Transformed Salmonella typhimurium SL7207/pcDNA-CCOL2A1 as an orally administered DNA vaccine

The use of attenuated bacteria for oral delivery of DNA vaccines is a recent innovation. We designed and constructed the naked plasmid DNA vaccine pcDNA-CCOL2A1, which effectively prevented and treated a rheumatoid arthritis model by inducing immunotolerance. We aimed to ensure a reliable, controllable dosage of this oral DNA vaccine preparation and establish its stability. We transformed pcDNA-CCOL2A1 via electroporation into attenuated Salmonella typhimurium SL7207. A resistant plate assay confirmed the successful construction of the transformed strain of the SL7207/pcDNA-CCOL2A1 oral DNA vaccine. We verified its identification and stability in vitro and in vivo. Significant differences were observed in the characteristics of the transformed and blank SL7207 strains. No electrophoretic restriction patterns or direct sequencing signals were observed in the original extract of the transformed strain. However, target gene bands and sequence signals were successfully detected after PCR amplification. CCOL2A1 expression was detected in the ilea of BALB/c mice that were orally administered SL7207/pcDNA-CCOL2A1. The pcDNA-CCOL2A1 plasmid of the transformed strain was retained under the resistant condition, and the transformed strain remained stable at 4 °C for 100 days. The concentration of the strain harboring the pcDNA-CCOL2A1 plasmid was stable at 10⁹ CFU/mL after 6-8 h of incubation. The results demonstrated that the transformed strain SL7207/pcDNA-CCOL2A1 can be expressed in vivo, has good stability, and may be used to prepare the oral DNA vaccine pcDNA-CCOL2A1 with a stable, controllable dosage and the capacity to provide oral immunization. This vehicle can effectively combine both oral immunotolerance and DNA vaccination.