Therapeutic Targeting of Chemokines with Monoclonal Antibodies Katrien L

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Current Immunology Reviews, 2012, 8, 141-148 141 Therapeutic Targeting of Chemokines with Monoclonal Antibodies Katrien L. de Graaf, Marie H. Kosco-Vilbois and Nicolas Fischer*

NovImmune SA, 14 Chemin des Aulx, Plan-les-Ouates 1228, Switzerland

Abstract: Chemokines cannot be easily antagonized by low molecular weight (LMW) compounds and are therefore more suitable for targeting clinically via ‘biologics’. Significant beneficial features of mAbs as compared to LMW compounds include a high selectivity for their target, reducing the risk of off-target side effects, as well as the prolonged pharmacokinetics, with half-lives ranging from days to weeks, necessitating less frequent dosing. In this HOT TOPIC, our aim is to focus on reviewing available information regarding anti-chemokine mAbs that have reached clinical development stage and discuss not only the target relevance and the clinical outcomes, but also describe the characteristics of the therapeutic antibodies. Indeed, as clinical efficacy - or lack thereof - is highly dependent on the biology of the target, so are the properties and administration modality of the drug which will also impact on the clinical outcome and thus on the validity of targeting chemokines in disease settings. Keywords: Chemokines, drug development, glycosaminoglycans, inflammation, monoclonal antibody.

INTRODUCTION In addition to triggering the migration process via their GPCRs, certain chemokines induce biological effects that Monoclonal antibodies (mAb) represent a rapidly may be directly relevant to the underlying pathology of expanding class of therapeutic molecules used successfully human diseases. For example, CXCL10 has been shown to in the treatment of oncology, inflammatory, infectious and impair function and decrease viability when cultured with neurodegenerative diseases. Since the first generation of a human pancreatic beta islet cells, suggesting a role in the mAb derived from a hybridoma, tremendous technological pathogenesis of diabetes [6]. Furthermore, antibodies have developments have provided multiple ways to identify been generated against chemokines as research tools for both highly specific and potent mAbs against diverse targets [1- in vitro and animal studies to better understand the biology 3]. It has now become possible to generate antibodies of this class of proteins and explore their potential as derived from human sequences that provide lower intrinsic therapeutic targets. Combining results obtained using these immunogenicity, to manipulate affinity and to alter Fc- tools with the observations obtained using chemokine and mediated effector functions. All of which allow the tuning, at chemokine receptor transgenic mouse strains and other will, of an antibody’s characteristics with the desired mode pharmacological antagonists (such as modified chemokines), of action [4]. has provided sufficient evidence to warrant the development of therapeutic mAbs against human chemokines. CHEMOKINES Chemokines are small basic proteins ranging in size ANTI-CHEMOKINE ANTIBODIES IN CLINICAL between 8-10 Kd that have been designated into one of four TRIALS families depending on the position and number of invariant mAbs Targeting CCL2 cysteines, i.e. CC, CXC, CX3C and C-. The fundamental role of chemokines is to orchestrate the process of immune CCL2 (monocyte chemoattractant protein-1; MCP-1) is a cell migration through tissues as well as blood and lymph potent chemotactic factor for monocytes that is produced by vessels. In the bloodstream, this function is part of a multi- a wide variety of cell types either constitutively or after step process which involves selectin-mediated rolling on the induction by oxidative stress or cytokines [7, 8]. CCL2 endothelium followed by triggering events signaled through exerts its action by binding to its unique receptor CCR2. Gi protein–coupled chemokine receptors (GPCRs) that in CCL2 is one of the most studied members of the chemokine turn, induce integrin-dependent firm adhesion. Once firm family and has been considered as a therapeutic target for a adhesion has been achieved, the leukocytes proceed through variety of diseases including chronic obstructive pulmonary steps that lead to migration across the endothelium and diseae (COPD), multiple sclerosis (MS), rheumatoid arthritis movement into a new body cavity. In order to effectively (RA) and atherosclerosis [9, 10]. In addition, CCL2 induce these events, many chemokines form higher order promotes angiogenesis and thus antagonism of CCL2 has oligomers which are presented to the rolling cell on the been proposed to reduce vasculogenesis and tumor growth glycosaminoglycans (GAGs) expressed on the luminal [11, 12]. These considerations are supported by data surface of the endothelium [5] (Fig. 1A). generated in animal models using mice deficient for CCL2 or neutralizing CCL2 mAbs. To date, two therapeutic mAbs

to CCL2 have been generated, ABN912 and CNTO 888

*Address correspondence to this author at the NovImmune SA, 14 Chemin (Table 1). des Aulx, Plan-les-Ouates 1228, Switzerland; Tel: +41225935184; Fax: +41225935139; E-mail: [email protected]

