Abstract
Interleukin-4 mediates important proinflammatory functions in asthma, including induction of the IgE isotype switch, expression of VCAM-1 on endothelium, mucin production, 15-lipoxygenase activity, and Th2 lymphocyte stimulation leading to the secondary synthesis of IL-4, IL-5, and IL-13. Soluble recombinant human IL-4 receptor (IL-4R; Nuvance; altrakincept) inactivates naturally occurring IL-4 without mediating cellular activation. Nebulized IL-4R has a serum half-life of approximately 1 wk. In this double-blind, placebo-controlled trial, 25 patients with moderate asthma requiring inhaled corticosteroids were randomly assigned to receive a single nebulized dose of IL-4R 1,500 μ g, IL-4R 500 μ g, or placebo after stopping inhaled corticosteroids. No drug-related toxicity was observed. Treatment with IL-4R produced significant improvement in FEV1 on Day 4 (1,500 μ g versus placebo; p < 0.05) and in FEF25–75 on Days 2 and 4 (1,500 μ g versus placebo; p < 0.05). Asthma symptom scores stabilized among patients treated with IL-4R 1,500 μ g, despite abrupt withdrawal of corticosteroids, but not in the IL-4R 500 μ g group or the placebo group (p < 0.05). Patients in the IL-4R 1,500 μ g group also required significantly less β2-agonist rescue use (p < 0.05). Anti-inflammatory effects were further demonstrated by significantly reduced exhaled nitric oxide (p < 0.05). Conclusions: A single dose of IL-4R appears safe and effective in moderate asthma. The 1,500 μ g dose appears as safe but significantly more effective than the 500 μ g dose. Borish LC, Nelson HS, Lanz MJ, Claussen L, Whitmore JB, Agosti JM, Garrison L. Interleukin-4 receptor in moderate atopic asthma: a phase I/II randomized, placebo-controlled trial.
Interleukin-4 (IL-4) contributes to the development of allergic inflammation and asthma through a variety of mechanisms. IL-4 induces the IgE isotype switch (1); it upregulates high affinity IgE receptors on mast cells (2) and low affinity IgE receptors on B lymphocytes and mononuclear phagocytic cells (3, 4); it upregulates expression of vascular cell adhesion molecule-1 (VCAM-1) on endothelium, promoting selective egress of eosinophils from the bloodstream (5, 6); it induces mucin production; and it enhances 15-lipoxygenase activity. IL-4 also promotes the differentiation of naive Th0 lymphocytes into Th2 lymphocytes that secrete IL-4, IL-5, IL-9, and IL-13 (7, 8). In the absence of IL-4, differentiation of Th2 lymphocytes is inhibited, and IL-4 and IL-5 secretion is reduced. Inhibition of IL-4 production and activity, therefore, has obvious potential in the treatment of allergic disorders such as asthma.
On the cell surface, IL-4 interacts with high-affinity receptors made up of heterodimers that consist of an independent high-affinity α-chain and a γ-chain shared with IL-2, IL-7, IL-9, and IL-15 (9). Both mediate cellular activation, but only α-chain receptors are required for ligand interaction (10). Secreted forms of α-chain IL-4R lack the transmembrane and cytoplasmic domains, but still interact with IL-4. Because they cannot transduce cellular activation, but still bind and sequester IL-4, they are considered a naturally occurring homeostatic mechanism to counter the effects of IL-4. Nuvance (Immunex Corp., Seattle, WA) is the soluble extracellular portion of the full-length human high-affinity receptor for IL-4, cloned, and is produced in a mammalian expression system. Soluble IL-4R has been shown to inhibit allergen-induced IgE production in preclinical models (11).
