Abstract
For reasons of efficiency Escherichia coli is used today as the microbial factory for production of plasmid DNA vaccines. To avoid hazardous antibiotic resistance genes and endotoxins from plasmid systems used nowadays, we have developed a system based on the food-grade Lactococcus lactis and a plasmid without antibiotic resistance genes. We compared the L. lactis system to a traditional one in E. coli using identical vaccine constructs encoding the gp120 of HIV-1. Transfection studies showed comparable gp120 expression levels using both vector systems. Intramuscular immunization of mice with L. lactis vectors developed comparable gp120 antibody titers as mice receiving E. coli vectors. In contrast, the induction of the cytolytic response was lower using the L. lactis vector. Inclusion of CpG motifs in the plasmids increased T-cell activation more when the E. coli rather than the L. lactis vector was used. This could be due to the different DNA content of the vector backbones. Interestingly, stimulation of splenocytes showed higher adjuvant effect of the L. lactis plasmid. The study suggests the developed L. lactis plasmid system as new alternative DNA vaccine system with improved safety features. The different immune inducing properties using similar gene expression units, but different vector backbones and production hosts give information of the adjuvant role of the silent plasmid backbone. The results also show that correlation between the in vitro adjuvanticity of plasmid DNA and its capacity to induce cellular and humoral immune responses in mice is not straight forward.
Highlights
Genetic immunization or DNA vaccination has initiated a new era of vaccine research
Sequence analysis showed that the L. lactis vector backbone had a lower GC content (37%) than the E. coli vector (48%) and contained two copies of a known immune stimulatory mouse CpG motifs (GACGTT), while the E. coli vector backbone only contained one CpG motif
We examined the use of a novel L. lactis vector as the plasmid backbone in DNA vaccines
Summary
Genetic immunization or DNA vaccination has initiated a new era of vaccine research. The technology involves the inoculation of plasmid DNA into a living host to elicit an immune response to a protein encoded on the plasmid [1]. The potential advantages of DNA vaccines include the induction of cellular and humoral immune responses, flexible genetic design, lack of infection risk, stability of reagents, and the relatively low cost of production in a microbial host. These advantages are being exploited for infections like HIV where traditional vaccines have proved unsuccessful [2,3,4,5]. The advantages of DNA vaccines have lead to extensive research primarily focused on the immune responses induced against a variety of antigens but less on the tools required for the microbial production of plasmids. Plasmid DNA used for DNA vaccinations (page number not for citation purposes)
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