NK Cell-Mediated Antitumor Effects of a Folate-Conjugated Immunoglobulin Are Enhanced by Cytokines

Optimally effective antitumor therapies would not only activate immune effector cells but also engage them at the tumor. Folate conjugated to immunoglobulin (F-IgG) could direct innate immune cells with Fc receptors to folate receptor-expressing cancer cells. F-IgG bound to human KB and HeLa cells, as well as murine L1210JF, a folate receptor (FR)-overexpressing cancer cell line, as determined by flow cytometry. Recognition of F-IgG by natural killer (NK) cell Fc receptors led to phosphorylation of the ERK transcription factor and increased NK cell expression of CD69. Lysis of KB tumor cells by NK cells increased by about 5-fold after treatment with F-IgG, an effect synergistically enhanced by treatment with IL2, IL12, IL15, or IL21 (P< 0.001). F-IgG also enhanced the lysis of chronic lymphocytic leukemia cells by autologous NK cells. NK cells significantly increased production of IFNγ, MIP-1α, and RANTES in response to F-IgG-coated KB target cells in the presence of the NK cell-activating cytokine IL12, and these coculture supernatants induced significant T-cell chemotaxis (P< 0.001). F-IgG-coated targets also stimulated FcR-mediated monocyte effector functions. Studies in a murine leukemia model confirmed the intratumoral localization and antitumor activity of F-IgG, as well as enhancement of its effects by IL12 (P =0.05). The antitumor effect of this combination was dependent on NK cells and led to decreased tumor cell proliferation in vivo Thus, F-IgG can induce an immune response against FR-positive tumor cells that is mediated by NK cells and can be augmented by cytokine therapy.

Abstract 2686: Anti-tumor effects of a folate-immunoglobulin conjugate are enhanced by cytokine treatment in vitro and in vivo

Folate conjugation is a means of selectively targeting therapeutics to folate receptor (FR)-expressing cancer cells. A novel folate-bound immunoglobulin (F-IgG) was tested for its ability to target natural killer (NK) cells to folate-receptor expressing cancer cells in the presence or absence of NK-activating cytokines.

FR expression by the KB and HeLa cell lines was confirmed by immunoblot analysis (IB) and flow cytometry. Binding of F-IgG to NK cell Fc receptors led to increased phosphorylation of the epidermal growth factor related kinase (ERK) as measured by IB. Lysis of FR+ KB tumor cells by NK cells was increased 8-fold following treatment with F-IgG as compared to C-IgG (p&lt;0.0001 across E:T ratios from 6.25:1 to 50:1). NK cell lysis of F-IgG- coated KB target cells was significantly enhanced following treatment of NK cells with IL-2, IL-12, IL-15 and IL-21 (all at 10ng/mL). NK cell production of IFN-γ, RANTES and MIP-1α was significantly enhanced by IL-12 in response to F-IgG-coated KB target cells as compared to control-treated cells (p&lt;0.005; IFN-γ-2100 vs. 1000pg/mL, RANTES-800 vs. 150pg/mL, MIP-1α 1800 vs. 500pg/mL, respectively). Studies using the L1210JF murine leukemia model confirmed the anti-tumor activity of F-IgG and the ability of NK-activating cytokines to significantly enhance its effects. NK cell depletion in tumor-bearing mice demonstrated that the anti-tumor effects of IL-12 and F-IgG are dependent on NK cells.

These studies indicate that F-IgG induces an immune response by NK cells against FR-positive cancer cell lines and that cytokine treatment has a synergistic effect on this response both in vitro and in vivo. Thus F-IgG has a potential to be used as a therapeutic antibody for the treatment of FR-positive cancers in combination with immune modulatory cytokines.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2686. doi:10.1158/1538-7445.AM2011-2686

IL-12 enhances the antitumor actions of trastuzumab via NK cell IFN-γ production

The antitumor effects of therapeutic mAbs may depend on immune effector cells that express FcRs for IgG. IL-12 is a cytokine that stimulates IFN-γ production from NK cells and T cells. We hypothesized that coadministration of IL-12 with a murine anti-HER2/neu mAb (4D5) would enhance the FcR-dependent immune mechanisms that contribute to its antitumor activity. Thrice-weekly therapy with IL-12 (1 μg) and 4D5 (1 mg/kg) significantly suppressed the growth of a murine colon adenocarcinoma that was engineered to express human HER2 (CT-26(HER2/neu)) in BALB/c mice compared with the result of therapy with IL-12, 4D5, or PBS alone. Combination therapy was associated with increased circulating levels of IFN-γ, monokine induced by IFN-γ, and RANTES. Experiments with IFN-γ-deficient mice demonstrated that this cytokine was necessary for the observed antitumor effects of therapy with IL-12 plus 4D5. Immune cell depletion experiments showed that NK cells (but not CD4(+) or CD8(+) T cells) mediated the antitumor effects of this treatment combination. Therapy of HER2/neu-positive tumors with trastuzumab plus IL-12 induced tumor necrosis but did not affect tumor proliferation, apoptosis, vascularity, or lymphocyte infiltration. In vitro experiments with CT-26(HER2/neu) tumor cells revealed that IFN-γ induced an intracellular signal but did not inhibit cellular proliferation or induce apoptosis. Taken together, these data suggest that tumor regression in response to trastuzumab plus IL-12 is mediated through NK cell IFN-γ production and provide a rationale for the coadministration of NK cell-activating cytokines with therapeutic mAbs.

Reciprocal regulation of activating and inhibitory Fc{gamma} 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 Fcgamma receptor (FcgammaR) 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 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.

RESULTS

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.

CONCLUSIONS

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.