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Although the recent treatment in melanoma through the use of anti-PD-1 immunotherapy is successful, the efficacy of this approach remains to be improved. Here, we explore the feasibility of combination strategy with the armed oncolytic adenovirus ZD55-IL-24 and PD-1 blockade. We find that combination therapy with localized ZD55-IL-24 and systemic PD-1 blockade leads to synergistic inhibition of both local and distant established tumors in B16-bearing immunocompetent mouse model. Our further mechanism investigation reveals that synergistic therapeutic effect is associated with marked promotion of tumor immune infiltration and recognition in both local and distant tumors as well as spleens. PD-1 blockade has no obvious effect on promotion of tumor immune infiltration and recognition. Localized therapy with ZD55-IL-24, however, can help PD-1 blockade to overcome the limitation of relatively low tumor immune infiltration and recognition. This study provides a rationale for investigation of such combination therapy in the clinic. [ABSTRACT FROM AUTHOR]

ZD55-IL-24 is an armed oncolytic adenovirus similar but superior to ONYX-015. Virotherapeutic strategies using ZD55-IL-24 have been demonstrated to be effective against several cancer types. However, it is unclear whether the traditional administration strategy is able to exert the maximal antitumor efficacy of ZD55-IL-24. In this study, we sought to optimize the administration strategy of ZD55-IL-24 in both A375-bearing immunocompromised mouse model and B16-bearing immunocompetent mouse model. Although the underlying antitumor mechanisms are quite different, the obtained results are similar in these two mouse tumor models. We find that the antitumor efficacy of ZD55-IL-24 increases as injection times increase in both of these two models. However, no obvious increase of efficacy is observed as the dose of each injection increases. Our further investigation reveals that the administration strategy of sustained ZD55-IL-24 therapy can achieve a better therapeutic effect than the traditional administration strategy of short-term ZD55-IL-24 therapy. Furthermore, there is no need to inject every day; every 2 or 3 days of injection achieves an equivalent therapeutic efficacy. Finally, we find that the sustained rather than the traditional short-term ZD55-IL-24 therapy can synergize with anti-PD-1 therapy to reject tumors in B16-bearing immunocompetent mouse model. These findings suggest that the past administration strategy of ZD55-IL-24 is in fact suboptimal and the antitumor efficacy can be further enhanced through administration strategy optimization. This study might shed some light on the development of clinically applicable administration regimens for ZD55-IL-24 therapy. [ABSTRACT FROM AUTHOR]