DICER controls macrophage polarization and tumor response to immunotherapy

Tumor-associated macrophages (TAMs) have immunosuppressive capacity in mouse models of cancer. Here we show that the genetic deletion of the microRNA (miRNA)-processing enzyme DICER in TAMs broadly programs them to a CD11c+MRC1-/low M1-like immunostimulatory phenotype characterized by activated interferon-? (IFN-?)/STAT1/IRF signaling. M1-like TAM programming fostered the recruitment of cytotoxic T-cells (CTLs), including tumor-antigen-specific CTLs, inhibited tumor growth, and enhanced the efficacy of PD1 checkpoint blockade. Bioinformatics analysis of TAM transcriptomes identified a limited set of miRNAs putatively involved in TAM programming. Re-expression of Let-7 in Dicer-deficient TAMs was sufficient to partly rescue the M2-like (protumoral) TAM phenotype and abate tumor CTL infiltration. Targeted suppression of DICER activity in TAMs may, therefore, stimulate antitumor immunity and enhance the efficacy of cancer immunotherapy. Overall design: To explore the role of DICER in the development, activation and immunological functions of TAMs, we crossed homozygous LysM-Cre (Clausen et al., 1999) with Dicerlox/lox (Harfe et al., 2005) mice to obtain mice with myeloid-cell-specific Dicer1 gene deletion (LysM-Cre;Dicer–/–, referred to as D–/–). These mice were then backcrossed to LysM-Cre to obtain the control LysM-Cre; Dicer+/+ mice (referred to as D+/+). Both LysM-Cre and Dicerlox/lox mutations were always homozygous in our experiment. We then inoculated Lewis lung carcinoma (LLC) cells subcutaneously (s.c.) in D–/– and control D+/+ mice. Once the tumors were established, we isolated by fluorescence-activated cell sorting (FACS) tumor-associated macrophages (F4/80+ cells).

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Baer C, Squadrito ML, Laoui D, Thompson D, Hansen SK, Kiialainen A, Hoves S, Ries CH, Ooi CH, De Palma M