Immunomodulatory and antitumor effects of type I interferons and their application in cancer therapy

Abstract

During the last decades, the pleiotropic antitumor functions exerted by type I interferons (IFNs) have become universally acknowledged, especially their role in mediating interactions between the tumor and the immune system. Indeed, type I IFNs are now appreciated as a critical component of dendritic cell (DC) driven T cell responses to cancer. Here we focus on IFN-α and IFN-β, and their antitumor effects, impact on immune responses and their use as therapeutic agents. IFN-α/β share many properties, including activation of the JAK-STAT signaling pathway and induction of a variety of cellular phenotypes. For example, type I IFNs drive not only the high maturation status of DCs, but also have a direct impact in cytotoxic T lymphocytes, NK cell activation, induction of tumor cell death and inhibition of angiogenesis. A variety of stimuli, including some standard cancer treatments, promote the expression of endogenous IFN-α/β, which then participates as a fundamental component of immunogenic cell death. Systemic treatment with recombinant protein has been used for the treatment of melanoma. The induction of endogenous IFN-α/β has been tested, including stimulation through pattern recognition receptors. Gene therapies involving IFN-α/β have also been described. Thus, harnessing type I IFNs as an effective tool for cancer therapy continues to be studied.

Keywords: IFNAR1/2; JAK-STAT; apoptosis; immunogenic cell death; necroptosis.

Figure 1. Intrinsic anti-tumor and anti-angiogenic functions of type I interferons

Interferon-α/β (IFN-α/β) has direct effects in tumor cells inducing growth arrest and cell death (left panel). After binding to the heterodimeric IFN-α/β receptor 1 and 2 (IFNAR1/IFNAR2), type I IFNs induce a cascade of intracellular events which culminates in expression of genes whose promoters contain the IFN-stimulated response element (ISRE). In this way, several immuno-regulatory cytokines, cell death factors and proteins related to antiviral response are produced, as well as more IFN-α/β, which in turn affects neighboring cells. In addition, anti-tumor effects of type I IFN may also be a consequence of its anti-angiogenic function, impairing tumor vessel formation and leading to death of tumors by lack of oxygen and nutrients (right panel). IFN-α/β can inhibit the production of angiogenic factors by tumor cells, and also directly affects endothelial cells (EC), inhibiting their proliferation and secretion of factors responsible for EC chemotaxis and remodeling of extracellular matrix. Tyrosine kinase 2 (TYK2), Janus kinase 1 (JAK1), signal transducer and activator of transcription (STAT), IFN-regulatory factor 9 (IRF9), IFN-stimulated gene factor 3 (ISGF3), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), interleukin-8 (IL-8), platelet endothelial cell adhesion molecule-1 (PECAM-1), promyelocytic leukemia protein (PML), matrix metalloproteinase 9 (MMP9).

Figure 2. The context dependent and complex role of type I interferons in cancer immunity

Activation or delivery of interferon-α/β (IFN-α/β) into the tumor microenvironment can result in immunomodulatory and regulatory functions. In the first scenario (left panel), in order to unleash an effective immune attack against cancer cells, type I IFNs modulate innate and adaptive compartments through multiple mechanisms to provide a pro-inflammatory context suitable for antigen recognition by tumor associated dendritic cells (DCs) and priming of T lymphocytes. Importantly, as type I IFNs enhance co-stimulatory molecules of DCs, they also increase the unique ability of DCs to cross-present phagocytized tumor antigens to CD8⁺ T cells. Additionally, immunogenic tumor clones (represented in pink) have their antigenicity increased by up regulating major histocompatibility complex class I (MHC-I) molecules. However, type I IFNs can also favor tumor progression and escape from immune control (right panel), especially under chronic exposure conditions, since they can induce macrophages (mϴ) to produce Interleukin-10 (IL-10), that along with tryptophan starvation mediated by indoleamine 2,3-dioxygenase (IDO) and expression of programmed death-ligand 1 (PD-L1) by immune evasive tumor cells (dark red), greatly impairs T cells functions. Tumor necrosis factor–α (TNF-α), plamacytoid DCs (pDCs), myeloid-derived suppressor cells (MDSC), regulatory T cell (T reg), C-C chemokine receptor type 7 (CCR7), natural killer cells (NK).

Figure 3. Signaling pathways of type I IFN inducers commonly used as adjuvants for cancer therapy

Nearly all cells are capable of producing type I IFNs after sensing pathogen-associated microbial patterns (PAMPs) and danger-associated molecular patterns (DAMPs). This strategy is used to improve therapeutic cancer vaccines, increasing the immunologic response. The activation of pattern-recognition receptors (PRRs) leads to signaling through the adaptor molecules toll/interleukin-1 receptor domain-containing adaptor protein inducing interferon-β (TRIF) and/or Myd88, which culminates in the activation of IFN-regulatory factor 3/7 (IRF3/7) (yellow arrows) or nuclear factor-ĸB (NF-ĸB) (blue arrows) transcription factors and, consequently, in the expression of type I IFNs or inflammatory cytokines. Regarding the dendritic cell (DC) subtypes, the PRRs toll-like receptor (TLR)1, TLR2, TLR3, TLR4, TLR6 and TLR8 are expressed by monocyte-derived DCs and myeloid DCs, while TLR7 and TLR9 are only expressed by plasmacytoid DC. Lipopolysaccharide (LPS), triacylated lipopeptides (Pam3CSK4), diacylated lipopeptides (Pam2CSK4), polyribosinic-polyribocytidylic acid [Poly(I:C)], oligodeoxynucleotide (CpG ODN), TIR domain-containing adaptor protein (TIRAP), TRIF-related adaptor molecule (TRAM), 2′-3′-cyclic GMP-AMP (cGAMP), cGAMP synthase (cGAS), stimulator of interferon genes (STING).

Figure 4. Harnessing type I interferons in cancer therapy

During the last decades several strategies have been developed in order to exploit the antitumor properties of type I interferons (IFNs) in the tumor microenvironment. Indeed, diverse strategies range from the stimulation of tumor cells to produce their own IFN-α/β [e.g., inducers of immunogenic cell death, agonists of toll like receptors (TLRs) and gene therapy] or to deliver it to the cancer microenvironment, for example recombinant protein or dendritic cells (DCs) modified ex vivo. Though there is no consensus on which strategy is likely to provide the best results and much more remains to be understood concerning type I IFN’s pleiotropic functions, its combination with other treatment modalities, such as checkpoint blockade immunotherapy, is expected to unleash the full force of the immune system against cancer. Newcastle disease virus (NDV), antibody (Ab), oligodeoxynucleotide (CpG ODNs), polyribosinic-polyribocytidylic acid [Poly(I:C)].