Interleukin 2

IL-2 is a member of a specific family of cytokines, each member of which has a four alpha helix bundle; this cytokine family also includes IL-4, IL-7, IL-9, IL-15 and IL-21. IL-2 signals through a IL-2 receptor, a complex consisting of three chains, termed alpha (CD25), beta (CD122) and gamma (CD132). The gamma chain is common to all family members.{{cite journal | vauthors = Liao W, Lin JX, Leonard WJ | title = IL-2 family cytokines: new insights into the complex roles of IL-2 as a broad regulator of T helper cell differentiation | journal = Current Opinion in Immunology | volume = 23 | issue = 5 | pages = 598–604 | date = October 2011 | pmid = 21889323 | pmc = 3405730 | doi = 10.1016/j.coi.2011.08.003 }}

The IL-2 receptor (IL-2R) α subunit binds IL-2 with low affinity (K_d~ 10⁻⁸ M). Interaction of IL-2 and CD25 alone does not lead to signal transduction due to its short intracellular chain but has the ability (when bound to the β and γ subunit) to increase the IL-2R affinity 100-fold.{{cite journal | vauthors = Wang X, Rickert M, Garcia KC | title = Structure of the quaternary complex of interleukin-2 with its alpha, beta, and gammac receptors | journal = Science | volume = 310 | issue = 5751 | pages = 1159–63 | date = November 2005 | pmid = 16293754 | doi = 10.1126/science.1117893 | bibcode = 2005Sci...310.1159W | s2cid = 85394260 }} Heterodimerization of the β and γ subunits of IL-2R is essential for signalling in T cells.{{cite journal | vauthors = Gaffen SL, Liu KD | title = Overview of interleukin-2 function, production and clinical applications | journal = Cytokine | volume = 28 | issue = 3 | pages = 109–23 | date = November 2004 | pmid = 15473953 | doi = 10.1016/j.cyto.2004.06.010 }} IL-2 can signalize either via intermediate-affinity dimeric CD122/CD132 IL-2R (K_d~ 10⁻⁹ M) or high-affinity trimeric CD25/CD122/CD132 IL-2R (K_d~ 10⁻¹¹ M). Dimeric IL-2R is expressed by memory CD8⁺ T cells and NK cells, whereas regulatory T cells and activated T cells express high levels of trimeric IL-2R.

Instructions to express proteins in response to an IL-2 signal (called IL-2 transduction) can take place via 3 different signaling pathways; they are: (1) the JAK-STAT pathway, (2) the PI3K/Akt/mTOR pathway and (3) the MAPK/ERK pathway. The signalling is commenced by IL-2 binding to its receptor, following which cytoplasmatic domains of CD122 and CD132 heterodimerize. This leads to the activation of Janus kinases JAK1 and JAK3 which subsequently phosphorylate T338 on CD122. This phosphorylation recruits STAT transcription factors, predominantly STAT5, which dimerize and migrate to the cell nucleus where they bind to DNA.{{cite journal | vauthors = Friedmann MC, Migone TS, Russell SM, Leonard WJ | title = Different interleukin 2 receptor beta-chain tyrosines couple to at least two signaling pathways and synergistically mediate interleukin 2-induced proliferation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 93 | issue = 5 | pages = 2077–82 | date = March 1996 | pmid = 8700888 | doi = 10.1073/pnas.93.5.2077 | pmc = 39912 | bibcode = 1996PNAS...93.2077F | doi-access = free }} with an "express other proteins" signal. The proteins expressed by means of the three pathways include bcl-6 (the PI3K/Akt/mTOR pathway), CD25 & prdm-1 (the JAK-STAT pathway) and certain cyclins (the MAPK/ERK pathway).

Gene expression regulation for IL-2 can be on multiple levels or by different ways. One of the checkpoints (in other words one of the things which needs to be done before IL-2 is expressed) is that there must be signaling through a conjunction of a T Cell Receptor (a TCR) and an HLA-peptide complex. As a result of that conjunction a signalling pathway (signalling a cell's protein making machinery to express or 'make' IL-2), a PhosphoLipase-C (PLC) dependent pathway, is set up. PLC activates 3 major transcription factors and their pathways: NFAT, NFkB and AP-1. In addition and after costimulation from CD28 the optimal activation of expression of IL-2 and these pathways is induced. In summary therefore before a cell will make IL-2 in accordance with this pathway there have to be two reactions: TCR+HLA and protein complex on the one hand and CD28 costimulation on the other indeed mere IL-2 ligation to its receptor is too low affinity to enable pathway.

At the same time Oct-1 is expressed. It helps the activation. Oct1 is expressed in T-lymphocytes and Oct2 is induced after cell activation.

NFAT has multiple family members, all of them are located in cytoplasm and signaling goes through calcineurin, NFAT is dephosphorylated and therefore translocated to the nucleus.

