Interleukins in cancer: from biology to therapy
Charles A
Interleukins and associated cytokines serve as the means of communication for innate and adaptive immune cells as well as non-immune cells and tissues. Thus, interleukins have a critical role in cancer development, progression and control. Interleukins can nurture an environment enabling and favouring cancer growth while simultaneously being essential for a productive tumour-directed immune response. These properties of interleukins can be exploited to improve immunotherapies to promote effectiveness as well as to limit side effects. This Review aims to unravel some of these complex interactions. This Review provides an update of interleukins in tumour biology, covering the milestones of the latest discoveries of interleukin-related mechanisms in cancer, together with their application in clinical practice. It includes an overview of current clinical trials and breakthrough preclinical concepts.
/static/images/favicons/nature/apple-touch-icon-f39cb19454.png
Nature
As some interleukins regulate immunosurveillance and thereby tumour control, clinicians have tried to utilize them for cancer therapy in the past few decades. However, cancer treatment by interleukins proved to be challenging as it has not lived up to its expectations in terms of effectiveness, while also encountering serious toxic effects in some cases. Because interleukins also nurture cancer progression, neutralization of their activity has emerged as a potential avenue.

There are reports suggesting several interleukins as biomarkers74,140,141,142,143, but so far no interleukin has been implemented as a biomarker in the US Food and Drug Administration guidelines for oncologic therapeutics, and their potential overall value has been extensively reviewed in ref.143.

Here, we summarize recent advances in the translation of therapeutic exploitation of interleukins, covering therapeutic neutralization of interleukins as well as the use of their recombinant and engineered forms (Fig. 4).

Therapeutic neutralization

Interleukin-1

The Canakinumab Anti-inflammatory Thrombosis Outcomes Study (CANTOS) provided the strongest evidence for the potential of IL-1-neutralization in cancer so far. The study enrolled patients with stable coronary artery disease receiving the standard of care, but with persistent elevation of the level of high-sensitivity C-reactive protein (hsCRP). Patients were treated with the anti-IL-1β antibody canakinumab and did not have a diagnosis of cancer at the time of enrolment. Canakinumab not only reduced hsCRP levels but also significantly lowered overall cancer mortality compared with the placebo group, especially concerning lung cancer144. This finding likely reflected the ability of IL-1β to impede invasion and metastasis of existing subclinical cancers rather than cancer initiation due to the median duration of the trial of 3.7 years145. In support of this, a substantial number of patients with diagnosed lung cancer already had circulating tumour DNA at the time of enrollment146. These findings spawned several clinical trials blocking IL-1β and other inflammatory interleukins in cancer with expected primary completion dates until 2024.

In 2018, a phase III trial of canakinumab as monotherapy compared with placebo started in patients with non-small-cell lung cancer (NCT03447769)147. Similarly, a phase II trial studying canakinumab monotherapy in myelodysplastic syndrome and chronic myelogenous leukaemia was initiated in 2020 (NCT04239157)148. Also, in 2018, a phase III trial using canakinumab in combination with pembrolizumab and chemotherapy in non-small-cell lung cancer (NCT03631199)149, and in 2019 a phase III trial with canakinumab and chemotherapy alone (NCT03626545) were started150. Several additional studies were initiated between 2016 and 2020 (see Supplementary Table 1).

Anakinra is an IL-1R antagonist in clinical trials for cancer therapy. In a phase II trial, 47 patients with smouldering myeloma were treated with anakinra alone for 6 months. If a patient did not achieve a minor response or better, anakinra was combined with dexamethasone. Three of 47 patients achieved a minor response to anakinra alone, highlighting the need for a combinatorial approach. Upon addition of dexamethasone, five partial responses and four minor responses were achieved151,152. Anakinra is also under investigation in several other clinical trials in multiple cancer types as monotherapy and in combination therapy (see Supplementary Table 1).

Interleukin-6

While the anti-IL-6 antibody siltuximab reduced tumour growth in a xenografted cholangiocarcinoma model153, it achieved only small effects in multiple myeloma as monotherapy154, in combination with the proteasome inhibitor bortezomib155 and with bortezomib, the cytostatic agent melphalan and the anti-inflammatory glucocorticoid prednisone156. Siltuximab was also not effective in solid tumours as monotherapy. In prostate cancer, the best outcome achieved was stable disease157, in renal cell carcinoma (RCC) the best outcome was a single partial response158 and no clinical efficacy was observed in a group of mixed solid tumours159. Furthermore, several clinical trials observed treatment-associated side effects, such as higher rates of infections upon siltuximab treatment154,155,156, which overall does not support a benefit of siltuximab therapy.

