Reciprocal regulation of activating and inhibitory Fc{gamma} receptors by TLR7/8 activation: implications for tumor immunotherapy.

Abstract

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 Fcgamma receptor (FcgammaR) function, as they are critical mediators of antibody therapy. 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 FcgammaR. Murine bone marrow-derived macrophages from WT and knockout mice were examined to determine the downstream pathway involved with regulating FcgammaR expression. The efficacy of R-848 as an adjuvant for antibody therapy was tested using a CT26-HER2/neu solid tumor model. Overnight incubation with R-848 increased FcgammaR-mediated cytokine production and antibody-dependent cellular cytotoxicity in human peripheral blood monocytes. Expression of FcgammaRI, FcgammaRIIa, and the common gamma-subunit was increased. Surprisingly, expression of the inhibitory FcgammaRIIb 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. These results show an as-yet-undiscovered regulatory and functional link between the TLR7/8 and FcgammaR pathways. This suggests that TLR7/8 agonists may be especially beneficial during antibody therapy.