AP-1 is a dimer and is composed of c-Jun and c-Fos proteins. It cooperates with other transcription factors including NFkB and Oct.

NFkB is translocated to the nucleus after costimulation through CD28. NFkB is a heterodimer and there are two binding sites on the IL-2 promoter.

IL-2 has essential roles in key functions of the immune system, tolerance and immunity, primarily via its direct effects on T cells. In the thymus, where T cells mature, it prevents autoimmune diseases by promoting the differentiation of certain immature T cells into regulatory T cells, which suppress other T cells that are otherwise primed to attack normal healthy cells in the body. IL-2 enhances activation-induced cell death (AICD). IL-2 also promotes the differentiation of T cells into effector T cells and into memory T cells when the initial T cell is also stimulated by an antigen, thus helping the body fight off infections. Together with other polarizing cytokines, IL-2 stimulates naive CD4⁺ T cell differentiation into T_h1 and T_h2 lymphocytes while it impedes differentiation into T_h17 and folicular T_h lymphocytes.{{cite journal | vauthors = Liao W, Lin JX, Leonard WJ | title = Interleukin-2 at the crossroads of effector responses, tolerance, and immunotherapy | journal = Immunity | volume = 38 | issue = 1 | pages = 13–25 | date = January 2013 | pmid = 23352221 | doi = 10.1016/j.immuni.2013.01.004 | pmc = 3610532 }}{{cite journal | vauthors = Spolski R, Li P, Leonard WJ | title = Biology and regulation of IL-2: from molecular mechanisms to human therapy | journal = Nature Reviews Immunology | volume = 18 | issue=10 | pages = 648–659 |date=2018 | doi = 10.1038/s41577-018-0046-y | pmid = 30089912| s2cid = 51939991 }}

IL-2 increases the cell killing activity of both natural killer cells and cytotoxic T cells.

Its expression and secretion is tightly regulated and functions as part of both transient positive and negative feedback loops in mounting and dampening immune responses. Through its role in the development of T cell immunologic memory, which depends upon the expansion of the number and function of antigen-selected T cell clones, it plays a key role in enduring cell-mediated immunity.{{cite journal | vauthors = Malek TR, Castro I | title = Interleukin-2 receptor signaling: at the interface between tolerance and immunity | journal = Immunity | volume = 33 | issue = 2 | pages = 153–65 | date = August 2010 | pmid = 20732639 | pmc = 2946796 | doi = 10.1016/j.immuni.2010.08.004 }}

IL-2 has been discovered in all classes of jawed vertebrates, including sharks, at a similar genomic location.{{cite journal | vauthors = Bird S, Zou J, Kono T, Sakai M, Dijkstra JM, Secombes C | title = Characterisation and expression analysis of interleukin 2 (IL-2) and IL-21 homologues in the Japanese pufferfish, Fugu rubripes, following their discovery by synteny | journal = Immunogenetics | volume = 56 | issue = 12 | pages = 909–923 | date = March 2005 | pmid = 15592926 | doi = 10.1007/s00251-004-0741-7 | s2cid = 6739341 }}{{cite journal | vauthors = Dijkstra JM | title = A method for making alignments of related protein sequences that share very little similarity; shark interleukin 2 as an example | journal = Immunogenetics | volume = 73 | issue = 1 | pages = 35–51 | date = February 2021 | pmid = 33512550 | doi = 10.1007/s00251-020-01191-5 | s2cid = 231770873 }} In fish, IL-2 shares a single receptor alpha chain with its related cytokines IL-15 and IL-15-like (IL-15L).{{cite journal | vauthors = Yamaguchi T, Chang CJ, Karger A, Keller M, Pfaff F, Wangkahart E, Wang T, Secombes CJ, Kimoto A, Furihata M, Hashimoto K, Fischer U, Dijkstra JM | title = Ancient Cytokine Interleukin 15-Like (IL-15L) Induces a Type 2 Immune Response | journal = Frontiers in Immunology | volume = 11 | pages = 549319 | date = 2020-10-29 | pmid = 33193315 | pmc = 7658486 | doi = 10.3389/fimmu.2020.549319 | doi-access = free }} This "IL-15Rα" receptor chain is similar to mammalian IL-15Rα,{{cite journal | vauthors = Fang W, Shao JZ, Xiang LX | title = Molecular cloning and characterization of IL-15R alpha gene in rainbow trout (Oncorhynchus mykiss) | journal = Fish & Shellfish Immunology | volume = 23 | issue = 1 | pages = 119–127 | date = July 2007 | pmid = 17101279 | doi = 10.1016/j.fsi.2006.09.011 | bibcode = 2007FSI....23..119F }} and in tetrapod evolution a duplication of its coding gene plus further diversification created mammalian IL-2Rα.{{cite journal | vauthors = Anderson DM, Kumaki S, Ahdieh M, Bertles J, Tometsko M, Loomis A, Giri J, Copeland NG, Gilbert DJ, Jenkins NA | title = Functional characterization of the human interleukin-15 receptor alpha chain and close linkage of IL15RA and IL2RA genes | journal = The Journal of Biological Chemistry | volume = 270 | issue = 50 | pages = 29862–29869 | date = December 1995 | pmid = 8530383 | doi = 10.1074/jbc.270.50.29862 | doi-access = free }}{{cite journal | vauthors = Dijkstra JM, Takizawa F, Fischer U, Friedrich M, Soto-Lampe V, Lefèvre C, Lenk M, Karger A, Matsui T, Hashimoto K | title = Identification of a gene for an ancient cytokine, interleukin 15-like, in mammals; interleukins 2 and 15 co-evolved with this third family member, all sharing binding motifs for IL-15Rα | journal = Immunogenetics | volume = 66 | issue = 2 | pages = 93–103 | date = February 2014 | pmid = 24276591 | pmc = 3894449 | doi = 10.1007/s00251-013-0747-0 }} Sequences, and structural analysis of grass carp IL-2, suggest that fish IL-2 binds IL-15Rα in a manner reminiscent of how mammalian IL-15 binds to IL-15Rα.{{cite journal | vauthors = Wang J, Wang W, Xu J, Jia Z, Liu Q, Zhu X, Xia C, Zou J | title = Structural insights into the co-evolution of IL-2 and its private receptor in fish | journal = Developmental and Comparative Immunology | volume = 115 | pages = 103895 | date = February 2021 | pmid = 33065202 | doi = 10.1016/j.dci.2020.103895 | s2cid = 223557924 }}

