The role of lipopolysaccharide in T-cell responses following DNA vaccination.

Bacterial products, including lipopolysaccharide (LPS), are potential impurities in plasmid DNA vaccines. LPS has immunostimulatory properties even at exceedingly low concentrations through activation of Toll-like receptor 4 (TLR4). The potency of T-cell responses after vaccination was tested with DNA containing high LPS or depleted of LPS in TLR4-competent and TLR4-deficient mice. CD8(+) T-cell responses were readily induced in TLR4-deficient mice immunized with DNA depleted of LPS. LPS in DNA vaccines is not required for CD8(+) T-cell responses.