IL-6 can protect cancer cells from therapy-induced DNA damage, oxidative stress and apoptosis and is known to induce immunosuppression and maintains highly therapy-resistant cancer stem cell populations74. Thus, IL-6 neutralization might reverse resistance to conventional cancer therapy. In combination with chemotherapy, the anti-IL-6R antibody tocilizumab yielded first positive results160. However, combining IL-6 neutralization with immune checkpoint inhibitors (ICIs) has engendered controversy. While IL-6 neutralization might enable patients to continue receiving ICIs by countering cytokine release syndrome (see Box 2), IL-6 inhibition was shown to suppress the expression of PD1 and programmed death ligand 1 (PDL1). This might decrease the effectiveness of ICIs161. As preclinical studies mainly demonstrate asynergy between IL-6 neutralization and ICIs, several clinical trials have been initiated to test the combination in a clinical setting (see Supplementary Table 1).

Publications highlight the potential of blocking IL-6 trans signalling in hepatocellular carcinoma162 and colorectal cancer163 by comparing carcinogenesis in wild-type mice and mice transgenic for soluble gp130Fc, which consists of gp130 fused to a human IgG1 domain164. These data may lead to clinical trials for olamkicept (also known as soluble gp130Fc) in patients with cancer in the future.

Interleukin-8

HuMax-IL-8 is an antibody neutralizing IL-8. While no objective responses were observed in monotherapy, no dose-limiting toxic effects were observed, and 73% of patients with solid tumours had stable disease165. IL-8 induces resistance to several chemotherapeutic agents and ICIs, as summarized elsewhere133,140,166. Therefore, several clinical trials are exploring the effect of HuMax-IL-8 in combination with nivolumab (NCT03400332 (ref.167), NCT04123379 (ref.168) and NCT04050462 (ref.169)), nivolumab and degarelix (NCT03689699 (ref.170)) and the anti-PD1 antibody nivolumab with stereotactic body radiotherapy (NCT04572451 (ref.171)).

Interleukin-17

Blocking IL-17 in a murine model of gastric cancer led to a reduction of tumour growth and in combination with anti-PD1 therapy to tumour rejections in 80% of the mice172. It also decreased the development of prostate cancer in a preclinical mouse model173. IL-17 can accelerate the progression of multiple myeloma174, and another study showed that IL-17 neutralization indeed can lead to a reduction in multiple myeloma growth175. A clinical trial that started in 2017 (NCT03111992 (ref.176)) is now exploring the efficacy of the anti-IL-17A antibody CJM112 in multiple myeloma.

Interleukin-23

In the context of castration-resistant prostate cancer, MDSC-derived IL-23 was shown to activate the androgen receptor pathway, thereby supporting survival and proliferation of cancer cells under androgen-deprived conditions. Neutralization with an anti-IL-23 antibody significantly reduced tumour growth and extended survival of mice177. This suggests anti-IL-23 therapy might support anti-androgen therapy regimens. To assess the potential of this, the anti-IL-23 antibody tildrakizumab is now being tested in a phase I/II trial in patients with castration-resistant prostate cancer in combination with abiraterone acetate, an inhibitor of androgen synthesis (NCT04458311 (ref.178)).

Interleukin-33

It was shown in a preclinical study that IL-33 may directly act on tumour cells, inducing polyploidy and rapid proliferation, and causing therapy resistance. Use of a specific IL-33-blocking antibody could restore the efficacy of anti-PD1 therapy in an otherwise ICI-resistant subclone of the B16F10 melanoma model179.

Recombinant and engineered interleukins

IL-2 was the first interleukin to be approved for cancer treatment, although its use entails major safety concerns180. Recent advances focusing on modifying interleukins to reduce toxicity and increase the efficacy of treatment with recombinant and/or engineered interleukins might help to overcome this issue.

Interleukin-2

Although high-dose therapy with IL-2 induced durable complete responses in some patients with melanoma and RCC, it comes with potentially life-threatening adverse events. Therefore, low-dose IL-2 schedules were evaluated in several trials. However, in low abundance, IL-2 binds preferentially to its high-affinity receptor expressed on Treg cells, potentially leading to immune evasion. Thus, several IL-2 variants with increased affinity for the IL-2Rβ–γc complex expressed by CTLs are in development.