Despite fish IL-2 and IL-15 sharing the same IL-15Rα chain, the stability of fish IL-2 is independent of it whereas IL-15 and especially IL-15L depend on binding to (co-presentation with) IL-15Rα for their stability and function. This suggests that, like in mammals, fish IL-2, in contrast to fish IL-15 and IL-15L, is not relying on "in trans" presentation by its receptor alpha chain. As a free cytokine, mammalian IL-2 that is secreted by activated T cells is important for a negative feedback loop by the stimulation of regulatory T cells, the latter being the cells with the highest constitutive IL-2Rα (aka CD25) expression.{{cite journal | vauthors = Busse D, de la Rosa M, Hobiger K, Thurley K, Flossdorf M, Scheffold A, Höfer T | title = Competing feedback loops shape IL-2 signaling between helper and regulatory T lymphocytes in cellular microenvironments | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 7 | pages = 3058–3063 | date = February 2010 | pmid = 20133667 | pmc = 2840293 | doi = 10.1073/pnas.0812851107 | bibcode = 2010PNAS..107.3058B | doi-access = free }}{{cite journal | vauthors = Boyman O, Sprent J | title = The role of interleukin-2 during homeostasis and activation of the immune system | journal = Nature Reviews. Immunology | volume = 12 | issue = 3 | pages = 180–190 | date = February 2012 | pmid = 22343569 | doi = 10.1038/nri3156 | s2cid = 22680847 }} Besides this negative feedback loop, mammalian IL-2 also participates in a positive feedback loop because activated T cells enhance their own IL-2Rα expression. As in mammals, fish IL-2 also stimulates T cell proliferation{{cite journal | vauthors = Corripio-Miyar Y, Secombes CJ, Zou J | title = Long-term stimulation of trout head kidney cells with the cytokines MCSF, IL-2 and IL-6: gene expression dynamics | journal = Fish & Shellfish Immunology | volume = 32 | issue = 1 | pages = 35–44 | date = January 2012 | pmid = 22051181 | doi = 10.1016/j.fsi.2011.10.016 | bibcode = 2012FSI....32...35C }} and appears to preferentially stimulate regulatory T cells.{{cite journal | vauthors = Wen Y, Fang W, Xiang LX, Pan RL, Shao JZ | title = Identification of Treg-like cells in Tetraodon: insight into the origin of regulatory T subsets during early vertebrate evolution | journal = Cellular and Molecular Life Sciences | volume = 68 | issue = 15 | pages = 2615–2626 | date = August 2011 | pmid = 21063894 | doi = 10.1007/s00018-010-0574-5 | s2cid = 22936159 | pmc = 11115099 }} Fish IL-2 induces the expression of cytokines of both type 1 (Th1) and type 2 (Th2) immunity.{{cite journal | vauthors = Wang T, Hu Y, Wangkahart E, Liu F, Wang A, Zahran E, Maisey KR, Liu M, Xu Q, Imarai M, Secombes CJ | title = Interleukin (IL)-2 Is a Key Regulator of T Helper 1 and T Helper 2 Cytokine Expression in Fish: Functional Characterization of Two Divergent IL2 Paralogs in Salmonids | journal = Frontiers in Immunology | volume = 9 | pages = 1683 | date = 2018-07-26 | pmid = 30093902 | doi = 10.3389/fimmu.2018.01683 | pmc = 6070626 | doi-access = free }}

