Abstract

Oncolytic viruses (OVs) are widely studied for their ability to lyse cancer cells and prime immune responses; however, the immune consequences triggered by OVs remain incompletely understood. Here, we discover that oncolytic VSVΔ51 treatment suppresses the T cell receptor signaling of tumor-infiltrating T cells. Mechanistically, VSVΔ51-infected cancer cells upregulate PCSK9 secretion, which triggers lysosomal degradation of major histocompatibility complex (MHC)-I in bystander cells. PCSK9 inhibition synergizes with VSVΔ51 treatment to suppress tumor growth in multiple colorectal cancer models and induce complete regression in a microsatellite-stable (MSS) tumor model. This combination fosters stem-like CD8 + T cells and establishes anti-tumor memory. Engineered VSVΔ51 expressing anti-PCSK9 single-chain variable fragments improves intra-tumor viral replication, sustains anti-tumor CD8 + T cell memory, and enhances anti-PD-1 therapy efficacy. Our results identify the role of PCSK9 in the immunosuppressive feedback following viral infection and propose a strategy for engineered oncolytic virotherapy.