Reciprocal Regulation of Activating and Inhibitory Fcγ Receptors by TLR7/8 Activation: Implications for Tumor Immunotherapy

Purpose: Activation of Toll-like receptors (TLR) 7 and 8 by engineered agonists has been shown to aid in combating viruses and tumors. Here, we wished to test the effect of TLR7/8 activation on monocyte Fc gamma receptor (Fc gamma R) function, as they are critical mediators of antibody therapy. Experimental Design: The effect of the TLR7/8 agonist R-848 on cytokine production and antibody-dependent cellular cytotoxicity by human peripheral blood monocytes was tested. Affymetrix microarrays were done to examine genomewide transcriptional responses of monocytes to R-848 and Western blots were done to measure protein levels of Fc gamma R. Murine bone marrow-derived macrophages from WT and knockout mice were examined to determine the downstream pathway involved with regulating Fc gamma R expression. The efficacy of R-848 as an adjuvant for antibody therapy was tested using a CT26-HER2/neu solid tumor model. Results: Overnight incubation with R-848 increased Fc gamma R-mediated cytokine production and antibody-dependent cellular cytotoxicity in human peripheral blood monocytes. Expression of Fc gamma RI, Fc gamma RIIa, and the common gamma-subunit was increased. Surprisingly, expression of the inhibitory Fc gamma RIIb was almost completely abolished. In bone marrow-derived macrophage, this required TLR7 and MyD88, as R-848 did not increase expression of the gamma-subunit in TLR7(-/-) nor MyD88(-/-) cells. In a mouse solid tumor model, R-848 treatment superadditively enhanced the effects of antitumor antibody. Conclusions: These results show an as-yet-undiscovered regulatory and functional link between the TLR7/8 and Fc gamma R pathways. This suggests that TLR7/8 agonists may be especially beneficial during antibody therapy. Clin Cancer Res; 16(7); 2065-75. (C)2010 AACR.