As has been found in some studies on mammalian IL-2,{{cite journal | vauthors = Fukushima K, Hara-Kuge S, Ideo H, Yamashita K | title = Carbohydrate recognition site of interleukin-2 in relation to cell proliferation | journal = The Journal of Biological Chemistry | volume = 276 | issue = 33 | pages = 31202–31208 | date = August 2001 | pmid = 11390392 | doi = 10.1074/jbc.M102789200 | doi-access = free }} data suggest that fish IL-2 can form homodimers and that this is an ancient property of the IL-2/15/15L-family cytokines.

Homologues of IL-2 have not been reported for jawless fish (hagfish and lamprey) or invertebrates.

While the causes of itchiness are poorly understood, some evidence indicates that IL-2 is involved in itchy psoriasis.{{cite journal | vauthors = Reich A, Szepietowski JC | title = Mediators of pruritus in psoriasis | journal = Mediators of Inflammation | volume = 2007 | pages = 1–6 | year = 2007 | pmid = 18288273 | pmc = 2221678 | doi = 10.1155/2007/64727 | doi-access = free }}

{{Infobox drug

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Aldesleukin is a form of recombinant interleukin-2. It is manufactured using recombinant DNA technology and is marketed as a protein therapeutic and branded as Proleukin. It has been approved by the Food and Drug Administration (FDA) with a black box warning and in several European countries for the treatment of cancers (malignant melanoma, renal cell cancer) in large intermittent doses and has been extensively used in continuous doses.{{cite journal | vauthors = Noble S, Goa KL | title = Aldesleukin (recombinant interleukin-2) | journal = BioDrugs | volume = 7 | issue = 5 | pages = 394–422 | date = May 1997 | pmid = 18031103 | doi = 10.2165/00063030-199707050-00007 | s2cid = 34226322 }}{{cite journal | vauthors = Bhatia S, Tykodi SS, Thompson JA | title = Treatment of metastatic melanoma: an overview | journal = Oncology | volume = 23 | issue = 6 | pages = 488–96 | date = May 2009 | pmid = 19544689 | pmc = 2737459 | url = http://www.cancernetwork.com/oncology-journal/treatment-metastatic-melanoma-overview }}

Interking is a recombinant IL-2 with a serine at residue 125, sold by Shenzhen Neptunus.{{cite web | work = Bloomberg BusinessWeek | date = 3 March 2014 | url = http://investing.businessweek.com/research/stocks/snapshot/snapshot.asp?ticker=8329:HK | archive-url = https://web.archive.org/web/20110227091103/http://investing.businessweek.com/research/stocks/snapshot/snapshot.asp?ticker=8329:HK | url-status = dead | archive-date = February 27, 2011 | title = Shenzhen Neptunus Interlng-H }}

Neoleukin 2/15 is a computationally designed mimic of IL-2 that was designed to avoid common side effects.{{cite journal | vauthors = Silva DA, Yu S, Ulge UY, Spangler JB, Jude KM, Labão-Almeida C, Ali LR, Quijano-Rubio A, Ruterbusch M, Leung I, Biary T, Crowley SJ, Marcos E, Walkey CD, Weitzner BD, Pardo-Avila F, Castellanos J, Carter L, Stewart L, Riddell SR, Pepper M, Bernardes GJ, Dougan M, Garcia KC, Baker D | title = De novo design of potent and selective mimics of IL-2 and IL-15 | journal = Nature | volume = 565 | issue = 7738 | pages = 186–191 | date = January 2019 | pmid = 30626941 | doi = 10.1038/s41586-018-0830-7 | pmc = 6521699 | bibcode = 2019Natur.565..186S }} However, clinical trials into this candidate were discontinued.{{cite web |url=https://www.biospace.com/article/neoleukin-therapeutics-slashes-workforce-drops-de-novo-protein-therapeutic-/|title= Neoleukin Drops de Novo Protein Therapeutic, Slashes Workforce - Updated|vauthors = Scott R |date=November 15, 2022 |website=BioSpace |publisher= |access-date= February 1, 2023}}

Various dosages of IL-2 across the United States and across the world are used. The efficacy and side effects of different dosages is often a point of disagreement.

The commercial interest in local IL-2 therapy has been very low. Because only a very low dose IL-2 is used, treatment of a patient would cost about $500 commercial value of the patented IL-2. The commercial return on investment is too low to stimulate additional clinical studies for the registration of intratumoral IL-2 therapy.

