Targeting γc family cytokines with biologics: current status and future prospects

ABSTRACT

Over the recent decades the market potential of biologics has substantially expanded, and many of the top-selling drugs worldwide are now monoclonal antibodies or antibody-like molecules. The common gamma chain (γc) cytokines, Interleukin (IL-)2, IL-4, IL-7, IL-9, IL-15, and IL-21, play pivotal roles in regulating immune responses, from innate to adaptive immunity. Dysregulation of cell signaling by these cytokines is strongly associated with a range of immunological disorders, which includes cancer as well as autoimmune and inflammatory diseases. Given the essential role of γc cytokines in maintaining immune homeostasis, the development of therapeutic interventions targeting these molecules poses unique challenges. Here, we provide an overview of current biologics targeting either single or multiple γc cytokines or their respective receptor subunits across a spectrum of diseases, primarily focusing on antibodies, antibody-like constructs, and antibody-cytokine fusions. We summarize therapeutic biologics currently in clinical trials, highlighting how they may offer advantages over existing therapies and standard of care, and discuss recent advances in this field. Finally, we explore future directions and the potential of novel therapeutic intervention strategies targeting this cytokine family.

Introduction

Cytokines are small glycoproteins secreted by immune cells that, upon binding to their respective receptors, regulate cellular processes such as differentiation, proliferation, and activation. The common gamma chain (γc) cytokine family includes Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21. All of these cytokines are type 1 four α-helical proteins that signal through the shared γc receptor unit and play a critical role in immunity in both steady state and disease¹ (Figure 1). The importance of this cytokine family for maintaining host immunity is underscored by the fact that loss of function mutations in the IL2RG gene, mapping to chromosome Xq13.1 and encoding for γc, lead to X-linked severe combined immunodeficiency (X-SCID).^2,3 Such mutations result in a near complete failure of the host to develop lymphocytes including T cells, natural killer (NK) cells, B cells and innate lymphoid cells (ILCs). Each γc cytokine has a unique α-subunit receptor chain, allowing for specific signal transduction across a range of cell types, ranging from hematopoietic stem cells to fully developed cell lineages.⁴ After binding, signaling occurs through Janus kinases (JAK) that are anchored to the intracellular domains of the receptor chains, with JAK1 and JAK3 being essential for γc signaling as studies have shown that mice lacking Jak1 or Jak3 signaling also lack functional γc signaling.^5,6 After receptor engagement, JAK1 and JAK3 become phosphorylated and auto-phosphorylate various signal transducer and activator of transcription (STAT) molecules, differing based on the involved α-subunit receptor chain. These STAT molecules dimerize and translocate to the nucleus, where they initiate transcription of their target genes. Dysregulation in this signaling pathway can lead to a range of diseases, including autoimmune diseases, inflammatory diseases and cancer, positioning γc cytokines and their receptors as key targets for therapeutic intervention⁷ (as depicted in Figure 1).

Figure 1.

The common gamma chain (γc) cytokine family. A, heterodimeric receptor complexes formed with γc. B, heterodimeric receptor complexes formed with alpha chain members of the γc family but without γc itself. DCs, dendritic cells; BM, bone marrow; ILC2s, group 2 innate lymphoid cell; TSLP, thymic stromal lymphopoietin; Treg, regulatory T cell; AICD, activation-induced cell death; GC, germinal center; BHR, bronchial hyperresponsiveness. Graphical representations were created with BioRender.com.

Biologics are therapeutic molecules derived from biological sources, such as microorganisms (e.g., bacteria and yeast) or mammalian cells that due to their complexity cannot be synthesized with chemical methods. Monoclonal antibodies (mAbs), the most successful class of biologics, offer high target specificity, strong bioavailability, and long half-lives, making them valuable tools for immunotherapy by selectively targeting disease-driving molecules at the molecular level. The global market for mAbs is projected to reach $300 billion by 2025, with biologics comprising a majority of the top-selling drugs in 2023.⁸ Over the past year, 16 new antibody therapeutics received first-time approval whereas 26 additional candidates were under marketing review. Moreover, numerous other investigational therapies are expected to undergo regulatory review by the end of 2024, illustrating the sustained rise in antibody-based therapeutics over the last two decades.⁹ In oncology, immune checkpoint inhibitors (ICIs) have greatly improved the prognosis of various malignancies, such as melanoma,¹⁰ lung cancer,¹¹ lymphoma^12,13 and breast cancer,¹⁴ often providing prolonged disease control in responsive patients.¹⁵ In addition, antibody-based therapies have proven effective for inflammatory and autoimmune diseases, with several approved treatments for allergic asthma and rheumatoid arthritis. Notably, one of the leading biologic agents on the market is the IL-4 Rα-targeting Dupilumab that simultaneously inhibits the IL-4 and IL-13 signaling pathways, which play a central role in type 2 high asthma.

Here, we explore biologics targeting single or multiple γc cytokines or their respective receptor subunits across multiple diseases, focusing primarily on antibodies, antibody-like constructs, and antibody-cytokine fusions. We give an overview of therapeutic intervention strategies, including both antagonistic and agonistic approaches, with a focus on recent developments in the field. We further discuss novel therapeutic biologics in clinical trials, highlighting their potential benefits over current standard of care. Finally, we examine the future potential of biologics targeting this cytokine family.

Receptor expression and signal transduction of γc cytokines

IL-2, the first member of the γc family, was discovered in 1976¹⁶ and its cDNA was cloned shortly thereafter.^17,18 Cloning of IL-2 Rα suggested a low-affinity interaction with IL-2,¹⁹ prompting investigation into other potential receptor components. This led to the identification of IL-2 Rβ^20,21 and IL-2 Rγ,^22,23 revealing that the heterodimeric IL-2 Rα/β receptor complex binds IL-2 with low affinity, whereas the heterotrimeric complex IL-2 Rα/β/γ binds IL-2 with high affinity. This high-affinity binding explains IL-2’s differential impact on effector and regulatory T cells.²⁴ IL-2 is essential for Treg development and activity,^25–27 induces terminal differentiation and activation in CD4⁺ and CD8⁺ effector T cells,²⁸ enhances CD8⁺ and NK cell cytotoxicity,^29,30 and promotes development of several T cells lineages, including T_H1, T_H2 and T_H9 cells.^31–33 However, it antagonizes T_FH^34,35 and T_H17^36,37 differentiation. IL-2 receptor engagement triggers activation-induced cell death (AICD) in the target cell, crucial for maintaining T cell homeostasis.^38,39 IL-2 has great therapeutic potential in immunotherapy (as reviewed in Ref.⁴⁰ While IL-2-based treatment of autoimmune diseases and graft rejection focuses on Treg expansion, cancer therapies mostly aim to selectively engage effector T cells without stimulating Tregs. Hence, targeting IL-2 in a highly selective manner will be key for the success of these approaches.