Men and women at least 18 yr of age with moderate atopic asthma were recruited by advertisements in the Denver area. Thirty-five patients were screened and 25 were enrolled. Moderate disease status was defined by a daily inhaled-corticosteroid requirement of four to eight puffs, and atopic asthma had to have been confirmed within at least 1 yr of enrollment. Atopy was confirmed by a positive skin-prick test reaction (wheal diameter > 5 mm) to one or more components of the Colorado allergen panel and by a history of allergic rhinitis. FEV1 had to be at least 65% of the predicted normal after washout of bronchodilators. At screening, patients had to demonstrate at least a 12% increase in FEV1 within 30 min after β2-agonist inhalation or at least a 15% difference between morning and evening peak expiratory flow rate (PEFR), as well as a 20% or greater decrease in FEV1 after exposure to methacholine of 7.5 mg/ml or less. Concomitant therapy with systemic corticosteroids, antihistamines, theophylline, cromolyn, and leukotriene modifiers was not allowed. Prestudy use of these agents was also proscribed for periods of 2 to 8 wk, depending on the agent. Patients were allowed concomitant nonantihistamine decongestants for rhinitis, antibiotics for infection, acetaminophen for analgesia, and albuterol by metered-dose inhaler (two puffs per dose ⩽ 12 puffs daily). Patients had to be nonsmokers for at least the previous 2 yr, with a smoking history of not more than 5 pack-years.
Patients were excluded if they had significant intercurrent illness; if they had ever required maintenance therapy with systemic corticosteroids for more than 1 yr; if they had experienced an acute asthma exacerbation requiring emergency treatment within 6 wk or hospitalization within the 6 mo; if they had a history of intubation for asthma exacerbation; or if they had undergone desensitization therapy within the 12 mo prior to enrollment. The protocol was approved by the investigational review board of the National Jewish Medical and Research Center in Denver, Colorado, where the study was conducted from December 1996 to May 1997.
The primary objective of this randomized, double-blind, placebo-controlled trial was to evaluate the safety of a single nebulized dose of IL-4R, 500 μg or 1,500 μg, in patients with moderate atopic asthma. Secondary evaluations included the effects of IL-4R on spirometric measures, asthma symptoms, and quality of life.
During the 1-wk prestudy phase before administration of study drug, eligible patients gave written informed consent and underwent a baseline evaluation that included medical history, vital signs, physical examination, EKG, chest radiography, urinalysis, chemistry panel, hematology profiles, and serum pregnancy test. All patients began a daily asthma symptom diary. Other baseline tests and measurements included methacholine challenge; morning and evening PEFRs; a standard three-part asthma quality-of-life questionnaire (AQLQ); and spirometry, including FEV1, FVC, and forced expiratory flow at 25 to 75% of FVC (FEF25–75). Immunologic evaluations included total serum IgE; allergen skin testing; anti-IL-4R antibody testing; exhaled nitric oxide concentration; radioallergosorbent test; and serum inflammation and allergy profile, which included serum vascular cell adhesion molecule-1 (VCAM-1), serum intracellular adhesion molecule-1 (ICAM-1), serum eosinophil cationic peptide (ECP), and serum IgE receptor (CD23).
Inhaled corticosteroids were stopped the day before administration of study drug. On Day 1 patients received a single nebulized dose of study drug (Aero-Tech II nebulizer; CIS-US, Inc., Bedford, MA). Relevant baseline tests and measures were repeated according to varying schedules on Days 1, 2, 4, 8, 15, 22, and 29; morning and evening PEFRs were measured daily. Because abruptly stopping inhaled corticosteroids can exacerbate asthma, patients were closely monitored and carefully managed: the need for systemic corticosteroids, the observation of nocturnal symptoms on two consecutive nights, or an increasing β2-agonist requirement (> 12 inhalations per day) prompted immediate withdrawal of the patient.
Recombinant soluble IL-4R is the extracellular domain of the human IL-4 receptor lacking the transmembrane and extracellular domains. The 54-kilodalton glycoprotein was cloned and expressed in Chinese hamster ovary cells and formulated in 20 mM tromethamine (Immunex Corp.). Endotoxin content is less than 1 endotoxin U/mg. Study drug was diluted to a final volume of 2.5 ml in sterile normal saline without preservative, USP. Placebo consisted of identical excipient.
