VG161 oncolytic virus remodels the tumor microenvironment by expanding CD3+ macrophages and enhancing antitumor immunity.

Oncolytic virotherapy has emerged as a promising strategy for cancer immunotherapy; however, its immunomodulatory mechanisms in colorectal cancer remain incompletely understood. Here, we evaluated the therapeutic effects of the oncolytic virus VG161 in murine colorectal cancer models (CT26.WT and MC38) and systematically characterized the associated tumor microenvironment (TME) remodeling. Using single-cell RNA sequencing, flow cytometry, and multiplex immunohistochemistry, we identified a distinct population of CD3+ macrophages that was markedly expanded following VG161 treatment. Functional analyses suggested that these cells exhibit enhanced phagocytic capacity and immunostimulatory properties, including the recruitment of CCL5high CD8+ effector memory T cells (Tem). Mechanistically, VG161-infected tumor cells were found to secrete complement-related factors, including complement factor B (CFB) and complement component 3 (C3), which may contribute to CD3 upregulation and the emergence of a CD3+ macrophage-associated state. These findings suggest that complement signaling may contribute to CD3 upregulation in macrophages, although the downstream mechanisms remain to be elucidated. Furthermore, VG161 treatment enhanced systemic antitumor immunity and improved responsiveness to immune checkpoint blockade. Collectively, these findings reveal a potential role for VG161 in orchestrating innate-adaptive immune interactions and provide a rationale for targeting macrophage-mediated pathways to improve colorectal cancer immunotherapy.