Initially discovered as a B cell growth factor in 1982,⁴¹ IL-4 is best known for its role in converting naïve T helper cells (T_H0) into T_H2 cells.⁴² Predominantly produced by T_H2 cells, through a positive feedback loop, IL-4 can also be expressed by germinal center (GC) B cells,⁴³ basophils⁴⁴ and mast cells.⁴⁵ Recently, we have shown that basophil-derived IL-4 plays a central role in stimulating pulmonary endothelial cells to recruit T_H2 cells via VCAM-1 and ICAM-1, thereby promoting allergic airway inflammation.⁴⁶ Beyond that, IL-4 supports type 2 immunity by inducing class-switch recombination (CSR) in B cells to IgG1 and IgE,^47,48 further amplifying the type 2 response. In presence of TGF-β, IL-4 plays a key role in T_H9 cell differentiation, necessary for optimal helminth defense.^49–51 IL-4 signaling requires IL-4 Rα which either heterodimerize with γc or IL-13 Rα1, forming the type 1 and type 2 IL-4 R, respectively (Figure 1). Type 1 receptors, primarily found on lymphocytes, signal through JAK3 and STAT6, while type 2 receptors, present on stromal and myeloid cells, signal through JAK2 and STAT6.⁵²

IL-7 regulates the development, survival, proliferation, and activation of immune cells.^53–55 Produced primarily by bone marrow and thymic stromal cells, IL-7 is critical for T and B cell development^56–58 and activates JAK1 and JAK3, which mainly phosphorylate STAT5,^59,60 and, to a lesser extent STAT3 and STAT1.^61,62 Moreover, IL-7 supports lymphoid progenitor development from hematopoietic stem cells and is essential for the development and survival of ILCs, particularly ILC2s and ILC3s,^63–65 whereas ILC1s rather require IL-15. In later stages of immune response, IL-7 signaling is required for memory T cell development and homeostasis.^66,67 Notably, IL-7 shares the IL-7 Rα domain with thymic stromal lymphopoietin (TSLP), which binds TSLPRα instead of γc⁶⁸ (as depicted in Figure 1).

IL-9 was identified in the late 1980s as a growth factor for mast cells and T cells⁶⁹ and is primarily produced by CD4⁺ T helper cells,⁷⁰ ILC2s⁷¹ and mast cells^72,73 in the context of type 2 immunity, allergy, and helminth infections. In the presence of IL-4 and TGF-β, CD4⁺ T cells produce high levels of IL-9, marking a T_H9 subset.^49,50 However, recent studies suggest that T_H9 cells may be a more adaptable subset of T_H2 cells, that can produce IL-9 after acquiring the transcription factors PU.1 and PPARγ,^74,75 rather than a distinct lineage. IL-9 plays a significant role in allergic asthma, with high levels detected in asthmatic patient lungs.^76,77 Recently, new interest in IL-9 has emerged with single-cell transcriptomics, identifying IL-9-producing T cells as a distinctive marker of human allergic asthma.^78,79 Moreover, using various mouse models of asthma we have recently shown that IL-9 and IL-21 differentially regulate type 2 inflammation by promoting the activation and expansion of ILC2s and T_H2 cells, respectively.⁸⁰ Beyond allergic disease, IL-9 has shown antitumor activity, especially in melanoma, where studies using adoptive transfer of T cells, T_H9 cells and IL-9 producing CD8⁺ T cells (T_C9) have been shown to directly promote antitumor responses.^81–83 Here, IL-9 is thought to act in an autocrine and paracrine manner, primarily on T cells to induce proliferation, activation, and survival in its target cells via phosphorylation of STAT5, STAT3 and STAT1.⁸⁴ Even though T_H9 skewed T cells initially show signs of reduced cytotoxicity with lower expression of Gzmb, Prf1 and Ifng, they are able to outperform T_H1 cells due to their higher expression of IL-2 and IL-9, resulting in a more prolonged anti-tumor response characterized by reduced expression of exhaustion markers such as KLRG-1, PD-1 and LAG-3.^85,86

Discovered in the 1990s, IL-15 shares the IL-2 Rβ chain with IL-2 and is essential for T and NK cell development as well as survival.⁸⁷ In vivo, it is predominantly produced by innate immune cells, such as dendritic cells,⁸⁸ monocytes⁸⁹ and macrophages,⁹⁰ in response to IFNγ. IL-15 is best known for its role in viral immunity and cancer therapies, promoting NK cell proliferation and activation^91,92 while also supporting memory CD8⁺ T cell development.⁹³ Although both IL-2 and IL-15 signal via JAK1 and JAK3,⁹⁴ which associate with IL-2 Rβ and γc, their unique alpha chains define their high-affinity binding and distinct biological effects. Notably, IL-15 does not induce AICD, allowing prolonged T cell activation.⁹⁵ The IL-15 Rα chain binds IL-15 with high affinity, enabling trans-presentation to neighboring cells, a unique feature contributing to IL-15’s prolonged effects in immune responses.⁹⁶ Although IL-2 is the predominant cytokine driving Treg development, both IL-7 Rα and IL-15 Rα signaling have been confirmed on Treg progenitor cells through STAT5 phosphorylation. Interestingly, in the absence of IL-2 the receptors for IL-7 and IL-15 are upregulated, suggesting compensatory mechanisms to exist.⁹⁷

IL-21 is a pleiotropic cytokine produced predominantly by adaptive immune cells, such as T_FH,⁹⁸ T_H17⁹⁹ and T_H2¹⁰⁰ cells. Its receptor is expressed by a wide variety of lineages including T cells,^100,101 B cells,¹⁰² NK cells,^103,104 dendritic cells,¹⁰⁵ monocytes¹⁰⁶ and macrophages,^107,108 underscoring its broad influence on immune responses. IL-21 signaling is essential for plasma cell differentiation,¹⁰⁹ antibody production,¹¹⁰ and class-switch recombination (CSR) in B cells.¹⁰² In particular, T_FH cells in the B cell follicle express high levels of IL-21,¹¹¹ which is critical for both B cell IgE isotype switching, through Blimp1-dependent mechanisms,¹¹² and optimal T_FH cell development and function.¹¹¹ Lung-resident IL-21-producing CD4⁺ T cells have been shown to drive allergic airway inflammation by increasing IL-33 sensitivity in both ILC2s and T_H2 cells by upregulation of T1/ST2.¹⁰⁰ Furthermore, studies show that IL-21 also promotes T_H17 differentiation in combination with TGF-β, enhancing IL-17 production.^99,113 IL-21 receptor signaling relies on JAK1 and JAK3, which predominantly phosphorylate STAT3.^114,115 Moreover, IL-21 possesses potent anti-tumor effects. While Il21^−/− mice retain a functional NK cell compartment, IL-21 is essential for NK cell maturation and maximal effector functions, such as cytotoxicity.¹¹⁶ IL-15 stimulated NK cells were shown to have reduced proliferation and survival in the presence of IL-21, but instead showed increased granularity and IFNγ production, indicating improved effector function and cytolytic potential.¹¹⁷ IL-21 signaling also upregulates molecules involved in type 1 immunity, including IFNγ, T-bet, IL-12 Rβ, and IL-18 R.¹¹⁸ Moreover, IL-21 stimulates CD8⁺ T cells by enhancing their co-stimulatory response to IL-15, through the upregulation of CD28,¹¹⁹ resulting in enhanced proliferation and expansion of naïve and memory CD8⁺ T cells.¹²⁰ Additionally, IL-21 can counterbalance IL-2 effects¹²¹ and reduce Treg suppressive function by inducing apoptosis,¹⁰¹ further contributing to its anti-tumor activity.

Taken together, the γc cytokine family mediates diverse effects across various innate and adaptive immune cells (Figure 1). Due to their pivotal role in regulating immunity in both homeostasis and disease states, these cytokines are attractive targets for therapeutic intervention. As a general concept, autoimmune and inflammatory diseases are marked by overactivation of the immune system and are therefore typically tackled with antagonistic approaches. In contrast, tumor growth occurs when the immune system fails to properly recognize malignant cells and therefore lacks activation or costimulation, which can be provided using agonistic approaches. In the following sections, we will discuss both antagonistic and agonistic approaches of targeting γc cytokines and their receptors with biologics.