C D

Fig. (1). Potential mode of action of therapeutic anti-chemokine antibodies with different characteristics. (A) Situation baseline = At the site of inflammation, a large fraction of the chemokine pool is immobilized on GAGs at the surface of the endothelium as well as located in the tissue. (B) Situation 1 = Inappropriate antibody profile. Therapeutic mAb only able to bind soluble chemokine and not in the context of GAGs on the endothelium, thus target remains available. (C) Situation 2 = Inappropriate antibody exposure. Therapeutic mAb dosed suboptimally will be incapable of saturating oligomeric and immobilized forms of the chemokine, thus target remains available as no free antibody left. (D) Situation 3 = Optimized mAb profile and dose. Sufficient exposure to a mAb capable of neutralizing the soluble, oligomeric and immobilized forms of the chemokine, first masks the target in the physiological context and eventually leads to mobilization into the serum, with the occurrence of long lived chemokine-antibody complexes perturbating further the chemokine gradient.

ABN912 is a human anti-human CCL2 neutralizing mAb demonstrated that administration of an anti-CCL2 mAb was developed by Novartis. This antibody of the IgG4 isotype well tolerated but did not result in any clinical benefit. A was generated by immunization of genetically engineered striking observation was that administration of ABN912 lead mice that contain human immunoglobulin (Ig) genes and has to an increase in total CCL2 serum levels (i.e. free CCL2 a high affinity for human CCL2 (Kd 43 pM) [13]. plus drug-bound CCL2). This increase was dose dependent and measurable for a prolonged period of time, up to 120 Data from a randomized placebo-controlled phase II trial days after the first drug injection. For the highest ABN912 in RA have been published [14]. In this trial, patients were dose administered, maximal total CCL2 levels were up to administered intravenous doses of ABN912 ranging from 0.3 2000 times higher than free CCL2 levels at baseline. A to 10 mg/kg. The antibody manifested pharmacokinetic properties typical for mAbs including linear kinetics and a similar phenomenon has been reported for anti-cytokine antibodies, where it has been demonstrated that the half-life of approximately 2 weeks. As far as therapeutic prolonged presence of cytokines in circulation following effects of mAb administration were concerned, this study Therapeutic Targeting of Chemokines with Monoclonal Antibodies Current Immunology Reviews, 2012, Vol. 8, No. 2 143

Table 1. Therapeutic Monoclonal Antibodies Targeting Chemokines

Company Antibody Target Isotype (Affinity) Indication Highest Clinical Phase (Originator)