Bempegaldesleukin, a pegylated IL-2 variant, is a non-α IL-2 variant that is already in clinical trials. In addition to increasing its half-life, the polyethylene glycol (PEG) residues coupled to IL-2 block its binding site for the high-affinity IL-2Rα subunit. Over time, the PEG groups are lost and continually release the active form of bempegaldesleukin, thereby minimizing the risk of overdosing181. Bempegaldesleukin was evaluated as monotherapy in a phase I clinical trial in patients with metastatic solid tumours, predominantly consisting of patients with melanoma or RCC. The best overall responses observed were stable disease182, which is disappointing in comparison with the 7% and 9% durable complete responses achieved by conventional IL-2 therapy in melanoma and RCC, respectively180,182. Nevertheless, bempegaldesleukin showed a favourable safety profile, encouraging combination with ICIs. A phase I study of bempegaldesleukin in combination with nivolumab in metastatic solid tumours achieved a complete response rate of 19%183. Several other clinical trials in combination with ICIs, including phase III clinical trials in patients with bladder cancer (NCT04209114 (ref.184)), RCC (NCT03729245 (ref.185)) or melanoma (NCT03635983 (ref.186)), are currently ongoing. Other non-α IL-2 variants are being tested in clinical trials in combination with ICIs, such as ALKS 4230, a circularly permuted IL-2 and IL-2Rα designed to selectively activate the intermediate-affinity IL-2R. It is tested in four clinical trials in patients with advanced solid tumours or non-cutaneous squamous cell carcinoma of the head and neck alone and in combination with pembrolizumab (see Supplementary Table 1). THOR707 is an engineered non-α IL-2 being tested in patients with solid tumours alone and in combination with an unspecified ICI or with an anti-EGFR antibody (NCT04009681 (ref.187)).

NARA1leukin is a fusion construct that consists of human IL-2 engineered into the anti-IL-2 antibody NARA1. NARA1 thereby permanently masks the CD25-binding site of IL-2 and thus abolishes the CD25-mediated Treg cell development, while mediating potent antitumour responses in a murine melanoma model188.

Another approach is the de novo design of Neo-2/15, a hyperstable interleukin that mimics only the binding site for IL-2Rβ–γc, but otherwise is structurally independent of IL-2 and IL-15. Therefore, it can mediate IL-2 and IL-15 signalling independently of IL-2Rα or IL-15Rα, and showed superior therapeutic activity compared with IL-2 in mouse models of melanoma and colon cancer189.

Several attempts have been made to couple IL-2 to tumour-targeting antibodies to reduce side effects caused by high systemic concentrations while increasing the efficacy by concentrating IL-2 at the tumour. Some of those IL-2-antibody fusion constructs reached the stage of clinical trials190. However, no breakthrough results have emerged so far (see Supplementary Table 1).

Interleukin-10

IL-10 has anti-inflammatory as well as CTL-stimulating properties, which led to its exploration as an anticancer therapeutic. The PEGylated IL-10 variant pegilodecakin can induce systemic immune activation, an increase of the levels of immunostimulatory cytokines and a reduction of TGFβ levels in patients with solid cancer. Additionally, partial responses and prolonged stable disease were observed upon pegilodecakin treatment191. In a follow-up trial, in a mixed group of solid cancers, expansion and activation of intratumoural CTLs in response to treatment were observed192. The first clinical data on the combination of pegilodecakin with ICIs were promising as well193; however, two follow-up trials testing pegilodecakin in combination with nivolumab (NCT03382912 (ref.194)) and the anti-PD1 antibody pembrolizumab (NCT03382899 (ref.195)) were terminated early due to an unfavourable risk–benefit ratio.

CmAb-(IL-10)2, a bispecific fusion protein with one arm derived from the anti-EGFR antibody cetuximab and the other arm containing an IL-10 dimer, is an agent still in preclinical investigation. It has shown superior antitumour activity compared with IL-10 fused to a non-tumour-targeting antibody196.

Interleukin-12

IL-12 is an interleukin that demonstrates striking immune activation and tumour control but causes severe adverse effects with the doses necessary to induce an antitumour effect. However, targeted delivery strategies to achieve high concentrations at the tumour site while avoiding high systemic amounts led to a renaissance of IL-12 cancer therapy197.

Gene therapy allows better control of the localization and amount of interleukins in a therapy regimen. Tavokinogene telseplasmid, an IL-12-encoding plasmid electroporated into melanoma lesions, achieved an overall response rate of 36% and a complete response rate of 18% in a phase II trial. Of note, 46% of patients also showed regression in at least one lesion and 25% had a net regression in all lesions into which tavokinogene telseplasmid had not been injected198, suggesting the induction of systemic antitumour immunity. In combination with pembrolizumab, the overall response rate was increased to 41%, with a complete response rate of 36%199. Several follow-up trials were initiated between 2017 and 2020 in triple-negative breast cancer (NCT03567720 (ref.200)), head and neck squamous cell carcinoma (NCT03823131 (ref.201)) and melanoma (NCT04526730 (ref.202) and NCT03132675 (ref.203)).

