IL-27, IL-30, and IL-35: A Cytokine Triumvirate in Cancer

Abstract

The role of the immune system in anti-tumor immunity cannot be overstated, as it holds the potential to promote tumor eradication or prevent tumor cell escape. Cytokines are critical to influencing the immune responses and interactions with non-immune cells. Recently, the IL-12 and IL-6 family of cytokines have accumulated newly defined members each with specific immune functions related to various cancers and tumorigenesis. There is a need to better understand how cytokines like IL-27, IL-30, and IL-35 interact with one another, and how a developing tumor can exploit these interactions to enhance immune suppression. Current cytokine-based immunotherapies are associated with cytotoxic side effects which limits the success of treatment. In addition to this toxicity, understanding the complex interactions between immune and cancer cells may be one of the greatest challenges to developing a successful immunotherapy. In this review, we bring forth IL-27, IL-30, and IL-35, "sister cytokines," along with more recent additions to the IL-12 family, which serve distinct purposes despite sharing structural similarities. We highlight how these cytokines function in the tumor microenvironment by examining their direct effects on cancer cells as well their indirect actions via regulatory functions of immune cells that act to either instigate or inhibit tumor progression. Understanding the context dependent immunomodulatory outcomes of these sister cytokines, as well as their regulation within the tumor microenvironment, may shed light onto novel cancer therapeutic treatments or targets.

Keywords: cancer; cytokines; immunotherapy; signaling; tumor microenvironment.

Figure 1

Receptor composition of IL-12 family members and related cytokines. (A) The IL-12 family members are heterodimeric in composition and signal via heterodimeric receptors. IL-27, composed of p28 and EBI3, shares common subunits with IL-35 (p35 and EBI3) and IL-39 (p19 and EBI3). The p28 subunit has also been shown to have biological activity in the absence of EBI3, known as IL-30. In addition to subunit sharing with IL-27 and IL-39, IL-35 shares the p35 subunit with IL-12. p28 is also known to form complexes with CLF and sIL-6Rα. Signaling of all IL-12 family members, IL-30, and other known p28 complexes, predominantly activate the JAK/STAT pathway. Each cytokine preferentially activates specific STATs to achieve its functional role, although other phosphorylated STATs have been observed. (B) Amino acid sequence overlays for human p28 (accession number: NP_663634.2) with p35 (accession number: NP_000873.2) and EBI3 (accession number: NP_005746.2) with p40 (accession number: NP_002178.2) were aligned using the T-COFFEE-espresso program (11). Shared amino acids are indicated by dark blue shading and homology between p28 and p35 was calculated to be 64% (44 of 169) and between EBI3 and p40 was calculated to be 33% (59 of 177).

Figure 2

The anti- and pro-tumor effects of IL-27, IL-30, and IL-35. Although IL-27, IL-30, and IL-35 share subunits, these cytokines have direct and indirect effects on the tumor resulting in either tumor progression or elimination. IL-27 has mainly been demonstrated to have anti-tumor effects, most notably decreasing proliferation, migration, and invasion, enhancing apoptosis, and promoting cytotoxic immune responses. Pro-tumor effects have also been observed for IL-27, such as upregulation of PD-L1. Alternatively, IL-30 has not been studied extensively but pro-tumor effects have been identified, such as promoting cancer cell proliferation, and decreasing Th1 differentiation. IL-35 has been implicated in promoting tumor advancement by increasing cancer cell proliferation, angiogenesis, metastasis, immune suppression, and T cell exhaustion. Contrastingly, IL-35 may have anti-tumor effects attributed to its potential role in decreasing cancer cell migration and invasion.

Figure 3

Studying the interplay between IL-27, IL-30, and IL-35. (A) The synthesis of IL-27 as a purified recombinant protein or transduced expression vector varies. Both of these forms of IL-27 are available in two formats: (1) containing a flexible amino acid linker sequence (indicated by the curved black arrow), that joins the EBI3 subunit lacking its signal sequence (indicated by the black box) to phenylalanine 29, after the signal sequence of p28 (A; left) or (2) the two subunits co-expressed which associate non-covalently (A; middle). Thus, engineered IL-27 may differ from its endogenously expressed counterpart whereby the flexible amino acid linker prevents the possibility of subunit dissociation. Furthermore, whether non-covalently associated IL-27 subunits can dissociate to form IL-30 (i.e., the p28 subunit) or if they associate with another binding partner is not known (A; right). (B) Studying the functions of cytokines using knockout mice is complex and the outcomes should be carefully considered. Using p28 knockout mice will result in IL-30 and IL-27 elimination, whereas knockout of p35 eliminates IL-35 and IL-12 (not depicted). Knockout of EBI3 removes both IL-27 and IL-35 (IL-39 is also removed, not shown). Using a WSX-1 receptor chain knockout will prevent IL-27 signaling and may prevent signaling of IL-30. Additionally, IL-35 signaling on B cells will be inhibited (not shown). (C) How these cytokines interact will influence tumor development. The pleiotropic effects of IL-27 produced by APCs can be seen here. IL-27 can promote differentiation of Treg cells which secrete IL-35 resulting in immune suppression and tumor development. Alternatively IL-27 can prevent Treg development and promote anti-cancer Th1 cell development. Importantly, IL-27 may undergo subunit dissociation giving rise to the pro-tumor cytokine IL-30, or can directly act on cancer cells resulting in apoptosis. Overall, the complex relationships between IL-27, IL-30, and IL-35 need to be considered when discussing their potential role in cancer immunity.