Design, development, and evaluation of gene therapeutics specific to KSHV-associated diseases

Kaposi sarcoma associated herpesvirus (KSHV) is the causative agent of Kaposi sarcoma (KS) and two human B cell lymphoproliferative diseases. KSHV-encoded latency-associated nuclear antigen (LANA) is expressed in KSHV-infected cancer cells. Thus, LANA is an attractive target for therapeutic intervention for KSHV-associated diseases. Here, we devised a cancer gene therapy vector using the adeno-associated virus (AAV), which capitalizes on the LANA's function to maintain terminal repeat (TR)-containing circular genomes and the TR's enhancer function for KSHV-inducible gene promoters. By including two TR copies with a lytic inducible gene promoter (TR2<i>-OriP</i>), we prepared an AAV vector, which expresses an engineered thymidine kinase (TK) selectively in KSHV-infected cells. Ganciclovir (GCV), an anti-herpesvirus drug, effectively eradicated multiple KSHV-infected cells that include induced pluripotent stem cell-derived epithelial colony-forming cells but not non-KSHV-infected counterparts in the presence of AAV8-TR2<i>-OriP</i>-TK. In addition, AAV8-TR2<i>-OriP</i>-TK prevents KSHV from producing virions from reactivated cells. Anti-cancer drugs, known to reactivate KSHV, stimulated TK expression from the vector and, therefore, synergized with AAV8-TR2<i>-OriP</i>-TK/GCV. Finally, the AAV8-TR2<i>-OriP</i>-TK/GCV effectively suppressed the growth of KSHV-infected cancer cells in the xenograft tumor model, whereas systemic intravenous AAV8-TR2<i>-OriP</i>-TK injection/GCV showed no detectable side effects. Our proof-of-concept studies highlight a promising strategy for targeting cancers driven by herpesviruses.