Development of attenuated Orf virus as a safe oncolytic viral vector for nasopharyngeal carcinoma treatment.

Background: Orf virus (ORFV) is gaining attention as a promising viral vector for cancer therapy because of its unique properties. Recent studies have shown that ORFV could be effective against various cancers, particularly nasopharyngeal carcinoma. This research explores the ability of wild-type ORFV and recombinant ORFVs, which lack specific virulence factors, to kill NPC cells and modulate the immune response.

Methods: Two NPC cell lines, HK1 (from Hong Kong) and TW02 (from Taiwan), were infected with wild-type ORFV and two recombinant ORFVs lacking either vascular endothelial growth factor (VEGF) or chemokine binding protein (CBP) virulence factors. The oncolytic effects were evaluated by assessing cell death pathways, particularly pyroptosis, which was monitored through the cleavage of gasdermin E (GSDME). The activation of survival pathways, such as focal adhesion kinase (FAK) and AKT, was also analyzed. In addition, the influence of ORFV infection on natural killer (NK) cell recruitment and cytotoxicity was investigated. In vivo experiments were conducted in a xenograft mouse model in which HK1 tumors were used to evaluate the antitumor activity of wild-type ORFV and two deletion-mutant ORFVs.

Results: Wild-type ORFV effectively killed NPC cells, especially HK1 cells. The recombinant ORFVs, despite being attenuated by the loss of VEGF or CBP, retained the ability to infect and cause NPC cell death, with the CBP-deleted virus showing notable effectiveness in HK1 cells. Early ORFV infection led to pyroptosis via GSDME cleavage, causing cell detachment and a reduction in FAK and AKT activation. ORFV also enhanced NK cell recruitment and boosted NK cell-mediated cytotoxicity in infected NPC cells. In the HK1 xenograft model, CBP-deleted ORFV significantly inhibited tumor growth.

Conclusion: ORFV, particularly the wild-type and CBP-deleted variants, has significant potential as an oncolytic viral vector for NPC therapy. It induces cell death via pyroptosis and enhances immune-mediated tumor cell destruction through NK cells. The attenuated CBP-deleted ORFV offers a safer and effective option for cancer treatment, making it a promising candidate for future therapeutic applications.