Adverse events were graded on a 5-point scale (0 to 4) based on the Common Toxicity Criteria derived from the National Cancer Institute toxicity criteria. Spirometry was conducted 1 and 2 h after study drug administration and on Days 2, 4, 8, 15, 22, and 29 using standard techniques (Koko system; PDS, Louisville, CO). Bronchial reactivity to methacholine was quantified by delivery of increasing doses of methacholine aerosol at 5-min intervals until FEV1 fell by 20% or more. The dose necessary to provoke a 20% decrease in FEV1 was designated the PD20. Lower PD20 values indicate more reactive airways. All patients had bronchial hyperreactivity at the screening evaluation after exposure to a methacholine concentration of 7.5 mg/ml or less. Methacholine testing was not performed if the patient's FEV1 was less than 65% of the predicted normal value.
Exhaled nitric oxide concentration, total eosinophil count, and serum concentration of VCAM-1, ICAM-1, ECP, and CD23 were determined on Days 2, 4, 8, 15, 22, and 29. Exhaled nitric oxide was quantified with a chemiluminescent analyzer (Dasibi Environmental Corp., Glendale, CA); patients inhaled 100% O2 and immediately exhaled into the analyzer. The best of three efforts was recorded. Other inflammatory markers were evaluated with commercially available ELISAs according to the manufacturers' directions: VCAM-1 and ICAM-1 (R&D Systems, Minneapolis, MN); CD23 (The Binding Site, San Diego, CA); and ECP (Pharmacia Biotech, Uppsala, Sweden).
Total IgE was measured using a commercially available ELISA with a lower limit of detection of 2.4 ng/ml (Abbott Laboratories, Abbott Park, IL). Changes in specific IgE were evaluated using radioallergosorbent test (Pharmacia Biotech). Titrated skin tests to two allergens to which the patient was sensitive were performed prestudy and on Days 8, 15, and 29. Full strength extract and serial tenfold dilutions were applied to determine the lower end point, i.e., the concentration producing a wheal less than 5 mm in diameter.
Patients completed a standard three-part asthma quality of life questionnaire (AQLQ) on Days 8, 15, and 29. Patients also kept daily records of asthma symptoms and β2-agonist use. Data from the asthma symptom diaries were used to derive a total asthma symptom score, which was the sum of individual scores for cough, wheezing, nocturnal asthma, chest tightness, and shortness of breath (0 to 15 possible points).
Some patients were expected to drop out from the study secondary to asthma exacerbation after withdrawal of inhaled corticosteroids. In following the intention-to-treat principle, for patients discontinued from the study, summarization and statistical analyses at subsequent time points were made with data derived using the last-observation-carried-forward (LOCF) method for all data except quality of life (12). This procedure replaces a missing value by the most recent previous value (i.e., prior to discontinuation). Differences between the treatment groups were evaluated using Wilcoxon's two-sample test for continuous and ordinal variables and Fisher's Exact Test for categorical variables.
Baseline patient and disease characteristics are summarized in Table 1. Eight patients were randomly assigned to receive placebo; eight to receive IL-4R 500 μg; and nine to receive IL-4R 1,500 μg. The treatment groups were well matched. One patient was replaced in the IL-4R 1,500 μg group for noncompliance on the AQLQ. That patient's AQLQ data were not usable, but all other data from that patient were analyzed. A ninth patient was recruited for the IL-4R 1,500 μg group to provide AQLQ data, and all other data from this patient were also analyzed.
