Transient activation of tumor-associated macrophages boosts anti-tumor immunity

Depletion of immunosuppressive tumor-associated macrophages (TAM) or reprogramming towards a pro-inflammatory activation state represent different strategies to therapeutically target this frequent myeloid population. Here we report that inhibition of colony-stimulating factor-1 receptor (CSF-1R) signaling sensitizes TAM to profound reprogramming in the presence of a CD40 agonist prior to their depletion. Despite the short-lived nature of macrophage hyperactivation, combined CSF-1R/CD40 stimulation of macrophages is sufficient to trigger a productive and durable T cell response in various mouse cancer models. The central role of macrophages in regulating T cell-dependent tumor rejections was substantiated by depletion experiments and transcriptomic analysis of ex vivo sorted TAM. Since CD40 expression on human TAM varies between different tumor types, co-expression of human CSF-1R and CD40 in colorectal adenocarcinoma and mesothelioma can serve as criteria to select these tumor types for clinical development Overall design: Female C57BL/6N mice (6-8 weeks in age, obtained from Charles River) were inoculated with 106 MC38 colorectal adenocarcinoma tumor cells subcutaneously. Tumor growth curves were monitored by caliper measurement and once tumor size reached 250 mm3 in average, groups were allocated for antibody treatment. Ten mice/group were treated with 30 mg/kg IgG1 isotype control antibody clone MOPC-21 (BioXCell), 4 mg/kg anti-CD40 rat IgG2a antibody clone FGK45 (BioXCell), 30mg/kg anti-CSF-1R antibody clone 2G2, 4 mg/kg rat IgG2a control clone 2A3 (BioXCell). For depletion experiments 4mg/kg mouse anti-CD4 antibody clone GK1.5 (Biolegend), 4mg/kg anti-NK1.1 antibody clone PK136 (BioXCell) and 4mg/kg anti-CD8a antibody clone 53-6.7 (BioXCell) were administered when tumor size reached 190mm3 in average. Antibodies were given every second day for four times. In between doses two and three of the depleting antibodies, animals were further treated with vehicle control (0,9% sodium saline), MOPC21, FGK45, 2G2 or combination of FGK45 and 2G2. The anti-CSF-1R antibody or respective IgG1 control antibody were administered weekly until tumors regressed completely or animals reached termination criteria, while the anti-CD40 antibody was only administered once at day 11 simultaneously with the anti-CSF-1R antibody. All antibodies were given intraperitoneally. All procedures were performed in accordance with the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals and European Union directives and guidelines.

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Hoves S, Ooi CH, Wolter C, Sade H, Bissinger S, Schmittnaegel M, Ast O, Giusti AM, Wartha K, Runza V, Xu W, Kienast Y, Cannarile MA, Levitsky H, Romagnoli S, De Palma M, Rüttinger D, Ries CH