Modulation of innate immunity in the tumor microenvironment

Abstract

A recent report from the Center for Disease Control identified melanoma as being among the highest causes of cancer-related mortalities in the USA. While interventions such as checkpoint blockade have made substantial impact in terms of improving response rates and overall survival, a significant number of patients fail to respond to treatment or become resistant to therapy. A better understanding of the tumor microenvironment in these patients becomes imperative for identifying immune suppressive mechanisms that impact the development of effective anti-tumor immune responses. We have investigated innate immune cells (dendritic cells, NK cells) in the tumor microenvironment (TME) in order to devise effective targeted anticancer immune therapies. We find that matrix metalloproteinase-2 (MMP-2), secreted from melanoma cells and stromal cells, cleaves IFNAR1 and stimulates TLR-2 on dendritic cells (DC) within the TME. Both these events independently culminate in programing the DCs to promote pro-tumorigenic TH2 T cell differentiation. In addition, we have shown that NK cells become functionally exhausted in melanoma patients. We identified the expression of Tim-3 as one of the factors responsible for NK cell exhaustion and showed that anti-Tim3 antibodies partially reversed this exhaustion. We have initiated local intervention strategies such as intra-tumoral administration of DC activating Poly-ICLC and compared the efficacy of different TLR agonists and melanoma antigens for use as combination tumor vaccine in clinical trials. Such approaches will provide a unique insight into tumor biology and will facilitate in development of highly effective and cell type-specific immune therapies.

Keywords: CIMT 2015; Dendritic cell; Immunotherapy; Matrix metalloproteinase-2; NK cell exhaustion; Tim-3.

Fig. 1

MMP-2 in the TME promotes DC driven T_H2 differentiation. MMP-2 derived from melanoma cells initiates two independent signaling cascades in DCs that cause T_H2 polarization. (1) MMP-2 cleaves IFNAR1 on DCs, thus inhibiting Stat1 phopshorylation and downregulating IL12 secretion and (2) MMP-2 interacts with TLR-2 to activate canonical NFκB signaling and upregulate T_H2-promoting OX40L

Fig. 2

Schematic representation of NK cell exhaustion phenotype and its in vitro reversal after checkpoint inhibitor treatment. Exhausted NK cells in melanoma are characterized by (1) reduction of proliferative capacity to IL-2 and cytotoxic activity against melanoma lines, as well as cytokine production (IFN-γ) in response to activation; (2) reduced expression of activation receptors and IL-2R subunits and NK cell regulatory transcription factors (T-bet, Eomes), (3) upregulation of inhibitory receptors. In this figure, we made a schematic representation for an in vitro assay shown in Da Silva., et al. where after 1 h treatment with anti-Tim-3-blocking antibody freshly isolated NK cells from melanoma donors were able to reverse this phenotype and state of exhaustion in vitro, restoring 30–65 % of the NK cell dysfunction. The black oval ligand represents anti-Tim-3-blocking antibody. Blockade of Tim-3 in vitro was able to overexpress IL-2 receptor on NK cell surface, as well as expression of the transcription factors T-bet and Eomes. Moreover, blockade of Tim-3 is enough for exhausted NK cells (1) to recover their capacity for producing IFN-γ after IL-12 stimulation, (2) to recover their cytotoxic capacity for killing other targets cells and (3) to proliferate

Fig. 3

Vaccine strategies to prime effective dendritic cell adjuvant function. Strategies for priming classical DCs in general by using (1) adjuvants or immune modulators, (2) combined therapies, (3) DC antigens and (4) mobilization modulators. Our vaccine trials in particular have been designed to target classical DCs (Poly-ICLC) and plasmacytoid DCs (imiquimod and resiquimod)