P11-18. Immunogenicity of Lactobacillus gasseri-FliC as an oral mucosal vaccine adjuvant for HIV

Background

Transmission of HIV-1 across mucosal surfaces is the most prevalent mode of viral infection. Therefore, a successful vaccine must induce broad anti-viral immunity at the mucosal surface. In the present study, we investigated the immunogenicity of a novel Lactobacillus gasseri mucosal vaccine vector for use in oral delivery of HIV antigens. L. gasseri was genetically engineered to express Salmonella spp. flagellin (L. gasseri-FliC) – the agonist for Toll-like receptor 5 (TLR5) and a potent activator of innate immune cells.

Methods

To evaluate the potential adjuvant activity of our vector, we determined the ability of L. gasseri-FliC to induce myeloid dendritic cell (DC) activation as measured by phenotypic activation and cytokine production. Briefly, myeloid DCs were isolated and co-cultured with live L. gasseri (w.t.), L. gasseri-pTRK (empty plasmid), L. gasseri-FliC, and Lactobacillus acidophilus, as well as TLR agonists rFliC (TLR5) and rFLS-1 (TLR2/6). After 24 hours of co-culture, cytokine production was analyzed via a 27-plex Luminex assay and DC phenotype determined through flow cytometry.

Results

Each Lactobacillus treatment induced a unique response from the DCs regardless of strain, though different from purified TLR agonists alone. All treatment groups yielded higher surface concentrations of CD86 than CD80 amongst populations of CD80⁺CD86⁺HLAII⁺ DCs, but only L. acidophilus, L. gasseri-FliC, and rFliC induced significant increases in the overall percent of DCs expressing co-stimulatory molecules. Elevated levels of cytokines IL10, IL1RA, IFNγ, IL6, TNFα, IL1β, GM-CSF, G-CSF, and chemokines IL8, MIP1α, MIP1β were produced by Lactobacillus-pulsed DCs. IL12, IL2 and IL15 were produced in minimal concentrations, with the IL10:IL12 ratio being 100-fold greater than that of TLR agonists alone.

Conclusion

These results suggest DC phenotypic maturation is significantly affected by Lactobacillus treatment and immunological recruitment is likely, but the functional significance of the mixed inflammatory and anti-inflammatory cytokine profile must be evaluated in vivo to include the immunological perspective of the mucosa.