| Characteristics | Placebo (n = 8) | IL-4R 500 μg (n = 8) | IL-4R 1,500 μg (n = 9) | |||
|---|---|---|---|---|---|---|
| Sex, M/F, no. | 2/6 | 2/6 | 5/4 | |||
| Age, yr | ||||||
| Median (range) | 38 (25–47) | 35 (26–62) | 38 (26–66) | |||
| Race, no. | ||||||
| White | 8 | 6 | 7 | |||
| Black | 0 | 1 | 1 | |||
| Hispanic | 0 | 1 | 1 | |||
| History of smoking | 1 | 3 | 3 | |||
| Duration of asthma, no. | ||||||
| ⩾ 1 < 5 yr | 1 | 1 | 1 | |||
| ⩾ 5 < 10 yr | 1 | 1 | 0 | |||
| ⩾ 10 < 15 yr | 2 | 1 | 2 | |||
| ⩾ 15 yr | 4 | 5 | 6 | |||
| Cause(s) of asthma exacerbation, no.* | ||||||
| Allergen | 8 | 6 | 7 | |||
| Cold air | 8 | 6 | 8 | |||
| Exercise | 5 | 6 | 6 | |||
| Respiratory infection | 6 | 8 | 6 | |||
| Tobacco smoke | 7 | 5 | 7 | |||
| Other | 6 | 6 | 7 | |||
| FEV1, % pred† | 87 ± 12 | 80 ± 13 | 79 ± 16 | |||
| FEF25–75, % pred† | 67 ± 24 | 55 ± 21 | 51 ± 18 | |||
| Total symptom score†,‡ | 3.9 ± 2.5 | 2.4 ± 0.9 | 2.2 ± 1.3 | |||
| β2-agonist use, puffs/d†,‡ | 5.4 ± 2.9 | 5.5 ± 2.1 | 4.4 ± 3.8 | |||
| Nitric oxide, ppb†,‡ | 24.8 ± 6.6 | 28.0 ± 14.7 | 21.1 ± 14.9 | |||
IL-4R was well tolerated. No respiratory complaint or decrease in spirometric values was associated with its administration. There were no deaths during the study, no Grade 4 adverse events, and no serious adverse events or premature discontinuations because of toxicity. One patient in the IL-4R 500 μg group experienced a Grade 3 (severe) asthma exacerbation, which was judged secondary to exposure to a cat. All other adverse events were mild to moderate (Table 2).
| Placebo (n = 8) | IL-4R 500 μg (n = 8) | IL-4R 1,500 μg (n = 9) | ||||
|---|---|---|---|---|---|---|
| Rhinitis | 3 | 2 | 1 | |||
| Headache | 1 | 0 | 2 | |||
| Lymphadenosis | 0 | 1 | 1 | |||
| Upper respiratory infection | 1 | 0 | 1 | |||
| Watery eyes | 0 | 2 | 0 | |||
| Syncope | 0 | 1 | 0 | |||
| Twitch | 1 | 0 | 0 | |||
| Asthma | 0 | 1 | 0 | |||
| Bronchospasm | 0 | 0 | 1 | |||
| Increased cough | 0 | 1 | 0 | |||
| Pharygnitis | 0 | 1 | 0 | |||
| Eczema | 1 | 0 | 0 | |||
| Dry skin | 1 | 0 | 0 | |||
| Otitis externa | 1 | 0 | 0 |
During the first 2 wk after administration of study drug, none of the nine patients in the IL-4R 1,500 μg group withdrew from the study for asthma exacerbation, compared with three of eight (38%) in the IL-4R 500 μg group and two of eight (25%) in the placebo group (p = 0.146).
No patients developed antibody to IL-4R.
IL-4R was associated with statistically significant differences (p < 0.05) in total asthma symptom score (Figure 1) and β2-agonist use (Figure 2). Scores on the third section of the AQLQ, i.e., patient's perception of general health and physical functioning, worsened in the placebo group and improved in the IL-4R 1,500 μg group (p = 0.052) (Figure 3).
Fig. 1. Total Asthma Symptom Score. Through Week 2, total asthma symptom score was stable in the IL-4R 1,500 μg group, but it increased in the placebo group and the IL-4R 500 μg group: 1,500 μg versus placebo (p = 0.048); 1,500 μg versus 500 μg (p = 0.008). Day 0 baseline is an average of prestudy values. *p < 0.05, **p < 0.01.
