzyme was inducible in E. coli exconjugants containing either scr-53 or scr-94.

Mutations in two Escherichia coli genes, sipA and sipB, result in a specific inhibition of the growth of certain hybrid lambdoid bacteriophages, A immRI2, that have the early regulatory regions and adjacent genes from bacteriophage P22. The sipB391 mutation maps near minute 56 and exerts the strongest inhibitory effect on the growth of the hybrid phages. The sipAl mutation maps near ninute 72 and plays an auxiliary role: enhancing the action of sipB391. Such a role is not limited to sipAl, since there is a similar enhancement by the nusAl and nusE71 mutations. The Sip-imposed restriction on the growth of X immP22 phages is not observed if the phage carries a mutation in the cl gene. Perhaps this reflects the fact that the cl product regulates phage DNA replication and is a major determinant in the decision governing whether the phage takes the lytic or lysogenic pathway. Consistent with this idea is the observation that A immP2 DNA replication is severely inhibited in bacteria carrying the sipB391 mutation. It is suggested that sip mutations exaggerate the normal role of cl in limiting lytic growth. This causes a failure in the expression of sufficient amounts of some or all of the lytic gene products required for phage growth.Host mutants that influence the growth of lambdoid bacteriophages have served as remarkable tools both for studying the action of phage gene products and for identifying genes whose products play important roles in the physiology of the host (19). One class of host factors is those that influence phage products active in the process of establishing repressor synthesis. The hfl (high frequency of lysogeny) (4, 5; F. Banuet and I. Herskowitz, personal communication) and the him and hip (host integration mediation and host integration protein) (33,41,44) genes control the level of cII protein, a bacteriophage X protein that plays a pivotal role in the decision determining whether the infecting phage follows the lytic or lysogenic route. This regulation is exerted in three ways: (i) controlling the establishment of cI (repressor) expression (26, 56); (ii) stimulating expression of the gene int, whose product is required for prophage integration (16); and (iii) reducing expression of late genes (13,40).The cl gene of lambdoid bacteriophage P22 maps in the same relative position as the cIT gene of X and encodes a protein that serves functions analogous to those of the cII protein (35, 52). P22, whose natural host is Salmonella typhimurium, is unable to infect Escherichia coli because it is unable to adsorb. Hybrid phages that are able to grow in E. coli have been engineered under special conditions by using in vivo recombination (10, 23, 28, 58). Some of these hybrids carry the early regulatory and replication genes of P22 and the late morphogenic genes of X including those encoding tail proteins. The relevant genetic structures of X and P22 are shown in Fig. 1. The hybrids used in our experiments carry the early regulatory region from P22 (immC), which includes the c2 (repressor) gene, and t...

A living oral vaccine, designed to protect against Shigella flexneri 2a infections, was constructed by using Escherichia coli K-12 as a carrier strain. The hybrid strain, designated EC104, contained both chromosomal and plasmid genes from S. flexneri donor strains, In addition to expressing the S. flexneri 2a somatic antigen, it had inherited the property of epithelial-celi invasion. After the oral administration to rhesus monkeys, EC104 was isolated from the feces for up to 3 days, but by day 4 all stool cultures were negative. The serum antibody response against S. flexneri 2a somatic antigen was variable, but the vaccine conferred significant protection against an oral challenge with virulent S. flexneri 2a.

The relative chromosomal location of the ViA determinant, a gene required for Vi antigen expression in Salmonella typhosa (and present also in S. typhimurium), was examined in S. typhimurium X S. typhosa matings. The position of this gene was determined with respect to the histidine (his) and methionine (metG) biosynthesis markers, and to the genetic determinants of somatic antigens 5 (0-5) and 4 (0-4) of S. typhimurium. The gene order established by analyses of the hybrid classes resulting from the genetic crosses was ViA-0-5-metG-0-4 (his). This order suggests that neither ViA nor 0-5 is a member of the complex of functionally related structural genes which constitute the 0-4 locus. It allows for the possibility, however, of a functional relationship between the genes of the ViA and 0-5 loci. At least two genetic determinants have been shown to be responsible for the expression of the Vi antigen of Salmonella typhosa (7). One of these, designated ViB, maps adjacent to the inositol utilization (inl) locus on the Salmonella chromosome. Introduction of the ViB gene into S. typhimurium by conjugation with an S. typhosa Hfr strain results in the expression of the Vi antigen in S. typhimurium. Thus, the absence of the ViB gene (or gene complex), or its failure to function, appears to be responsible for the lack of expression of the Vi antigen in S. typhimurium