TGFβ blocks STING-induced IFNα/ β release and tumor rejection in spontaneous mammary tumors
Type I interferons (IFN) are being rediscovered as potent anti-tumoral agents. Activation of the STimulator of INterferon Genes (STING) by DMXAA can induce a strong production of IFN/{beta} and the rejection of transplanted primary tumors. In the present study, we addressed whether targeting STING with DMXAA also leads to the regression of spontaneous MMTV-PyMT mammary tumors. We show that these tumors are refractory to DMXAA-induced regression. This is due to a blockade in the phosphorylation of IRF3 and the ensuing IFN/{beta} production. Mechanistically, we identified TGF{beta} abundant in spontaneous tumors, as a key molecule limiting this IFN-induced-tumor regression by DMXAA. Finally, blocking TGF{beta} restores the production of IFN by activated MHCII+ tumor-associated macrophages, and enables tumor regression induced by STING activation. On the basis of these findings, we propose that type I IFN-dependent cancer therapies could be greatly improved by combinations including the blockade of TGF{beta}.