KLS-3021: Innovative oncolytic virotherapy for the treatment of advanced primary and metastatic cutaneous squamous cell carcinoma.

Cutaneous squamous cell carcinoma (cSCC) is a highly prevalent malignancy with increasing incidence and limited therapeutic options in advanced or metastatic stages. Patients with high-risk or metastatic cSCC often experience poor outcomes, underscoring the need for novel therapeutic strategies. We investigated the potential of KLS-3021, a recombinant oncolytic vaccinia virus encoding hyaluronidase, interleukin-12, and soluble programmed cell death 1 fused to an Fc domain. KLS-3021 exhibited tumor-selective cytotoxicity and robust replication in cSCC cell lines while sparing normal keratinocytes. In an orthotopic primary cSCC model generated by intradermal injection of A-431 cells, a single intratumoral injection of KLS-3021 induced complete tumor regression. In a metastatic model involving sentinel lymph node lesions, KLS-3021 suppressed tumor progression not only at the primary site but also in metastatic lymph nodes, where viral spread was detected. Histological analyses revealed extensive hyaluronan degradation, viral dissemination, immune cell infiltration, and hallmark features of immunogenic cell death. Similar findings were observed in metastatic lymph nodes, demonstrating viral activity and tumor suppression. Collectively, these results indicate that KLS-3021 exerts potent anti-tumor efficacy in both primary and metastatic cSCC models, supporting its clinical translation as a multifunctional oncolytic virotherapy targeting the physical and immunological barriers of the tumor microenvironment.