γc-targeted therapies in autoimmune and inflammatory diseases

IL-2

Due to its dual role on both effector T cells and Tregs, IL-2 targeted therapies usually aim to specifically inhibit either of the two cell types while keeping the other one untouched, thereby inducing IL-2 signaling only in the desired target cells. In the past, low-dose IL-2 (LD-IL-2) therapy, which has been shown to primarily activate Tregs due to their high CD25 expression, has been assessed. However, this approach faced challenges due to IL-2‘s short half-life (~6 hours).¹²²

The earliest approaches of targeting the IL-2 axis include the IL-2 Rα-targeting mAbs Basiliximab and Daclizumab, designed to prevent organ rejection. While Basiliximab is still used for this in the clinic, Daclizumab was withdrawn from the market due to emergence of severe side effects in 2018 after being investigated for treatment of multiple sclerosis.¹²³ To mitigate the side-effects associated with LD-IL-2 administration, combination therapy approaches are being investigated. Coya Therapeutics is currently evaluating a combination of LD-IL-2 with the immunosuppressive CTLA-4-Ig fusion protein for amyotrophic lateral sclerosis (ALS)¹²⁴ in Phase 1 clinical trials.¹²⁵ Moreover, there are numerous mutein-based approaches in clinical development for a variety of autoimmune diseases, including ulcerative colitis (UC), psoriasis and systemic lupus erythematosus (SLE). All of these muteins aim at specifically targeting Tregs through CD25-biased binding, while half-life extension is achieved either through PEGylation or genetic fusion to the c-termini of the heavy chain of mAbs or Fc fragments⁴⁰ (Table 1, Figure 2). For broad γc cytokine family antagonism, Regeneron has developed a high affinity species cross-reactive antagonistic antibody that blocks the γc receptor unit, effectively abrogating signaling of the entire cytokine family.¹²⁷ The company is investigating the potential of this antibody in graft rejection and in the hematological disease severe immune aplastic anemia.¹⁴⁸ In humanized IL2RG transgenic mice, this approach effectively suppressed T and NK cells without affecting granulocyte, erythrocyte, or platelet levels. Currently, the safety of this mAb is assessed in Phase 1/2 clinical trials.¹⁴⁹

Table 1.

Overview of biologics targeting the γc cytokine family with development stages.

	Targeted pathway	Name	Format	Target/MoA	Indications	Stage/Phase	Ref
Autoimmune and inflammatory diseases	IL-2	Daclizumab	mAb	CD25 antagonist	MS, kidney graft rejection	Approved, withdrawn	123
		Basiliximab	mAb	CD25 antagonist	Kidney/liver graft rejection	Approved	126
		NKTR-358	PEGylated mutein	IL-2R agonist (CD25-enhanced)	SLE, Psoriasis, UC	2	NCT04677179, NCT03556007
		AMG-592	Mutein-Fc fusion	IL-2R agonist (CD25-enhanced)	UC	2	NCT05672199
		REGN7257	mAb	CD132 antagonist	Severe aplastic anemia	1/2	,127 NCT04409080
		THOR-809 (SAR444336)	PEGylated mutein	IL-2R agonist (CD25-enhanced)	Inflammatory diseases	1	NCT05876767
		RG7835 (RO7049665)	mAb-mutein fusion	IL-2R agonist (CD25-enhanced)	UC	1, discontinued	NCT03943550
		PT101 (MK-6194)	Mutein-Fc fusion	IL-2R agonist (CD25-enhanced)	UC	1	NCT04924114
		DEL106 (CC-92252)	Mutein-Fc fusion	IL-2R agonist (CD25-enhanced)	Psoriasis	1	NCT03971825
		CUG252	Mutein-Fc fusion	IL-2R agonist (CD25-enhanced)	SLE	1	NCT05328557
		LD-IL-2	LD-IL-2 + CTLA4-Ig	CD25 agonist	Autoimmune diseases, GvHD	1	NCT06307301
		MDNA209	Mutein-Fc fusion	IL-2R agonist (CD122/CD132 antagonist)	Autoimmune diseases, GvHD	Preclinical	40
		F5111.2	mAb	IL-2 (CD122 antagonist, CD25 agonist)	Autoimmune diseases, GvHD	Preclinical	128
		UFKA-20	mAb	IL-2 (CD122 antagonist, CD25 agonist)	Autoimmune diseases, GvHD	Preclinical	129
		BD3	mAb	IL-2 (CD122 antagonist, CD25 agonist)	Autoimmune diseases, GvHD	Preclinical	130
	IL-4	Dupilumab	mAb	IL-4Rα antagonist	Asthma, AD	Approved	131
		Rademikibart	mAb	IL-4Rα antagonist	Asthma, AD	2	132 NCT05017480
		Pascolizumab	mAb	IL-4 antagonist	Asthma	2, discontinued	NCT00024544
		Pitrakinra, AEROVANT	Mutein	IL-4Rα antagonist	Asthma	2, discontinued	NCT00801853
		Romilkimab	mAb	IL-4 x IL-13antagonist	SSc, IPF	2	NCT02921971
		PF-07264660	mAb	IL-4 x IL-13 x IL-33 antagonist	AD	2	NCT05995964
		PF-07275315	mAb	IL-4 x IL-13 x TSLP antagonist	AD	2	NCT05995964
		APG808	mAb	IL-4Rα antagonist	Asthma, AD	1	ACTRN12624000238572
		RC1416	mAb	IL-4Rα x IL-5 antagonist	Asthma	1	NCT06067490
		LQ036	Bivalent nanobody	IL-4Rα antagonist	Asthma	Preclinical	133
		Elarekibep, PRS-060	Recombinant protein	IL-4Rα antagonist	Asthma	Preclinical	134
	IL-7	Bempikibart (ADX-914)	mAb	IL-7Rα antagonist	Alopecia areata, Moderate to severe AD	2	NCT05509023
		GSK2618960	mAb	IL-7Rα antagonist	Primary Sjögren’s Syndrome	2, discontinued	NCT03239600
		Lusvertikimab/OSE-127	mAb	IL-7Rα antagonist	Ulcerative colitis	2	NCT04882007
		GSK3888130B	mAb	IL-7 antagonist	MS	1	NCT05131971
		PF-06342674	mAb	IL-7Rα antagonist	MS, type 1 diabetes	1, discontinued	NCT02045732, NCT02038764
	IL-9	Enokizumab	mAb	IL-9 antagonist	Asthma	2, discontinued	135
	IL-15	Ordesekimab (AMG714)	mAb	IL-15 antagonist	Coeliac disease	2	NCT04424927
		TEV-53408	mAb	IL-15 antagonist	Coeliac disease, Vitiligo	1	NCT06625177
		CALY-002	mAb	IL-15 antagonist	Coeliac disease, Eosinophilic Esophagitis	1	NCT04593251
	IL-21	Avizakimab	mAb	IL-21 antagonist	SLE	2	NCT03371251
		LY3200327, Ab327	mAb	IL-21 antagonist	SLE	2	NCT05156034
		ATR-107	mAb	IL-21R antagonist	SLE	1, discontinued	NCT01162889
		NNC0114­0006, NN-8828	mAb	IL-21 antagonist	Crohn’s disease, RA, SLE, type 1 diabetes	2, discontinued	NCT02443155
Cancer	IL-2	Nemvaleukin Alfa, ALKS4320	Mutein	IL-2R agonist (CD25-dead)	Melanoma, ovarian cancer	2,3	NCT04830124, NCT05092360
		Imneskibart (Au-007)	mAb	IL-2 (CD25 antagonist, CD122/CD132 agonist)	Advanced solid tumors	1/2	NCT05267626
		SLC-3010	mAb	IL-2 (CD25 antagonist, CD122/CD132 agonist)	Advanced solid tumors	1/2	NCT05525247
		MDNA11	mutein	IL-2R (CD25 antagonist, CD122/CD132 agonist)	Advanced solid tumors	1/2	NCT05086692
		GI-101	CD80-IgG4 Fc-IL-2 fusion	IL-2R	Advanced solid tumors	1/2	NCT04977453
		IPH-6501	Tetraspecific NK cell engager	IL-2R (CD25 antagonist, CD122/CD132 agonist)	B-cell Non-Hodgkin Lymphoma	1/2	NCT06088654
		STK-012	Mutein	IL-2R (CD25-enhanced) agonist	Solid tumors	1	NCT05098132
		DF6215	Mutein-Fc fusion	IL-2R (CD122/CD132 enhanced) agonist	Advanced solid tumors	1	NCT06108479
		IBI363	bsAb	PD-1 antagonist x IL-2 (CD25-enhanced) agonist	Advanced solid tumors/Lymphoma	1	NCT05460767
		NARA1leukin	mAb-mutein graft	IL-2 (CD25 antagonist, CD122/CD132 agonist)	Cancer	Preclinical	136
		BPT331	mAb-mutein fusion	PD-1 antagonist x IL-2R agonist (CD25-dead)	Cancer	Preclinical	137
		bsAb-1	mAb	CD122 x CD132 agonist	Cancer	Preclinical	138
		LAP(mut) IL-2	LAP-masked mutein	IL-2R agonist	Cancer	Preclinical	139
		IOV-3001	mAb-mutein graft	IL-2R agonist (CD25 dead)	Cancer	Preclinical	140
		REGN10597	mAb-CD25-IL-2 fusion	PD-1 antagonist x IL-2R agonist	Cancer	Preclinical	141
		B10/G28 iAb	i-shaped bsAb	CD122 x CD132 agonist	Cancer	Preclinical	142
	IL-4	IL-4-Fc	IL-4-Fc	IL-4R agonist	Cancer	Preclinical	143
		GIFT4	IL-4-GM-CSF fusion	IL-4R x CSF2Ra agonist	Cancer	Preclinical	144
	IL-7	MDK-703	Peptide-Fc fusion	IL-7Rα agonist	Advanced or metastatic solid tumors	1/2, discontinued	NCT05716295
		NT-I7	Mutein-Fc fusion	IL-7Rα agonist	Lymphopenia in patients with PML	1	NCT04781309
		B12	mAb	IL-7Rα antagonist	ALL	Preclinical	30850736
		Lusvertikimab/OSE-127	mAb	IL-7Rα antagonist	ALL	Preclinical	38518105
	IL-15	N-803, ANKTIVA, ALT-803	IL-15R-IL-15 fusion	IL-15R agonist	Bladder cancer (Approved) NSCLC	Approved, 2/3	NCT05096663
		NKTR-255	PEGylated IL-15	IL-15R agonist	Relapsed/refractory B-cell lymphoma	2/3	NCT05664217
		Nanrilkefusp Alfa, SOT101	IL-15-IL15Rα fusion	IL-15R agonist	Advanced solid tumors, colorectal cancer	2	NCT05256381, NCT05619172
		JK08	mAb-IL-15Rα-15 fusion	CTLA-4 antagonist x IL-15R agonist	Advanced or Metastatic Cancer	1/2	NCT05620134
	IL-21	Latikafusp/AMG256	mAb-IL-21 fusion	PD-1 antagonist x IL-21R agonist	Advanced solid tumors	1	NCT04362748
		JS-014	mAb-IL-21 fusion	HSA for half-life extension (IL-21R agonist)	Solid tumors	1	NCT05296772
		Hu14.18-IL21	mAb-IL-21 fusion	GD1 antagonist x IL-21R agonist	Neuroblastoma	Preclinical	145
		AB821	mAb-mutein fusion	CD8 (IL-21R agonist)	Cancer	Preclinical	146
		2P2	mAb	IL-21 (IL-21R agonist)	Cancer	Preclinical	147

