Intratumoural oncolytic HSV-1 reshapes the local and systemic immune landscape through CD8 ^⁺ T cell reprogramming

Most oncolytic viruses are delivered by intratumoural injection, and local administration can induce regression of both injected and distant tumours in mice and patients. However, the mechanisms by which local viral infection reprograms systemic immunity remain poorly understood. Here we show that intratumoural RP1, an oncolytic HSV-1 encoding GM-CSF and GALV-GP-R ^⁻ , drives regression of injected and uninjected murine melanoma tumours and prolongs survival. RP1 elicits coordinated CD4 ^⁺ and CD8 ^⁺ T cell infiltration accompanied by local cytokine remodelling, reshaping the immune landscape at both tumour sites. Leveraging the Timer of Cell Kinetics and Activity (Tocky) system and Kaede photoconvertible protein technology, we resolve the temporal dynamics of CD8 ^⁺ T cell responses following local virotherapy and identify two systemically induced, virus-driven CD8 ^⁺ T cell populations distinguished by TCR engagement kinetics: antigen-engaged Timer-positive ‘viral-induced precursors’ (VIPs) and Timer-negative KLRG1 ^⁺ ‘viral-induced terminal effectors’ (VITEs). Single-cell transcriptomic and pseudotime analyses reveal divergent differentiation trajectories; VIPs exhibit sustained antigen engagement within the tumour microenvironment (TME), a transcriptional programme associated with self-renewal, and preferential homing to draining lymph nodes. A VIP-associated gene signature correlates with clinical response to RP1 plus PD-1 blockade in the IGNYTE trial of RP1 and nivolumab in PD-1-refractory melanoma and is independently associated with response to immune checkpoint inhibitor (ICI) therapy in melanoma. These findings establish a mechanistic link between local oncolytic virotherapy, systemic CD8 ^⁺ T cell reprogramming, and durable regression of distant lesions in patients.