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Fig. 2. β2-Agonist Use. Through Week 2, average daily β2-agonist use decreased by 0.6 puffs/d in the IL-4R 1,500 μg group, but it increased 1.7 puffs/d in the placebo group and 1.6 puffs/d in the IL-4R 500 μg group. The frequency of β2-agonist use was significantly lower in the IL-4R 1,500 μg group: 1,500 μg versus placebo (p = 0.048); 1,500 μg versus 500 μg (p = 0.044). Day 0 baseline is an average of prestudy values. *p < 0.05.
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Fig. 3. Asthma Quality of Life Questionnaire, Section 3, Health and Social Perceptions (AQLQ3): Change from Baseline. Through Week 2, mean scores for AQLQ3 decreased (improved) in the 1,500 μg group. Scores increased (worsened) in the placebo group and the IL-4R 500 μg group, but compared with the IL-4R 1,500 μg group, the differences were not statistically significant (p = 0.052).
[More] [Minimize]Overall, treatment with 1,500 μg IL-4R was associated with statistically significant (p < 0.05) differences in FEV1 at 2 h post-treatment and on Days 2, 4, and 15 (Figure 4). FEF25–75 was significantly (p < 0.05) different at 2 h post-treatment and on Days 2 and 4 (Figure 5). No statistically significant differences were observed in morning and evening PEFR. Methacholine testing could not be performed on Day 8 in four patients in the placebo group (50%) and in five in the IL-4R 500 μg group (63%) because of early dropout, inadequate pulmonary function, or β2-agonist use before the evaluation. Methacholine testing was performed in eight of nine patients in the IL-4R 1,500 μg group at Day 8; six showed decreased sensitivity to methacholine.
Fig. 4. Percent of Predicted FEV1: Change from Baseline. Through Week 2, FEV1 was at least maintained at baseline levels after acute discontinuation of inhaled corticosteroids with IL-4R 1,500 μg, whereas steady declines in FEV1 were seen with IL-4R 500 μg and placebo. On Day 4, the difference between the IL-4R 1,500 μg group and the placebo group was statistically significant (p = 0.048). At 2 h and on Days 2 and 15, the differences between the IL-4R 1,500 μg and 500 μg groups were statistically significant (p = 0.008 for each time point). *p < 0.05, **p < 0.01.
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Fig. 5. Percent of Predicted FEF25–75: Change from Baseline. Through Week 2, FEF25–75 was improved from baseline levels with IL-4R 1,500 μg, whereas steady declines were seen with IL-4R 500 μg and placebo. On Days 2 and 4, the differences between the IL-4R 1,500 μg and placebo groups were statistically significant (p = 0.014 for each time point). At 2 h and on Days 2 and 4, the differences between the IL-4R 1,500 μg and 500 μg groups (p = 0.011, p = 0.008, and p = 0.048, respectively) were statistically significant. *p < 0.05.
[More] [Minimize]Exhaled nitric oxide increased in both the placebo and the low-dose groups after discontinuation of inhaled corticosteroids, but the 1,500 μg group declined to levels significantly lower than placebo (Figure 6). No significant differences were observed in the serum markers VCAM-1, ICAM-1, ECP, and CD23, although trends (Figures 7 and 8) towards diminished Day 15 serum levels of VCAM-1, ICAM-1 and ECP were observed in the 1,500 μg group. The serum levels of these markers may not reflect the status of these markers on the cell surface or within the lungs. No significant differences were seen in total IgE, specific IgE, or total blood eosinophil counts.
Fig. 6. Exhaled Nitric Oxide: Change from Baseline. Through Week 2, exhaled nitric oxide levels (ppb) appeared to decrease relative to baseline in the IL-4R 1,500 μg group. On Day 4, the difference between the IL-4R 1,500 μg group and the placebo group was statistically significant (p = 0.026). *p < 0.05.
