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Protein transduction domains (PTDs) are small peptides that facilitate the transduction of large molecules such as polyproteins, DNA and viruses into a eukaryotic cell. Here, we demonstrated that a novel PTD (HP4) derived from herring protamine appeared to enter C6Bu1 rat glioma cell lines more rapidly than other known PTDs such as Tat, Antp and Hph-1. Moreover, HP4 significantly enhanced in vitro transduction of recombinant adenoviruses (rAds) into various cancer cell lines, mesenchymal stem cells (MSCs) and dendritic cells, which are relatively resistant to rAd infection. Enhancement of rAd delivery into C6Bu1 and MSCs by HP4 is 20 and 7 times higher than that by Tat, respectively. The increase in the expression of rAd encoding IL-12N220L by HP4 is proportional to its antitumor effect in the ex vivo transduced mouse colon cancer model. Thus, these results suggest that HP4 could be utilized to improve the transduction efficiency of rAd, resulting in enhanced efficacy of rAd-mediated gene therapy, especially for ex vivo-transduced cell therapy.

A novel cytokine interleukin (IL)-23 bears a structural and functional resemblance to IL-12. A recombinant adenovirus expressing IL-23N220L (recombinant replication-defective adenovirus (rAd)/IL-23N220L) that selectively secrets IL-23 was constructed and compared with rAd/IL-12N220L in terms of immunological and antitumor effects. In a prophylactic setting, vaccination with rAd/ovalbumin (OVA) and rAd/IL-23N220L enhanced OVA-specific CD8(+) T-cell responses that were closely associated with complete protection against the subsequent challenge of OVA-expressing E.G7 thymoma. However, in a therapeutic setting, the intratumoral injection of rAd/IL-23N220L showed only marginal antitumor activity against several established tumors such as E.G7, CT26 and B16F10. Interestingly, whereas IL-23 still induced tumor-specific CD8(+) T-cell responses, it could not activate natural killer (NK) cells in vitro and in vivo. In addition, the adoptive transfer of activated NK cells partially restored the therapeutic antitumor effect of IL-23, indicating that NK cells are one of the crucial factors responsible for the regression of established tumors. Taken together, we demonstrated that adenovirus-mediated gene transfer of IL-23 induces a potent prophylactic, but not a therapeutic, antitumor effect.