Lactococcus lactis carrying the pValac eukaryotic expression vector coding for IL-4 reduces chemically-induced intestinal inflammation by increasing the levels of IL-10-producing regulatory cells

Background: Inflammatory bowel diseases are characterized by chronic intestinal inflammation that leads to severe destruction of the intestinal mucosa. Therefore, the understanding of their aetiology as well as the development of new medicines is an important step for the treatment of such diseases. Consequently, the development of Lactococcus lactis strains capable of delivering a eukaryotic expression vector encoding the interleukin 4 (IL-4) of Mus musculus would represent a new strategy for the elaboration of a more effective alternative therapy against Crohn's disease. Results: The murine IL-4 ORF was cloned into the eukaryotic expression vector pValac(sic)dts. The resulting plasmid-pValac(sic)dts(sic)IL-4-was transfected into CHO cells so that its functionality could be evaluated in vitro. With fluorescent confocal microscopy, flow cytometry and ELISA, it was observed that pValac(sic)dts(sic)IL-4-transfected cells produced-IL-4, while non-transfected cells and cells transfected with the empty vector did not. Then, pValac(sic)dts(sic)IL-4 was inserted into L. lactis MG1363 FnBPA(+) in order to evaluate the therapeutic potential of the recombinant strain against TNBS-induced colitis. Intragastric administration of L. lactis MG1363 FnBPA(+) (pValac(sic)dts(sic)IL-4) was able to decrease the severity of colitis, with animals showing decreased levels of IL-12, IL-6 and MPO activity; and increased levels of IL-4 and IL-10. Finally, LP-isolated cells from mice administered TNBS were immunophenotyped so that the main IL-4 and IL-10 producers were identified. Mice administered the recombinant strain presented significantly higher percentages of F4/80(+)MHCII(+)Ly6C-IL-4(+), F4/80(+)MHCII(+)Ly6C-IL-10(+), F4/80(+)MHCII(+)Ly6C-CD206(+)CD124(+)IL-10(+) and CD4(+)Foxp3(+)IL10(+) cells compared to the other groups. Conclusions: This study shows that L. lactis MG1363 FnBPA(+) (pValac(sic)dts(sic)IL-4) is a good candidate to maintain the anti-inflammatory and proinflammatory balance in the gastrointestinal tract, increasing the levels of IL-10-secreting regulatory cells and, thus, demonstrating the effectiveness of this novel DNA delivery-based strategy.