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Fig. 7. Serum VCAM-1 and ECP: Median Percent Change from Baseline. Change from Baseline. At Day 15, median serum levels of VCAM-1 and ECP declined in the 1500 mcg group and increased for the placebo group although this is not statistically significant.
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Fig. 8. Serum ICAM-1 and CD23: Median Percent Change from Baseline. At Day 15, median serum levels of ICAM-1 declined in the 1,500 μg group and increased for the placebo group, although this was not statistically significant. The median serum CD23 levels increased in the 1,500 μg group and decreased in the placebo group, although this was not statistically significant.
[More] [Minimize]IL-4 is critical to the development of allergic inflammation. It is associated with induction of the ɛ-isotype switch and secretion of IgE by B lymphocytes (1). IgE-mediated immune responses are probably further enhanced by IL-4 through its ability to induce upregulation of IgE receptors on the cell surface—the low affinity IgE receptors, FcɛRII or CD23 (3, 4) and the high affinity IgE receptor, FcɛRI (2). IL-4 also induces VCAM-1 (5, 6), which, through interaction with the α4 integrins (α4β1 [VLA-4] and α4β7) and αdβ2, is able to direct the migration of T-lymphocytes, monocytes, basophils, and eosinophils, but not neutrophils, to inflammatory loci. IL-4 is thereby associated with the specific adherence and transmigration of eosinophils across endothelium (6).
IL-4 induces mucin production, further compromising airway patency. Furthermore, IL-4 enhances 15-lipoxygenase activity and incorporation of 15(s)-hydroxyeicosatetraenoic acid into cellular phospholipids. IL-4 also activates osteocytes, thereby generating osteoporosis. This was shown by the development of osteoporosis in transgenic mice in which IL-4 production was driven by the T-helper-lymphocyte-specific lck tyrosine kinase gene promoter (13). Osteoporosis frequently develops in asthma and hyper-IgE syndromes, and both osteoporosis and diminished activity of osteocytes, as evidenced by serum osteocalcin concentrations, can be demonstrated even in the absence of systemic or inhaled corticosteroid use.
Many of these biologic activities of IL-4, including IgE production and VCAM-1 expression, are shared with IL-13. This redundancy would tend to mitigate the biologic usefulness of a compound designed to interfere with IL-4 function; however, blocking Th2 differentiation will likely decrease IL-13 levels. It is also possible that some of the biologic effects of the sIL-4R are mediated through inhibition of IL-13 signaling. The functional IL-13R complex includes the low affinity IL-13Rα1 chain, the high affinity IL-13Rα2 chain, and the IL-4Rα chain. Although the IL-4Rα chain appears to be required for IL-13- mediated signal transduction, it cannot by itself bind IL-13. Thus, the soluble IL-4Rα protein is incapable of blocking the interaction of free IL-13 with the IL-13R complex. However, it remains to be demonstrated whether sIL-4R (IL-4Rα lacking the transmembrane and cytoplasmic regions) can interact with one of the IL-13R chains to which IL-13 had previously bound. If this were to occur, one might speculate that the soluble IL-4R could also inhibit IL-13 activity by replacing the full-length IL-4Rα signaling component of the IL-13R complex. Blocking IL-13 specifically has been shown to attenuate the asthma phenotype in murine models (14, 15).
In contrast to IgE production and VCAM-1 expression, a unique biologic activity of IL-4 essential to the development of allergic inflammation and not shared with IL-13 is its ability to drive the differentiation of naive Th0 lymphocytes into the Th2 phenotype (7, 8, 16). In the presence of IL-4, Th0 lymphocytes acquire the tendency to secrete IL-4, IL-5, IL-13, and other cytokines associated with Th2 lymphocytes and lose their tendency to produce interferon-γ. This has been established in studies using transgenic mice with single antigen-specific T-cell receptors (8). The tendency of these T cells to produce IL-4 is enhanced in a dose-dependent fashion in the presence of additional IL-4, whereas neutralizing anti-IL-4 antibodies abrogate their ability to produce Th2 cytokines. Similarly, in human studies, the presence of exogenous IL-4 is associated with the generation of Th2 T-lymphocyte clones, whereas anti-IL-4 is inhibitory (17). Blocking Th2 differentiation could therefore block further production of IL-4, IL-5, and IL-13.