MS, multiple sclerosis; UC, ulcerative colitis; GvHD, graft versus host disease; SSc, systemic sclerosis; IPF, Idiopathic Pulmonary Fibrosis; AD, atopic dermatitis; PML, Progressive multifocal leukoencephalopathy; ALL, acute lymphoblastic leukemia, NSCLC, Non-small cell lung cancer.

Figure 2.

Biologic-based therapeutic strategies targeting the γc cytokine family. (a) Approaches of targeting γc family cytokines or their receptors in autoimmune or inflammatory diseases or (b) cancer. Graphical representations were created with BioRender.com.

Preclinical mAb-based approaches aim to target IL-2 in a highly selective manner. In autoimmune diseases, these mAbs bind IL-2 on its IL-2 Rβ binding site, thereby inhibiting effector T cell activation. Consequently, binding to IL-2 Rα expressing cells is sustained, thereby starving the disease-causing effector T cells while promoting the disease inhibiting Treg cells. For example, antibody clone F5111.2 selectively inhibits IL-2 signaling in CD8⁺ T cells and NK cells at lower concentrations, expanding Tregs in type 1 diabetes models.¹²⁸ Similarly, UFKA-20 demonstrated selective Treg activation in human PBMC samples when complexed with IL-2,¹²⁹ and BD3, a computationally designed antibody, shows comparable selectivity and is currently in the preclinical stage.¹³⁰ More detailed data about these antibodies, including structural insights and reports from first clinical trials, will likely shed light onto the feasibility of this strategy. Another cell-targeted approach was developed by a research team from the University of Miami. The team has developed an IL-2:IL-2 Rα fusion protein connected with a non-cleavable linker peptide, thereby directing signaling selectively toward Tregs in vivo.¹⁵⁰ Moreover, the IL-2 mutein Fc-fusion MDNA209 was designed to antagonize the IL-2 Rβγ interaction, thereby enhancing Treg expansion to treat autoimmune diseases.⁴⁰

IL-4

IL-4 and its receptor are amongst the most frequent therapeutic targets in type 2-mediated diseases,⁴⁴ resulting in a long list of different biologics targeting this pathway.

While early anti-IL-4 therapies like Pascolizumab were unsuccessful in asthma,¹⁵¹ subsequent IL-4 Rα targeting mAbs like Dupilumab, have seen widespread success by inhibiting both IL-4 and IL-13 signaling. This mAb was developed by Regeneron and is amongst the best-selling antibody therapeutics worldwide, a success that led to the development of numerous biosimilar approaches.^152–155 Currently, many companies are developing improved versions, such as Connect Biopharma’s Rademikibart, which requires less frequent dosing due to slightly higher affinity.¹³² Using an alternate approach, APG808 from Apogee Therapeutics is a human IgG1 mAb carrying the YTE and LALA mutations for extended half-life through increased FcRn binding and ablated FcγR binding, respectively.¹⁵⁶ Another antagonistic IL-4 Rα approach was used for Pitrakinra, which is an IL-4 mutein encompassing two point mutations to potently block IL-4 and IL-13-mediated signaling through IL-4 Rα.¹⁵⁷ Despite showing some beneficial clinical outcomes such as improved FEV1 levels from baseline, Pitrakinra was ultimately discontinued after Phase 2b clinical trials.¹⁵⁸ Moreover, targeting both IL-4 and IL-13 with bispecific antibodies has been assessed in the past with GSK2434735 and Romilkimab, but this approach was less efficacious in comparison to targeting IL-4 Rα instead.^159,160 Next-generation approaches aim to improve upon Dupilumab’s efficacy, such as RC1416, by simultaneously targeting IL-4 Rα and IL-5 to address high blood-eosinophilia side effects.¹⁶¹ Pfizer is currently advancing novel tri-specific mAbs with PF-07264660 and PF-07275315, which inhibit multiple type 2 cytokines involved in driving atopic dermatitis by simultaneously neutralizing IL-4, IL-13, IL-33 and IL-4, IL-13, TSLP, respectively,¹⁶² aiming for enhanced therapeutic effects compared to Dupilumab.

