Lactobacillus as a vaccine vehicle for therapy

Abstract

Lactobacilli are attractive candidates for vaccine delivery vehicles because they are considered as GRAS (Generally regarded as safe) organisms with a very long record of safe oral consumption. They have greater intrinsic immunogenicity and colonizing ability in the GI tract that make them potentially better candidates for vaccination. The health promoting effects of Lactobacillus rhamnosus GG have also been studied extensively; however it has been poorly exploited as a vaccine delivery vehicle. This dissertation aims to characterize LGG as vaccine delivery vehicle. Mucosal immunization with LGG expressing GFP or IL2-GFP induced GFP specific serum IgG and IgA. The fusion of IL2 to GFP resulted in significantly increased GFP specific serum IgA and IgG and SIgA titers compared to LGG-GFP immunization. Immunization in nasal route showed no abnormal lung damage though increased cellular infiltration was seen initially and subsequently reverted close to normal. Immunohistochemical staining of the lung tissue showed IgA producing B cells at 80th day of post primary immunization. There were increased GFP specific CD8 T cells in the recall assay which was significantly increased by IL2- GFP mucosal delivery. Members of ¿c cytokine family (IL7, IL15 and IL2) have been expressed with PSA in LGG and co-cultured in vitro with DC or neutrophils to study the antigen presentation. LGG itself have stimulatory effects on DC maturation and increased the expression of CD86, CD80, CD40 and MHC II . IL15-PSA or IL2¿PSA secreting LGG reduced IL10 production by DC, IL7 did not, but all three resulted in increased IL12p70 production. However, the T cell response did not correlate with differences in IL12 or IL10 production.LGG-S-IL15-PSA treated DC primed T cells showed high IFN¿ production and CTL response on target cells indicating efficient antigen presentation to T cells. LGG treated neutrophils did not induce any of the co-stimulatory molecules or MHC II expression but only showed elevated expression of the MHC I molecules. LGG treated neutrophils produced high and moderate levels of IL10 and IL12p70 respectively and efficiently induced allogeneic T cell proliferation. LGG treated neutrophils increased the expression of co-stimulatory molecules on DC that clearly showed bacteria treated neutrophils could deliver the maturation signals to immature DC. Recombinant LGG treated neutrophils provided antigen specificity to DC by unknown mechanism when it was co-cultured with DC and also rendered a cytotoxic effect in T cell presentation. This ensures the efficacy of LGG based antigen delivery in inducing immune response through neutrophils alone in the absence of direct bacteria-DC encounter. This dissertation showed that LGG as a promising antigen delivery vehicle and that IL15 is a good vaccine adjuvant especially when administered as fusion protein with antigen.