Targeting the gene encoding human T-cell leukemia virus type 1 basic zip factor via CRISPR/Cas9 potentially mitigates viral infection

Herein, we investigated the role of an essential transcription factor in the human T-cell leukemia virus type 1 (HTLV-1) provirus, the HTLV-1 basic zip factor (HBZ), in HTLV-1 infections and adult T-cell leukemia/lymphoma (ATL). We designed five synthetic guide RNAs (sgRNAs) targeting HBZ and introduced them into ATL and HTLV-1 infected cell lines using clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR/Cas9). Of all sgRNAs, sgRNA 171 was the most efficient in introducing mutations at the target site as 70–80% of Cas9/sgRNA 171-transfected host cells contained mutations. Various types of mutations, including deletions, substitutions, insertion, and combinations, were detected in the Cas9/sgRNA 171-treated cells. Based on the predicted peptide sequence, most mutant clones were assumed to inactivate the HBZ mRNA. The mRNA levels of the transactivator from the X-gene region ( tax ) increased after HBZ editing by Cas9/sgRNA 171. No off-target effects were observed in the four human genome regions partially homologous to the sgRNA 171 target sequence. Furthermore, ST-1 cells transfected with Cas9/sgRNA 171 displayed significantly reduced proliferation. These findings suggest that the HBZ mRNA might be crucial for the survival of HTLV-1-infected cells, including ATL, providing insights into the molecular pathogenesis of the HTLV-1 provirus.