Preclinical approaches include inhalable IL-4 Rα nanobodies by Novamab¹³³ and engineered proteins like Elarekibep, an inhaled version of Lipocalin 1, designed to bind IL4Rα with high affinity, thereby preventing IL-4-signaling.¹³⁴ These approaches are distinguished from current therapies by their administration route, and future clinical trials will be crucial to evaluate the potential of inhalation as a delivery route for biologics.

IL-7

Dysregulated IL-7 signaling is involved in a variety of disorders, including cancer, autoimmune disorders, inflammatory gut diseases, and type 2-mediated conditions such as atopic dermatitis.¹⁶³ To counteract this, IL-7 signaling is and has been a primary target for therapeutic antibodies in clinical trials.

One such antibody, Bempikibart, is a fully human mAb developed by Q32 Bio directed against the IL-7 Rα domain to effectively inhibit both IL-7 and TSLP signaling. It is currently being investigated in Phase 2a clinical trials for conditions, such as alopecia areata¹⁶⁴ and atopic dermatitis.¹⁶⁵ Similarly, GSK previously pursued a comparable IL-7 Rα-targeted strategy with GSK2618960, but discontinued development after Phase 2 trials in primary Sjögren’s syndrome¹⁶⁶ and relapsing-remitting multiple sclerosis¹⁶⁷ without disclosing results of these trials. However, GSK recently reevaluated the anti-IL-7 antibody GSK3888130B in healthy volunteers,¹⁶⁸ suggesting renewed interest in this approach. Another humanized IL-7 Rα antibody, Lusvertikimab, is under development by OSE Immuno Therapeutics for use in ulcerative colitis.¹⁶⁹ Pfizer investigated IL-7 Rα for the treatment of type 1 diabetes¹⁷⁰ for several years, but discontinued the program in 2018 due to corporate strategic considerations.

Results of ongoing and future Phase 3 clinical trials will reveal the therapeutic value of these antibodies in treating autoimmune diseases.

IL-9

IL-9 has been reported to induce the development of a number of autoimmune disorders such as Inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and SLE.^171–173 However, there are some conflicting reports from murine studies suggesting IL-9 may suppress experimental autoimmune encephalomyelitis.^174,175 Moreover, IL-9 contributes to the pathophysiology of allergic disease, like asthma, and in various cancers.¹⁷⁶ The therapeutic potential of IL-9 antibody blockade has not been as extensively explored in comparison to other γc family members. Enokizumab, an anti-IL-9 humanized IgG1 mAb previously tested in clinical trials for asthma, demonstrated a favorable safety profile and reduced exacerbations, but was ultimately discontinued due to limited efficacy.^135,177 The failure of Enokizumab could be explained by suboptimal patient selection criteria, as it was tested in mild and persistent asthma rather than in a subgroup of patients with an IL-9-driven phenotype. Recent studies have again sparked interest in targeting this cytokine, as the presence of IL-9 producing T cells clearly distinguishes allergic asthmatics from non-allergic controls.^78,79 Moreover, we have recently shown that IL-9 blockade can be a promising approach, especially when airway inflammation is ILC2 driven or in more acute settings when combined with IL-21 blockade.⁸⁰

Additional translational studies are necessary to identify the patient groups that could benefit most from IL-9-targeted therapies, enabling precise patient selection as these treatments progress toward clinical application.

IL-15

Given the established link between IL-15 signaling and celiac disease,¹⁷⁸ Amgen has been conducting trials with its anti-IL-15 mAb AMG714 (Ordesekimab) for this condition,^179,180 but it has also been assessed in other inflammatory skin conditions, including psoriasis,¹⁸¹ vitiligo,¹⁸² and rheumatoid arthritis.¹⁸³ In the initial celiac disease trials, AMG714 did not show a statistically significant difference in lymphocyte reduction in the intraepithelial space or primary endpoints compared to placebo, indicating further research is needed to validate its therapeutic potential. Phase 2 clinical trials have been completed recently, but no results have yet been published. Two other mAbs targeting IL-15 are currently under clinical development, both in Phase 1. TEV53408 by Teva Pharmaceuticals is currently being assessed in celiac disease and vitiligo,¹⁸⁴ while Calypso Biotech’s CALY-002 is being tested in celiac disease and eosinophilic esophagitis (EoE).¹⁸⁵ Results from potential Phase 2 clinical trials will be needed to reveal which of these antibodies performs best in terms of efficacy and safety (Table 1).

IL-21

IL-21 is increasingly recognized as a key player in autoimmune diseases such as SLE, type 1 diabetes, and rheumatoid arthritis. Boston Pharmaceuticals developed a half-life extended anti-IL-21 antibody, Avizakimab,¹⁸⁶ and assessed its efficacy in a Phase 2 clinical trial for SLE that was completed in 2022, but results have never been reported and development was discontinued after that.¹⁸⁷ Eli Lilly also developed an anti-IL-21 antibody that, after initial safety trials,¹⁸⁸ was transferred to Sarkana Pharma for continued exploration.¹⁸⁹ Novo Nordisk explored IL-21 blockade with their candidate NNC0114­0006 in rheumatoid arthritis,^190,191 SLE,¹⁹² Crohn’s disease,¹⁹³ and type 1 diabetes mellitus.¹⁹⁴ However, all of these efforts were stopped. Recently, Almirall has obtained the exclusive global rights to develop this antibody in inflammatory dermatological disorders.¹⁹⁵ Pfizer followed a different approach by targeting IL-21 R with ATR-107 for lupus.¹⁹⁶ However, Phase 1 trials uncovered high immunogenicity, with anti-drug antibodies developing in 76% of subjects dosed,¹⁹⁷ leading to dendritic and T cell activation and subsequent trial termination.¹⁹⁸ Further studies are required to elucidate the role and potential of IL-21 and its receptor in these therapeutic areas.

Collectively, these therapeutic strategies across various γc cytokine family members reflect the ongoing efforts to develop targeted biologics to treat complex immune-mediated diseases (Figure 2, Table 1).

Targeting γc cytokines for cancer immunotherapy

IL-2

IL-2 is a key stimulator of lymphocytic cell differentiation and activation, and its use has been explored extensively in cancer immunotherapy. However, high-dose IL-2 (HDIL-2) treatment often induces significant adverse effects, including hypotension, oliguria, pulmonary edema, pre-renal azotemia, and capillary leak syndrome,¹⁹⁹ which restricts its clinical use in cancer immunotherapy. While in autoimmunity Treg activation is crucial, in cancer, therapeutic strategies aim at promoting effector T cell activity while suppressing Tregs.