Usually, in the U.S., the higher dosage option is used, affected by cancer type, response to treatment and general patient health. Patients are typically treated for five consecutive days, three times a day, for fifteen minutes. The following approximately 10 days help the patient to recover between treatments. IL-2 is delivered intravenously on an inpatient basis to enable proper monitoring of side effects.American Cancer Society. [http://www.cancer.org/Treatment/TreatmentsandSideEffects/GuidetoCancerDrugs/INTERLEUKIN-2 Interleukin-2 (Aldesleukin)] {{Webarchive|url=https://web.archive.org/web/20150212072442/http://www.cancer.org/treatment/treatmentsandsideeffects/guidetocancerdrugs/interleukin-2 |date=2015-02-12 }}. Date accessed: 07 Nov 10.

A lower dose regimen involves injection of IL-2 under the skin typically on an outpatient basis. It may alternatively be given on an inpatient basis over 1–3 days, similar to and often including the delivery of chemotherapy.

Intralesional IL-2 is commonly used to treat in-transit melanoma metastases and has a high complete response rate.{{cite journal | vauthors = Shi VY, Tran K, Patel F, Leventhal J, Konia T, Fung MA, Wilken R, Garcia MS, Fitzmaurice SD, Joo J, Monjazeb AM, Burrall BA, King B, Martinez S, Christensen SD, Maverakis E | title = 100% Complete response rate in patients with cutaneous metastatic melanoma treated with intralesional interleukin (IL)-2, imiquimod, and topical retinoid combination therapy: results of a case series | journal = Journal of the American Academy of Dermatology | volume = 73 | issue = 4 | pages = 645–54 | date = October 2015 | pmid = 26259990 | doi = 10.1016/j.jaad.2015.06.060 | doi-access = free }}

In preclinical and early clinical studies, local application of IL-2 in the tumor has been shown to be clinically more effective in anticancer therapy than systemic IL-2 therapy, over a broad range of doses, without serious side effects.{{cite journal | vauthors = Den Otter W, Jacobs JJ, Battermann JJ, Hordijk GJ, Krastev Z, Moiseeva EV, Stewart RJ, Ziekman PG, Koten JW | title = Local therapy of cancer with free IL-2 | journal = Cancer Immunology, Immunotherapy| volume = 57 | issue = 7 | pages = 931–50 | date = July 2008 | pmid = 18256831 | pmc = 2335290 | doi = 10.1007/s00262-008-0455-z }}

Tumour blood vessels are more vulnerable than normal blood vessels to the actions of IL-2. When injected inside a tumor, i.e. local application, a process mechanistically similar to the vascular leakage syndrome, occurs in tumor tissue only. Disruption of the blood flow inside of the tumor effectively destroys tumor tissue.{{cite journal | vauthors = Jacobs JJ, Sparendam D, Den Otter W | title = Local interleukin 2 therapy is most effective against cancer when injected intratumourally | journal = Cancer Immunology, Immunotherapy| volume = 57 | issue = 7 | pages = 931–50 | date = July 2005 | pmid = 15685449 | doi = 10.1007/s00262-004-0627-4 | s2cid = 41522233 | pmc = 11033014 }}

In local application, the systemic dose of IL-2 is too low to cause side effects, since the total dose is about 100 to 1000 fold lower. Clinical studies showed painful injections at the site of radiation as the most important side effect, reported by patients. In the case of irradiation of nasopharyngeal carcinoma the five-year disease-free survival increased from 8% to 63% by local IL-2 therapy {{cite journal | vauthors = Jacobs JJ, Hordijk GJ, Jürgenliemk-Schulz IM, Terhaard CH, Koten JW, Battermann JJ, Den Otter W | title = Treatment of stage III-IV nasopharyngeal carcinomas by external beam irradiation and local low doses of IL-2 | journal = Cancer Immunol Immunother| volume = 57 | issue = 8 | pages = 792–8 | date = August 2005 | pmid = 15685449 | doi = 10.1007/s00262-004-0627-4 | s2cid = 41522233 | pmc = 11033014 }}

Systemic IL-2 has a narrow therapeutic window, and the level of dosing usually determines the severity of the side effects.{{cite journal | vauthors = Shaker MA, Younes HM | title = Interleukin-2: evaluation of routes of administration and current delivery systems in cancer therapy | journal = Journal of Pharmaceutical Sciences | volume = 98 | issue = 7 | pages = 2268–98 | date = July 2009 | pmid = 19009549 | doi = 10.1002/jps.21596 }} In the case of local IL-2 application, the therapeutic window spans several orders of magnitude.

