melanoma

Injecting a virus directly into melanoma tumors trains the immune system to attack cancer throughout the body

Oncolytic viruses — engineered viruses that preferentially infect and kill cancer cells — are a promising cancer immunotherapy approach. When injected directly into a tumor, they can sometimes trigger shrinkage of distant, uninjected tumors as well. But exactly how this 'abscopal' effect works at…

Dan Manning

Dan Manning

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Injecting a virus directly into melanoma tumors trains the immune system to attack cancer throughout the body

Injecting a virus directly into melanoma tumors trains the immune system to attack cancer throughout the body

Oncolytic viruses — engineered viruses that preferentially infect and kill cancer cells — are a promising cancer immunotherapy approach. When injected directly into a tumor, they can sometimes trigger shrinkage of distant, uninjected tumors as well. But exactly how this 'abscopal' effect works at the immune level has been unclear.

This study examined RP1, an oncolytic HSV-1 virus encoding immune-stimulating factors (GM-CSF and GALV-GP-R), in murine melanoma models. Direct injection of RP1 caused regression of both injected and distant tumors and improved survival. The researchers identified two key T cell populations that RP1 induces — 'viral-induced precursors' (progenitor-like, with active TCR engagement) and 'viral-induced terminal effectors' (highly cytotoxic) — and showed these populations are present in both injected and uninjected tumor sites.

Using the sophisticated 'Tocky' system to track T cell kinetics, this study maps how a local viral infection reprograms T cell immunity system-wide, providing mechanistic insight that could guide combination strategies and patient selection for oncolytic virus therapy.

Key Findings

  • Intratumoural RP1 (oncolytic HSV-1) induces regression of both injected and distant uninjected melanoma tumors
  • Two virus-induced CD8+ T cell populations are identified: progenitor-like precursors and terminal effectors
  • RP1 treatment reshapes the immune landscape at both injected and uninjected tumor sites
  • Local viral infection coordinates systemic CD4+ and CD8+ T cell infiltration and cytokine release
  • The Tocky system revealed TCR engagement dynamics that define the two virus-induced T cell populations

Implications

Understanding the T cell programs induced by oncolytic viruses like RP1 (which is in clinical trials as part of the combination therapy that became cemiplimab + RP1/vusolimogene oderparepvec) could help predict which patients will have systemic responses. These findings support rationale for combining oncolytic viruses with checkpoint inhibitors to amplify the systemic immune effect.

Caveats

Preprint, not peer reviewed. Mouse melanoma models may not fully represent human tumor immunology. Translation to clinical response rates in human patients requires validation. Summary based on abstract only.

Source: bioRxiv — 2026-04-10

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