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

Intratumoural delivery of oncolytic viruses can drive regression of both injected and distant tumours, but how local infection reprograms systemic T cell immunity remains unclear. Here, we show that intratumoural administration of the oncolytic HSV-1 RP1, encoding GM-CSF and GALV-GP-R, induces regression of both injected and uninjected murine melanomas and prolongs survival. RP1 triggers coordinated infiltration of CD4+ and CD8+ T cells and local cytokine release, reshaping the immune landscape across injected and uninjected tumour sites. Using the Timer of Cell Kinetics and Activity (Tocky) system, we identify two virus-induced CD8+ populations defined by TCR engagement dynamics: Timer+KLRG1- progenitor exhausted-like "viral-induced precursors" and Timer-KLRG1+ "viral-induced terminal effectors". Single-cell transcriptomics and pseudotime analyses reveal distinct differentiation trajectories, with precursor cells showing antigen engagement, self-renewal, and systemic dissemination. Analysis of patient data shows that a precursor-associated gene signature correlates with clinical response to RP1 therapy in combination with PD-1 blockade and in a separate analysis to immune checkpoint inhibitor (ICI) therapy in melanoma. These data link the effects of local viral therapy to systemic anti-tumour T cell reprogramming and clinical benefit from current immunotherapy.