Some common side effects:

• flu-like symptoms (fever, headache, muscle and joint pain, fatigue)
• nausea/vomiting
• dry, itchy skin or rash
• weakness or shortness of breath
• diarrhea
• low blood pressure
• drowsiness or confusion
• loss of appetite

More serious and dangerous side effects sometimes are seen, such as breathing problems, serious infections, seizures, allergic reactions, heart problems, kidney failure or a variety of other possible complications. The most common adverse effect of high-dose IL-2 therapy is vascular leak syndrome (VLS; also termed capillary leak syndrome). It is caused by lung endothelial cells expressing high-affinity IL-2R. These cells, as a result of IL-2 binding, causes increased vascular permeability. Thus, intravascular fluid extravasate into organs, predominantly lungs, which leads to life-threatening pulmonary or brain oedema.{{Cite journal|date=2011-12-28|title=Correction for Krieg et al., Improved IL-2 immunotherapy by selective stimulation of IL-2 receptors on lymphocytes and endothelial cells|journal=Proceedings of the National Academy of Sciences|volume=109|issue=1|pages=345|doi=10.1073/pnas.1119897109|issn=0027-8424|pmc=3252892|doi-access=free}}

Other drawbacks of IL-2 cancer immunotherapy are its short half-life in circulation and its ability to predominantly expand regulatory T cells at high doses.

Intralesional IL-2 used to treat in-transit melanoma metastases is generally well tolerated. This is also the case for intralesional IL-2 in other forms of cancer, like nasopharyngeal carcinoma.

Eisai markets a drug called denileukin diftitox (trade name Ontak), which is a recombinant fusion protein of the human IL-2 ligand and the diphtheria toxin.{{cite journal | vauthors = Figgitt DP, Lamb HM, Goa KL | title = Denileukin diftitox | journal = American Journal of Clinical Dermatology | volume = 1 | issue = 1 | pages = 67–72; discussion 73 | date = 2000 | pmid = 11702307 | doi = 10.2165/00128071-200001010-00008| s2cid = 195358361 }} This drug binds to IL-2 receptors and introduces the diphtheria toxin into cells that express those receptors, killing the cells. In some leukemias and lymphomas, malignant cells express the IL-2 receptor, so denileukin diftitox can kill them. In 1999 Ontak was approved by the U.S. Food and Drug Administration (FDA) for treatment of cutaneous T cell lymphoma (CTCL).{{cite web | publisher = FDA | date = May 11, 2009 | url = https://www.fda.gov/AboutFDA/CentersOffices/OfficeofMedicalProductsandTobacco/CDER/ucm095661.htm | archive-url = https://web.archive.org/web/20111125071549/http://www.fda.gov/AboutFDA/CentersOffices/OfficeofMedicalProductsandTobacco/CDER/ucm095661.htm | url-status = dead | archive-date = November 25, 2011 | title = Changes in the Ontak (denileukin diftitiox) | work = Package Insert to Include a Description of Ophthalmologic Adverse Events }}

IL-2 does not follow the classical dose-response curve of chemotherapeutics. The immunological activity of high and low dose IL-2 show sharp contrast. This might be related to different distribution of IL-2 receptors (CD25, CD122, CD132) on different cell populations, resulting in different cells that are activated by high and low dose IL-2. In general high doses are immune suppressive, while low doses can stimulate type 1 immunity.{{cite journal | vauthors = Tomova R, Pomakov J, Jacobs JJ, Adjarov D, Popova S, Altankova I, Den Otter W, Krastev Z | title = Changes in cytokine profile during local IL-2 therapy in cancer patients | journal = Anticancer Research | volume = 26 | issue = 3A | pages = 2037–47 | date = May–June 2006 | pmid = 16827142 }} Low-dose IL-2 has been reported to reduce hepatitis C and B infection.{{cite journal | vauthors = Tomova R, Antonov K, Ivanova A, Jacobs JJ, Koten JW, Den Otter W, Krastev Z | title = CLow-dose IL-2 therapy reduces HCV RNA and HBV DNA: case report. | journal = Anticancer Research | volume = 29 | issue = 12 | pages = 5241–4 | date = December 2009 | pmid = 20044643}}

IL-2 has been used in clinical trials for the treatment of chronic viral infections and as a booster (adjuvant) for vaccines. The use of large doses of IL-2 given every 6–8 weeks in HIV therapy, similar to its use in cancer therapy, was found to be ineffective in preventing progression to an AIDS diagnosis in two large clinical trials published in 2009.{{cite web | url = http://www.nih.gov/news/health/feb2009/niaid-10.htm | title = IL-2 Immunotherapy Fails to Benefit HIV-Infected Individuals Already Taking Antiretrovirals | date = February 10, 2009 | work = News Release | publisher = National Institutes of Health (NIH) }}