The most advanced mAb-based approaches include Imneskibart and SLC-3010. Imneskibart, developed by Aulus Bioscience, is a fully computationally designed mAb that targets IL-2 in a highly specific manner. By occupying the IL-2 Rα binding interface, it prevents IL-2 signaling selectively in Tregs, thereby enhancing effector T cell function and showing promising results in Phase 2 trials for solid tumors across various malignancies.²⁰⁰ Using a similar mode of action, Selecxine’s SLC-3010 is a non-covalent conjugation of IL-2 with the anti-IL-2 antibody TCB2c to directly provide IL-2 to CD8⁺ T cells and NK cells, while sparing Tregs.²⁰¹ After loss of the conjugational payload, TCB2 is able to persist in circulation, where it is able to bind endogenous IL-2. There are multiple mutein-based approaches designed to achieve selective effector T cell activation, while sparing Tregs. The most clinically advanced IL-2 mutein is Nemvaleukin Alfa (ALKS4320). It is an engineered fusion protein containing circularly permuted IL-2 with the extracellular IL-2 Rα domain, and can selectively activate effector cells that express the intermediate-affinity IL-2 Rβγ²⁰² while also possessing increased half-life in vivo. It is currently being evaluated in Phase 2 clinical trials for numerous solid cancers with and without checkpoint blockade. MDNA11 is a half-life extended IL-2 mutein tackling the specificity and low half-life issues simultaneously.²⁰³ Half-life extension is achieved by genetic fusion to human serum albumin, whereas specific mutations in the IL-2 sequence result in complete abrogation of IL-2 Rα binding, thereby specifically targeting the intermediate βγ-complex to expand CD8⁺ T cells and NK cells for augmented anti-tumor responses. The molecule is currently being evaluated in a Phase 1/2 study as both a monotherapy and in combination with PD-1 blockade.²⁰⁴ GI Innovation is following the strategy to combine CTLA-4 inhibition with effector T cell-targeted IL-2 delivery using their CD80-IgG4 Fc-IL-2 molecule GI-101. This novel bispecific fusion protein was well tolerated with and without PD-1 blockade in Phase 1/2 clinical trials.²⁰⁵ Further clinical investigation is required to move this approach further into the clinic. Innate Pharma’s IPH-6501 is a tetra-specific NK cell engager²⁰⁶ that engages NKp46, CD16a and IL-2 Rβ via a CD25-dead IL-2 variant. The fourth binding domain is directed against CD20, which is highly expressed on the malignant B cells. This highly specific approach is currently being evaluated in Phase 1 clinical trials for B cell lymphoma. Dragonfly Therapeutics designed a βγ-biased IL-2 mutein-Fc fusion (DF6215) to tackle effector cell specificity together with increased half-life. The company is conducting a multi-part study to assess the compounds safety and biological activity in patients with advanced solid tumors.²⁰⁷ In contrast, Synthekine’s STK-012 employs an entirely different strategy. Since CD25 is not only expressed by Tregs but also by activated cytotoxic effector T cells, this molecule was engineered for enhanced CD25 binding. Novel findings indicate that CD25-dead IL-2 variants can effectively expand systemic T cells and NK cells but do not necessarily enhance anti-tumor responses through tumor-reactive cytotoxic T cells.^141,208 Therefore, it is likely that CD25-dead IL-2 primarily expands naïve T cells rather than tumor-specific T cells. Phase 1 clinical trials for this compound have been completed, and further studies will determine the true value of this strategy over CD25-dead muteins. Similarly, Innovent Biologic’s bispecific antibody IBI363 aims to deliver CD25-enhanced IL-2 specifically to PD-1 expressing tumor reactive CTLs, combining checkpoint blockade with targeted cytokine delivery.²⁰⁹ This approach is currently being assessed in Phase 1/2 clinical trials for solid tumors and lymphomas.

Preclinical strategies include both mutein- and antibody-based approaches as well as combinations of the two. Bright Peak Therapeutics is engineering IL-2 muteins with reduced CD25 affinity to spare Treg activation¹³⁷ while enhancing effector T cells, leveraging their chemical-based protein synthesis platform. A more targeted approach by Stealthyx Therapeutics involves encapsulating IL-2 within a protease-sensitive LAP TGF-β envelope. This design extends IL-2’s half-life and enables localized release in the tumor microenvironment (TME) where metalloproteinase activity is high.¹³⁹ NARA1 is an antibody binding to IL-2 on its CD25 binding site, and it is injected complexed with IL-2. To avoid residual binding to Tregs due to dissociation of the complex, NARA1 was further developed into NARA1leukin, which consists of IL-2 covalently grafted onto the light chain complementary determining regions (CDR) residues of NARA1, thereby preventing dissociation and assuring no off-target binding on Tregs.¹³⁶ Similarly, IOV-3001 is another novel IL-2 targeting approach, initially developed by Novartis, and consists of an engineered dimeric IL-2 grafted onto the CDRs of Palivizumab for improved half-life and better safety profile. The IL-2 mutein is designed to interact selectively with IL-2 Rβγ-expressing cells minimizing Treg activation.¹⁴⁰ A different strategy aims to selectively target the IL-2 Rβ and IL-2 Rγ domain with a bispecific antibody, thereby inducing heterodimerization and signaling specifically on cells expressing the intermediate IL-2 R.¹³⁸ With the same intent, Genentech recently reported the discovery of a similar bispecific antibody targeting IL-2 Rβ and IL-2 Rγ¹⁴² using their novel i-shaped antibody format based on mutations in the CH1 region of IgG1 antibodies. Addition of those mutations turned non-agonistic clones into agonistic ones, highlighting the potential of this technology.

Regeneron recently introduced a novel approach similar to STK-012, focusing on the targeted delivery of IL-2 to exhausted CD25⁺ CD8⁺ T cells.¹⁴¹ For enhanced selectivity and safety, they developed a PD-1 targeted receptor-masked IL-2 (REGN10597) by c-terminally fusing CD25 and IL-2 to a PD-1 antibody. This construct utilizes the CD25 domain to mask IL-2, reducing off-target binding. Occasionally, IL-2 is unmasked while maintaining the ability to bind CD25 on PD-1-expressing target cells. While preclinical studies in humanized PD-1 mice show promising results, the potential immunogenicity of such constructs remains a concern and warrants further investigation.

IL-4

Although tumor immunity is generally associated with a robust type 1 immune response, type 2 cytokines have recently gained increasing attention in cancer immunotherapy. Initial studies investigating the use of recombinant IL-4 in clinical trials for advanced renal cell carcinoma failed, as significant side effects were observed while none of the patients achieved complete or even partial responses. It was concluded that the concentration and dosing scheme of IL-4 were suboptimal, despite observing some positive effects on tumor growth.²¹⁰ In contrast, the potential of blocking the IL-4 pathway as a cancer treatment strategy has also been assessed, with studies reporting delay in tumor growth after neutralizing IL-4 or IL-4 R.²¹¹ Moreover, IL-4 has recently been reported to drive resistance to PD-1 checkpoint blockade.²¹² These findings suggest that already approved antagonists of the IL-4 pathway may be repurposed for application in certain types of cancers.

However, in recent preclinical studies using tumor mouse models, Feng et al. demonstrated that an IL-4-Fc fusion protein could reinvigorate exhausted CD8⁺ T cell populations.¹⁴³ Mechanistically, IL-4-Fc induced STAT6 phosphorylation and activation of the mTOR pathway, thereby enhancing glycolytic metabolism in the target cells to restore CD8⁺ T cell activity within the TME. These findings align with single-cell analyses from a long-term remission case of acute lymphocytic leukemia (ALL) after adoptive CAR T cell therapy, which showed active type 2 cytokine signaling,²¹³ supporting the notion that type 2 immunity may counteract T cell exhaustion and extend type 1 immune responses. Another approach to harness IL-4 for cancer treatment involves genetic fusion to GM-CSF, resulting in the fusion protein GIFT4, which specifically activates B cells to enhance the antitumor response of CD8⁺ T cells.¹⁴⁴ The efficacy of GIFT4 was found to depend on the presence of B cells, as it failed to affect tumor burden in B cell-deficient mice. Treatment with GIFT4 induced a broad costimulatory phenotype on the B cells marked by upregulated expression of CD80, CD86, MHC I and MHC II. This resulted in an augmented CD8⁺ T cells response marked by activation, proliferation and IFNγ production.¹⁴⁴

