Dual targeting of CCR2+ monocytes and neutrophils enhances anti-tumor immunity
Targeting immunosuppressive tumor-associated myeloid populations has emerged as a promising strategy to enhance anti-tumor immunity. The CCL2-CCR2 axis plays a central role in the recruitment of monocytes that differentiate into tumor-associated macrophages (TAMs), yet the therapeutic potential of CCR2 targeting remains limited. Using transgenic CCR2-DTR mice, we show that depletion of CCR2+ monocytes and TAMs reduced tumor growth across multiple models, accompanied by remodeling of the tumor microenvironment (TME). Residual CCR2-independent TAMs exhibited a pro-inflammatory and less immunosuppressive phenotype, and expressed the alternative recruitment receptor CCR3. Concomitantly, CCR2 depletion markedly enhanced anti-tumor immunity by increasing infiltration of activated CD8+ T cells. Splenocytes from tumor-bearing CCR2-DTR mice showed an increased IFN{gamma} response to a cancer-associated antigen. Furthermore, CCR2 depletion synergized with immune checkpoint blockade to enhance tumor control. Despite these effects, compensatory tumor infiltration of neutrophils following CCR2 targeting limited therapeutic benefit. These neutrophils exhibited a terminally differentiated, immunosuppressive phenotype and were associated with increased cancer cell-intrinsic expression of the neutrophil-recruiting chemokines Cxcl2 and Cxcl5. Importantly, combined depletion of CCR2+ cells and neutrophils overcame this resistance mechanism, resulting in reduced tumor growth, prolonged survival, and complete tumor clearance in 25% of the mice. Dual depletion of CCR2+ cells and neutrophils was also associated with a synergistic increase in circulating CD8+ T cells. These findings highlight the dynamic remodeling of the TME upon CCR2 depletion and suggest that combinatorial strategies addressing immunosuppressive neutrophil infiltration may improve the efficacy of CCR2 targeting therapies.