**Abbreviations**

*Viruses and Viral Infections in Developing Countries*

gene therapy.

**6. Summary**

gene mutations.

**Acknowledgements**

**Conflicts of interest**

P2013-201).

future.

The stable integration of retroviral vectors is suitable to deliver therapeutic genes into cells to correct genetic diseases. MLV-based retroviral vectors are one of the most frequently used gene delivery vehicles in gene therapy studies for primary immunodeficiencies such as adenosine deaminase deficiency-severe combined immunodeficiency [10, 18, 19]. However, a subset of patients developed serious adverse events including leukemia that could be attributed to the integration pattern and vector design [10, 18]. MLV-based retroviral vectors integrate in the vicinity of transcription start site through the interaction between the C-terminal tail of MLV integrase (amino acids 381–408) and the ET domain of BET family of proteins [18, 20]. To resolve side effects such as leukemia, BET-independent MLV vectors have been developed by truncation of the C-terminal tail of MLV integrase or the single W390A mutation [18, 20]. Most recently, next-generation BET-independent MLV vectors have been engineered with the addition of the chromodomain of Chromobox protein homolog 1 (CBX1) to MLV integrase\_W390A. The MLV integrase\_W390A-CBX1 efficiently targets integration away from traditional markers of MLV integration including gene regulatory elements [10]. These findings open new avenues to improve the biosafety of gammaretroviral vectors for

We followed the history of viral carcinogenic research in this review. The topic of viral carcinogenesis mentioned here is a case where the viral genome is inserted into the host genome. Because the molecular mechanism of viral carcinogenesis has been elucidated, significant novel technical methods will be developed in the

Clinical sequence analyzes gene changes occurring at diseased sites and provides information useful for diagnosis and treatment of diseases based on the results of

In addition to the various nucleic acid analysis methods such as conventional PCR and LAMP, next-generation sequencing and other rapid technological innovation will aid in the measurement and analysis of numerous gene sequences in a short period. Furthermore, these technologies are expected to be used in the future to analyze infectious diseases such as cancer virus types, HPV high-risk groups, and virus insertion sites. Information on cancer virus infection will also be valuable for

This work was supported by a Grant-in-Aid from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (no. 15H05721) and a Grantin-Aid from the Scientific Research on Innovative Areas, MEXT, Japan (no.

designing personalized drugs for cancer patients in the future.

The authors declare no conflicts of interest.

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