In mice with B16F10 melanoma, therapeutic treatment with the Trp1/gp75-targeting monoclonal antibody TA99 had no effect, but combination of TA99 with IL-2 and either a TLR agonist (TLR3, 7/8, or 9) or a CD40 agonist increased survival. The triple combination with the TLR7/8 agonist was dependent on CD8+ T cells and NK cells as well as activating FcγRs on macrophages (primarily FcγRI). TA99 monotherapy decreased the relative amount of inflammatory macrophages (which exhibited high levels of FcγRs) within the tumor microenvironment, while the combination treatment kept the level of this cell subset constant.
Therapy with tumor-specific Abs is common in the clinic but has limited success against solid malignancies. We aimed at improving the efficacy of this therapy by combining a tumor-specific Ab with immune-activating compounds. In this study, we demonstrate in the aggressive B16F10 mouse melanoma model that concomitant application of the anti-TRP1 Ab (clone TA99) with TLR3-7/8 or -9 ligands, and IL-2 strongly enhanced tumor control in a therapeutic setting. Depletion of NK cells, macrophages, or CD8(+) T cells all mitigated the therapeutic response, showing a coordinated immune rejection by innate and adaptive immune cells. FcgammaRs were essential for the therapeutic effect, with a dominant role for FcgammaRI and a minor role for FcgammaRIII and FcgammaRIV. FcgammaR expression on NK cells and granulocytes was dispensable, indicating that other tumoricidal functions of NK cells were involved and implicating that FcgammaRI, -III, and -IV exerted their activity on macrophages. Indeed, F4/80(+)Ly-6C(+) inflammatory macrophages in the tumor microenvironment displayed high levels of these receptors. Whereas administration of the anti-TRP1 Ab alone reduced the frequency of these macrophages, the combination with a TLR agonist retained these cells in the tumor microenvironment. Thus, the addition of innate stimulatory compounds, such as TLR ligands, to tumor-specific Ab therapy could greatly enhance its efficacy in solid cancers via optimal exploitation of FcgammaRs.