Why IL-2 Still Holds Promise in Therapeutics of Cancer and Autoimmunity

Aclidineleukin (high-dose IL-2) is the first FDA-approved cancer immunotherapy for metastatic renal cell carcinoma (RCC) and melanoma, but the widespread clinical use of aclidinein has been limited by its short half-life, serious side effects, and simultaneous stimulation of Treg activation.

With the breakthrough of studies of immune checkpoint inhibitors, IL-2-based therapeutics has regained widespread attention, stimulating the enthusiasm of many pharmaceutical companies for the development of IL-2-based drugs. Here we will talk about IL-2, a therapeutic target still holds promise in therapeutics of cancer and autoimmunity.

What are IL-2 and IL-2 receptor

Interleukin-2 (IL-2) is a type of cytokine signaling molecule in the immune system. The interleukin-2 receptor (IL-2R), capable of binding to cytokine IL-2, is a heterotrimeric protein expressed on the surface of certain immune cells. 

IL-2R has three forms, generated by different combinations of three varying proteins, also commonly referred to as “chains”: IL-2Rα (also called CD25), IL-2Rβ (also called CD122), and IL-2Rγ (often called CD132). The three receptor chains present different expression on various cell types and varying binding affinity to IL-2 through assemblage in different combinations, such as, IL-2Rα has low binding affinity to IL-2, the combination of IL-2Rβ and IL-2Rγ binds IL-2 with intermediate affinity, and all three chains form a complex, capable of binding IL-2 with high affinity. 

The intermediate affinity receptor form, present on memory T cells and NK cells, and high affinity receptor form, commonly highly expressed on activated T cells and regulatory T cells, are functional and cause changes when binding with IL-2.

IL-2 Binds to Varying IL-2R Forms with Low, Intermediate and High Affinity

How IL-2 and IL-2R function in immune responses

All three IL-2 receptor chains are transmembrane proteins, which can deliver molecular signals to the cell interior. IL-2Rα has no participation in molecular signaling, but IL-2Rβ can form complex by recruiting Janus kinase 1 (JAK1). Similar to IL-2Rβ, IL-2Rγ can  form complex with another tyrosine kinase called JAK3. JAK1 and JAK3 can be activated once IL-2 binds to the external domains of the IL-2R, which can initiate three classical molecular signaling pathways in cells, the MAPK pathway, the PI3K/Akt/mTOR pathway, and the JAK/STAT pathway. These pathways impact gene expression to regulate cellular growth, death, and immune function in IL-2R-bearing cells.

Following IL-2 binding to the IL-2R, and molecular signaling lasting very short time, rapid degradation of IL-2, IL-2Rβ, and IL-2Rγ occurs, but IL-2Rα can be recycled to the cell surface. IL-2/IL-2R play key roles in activation and regulation of the immune responses by direct effecting on T cells. IL-2/IL2R also promote the differentiation of T cells into effector T cells and into memory T cells when the immune responses are initiated by stimulation of antigens.

                                      IL-2 Mediated Molecular Signaling Pathways

Clinical prospects of IL-2/IL-2R in therapeutics of autoimmunity and cancer

IL-2 has been reported to have double-edged effects: high dose IL-2 can facilitate proliferation of effector T cells, thereby exerting tumor-suppressive effect, and low dose IL-2 is capable of activating Treg cells selectively, so as to suppress activation of immune responses. Therefore, IL-2 is applicable to therapeutics of both anti-tumor and autoimmune diseases.

IL-2 is the first FDA-approved cytokine for tumor immunotherapy, which can not only activates NK cells, cytotoxic CD8+ T (CTL) cells and lymphokine activated killer (LAK) cells, but also induces other immune cells to produce IFN, TNF, CSF and other cytokines to synergistically enhance immune cell activity.