Neutralizing IL-4 with anti-IL-4 antibodies prevents development of allergen-specific IgE (18, 19) and reduces eosinophilic inflammation (18, 19) and airway reactivity (20). Similarly, studies using IL-4 knockout mice have confirmed that IL-4 is necessary for the development of allergen-specific IgE (21, 22) and important to the development of airway eosinophilia (18, 21, 22), and airway hyperreactivity (22). By inhibiting Th2-like lymphocyte differentiation, IL-4 blockade will inhibit the biologic activities of IL-4, but also reduce the production of IL-5 (16). Thus, anti-IL-4 antibodies prevented allergen-sensitized and challenged mice from producing IL-5 (18). Nonetheless, mice deficient for IL-4 maintain residual Th2 responses (16, 23, 24), which may explain the persistent expression of IL-5 (21), eosinophilia (19, 20, 22), and airway hyperreactivity (21) observed in many of these murine studies. There is a danger in overinterpreting data derived from animal models since these models may merely act to validate themselves and do not necessarily reflect human disease. These data do, however, support important influences of IL-4, not only on allergen-specific IgE production but also on the production of IL-5, IL-13, eosinophilia, and airway hyperreactivity and support the concept of IL-4 blockade as a useful therapeutic approach in human asthma. Circulating IL-4 levels are usually low or undetectable in asthma, however, since endogenous IL-4 is avidly bound to its cell surface receptor. As such, circulating levels do not accurately reflect the total amount of biologically active IL-4 present.
The recombinant murine soluble IL-4R has been shown to block a number of IL-4 mediated biologic activities in vivo, including induction of polyclonal IgE secretion in anti-IgD- treated mice (25); host versus graft disease; and VCAM-1 and ICAM-1 expression on cardiac endothelial cells (26). Treatment with sIL-4R prevented fatal aspergillosis (27) and candidiasis (28) in otherwise susceptible animals, and this antifungal effect was accompanied by a switch from a Th2-like to a Th1-like immune response phenotype (29). Finally, similar to the studies previously discussed with the neutralizing anti-IL-4 antibodies or with IL-4 knockout mice, soluble mIL-4R significantly suppressed allergen-specific IgE production and airway hyperresponsiveness in ovalbumin-challenged mice (11, 30). In vitro studies with the soluble recombinant human IL-4 receptor (IL-4R) have demonstrated its ability to neutralize the biologic activities of IL-4, including producing a dose-dependent inhibition of IL-4-mediated T-cell proliferation (31).
These findings led to the current investigation wherein IL-4R proved safe and effective in the treatment of naturally occurring asthma. No significant toxicity was observed, and administration of IL-4R by nebulizer was practical and produced significant elevation in serum levels of soluble IL-4R over the basal endogenous levels. It is therefore possible that systemic neutralization of IL-4 occurs even though IL-4R is delivered to the airway. Clearance of IL-4R is prolonged; the estimated serum half-life of a single nebulized dose in human subjects is 6 to 8 d in other studies (unpublished data). This is not surprising since soluble IL-4R is a naturally occurring human protein, and there are no obvious reasons or intrinsic mechanisms for its hepatic or renal clearance. A prolonged half-life suggests that weekly therapy with IL-4R would be feasible. Weekly therapy might enhance patient compliance if IL-4R were administered at home. Alternatively, IL-4R could be administered weekly, as directly observed therapy, in a physician's office. Many patients with asthma, as well as other allergic persons, already make weekly visits to a physician's office for immunotherapy injections.