IL-7

Solid tumors

IL-7 R agonism has been explored through a wide variety of molecules in the context of cancer immunotherapy or lymphopenia.^214,215 The main strategies involve genetic fusion of IL-7 to Fc fragments or full-length mAbs to expand CD8⁺ or CD4⁺ T cell populations.²¹⁶ The company Medikine has developed the small peptide-based IL-7 Rα agonist MDK-703 fused to an Fc for half-life extension. Since the peptide is structurally unrelated to native IL-7, this approach potentially has a better safety and immunogenicity profile as the host cannot develop neutralizing antibodies against IL-7.²¹⁶ However, Phase 1/2 clinical trials for this compound were recently terminated due to corporate decisions. As a result, NeoImmuneTech’s NT-I7 is currently the only IL-7 R agonist under clinical development. NT-I7 is a stable, truncated IL-7 variant fused to a human Fcγ domain^187,212. When combined with anti-PD-1 therapy, NT-I7 has shown promising results in enhancing CD8⁺ T cell infiltration into otherwise resistant colorectal and pancreatic tumors.²¹⁷ Moreover, mechanistic studies revealed that direct genetic fusion of IL-7 to PD-1 antibodies supports T cell persistence by expanding TCF-1⁺ CD8⁺ T cells,^218,219 which are noted for their stem-like and proliferative capabilities.²²⁰

Preclinically, Medikine is also developing an IL-2 mutein designed to avoid IL-2 Rα binding, thus specifically targeting the IL-2/15 Rβγ complex. This IL-2 mutein is also under exploration in combination with an IL-7 Rα agonist to maximize the selective signaling pathways of each cytokine.²²¹ Additionally, Medikine is testing a cis-acting fusion of IL-2/IL15Rβγ with an anti-PD-1 antibody,²²² which may provide synergistic benefits by simultaneously enhancing cytokine signaling and immune checkpoint inhibition in cancer therapy.

Hematological malignancies

Preclinical studies with the fully human anti-IL-7 Rα antibody B12, developed by Philochem AG, have shown efficacy in T-cell acute lymphoblastic leukemia (T-ALL), where it promotes cell-killing via antibody-dependent cellular cytotoxicity (ADCC) and sensitizes T-ALL cells to dexamethasone treatment.²²³ Clinical trials will be necessary to validate these findings. As discussed in the autoimmune section above, the anti-IL-7 Rα biologic Lusvertikimab is under development by OSE Immuno Therapeutics for use in ulcerative colitis, but it is also being evaluated preclinically for use in acute lymphoblastic leukemia.²²⁴ Overall, while anti-IL-7 Rα mAbs could offer targeted therapy with potential for both signaling blockade and ADCC in liquid tumors, administration of rhIL-7 and fusion proteins thereof provide broad immune stimulation by increasing overall T cell numbers, thereby enhancing immunity against solid tumors.

IL-9

In the context of cancer, many preclinical studies have reported pro-tumorigenic effects of IL-9, particularly in hematological malignancies were the cancer cells express IL-9 R.^225,226 In contrast, substantial evidence suggests that IL-9 and IL-9-producing cells can exert anti-tumor effects, especially in solid tumors like melanoma.^81–83 Notably, no IL-9 fusion proteins or antibody-based agonistic approaches have yet been reported. Nevertheless, Kalbasi et al. demonstrated that synthetic IL-9 R signaling, based on an orthogonal IL-2 variant, can enhance the anti-tumor effects of CAR T cells, outperforming other γc cytokines.⁸⁴ This highlights the potential of utilizing IL-9 in an agonistic manner to improve tumor immunity. Additionally, clinical data suggest that levels of IL-9 or IL-9-producing T cells correlate with response to checkpoint blockade.^227,228 Clearly, further translational and clinical research is required to bring IL-9-targeted biologics to the market.

IL-15

While both mAbs and recombinant cytokines have therapeutic potential, mAbs generally offer improved safety profiles and dosing regimens. However, the development of engineered cytokine complexes aims at overcoming some limitations of recombinant cytokines while maintaining their immunostimulatory benefits. The US Food and Drug Administration (FDA) recently approved ImmunityBio’s first-in-class IL-15 receptor (IL-15 R) super-agonist N-803 (Nogapendekin alfa inbakicep; Anktiva) for the treatment of muscle-invasive bladder cancer. This molecule combines a human IL-15N72D mutein with a human IL-15 Rα sushi domain-Fc to promote the expansion of native NK and CD8⁺ T cells without stimulating Tregs.²²⁹ This IL-15 superagonist increases IL-2 Rβγ binding and IL-15 biologic activity by approximately 5-fold and exhibits superior immunostimulatory activity, more potent anti-myeloma activity, and prolonged half-life compared to IL-15 in mouse models.²³⁰ The drug is also being investigated in clinical trials targeting a variety of cancers, including Lynch syndrome, ovarian cancer, acute myeloid leukemia, head and neck cancer, and NSCLC where it has shown promising clinical activity in combination with nivolumab treatment²³¹ (Table 1). Similarly, Sotio Biotech’s SOT101, another superagonist fusion protein of IL-15 and IL-15 Rα sushi domain, has been reported to improve NK cell-dependent tumor immunity.²³² Even though results from initial clinical studies showed some benefit of SOT101 in advanced/metastatic solid tumors in combination with pembrolizumab,²³³ the company ultimately terminated clinical efforts due to insufficient efficacy in 2023. Nektar Therapeutics developed a PEGylated version of recombinant IL-15 (NKTR-255) to extend the molecule’s half-life. Its therapeutic use was tested in clinical trials for refractory hematological malignancies²³⁴ and multiple myeloma (MM).²³⁵ Currently, NKTR-255 is undergoing evaluation in Phase 2/3 clinical trials for B cell malignancies, urothelial carcinoma and solid tumors (Table 1). Other IL-15-based strategies involve genetic fusion to mAbs. For instance, JK08 is an anti-CTLA-4 antibody fused to IL-15 and an IL-15 Rα sushi domain, combining IL-15’s cell-stimulating potential with CTLA-4 blockade. This design allows ADCC-driven Treg depletion while simultaneously promoting the activation of CD8⁺ T cells and NK cells. JK08 is currently undergoing Phase 1/2 clinical trials for unresectable or metastatic tumors.²³⁶

IL-21

IL-21’s broad antitumor effects on NK and CD8⁺ T cells spurred initial clinical trials for metastatic melanoma and renal carcinoma,^237,238 where treatment demonstrated benefits in progression-free survival and overall survival. However, these trials were stopped after Phase 2,²³⁹ possibly due to IL-21’s limited bioavailability and short half-life.

Since then, several strategies have emerged to optimize the use of IL-21 for cancer immunotherapy. Primarily tackling the apparent short half-life of IL-21, JS-014, a fusion of IL-21 with an albumin-targeting single-domain antibody (IL-21-αHSA), achieved a 10-fold increase in half-life and improved stability compared to recombinant IL-21.²⁴⁰ Notably, combination of this fusion protein with checkpoint inhibitors to PD-1 or TIGIT resulted in synergistic effects on tumor growth. Moreover, this treatment induced long-term tumor immunity through memory formation shown by using tumor re-challenge models.^241,242 The safety of this approach is currently being evaluated in Phase 1 clinical trials. Latikafusp (AMG256), also in Phase 1 clinical trials, is composed of an IL-21 mutein C-terminally fused to an anti-PD-1 mAb. In vivo, Latikafusp reinvigorates exhausted CD8⁺ T cells through PD-1 blockade, while the IL-21 mutein’s reduced affinity for IL-21 R helps to minimize off-target effects, focusing cis-IL-21 signaling specifically to PD-1-expressing cells.²⁴³