           Mechanistic Diagram of IL-2/IL-2R-based Anti-tumor Antibody

Autoimmune diseases are characterized by decreased IL-2 secretion and dysregulated immune cell response, leading to defective Treg cell function and excessive proliferation of effector T cells, especially CTL cells and CD4+ T cells. Treg cell function deficits are found in many inflammatory/autoimmune diseases, such as type 1 diabetes mellitus (T1D) and systemic lupus erythematosus. IL-2 can promote the proliferation of Treg cells and rescue CD25 expression, allowing exogenous IL-2 to be potential in therapeutics for a variety of autoimmune diseases.

                                           IL-2/IL-2R-based Signaling Pathways and Diseases

Thus, numerous pharmaceutical companies have shifted their attention to development of IL-2/IL-2R-targeted drugs. The following table demonstrates some representative FDA-approved IL-2/IL-2R-targeted drugs and those undergone clinical trials.

SMOC humanized mice for IL-2/IL-2R-targeted therapeutics research

Smoc has been striving to develop therapeutic target-humanized mice, including IL-2/IL-2R humanized mice, which work as powerful tools for efficacy evaluation and safety assessment of therapeutics. The following table presents SMOC genetically modified mice intended for research of IL-2/IL-2R-targeted therapeutics.

Part of representative validation data of IL-2/IL-2R humanized mice

hIL2 mice (NM-HU-190048)

 Figure 1. Detection of human IL-2 expression in spleen of homozygous hIL-2 mice by FACS.

hIL2RA mice (NM-HU-190064)

Figure 2. FACS analysis of human IL-2Rα(hIL2RA) expression on naive Tregs from hIL2RA knockin mice (In collaboration with CrownBio). (A) hIL2A expression on naive Tregs in peripheral blood of homozygous hlL2RA knockin mice; (B) hlL2A expression on naive Treg cells in spleen of homozygous hlL2RA knockin mice. 

Figure 3. FACS analysis of human IL-2Rα (hIL2RA) expression on activated Tregs from hIL2RA knockin mice (In collaboration with CrownBio).(A) hlL-2RA expression on activated Tregs in spleens of IL-2RA humanized mice; (B) hlL-2RA expression on activated NK cells in spleens of IL-2RA humanized mice.

Figure 4. In vivo efficacy study in MC38-bearing hIL-2RA knockin mice (In collaboration with CrownBio). (A) Tumor growth curves upon treatment; (B) Body weight change over time upon treatment.

hIL2/hIL2RA/hIL2RB/hIL2RG mice (NM-HU-210415)

Figure 5. Immunophenotyping of peripheral blood from hIL2/hIL2RA/hIL2RB/hIL2RG qKI mice.

Figure 6. Immunophenotyping of spleen tissue from hIL2/hIL2RA/hIL2RB/hIL2RG qKI mice.

Figure 7. Detection of STAT5 Signaling integrity in hIL2/hIL2RA/hIL2RB/hIL2RG qKI mice.

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References

[1] Spolski, Rosanne et al. “Biology and regulation of IL-2: from molecular mechanisms to human therapy.” Nature reviews. Immunology vol. 18,10 (2018): 648-659. doi:10.1038/s41577-018-0046-y

[2] Peng, Yujia et al. “CD25: A potential tumor therapeutic target.” International journal of cancer vol. 152,7 (2023): 1290-1303. doi:10.1002/ijc.34281

[3] Yuan, Yeshuang et al. “Therapeutic potential of interleukin-2 in autoimmune diseases.” Trends in molecular medicine vol. 28,7 (2022): 596-612. doi:10.1016/j.molmed.2022.04.010

[4] Raeber, Miro E et al. “Interleukin-2-based therapies in cancer.” Science translational medicine vol. 14,670 (2022): eabo5409. doi:10.1126/scitranslmed.abo5409

[5] Hernandez, Rosmely et al. “Engineering IL-2 for immunotherapy of autoimmunity and cancer.” Nature reviews. Immunology vol. 22,10 (2022): 614-628. doi:10.1038/s41577-022-00680-w