Mechanisms of TLR4 agonists enhance the expression of target protein in the composition of the adenoviral vector into antigen presenting cells

Non-replicating recombinant adenovirus vectors (rAd) are effective tools for delivery of vaccine antigens into antigen presenting cells. The efficacy of humoral and cellular responses of an organism to the antigen encoded by rAd depends on the antigen expression in antigen presenting cells. We have previously shown that expression of target antigen encoded in rAd could be enhanced by activation of antigen presenting cells via Toll-like receptor 4 (TLR4). Here we studied TLR4 agonist-induced cellular mechanisms involved in enhancing of the target gene expression in rAd-transduced cells. We examined possible influence of TLR4-agonists on different rAd lifecycle phases in antigen presenting cells. It was shown that agonists of TLR4 significantly enhanced transgene mRNA transcription rate. TLR4-agonist induced phosphorylation of NF-kB transcription factor, which in turn activated NF-kB-sensitive transgene promoter, thus providing efficient transcription of transgene encoded in rAd. TLR4-agonists had neither effect on the rAd entry into antigen presenting cells nor target protein translation processes. Additionally, we showed the signals amplifying transgene expression could be transferred by a paracrine manner from TLR4 agonists-activated to intact cells. Pro-inflammatory cytokines, particularly TNF-α, could play their role in the paracrine enhancement of transgene expression.