More recently low dose IL-2 has shown early success in modulating the immune system in disease like type 1 diabetes and vasculitis.{{cite journal | vauthors = Hartemann A, Bensimon G, Payan CA, Jacqueminet S, Bourron O, Nicolas N, Fonfrede M, Rosenzwajg M, Bernard C, Klatzmann D | title = Low-dose interleukin 2 in patients with type 1 diabetes: a phase 1/2 randomised, double-blind, placebo-controlled trial | journal = The Lancet. Diabetes & Endocrinology | volume = 1 | issue = 4 | pages = 295–305 | date = December 2013 | pmid = 24622415 | doi = 10.1016/S2213-8587(13)70113-X }} There are also promising studies looking to use low dose IL-2 in ischaemic heart disease.{{ClinicalTrialsGov|NCT03113773|Low Dose Interleukin-2 in Patients With Stable Ischaemic Heart Disease and Acute Coronary Syndromes (LILACS)}}

IL-2 cannot accomplish its role as a promising immunotherapeutic agent due to significant drawbacks which are listed above. Some of the issues can be overcome using IL-2 ic. They are composed of IL-2 and some of its monoclonal antibody (mAb) and can potentiate biologic activity of IL-2 in vivo. The main mechanism of this phenomenon in vivo is due to the prolongation of the cytokine half-life in circulation. Depending on the clone of IL-2 mAb, IL-2 ic can selectively stimulate either CD25^high (IL-2/JES6-1 complexes), or CD122^high cells (IL-2/S4B6). IL-2/S4B6 immune complexes have high stimulatory activity for NK cells and memory CD8⁺ T cells and they could thus replace the conventional IL-2 in cancer immunotherapy. On the other hand, IL-2/JES6-1 highly selectively stimulate regulatory T cells and they could be potentially useful for transplantations and in treatment of autoimmune diseases.{{cite journal | vauthors = Boyman O, Kovar M, Rubinstein MP, Surh CD, Sprent J | title = Selective stimulation of T cell subsets with antibody-cytokine immune complexes | journal = Science | volume = 311 | issue = 5769 | pages = 1924–7 | date = March 2006 | pmid = 16484453 | doi = 10.1126/science.1122927 | bibcode = 2006Sci...311.1924B | s2cid = 42880544 | doi-access = free }}

According to an immunology textbook: "IL-2 is particularly important historically, as it is the first type I cytokine that was cloned, the first type I cytokine for which a receptor component was cloned, and was the first short-chain type I cytokine whose receptor structure was solved. Many general principles have been derived from studies of this cytokine including its being the first cytokine demonstrated to act in a growth factor–like fashion through specific high-affinity receptors, analogous to the growth factors being studied by endocrinologists and biochemists".{{rp|712}}

In the mid-1960s, studies reported "activities" in leukocyte-conditioned media that promoted lymphocyte proliferation.{{cite journal | vauthors = Chavez AR, Buchser W, Basse PH, Liang X, Appleman LJ, Maranchie JK, Zeh H, de Vera ME, Lotze MT | title = Pharmacologic administration of interleukin-2 | journal = Annals of the New York Academy of Sciences | volume = 1182 | issue = 1| pages = 14–27 | date = December 2009 | pmid = 20074271 | doi = 10.1111/j.1749-6632.2009.05160.x | bibcode = 2009NYASA1182...14C | s2cid = 1100312 }}{{rp|16}} In the mid-1970s, it was discovered that T-cells could be selectively proliferated when normal human bone marrow cells were cultured in conditioned medium obtained from phytohemagglutinin-stimulated normal human lymphocytes.{{cite book | vauthors = Paul WE | title = Fundamental immunology | date = 2008 | publisher = Wolters Kluwer/Lippincott Williams & Wilkins | location = Philadelphia | isbn = 978-0-7817-6519-0 | edition = 6th }}{{rp|712}} The key factor was isolated from cultured mouse cells in 1979 and from cultured human cells in 1980.{{cite journal | vauthors = Welte K, Wang CY, Mertelsmann R, Venuta S, Feldman SP, Moore MA | title = Purification of human interleukin 2 to apparent homogeneity and its molecular heterogeneity | journal = The Journal of Experimental Medicine | volume = 156 | issue = 2 | pages = 454–64 | date = August 1982 | pmid = 6980256 | pmc = 2186775 | doi = 10.1084/jem.156.2.454 }} The gene for human IL-2 was cloned in 1982 after an intense competition.{{cite book | vauthors = Rabinow P | title = Making PCR: A story of biotechnology | url = https://archive.org/details/makingpcrstoryof00rabi | url-access = registration | year = 1997 | publisher = University of Chicago Press | location = Chicago, IL, USA | isbn = 978-0226701479 | edition = Paperback }}{{rp|76}}

