Murine Cytomegalovirus Infection of Melanoma Lesions Delays Tumor Growth by Recruiting and Repolarizing Monocytic Phagocytes in the Tumor

Cytomegalovirus (CMV) is an exciting new platform for vaccines and cancer therapy. Although CMV may delay tumor growth in some settings, there is also evidence that CMV may promote cancer development and progression. Thus, defining the impact of CMV on tumors is critical. Using a mouse model of melanoma, we previously found that murine CMV (MCMV) delayed tumor growth and activated tumor-specific immunity although the mechanism was unclear. We now show that MCMV delayed tumor growth through a mechanism that required monocytic phagocytes and a viral chemokine that recruited macrophages to the tumor. Furthermore, MCMV infection altered the functional state of macrophages. Although the effects of MCMV on tumor growth were transient, we found that repeated MCMV injections sustained the antitumor effect, suggesting that active viral infection was needed. Thus, MCMV altered tumor growth by actively recruiting macrophages to the tumor, where they were modulated to promote antitumor immunity.