Following a similar strategy, there are numerous preclinical studies testing IL-21 fusion with various checkpoint inhibitors.^244–246 Comparative studies with IL-21 and other cytokines highlight IL-21’s potent antitumor effects, particularly in the context of neuroblastoma. Here, genetic fusion of IL-21 to anti-GD2 antibodies outperformed similar constructs fused with IL-15, achieving complete remission in patient-derived xenograft experiments.¹⁴⁵ Another IL-21-based molecule, AB821, consists of a low-affinity IL-21 mutein fused to an anti-CD8α antibody. Functionally, this design leads to specific cis-targeting of CD8⁺ T cells resulting in 1000-fold increased potency in comparison to recombinant IL-21.¹⁴⁶ Similar cis-targeting approaches are being explored with IL-2 mutein fusions as well.²⁴⁷ By screening antibody libraries with an IL-21-sensitive B cell proliferation assay, the IL-21 agonist antibody 2P2 was discovered. Besides extending the half-life of IL-21, this mAb was shown to potentiate CD8⁺ T cell expansion, likely due to conformational changes of IL-21 that favor IL-21 R engagement. In vitro assays confirmed that in presence of this antibody IL-21-dependent STAT3-phosphorylation is enhanced approximately 5-fold.¹⁴⁷

In summary, with exception of IL-9, all members of the γc cytokine family have been targeted with biologics in the context of cancer (Figure 2, Table 1).

Future directions for therapeutic targeting of the γc cytokine family

The γc cytokine family and its receptors serve as therapeutic targets across various diseases, including autoimmunity, inflammatory disorders, and cancer.¹ While in vitro studies using cell lines or primary cells from mice or human donors have yielded key insights into these cytokines’ mechanisms, in vivo applications remain challenging due to the diverse abundance and differential expression of their respective receptors across various immune cell types. To expand our understanding in that direction, two recent studies investigated how systemic administration of γc cytokines influence immune cells in vivo. Following cytokine administration, immune cells of different lineages were isolated from the peritoneum, spleen, or lymph nodes, then subjected to fluorescence-activated cell sorting and RNA-seq analysis. Analyses of these data revealed unprecedented engagement of metabolic pathways, chromatin remodeling, and mRNA destabilization, with broad and overlapping effects across different cell types, highlighting the pleiotropic nature of these cytokines in vivo.^4,248 Such complexity comes with challenges when designing cytokine-based therapeutics, and ultimately limit the success rate of novel biologics. However, advances in structural biology, protein engineering, high-throughput screening, artificial intelligence, machine learning algoritms,²⁴⁹ and receptor pharmacology have made it possible to shift cytokine effects from pleiotropy toward specificity.²⁵⁰

Biologics are ideal molecules for such therapeutic intervention strategies, as they are generally characterized by good developability, manufacturability and moreover possess excellent half-life properties and specificity in comparison to small molecules inhibitors. As a result, FDA approvals of biologics surpassed those of small molecules for the first time in 2022.²⁵¹

Antibodies and cytokine-based therapies are key modalities in immunotherapy, each offering distinct benefits and limitations. Antibodies offer high specificity, extended half-life, and well-established manufacturing processes, but face obstacles such as limited tissue penetration and potential immunogenicity. On the other hand, cytokines and muteins, effectively stimulate the immune system, but are limited by short half-lives and systemic toxicities. Antibody-cytokine fusion proteins aim to combine the advantages of both strategies, potentially improving efficacy and reducing toxicity. However, characterization, manufacturing and purification can be more challenging. Hence, each modality has trade-offs in terms of developability, immunogenicity, and pharmacokinetics, requiring thoughtful consideration to determine the most appropriate format for specific therapeutic applications.

Clinical results from the IL-21 Rα-targeting mAb ATR-107 suggest that targeting receptors rather than cytokines may carry a higher risk of immunogenicity.¹⁹⁷ This increased risk could be attributed to the formation of novel epitopes resulting from complexation on the surface of cells expressing the target. On the other hand, it also enables the engagement of pathways that include multiple cytokines, as seen with IL-4 Rα and IL-7 Rα, which mediate additional receptor activities (IL-13 and TSLP, respectively).¹³¹ Clinical data indicate that single-cytokine blockade or agonism often fail to provide meaningful efficacy,⁹ and thus, bifunctional or even tri-specific approaches are emerging.^127,161,162 These methods shut down multiple pathways simultaneously or combine target neutralization with specific cytokine delivery through genetic fusion.^{204,236,244,246} This complexity is also evident in agonistic approaches, where a high degree of dysregulation in diseases like autoimmunity and cancer often necessitates combination therapies rather than single-pathway interventions. The increasing complexity of such multi-specific modalities can be extremely challenging during preclinical development, as many cytokines or their receptors have low human to murine sequence homology, and therefore often require generation of humanized mouse models. Translation is further complicated by differences in how human and murine antibodies engage with the neonatal Fc receptor (FcRn)^252,253 as well as Fc-γ receptors, as they bind with different affinities.²⁵⁴ This makes selecting the appropriate IgG-isotype and glycosylation patterns critically important. When multiple ligands are involved, the development process can be further delayed, as generation of double transgenic mice may sometimes be required.²⁵⁵ However, development of novel biologics solely based on preclinical mouse models may not be the way forward. Instead, translational-oriented approaches or even patient-centered strategies could be more promising, for instance in diseases such as allergic asthma, where only subsets of patients respond to treatments due to patient heterogeneity and disease endotypes that change over time.⁷³ Another example is oncology, where the standard checkpoint inhibitor therapy (PD-1 and CTLA-4) yields only a 20–30% response rate in patients, further emphasizing the need for patient-centered strategies.^256–258 Identifying new or treatment-specific biomarkers could enhance the selection of non-responders for more targeted clinical trials, as observed in the past with the IL-5 antagonist Mepolizumab, which only showed efficacy in patients with high sputum eosinophilia.^259,260

In conclusion, research around the γc cytokine family is highly active, with novel biologics continuously being developed to target either the cytokines or their receptors. IL-9 remains an understudied member, as no agonistic biologics have yet been developed, despite its potential application in tumor immunity and beyond.^82,261 Future studies focusing on bridging this technological gap could potentially provide valuable treatment options for cancer patients, for instance by exploring the feasibility of fusing this cytokine to checkpoint inhibitors or Fc fragments. Given that increased IL-9 levels are associated with better response to checkpoint inhibitors,^227,228 such strategies require prompt experimental investigation. In line with that, IL-9 (and IL-21) targeted approaches are currently underrepresented in the clinic (Table 1), pointing out that further preclinical studies are required for those cytokines to move forward. The majority of ongoing clinical trials evaluate therapeutic targeting of IL-2, IL-4, IL-7 and IL-15. Learnings from those ongoing trials will not only shed light onto which approaches will make it to approval but will also greatly expand our understanding of how this cytokine family can be utilized to its fullest potential using biologic-based therapeutic approaches.

Funding Statement

This work was funded by a Baekeland Mandate of Flanders Innovation & Entrepreneurship (VLAIO) [HBC.2019.2598] to F.B. B.N.L. acknowledges support from ERC advanced grant [789384 ASTHMA CRYSTAL CLEAR], a concerted research initiative grant from Ghent University [GOA, 01G010C9], an FWO Methusalem grant [01M01521] and an FWO EOS research grant [3G0H1222], and the Flanders Institute of Biotechnology (VIB). M.J.S. acknowledges support from FWO [3E008521], Stichting tegen Kanker [2023-048 and 365N09123], and Foundation ACTERIA.

Disclosure statement

C.B. is consultant and shareholder of argenx. B.N.L. receives consultancy fees from GSK Biologics, Novartis, Sanofi, AstraZeneca, ALK, OncoArendi, argenx and has research grants from ALK, argenx, AstraZeneca, GSK, GSK Biologics and Johnson & Johnson. All other authors have nothing to disclose.