Commercial activity to bring an IL-2 drug to market was intense in the 1980s and 1990s. By 1983, Cetus Corporation had created a proprietary recombinant version of IL-2 (Aldesleukin, later branded as Proleukin), with the alanine removed from its N-terminal and residue 125 replaced with serine.{{rp|76–77}}{{cite journal | vauthors = Almeida H | url = http://www.scielo.br/pdf/bjps/v47n2/v47n2a02.pdf | title = Drugs obtained by biotechnology processing | journal = Brazilian Journal of Pharmaceutical Sciences | date = April–June 2011 | volume = 47 | issue = 2 | pages = 199–207 | doi=10.1590/s1984-82502011000200002| doi-access = free }}{{rp|201}} Amgen later entered the field with its own proprietary, mutated, recombinant protein and Cetus and Amgen were soon competing scientifically and in the courts; Cetus won the legal battles and forced Amgen out of the field.{{rp|151}} By 1990 Cetus had gotten aldesleukin approved in nine European countries but in that year, the U.S. Food and Drug Administration (FDA) refused to approve Cetus' application to market IL-2.{{cite web |url= https://www.nytimes.com/1990/07/31/business/cetus-drug-is-blocked-by-fda.html |title=Cetus Drug Is Blocked By F.D.A. |work=New York Times |author=Pollack A |date=July 31, 1990}} This source mentions approval in 9 European countries. The failure led to the collapse of Cetus, and in 1991 the company was sold to Chiron Corporation.{{cite web | vauthors = Pollack A | url = https://www.nytimes.com/1991/07/23/business/2-biotech-pioneers-to-merge.html | title = 2 Biotech Pioneers To Merge |work=New York Times | date = July 23, 1991 }}{{cite web | vauthors = Lehrman S | url = http://www.the-scientist.com/?articles.view/articleNo/12113/title/Cetus–A-Collision-Course-With-Failure/ |title=Cetus: A Collision Course With Failure |work=The Scientist Magazine | date = January 20, 1992 }} Chiron continued the development of IL-2, which was finally approved by the FDA as Proleukin for metastatic renal carcinoma in 1992.{{cite journal | vauthors = Dutcher JP | title = Current status of interleukin-2 therapy for metastatic renal cell carcinoma and metastatic melanoma | journal = Oncology | volume = 16 | issue = 11 Suppl 13 | pages = 4–10 | date = November 2002 | pmid = 12469934 }}

By 1993 aldesleukin was the only approved version of IL-2, but Roche was also developing a proprietary, modified, recombinant IL-2 called teceleukin, with a methionine added at is N-terminal, and Glaxo was developing a version called bioleukin, with a methionine added at is N-terminal and residue 125 replaced with alanine. Dozens of clinical trials had been conducted of recombinant or purified IL-2, alone, in combination with other drugs, or using cell therapies, in which cells were taken from patients, activated with IL-2, then reinfused.{{cite journal | vauthors = Whittington R, Faulds D | title = Interleukin-2. A review of its pharmacological properties and therapeutic use in patients with cancer | journal = Drugs | volume = 46 | issue = 3 | pages = 446–514 | date = September 1993 | pmid = 7693434 | doi = 10.2165/00003495-199346030-00009 | s2cid = 209143485 }}{{cite web |url=http://www.genome.jp/dbget-bin/www_bget?dr:D02749 |title=D02749 (Teceleukin) |work=KEGG drug }} Novartis acquired Chiron in 2006{{cite web |url=http://www.swissinfo.ch/eng/chiron-shareholders-approve-novartis-deal/5134216 |title=Chiron shareholders approve Novartis deal |work=SWI swissinfo.ch |date=Apr 19, 2006}} and licensed the US aldesleukin business to Prometheus Laboratories in 2010{{cite web |url=http://www.thepharmaletter.com/article/novartis-sells-rights-to-proleukin-in-the-usa-to-prometheus-gets-license-for-vaccine-from-iig-and-pleads-guilty-over-trileptal |title=Novartis sells rights to Proleukin in the USA to Prometheus; gets license for vaccine from IIG; and pleads guilty over Trileptal |work=Pharmaletter |date=January 27, 2010}} before global rights to Proleukin were subsequently acquired by Clinigen in 2018 and 2019.

{{reflist|33em}}

{{commons category|Interleukin-2}}

• [http://www.proleukin.com Proleukin website]
• [http://www.netpath.org/pathways?path_id=NetPath_14 IL-2 Signaling Pathway] {{Webarchive|url=https://web.archive.org/web/20200111235452/http://www.netpath.org/pathways?path_id=NetPath_14 |date=2020-01-11 }}
• {{cite journal | vauthors = Rosenberg SA | title = IL-2: the first effective immunotherapy for human cancer | journal = Journal of Immunology | volume = 192 | issue = 12 | pages = 5451–8 | date = June 2014 | pmid = 24907378 | pmc = 6293462 | doi = 10.4049/jimmunol.1490019 }}
• {{PDBe-KB2|P60568|Interleukin-2}}

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{{Interleukins}}

{{Interleukin receptor modulators}}

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