“Background Attenuated Salmonella are being developed as v


“Background Attenuated Salmonella are being developed as vaccines to protect against typhoid fever [1–3]. There are also endeavors employing Salmonella as delivery vectors for therapeutic molecules. One strategy utilizes attenuated Salmonella, which expresses a gene or gene fragment encoding a protective antigen as vaccine against bacterial

pathogens [4–6]. The heterologous genes can be expressed from the Salmonella chromosome, or, more often, from a multi-copy plasmid [7, 8]. Another strategy exploits Salmonella as a delivery vector of S63845 supplier DNA vaccine against viral pathogens [4, 5, 9]. The later strategy is also used to deliver DNA encoding tumor antigen or cytokine for therapeutic applications in oncology [10, 11]. In addition, Salmonella is used to deliver small interfering RNAs (siRNA) [12], ribozymes [13] and large DNA molecules encoding a viral genome [14]. For instance, in vivo delivery of an artificial bacterial chromosome (BAC) carrying the viral genome of the murine cytomegalovrirus (MCMV) by Salmonella Typhimurium led to a productive virus infection in mice

and resulted in elevated titers of specific antibodies against lethal MCMV challenge [14]. Most vaccine designs utilize AMN-107 Salmonella delivery vectors carrying a single plasmid for expression of a single antigen or of a fusion protein carrying epitopes from more than one antigen [15]. To induce also broader immunity against a particular pathogen or various pathogens, one might need to express multiple Selleckchem LY3023414 antigens from a single plasmid carrying different antigen cassettes or from multiple plasmids in a single cell, each expressing one or more relevant antigens. Co-delivery of plasmids encoding tumor antigens and cytokines by Salmonella has been successfully demonstrated to improve protective immunity against cancer [16]. In

the case where multiple plasmids are carried in the same Salmonella vector strain, there are most likely regions of homology between the plasmids, since the widely used pUC- and pBR-based plasmids have origins of replication that are nearly identical and both share regions of homology with the p15A ori. Additionally, commonly used promoter sequences, transcriptonal terminators and other expression plasmid components may also be present on plasmids coexisting in the same bacterial cell. The presence of these similar or identical DNA sequences would serve to facilitate undesirable interplasmid recombination. In some cases the bacterial vector may intentionally harbor multiple copies of the same DNA sequence, which may lead to plasmid instability. Recently, we encountered such a situation during the development of a bacterial based influenza vaccine. We constructed a single plasmid carrying eight head-to-tail connected influenza cDNA cassettes [17]. The plasmid was intended for delivery into host cells by an attenuated Salmonella strain.

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