Other therapeutic strategies using IL-12 have been extensively discussed elswhere107,197, and recent clinical trials are listed in Supplementary Table 1.

CBD–IL-12 is a fusion protein consisting of IL-12 and a collagen-binding domain. It accumulates in the tumour due to exposed collagen in the disordered tumour vasculature and demonstrates antitumour effects superior to those of IL-12 by a broad activation of the immune system at the tumour site204.

Li et al. designed multifunctional oncolytic nanoparticles with the intent to send several different signals triggering antitumour responses at once. They showed that the composition of nanoparticles containing self-replicating RNA can induce immunogenic cell death of tumour cells, as the contained RNA serves as a signal for pathogen-recognition receptors as well as coding for IL-12 to further enhance the induced immune response. When delivered intratumourally, control of large tumours is achieved in several tumour models205.

Interleukin-15

In contrast to IL-2, IL-15 does not lead to Treg cell expansion, while having similar immunostimulatory properties. However, monotherapy with IL-15 and several engineered variants was ineffective, although there are several promising combination therapies in clinical trials206.

An example of this is ALT-803, consisting of recombinant IL-15 with an N72D mutation linked to the Sushi domain of IL-15Rα fused to an immunoglobulin G (IgG) Fc-fragment. While the N72D mutation increases binding to IL-15Rβ, the Sushi domain provides the IL-15Rα part and the Fc fragment increases its half-life. However, ALT-803 had only a limited effect as monotherapy in patients with solid tumours207 and showed responses in only 19% of patients with haematological malignancies208. Strikingly, in combination with intravesical bacillus Calmette–Guérin (BCG) therapy, complete responses were achieved in all nine patients with bladder cancer209, which led to the expansion of the trial to enrol nearly 600 patients (NCT02138734 (ref.210)).

Other IL-15-based therapeutic strategies include combination with ICIs and tumour-targeting antibodies (Supplementary Table 1); approaches for IL-15 in combination therapy for cancer have been extensively reviewed206,211.

Interleukin-18

IL-18 therapy has shown little preclinical efficacy, potentially due to IL-18BP, a high-affinity IL-18 decoy receptor. Using direct evolution, Zhou et al. developed decoy-resistant IL-18 (DR-18), which maintains signalling potential and unlike IL-18 exerted potent antitumour responses in mice, by supporting effector T cell development, reducing T cell exhaustion and enhancing activity and maturation of NK cells97.

Interleukin-23 and interleukin-36

IL-36γ together with IL-23 can be successfully used in combination with OX40 ligand to promote acute inflammation for efficient tumour control212 and is currently under investigation in a clinical trial (NCT03739931 (ref.213)).

Complementing ACT

Interleukins play a key role in ACT, a breakthrough achievement in cancer therapy in the past decade. Interleukins such as IL-2, IL-7 and IL-15 have been widely used to improve in vitro expansion and differentiation of adoptive cells and to complement ACT therapy in humans by co-administration or by genetically engineering them into the transferred cells.

Interleukin-2

Treatment of patients with IL-2 to support ACT has been studied with variable success in several cancer types. For example, IL-2 was combined with tumour-infiltrating lymphocytes in melanoma214. While some of those trials yielded benefits, for example a correlation of chimeric antigen receptor (CAR) T cell engraftment with IL-2 concentrations215, this approach still faces toxicity problems similar to those of using interleukins alone.

A strategy to overcome the toxic effect of systemic IL-2 treatment while retaining its ability to support ACT therapy is orthogonal IL-2–IL-2R pairs. The designed orthogonal IL-2 cannot bind to the wild-type IL-2R but transfers native IL-2 signalling when binding to the designed orthogonal IL-2Rβ, which was transduced into T cells. This creates a system where only the ACT product reacts to the orthogonal IL-2 treatment and systemic toxicity is avoided. Orthogonal IL-2 showed efficacy in a mouse melanoma model with the enhanced expansion of the orthogonal IL-2Rβ ACT product and negligible toxic effects. These data might indicate a potential advantage for clinical use in ACT216.