In the present study, clinical efficacy was demonstrated by lack of deterioration in spirometric parameters, including FEV1 and FEF25–75, despite abrupt discontinuation of inhaled corticosteroids (Figures 4 and 5). Patients' asthma symptom scores were significantly better, coincident with reduced β2-agonist use (Figures 1 and 2). We could not document intergroup differences in airway reactivity as measured by methacholine challenge because of early dropout and the use of β2-agonists in the placebo group and the IL-4R 500 μg group. Nor did we see statistically significant improvement in the IL-4-induced inflammatory indices, VCAM-1, ICAM-1, ECP, and CD23, but this may reflect the numerous IL-4–independent pathways for their production. However, it is our expectation that abrogation of IL-4 should inhibit the differentiation of Th2 lymphocytes and reduce the ability of IL-4 to support proliferation and survival of established Th2 cells already present in the airway. This should mitigate the expression of IL-3, IL-5, IL-13, granulocyte-macrophage colony-stimulating factor, and other cytokines responsible for the differentiation, recruitment, and survival of eosinophils, as well as decrease cytokines and chemokines responsible for the recruitment of these inflammatory factors. Although there was not a decrease in eosinophilia, levels of circulatory eosinophils may not reflect the status of activated eosinophils within the lungs. It is plausible that reduction of inflammatory indices may require a more prolonged exposure to IL-4R than following the single dose in this study. In contrast, IL-4R reduced exhaled nitric oxide consistent with an anti-inflammatory effect (Figure 6). It is conceivable that more prolonged IL-4R therapy might ultimately eliminate Th2 lymphocytes, restoring the patient's immune system to its status prior to the development of asthma and atopy, thus providing long-term relief of symptoms.
There are theoretical concerns regarding the long-term effects of blockade of the biologic activities of IL-4. Whereas the ability to mount allergic immune responses does not seem to offer any immunologic advantages, Th2-mediated eosinophilic responses may be important in the immune responses to parasites. Mice constitutively overexpressing soluble IL-4R exhibit no obvious physiologic or developmental abnormalities (32 and unpublished data). Although Th2-like responses have been shown to be involved in expulsion of the extracellular parasite Nippostrongylus brasiliensis (33), mice deficient in IL-4 production (IL-4−/−) are able to expel the worms normally (34). This suggests that blocking IL-4 alone would not lead to increased susceptibility to extracellular parasites. However, this contention is challenged by the observed inability of mice treated with anti-IL-4 mAb to reject another worm pathogen, Heligmosomoides polygyrus (35). Of note, mice deficient in IL-4Rα expression (IL-4Rα−/−) are incapable of expelling N. brasiliensis, and this effect appears to be due to the inability of IL-13 to signal in the absence of IL-4Rα, since the IL-13 receptor complex consists of a heterodimer of IL-4Rα and IL-13Rα (34). Thus, if the soluble IL-4R is able to block both IL-4 and IL-13 through the mechanism described above, then resistance to worm infections might be decreased; however, this has not been tested experimentally. The concern that IL-4 blockade might inhibit a recipient's ability to successfully resist parasitic infections is mitigated in environments that lack a high prevalence of systemic helminthic parasites.
Finally, although this study was performed on patients with allergic (“extrinsic”) asthma, who would be predicted to have an IL-4-mediated disease, IL-4R should be equally effective in patients with nonallergic forms of asthma. Although these patients do not demonstrate allergen-specific IgE, the presence of eosinophilic inflammation suggests the differentiation of Th2-like lymphocytes, which are responsible for the production of IL-5 and other cytokines that promote the development of eosinophilia. Based on our current knowledge of the differentiation of IL-5-producing Th2-like lymphocytes, the process is IL-4-dependent and should, therefore, be susceptible to suppression by IL-4R therapy. Other atopic disorders such as allergic rhinitis and atopic dermatitis are thought to be mediated by IL-4 and may also respond to IL-4 blockade with IL-4R therapy.
The writers wish to acknowledge the assistance of Donetta Leavesley and Alexis Cunningham in preparation of the manuscript.
Supported by a grant from Immunex Corporation.
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