**5. Acknowledgments**

This work was supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Culture, Sports, Science, and Technology, Japan, and a Grant for Strategic Research on Cancer from the Ministry of Health, Labor, and Welfare, Japan (No. 72602-010- A03-0001) (http://www.jsps.go.jp/j-grantsinaid/index.html). The funders had no role in study design, data collection or analysis, in the decision to publish, or in preparation of the manuscript. The method described in this manuscript has been registered as "Nucleic acid having retroviral integration target-activity," patent number 4631084 in Japan (GenBank, DD323298). In relation to this patent, we also declare no conflict of interest. We are grateful to Masakazu Hatanaka and Tomokazu Yoshinaga for their helpful advice and insightful comments regarding this manuscript. In particular, we are also grateful to Dr. Tasuku Honjo and Dr. Hiroshi Hiai (Kyoto University) for their review of this study and for providing critical advice, and to Miss Hiroko Saito for her excellent technical support.