Interleukin-8

A quite different approach is to use tumour-associated interleukins, such as IL-8, to improve infiltration of CAR T cells into the tumour by overexpressing their respective receptors. The expression of the IL-8 receptors CXCR1 or CXCR2 in CAR T cells markedly enhanced migration and persistence in the tumour and induced complete regression and long-lasting immunological memory in preclinical models of glioblastoma, ovarian cancer and pancreatic cancer217.

Interleukin-12

Another strategy currently pursued in several trials is the expression of certain interleukins by cellular therapy products. In this manner, the interleukins should be expressed only locally at the tumour site, thereby avoiding systemic toxic effects and recruiting additional immune cells to establish immune responses against CAR antigen-negative tumour cell populations. In the case of T cells, this approach was named ‘T cells redirected for antigen-unrestricted cytokine-initiated killing’ (TRUCKs). The first interleukin used as a proof of concept for TRUCKs was IL-12 (ref.218), and other interleukins, such as IL-7, IL-15 and IL-23, have since been used to engineer T cells as well.

In preclinical testing, IL-12 expression by CAR T cells led to the recruitment and activation of macrophages critical for the elimination of cancer cells with antigen loss that would normally escape from CAR-induced killing218. The first in-human trial was a study expressing IL-12 under the control of a nuclear factor of activated T cells (NFAT)-inducible promotor in tumour-infiltrating lymphocytes from patients with metastatic melanoma. However, the study had to be terminated due to severe toxic effects likely caused by excessive IL-12 release219. Recently, several clinical trials were started using IL-12-expressing CAR T cells, trying to avoid uncontrolled IL-12 release by the more restricted activation of CARs compared with polyclonal tumour-infiltrating lymphocytes and by using safety switches (see Supplementary Table 1).

Another approach is to induce only transient expression of IL-12 by electroporating IL-12 mRNA into ovalbumin-specific OT-I TCR transgenic CD8+ T cells. Injected intratumorally, but not intravenously, these cells led to complete rejections of lesions into which they had been injected and distant lesions in a B16-ovalbumin tumour model. The study authors claim that the transient expression was likely helpful in restricting IL-12-induced adverse events but do not show any data to prove this assumption220.

A recent clinical trial using intratumourally injected activated DCs showed that successful DC therapy was associated with higher expression of IL-12 subunit p40 and IL-8 (ref.221). This may indicate a favourable interplay between DC therapy and interleukin therapy.

Interleukin-7

Over time, the idea to express interleukins in the ACT product has spread from IL-12 to other interleukins. IL-7 and CC-chemokine ligand 19 (CCL19) are essential for the maintenance of T cell zones in lymphoid organs. In a preclinical setting, CAR T cells engineered to express IL-7 and CCL19 were superior in tumour killing in comparison with conventional CAR T cells. Histopathological analysis showed increased infiltration of DCs and CAR T cells as well as endogenous T cells into the tumour. The depletion of endogenous T cells dampened the therapeutic effect of IL-7 and CCL19-expressing CAR T cells. Together with the observation of abundance of memory CAR T cells and endogenous T cells in the spleen, this suggests co-expression of IL-7 and CCL19 by CAR T cells can initiate a CAR-independent immune response222. Four clinical trials evaluating the effect of CAR T cells overexpressing IL-7 and CCL19 were initiated between 2017 and 2020 (see Supplementary Table 1).

Interleukin-15

Preclinical studies showed that the expression of IL-15 in NKT cells led to a decreased expression of exhaustion markers, enhanced in vivo persistence, increased localization at the tumour site and improved tumour control223. In CAR T cells, membrane-bound IL-15 led to an increase in the abundance of T memory stem cells with long persistence and potent rejection of CD19+ leukaemia224. This led to a collection of ongoing clinical trials engineering IL-15 into CAR T cells and CAR NKT cells (Supplementary Table 1). An interim analysis showed that anti-GD2 CAR NKT cells expressing IL-15 did not cause any dose-limiting toxic effects in three heavily pretreated children with neuroblastoma. CAR NKT cells were shown to be present at the tumour sites, and one patient achieved regression of bone metastatic leasions225.

Recently, a novel approach to reduce the toxicity of IL-15 was reported. Tang et al. designed a cell surface-conjugated nanogel that can be loaded with large quantities of protein drugs226. The nanogel is designed to release its cargo upon an increase in T cell surface reduction potential, which is induced by T cell–antigen encounter. Thereby, the drug release is limited to places of TCR activation, predominantly the tumour site. The study authors also show that the system is translatable to CAR T cells. The potential to expand this method to other cytokines and protein drugs, maybe even combinations thereof, makes this system especially noteworthy, although the approach is inherently self-limiting as the nanogels will be depleted of their drugs over time226.

Interleukin-23