Rheumatoid arthritis, ABN912 CCL2 Novartis HuIgG4 (Kd 43 pM) [13] Phase II (development discontinued) COPD Cancer, pulmonary CNTO 888 CCL2 Centocor HuIgG1 Phase II fibrosis Cambridge Bertilimumab Allergic conjunctivitis, CCL11 Antibody HuIgG4 (Kd 8.8 pM) [26] Phase II (CAT-213, iCo-008) allergic rhinitis Technology Cancer, COPD, ABX-IL8 CXCL8 Xenotech HuIgG2 (Kd 21 pM) [31] Phase II (development discontinued) rheumatoid arthritis, psoriasis MDX 018 Palmoplantular pustulosis, (HuMax-IL8, CXCL8 Genmab HuIgG1 (Kd 20 pM) [32] Phase I/II glioblastoma, COPD HuMax-Inflam) Ulcerative colitis, MDX 1100 CXCL10 Medarex HuIgG1 Phase II rheumatoid arthritis NI-0801 CXCL10 NovImmune HuIgG1 (Kd 170 pM) Autoimmune disorders Phase I mAb administration results from the generation of antibody- activity. Currently, a phase II trial of CNTO 888 in patients cytokine complexes, which typically have a much longer with metastatic prostate cancer and a phase II trial in half-life than the free ligand [15, 16]. idiopathic pulmonary fibrosis are ongoing. The investigators suggested that bioactive CCL2 released from the ABN912-CCL2 complexes might explain the lack A mAb Targeting CCL11 of efficacy. However, the study was not powered to be able CCL11 (eotaxin-1) is a CC chemokine that is produced to determine if this was a significant clinical result. after induction by pro-inflammatory mediators by a variety Furthermore, higher doses were not tested, thus too low dosing could not be ruled out. Finally, the authors could not of cell types including eosinophils, eptithelial cells, fibroblasts, endothelial cells, T-lymphocytes, monocytes and exclude the possibility that CCL2 is not an appropriate target macrophages. CCL11 binds with a high affinity to CCR3, in RA as some animal studies suggest an ambivalent role for which is mainly expressed on eosinophils and basophils and the CCR2-CCL2 pathway in inflammation [17, 18]. This is a key regulator of eosinophil function [22, 23]. Diseases notion is further supported by the fact that clinical trials such as asthma, allergic rhinitis and conjunctivitis are conducted in RA patients using the CCR2 antagonis MK 0812 or the CCR2-specific antibody MLN 1202 failed to characterized by a marked accumulation of eosinophils and therefore support the potential therapeutic value of CCL11 demonstrate clinical benefit [19]. neutralization in these conditions [24, 25]. ABN912 was also in development for COPD and asthma. Bertilimumab is a therapeutic anti-CCL11 mAb Limited data for a clinical trial in COPD were presented at developed originally by Cambridge Antibody Technology the International Conference of the American Thoracic Society (2006). As for the trial conducted in RA, an increase (now part of MedImmune) [26]. It is a high affinity human IgG4 mAb (Kd 8.8 pM) that was isolated from human Ig in total circulating CCL2 levels was reported upon ABN912 libraries using phage display technology. The inhibitory administration. The development of ABN912 for the effects of bertilimumab on eosinophil recruitment after treatment of RA as well as COPD has been discontinued and injection of human eotaxin were confirmed in vivo in mice no further information on the current development status of and cynomolgus monkeys [27]. In addition, eosinophil this compound is available. chemotactic activity in sputum of moderate to severe CNTO 888 is a human IgG1 monoclonal antibody with asthmatics was significantly inhibited by bertilimumab [24]. high affinity for human CCL2 which is actively being Initially, a phase I study to investigate safety and PK developed by Centocor for treatment of solid tumors and properties of a single intravenous dose of bertilimumab was pulmonary fibrosis. In vivo anti-tumor activity of CNTO 888 conducted in healthy volunteers. No serious adverse events was demonstrated in a mouse model of prostate cancer [11, 20]. were reported and the drug was well tolerated. The terminal t1/2 varied from 0.6 to 8.4 days for doses ranging from 0.1 to Results from a first-in-human study in solid tumors have 10 mg/kg [26]. No data are available on serum eotaxin levels recently been reported [21] showing that CNTO 888 is well upon mAb administration. tolerated and manifests linear kinetics with a half-life of 4.4 A phase II trial was conducted to investigate the effect of to 8.7 days. Similarly to ABN912, CNTO 888 administration lead to a dose-dependent increase in total circulating CCL2 bertilimumab on allergen-induced nasal responses in patients with seasonal allergic rhinitis that were challenged with levels of up to 1000-fold. The results of the trial were grass pollen outside of the allergy season. Bertilimumab was encouraging and suggest preliminary evidence of anti-tumor administered intravenously or intranasally and both routes of 144 Current Immunology Reviews, 2012, Vol. 8, No. 2 de Graaf et al. administration lead to a reduction of the post-allergy nasal Clinical trials were conducted with ABX-IL8 in obstruction and significantly reduced the infiltration of psoriasis, rheumatoid arthritis and COPD. The antibody was submucosal mast cells. The infiltration of submucosal generally well tolerated and the t1/2 of a single dose of the eosinophils was also reduced by nasal drug administration. antibody was two to three weeks. The results from a phase II However, clinical symptoms were not significantly affected study in COPD demonstrated improvement in the transition by the treatment [28, 29]. dyspnea index upon ABX-IL8 administration, however, no significant differences were observed versus placebo for Interestingly, a recent publication demonstrated reduced lung function and quality of life [42]. Following tissue eosinophilia in patients with allergic rhinitis upon disappointing results in phase II trials in psoriasis and steroid treatment [30]. Simultaneously, tissue expression of rheumatoid arthritis, development of this mAb was CCL5 but not CCL11 was shown to be reduced, suggesting that CCL5 might actually be the more relevant therapeutic discontinued. target in allergic rhinitis. Genmab has developed HuMax-IL8 (MDX 018; HuMAx-Inflam), an anti-CXCL8 antibody for the treatment Additionally, a phase I/II allergen challenge study of of palmoplantar pustulosis, glioblastoma and autoimmune topically applied bertilimumab in patients with allergic disorders. This fully human IgG1 antibody was generated conjunctivitis has been performed. Although the results of this trial confirmed that the mAb was safe and well tolerated, using transgenic mice expressing human Ig genes and binds with high affinity to human CXCL8 (Kd=20 pM). The no effect on symptoms could be assessed as the allergen antibody efficiently blocks CXCL8 binding to neutrophils as challenge did not provoke a large enough late phase response well as CXCL8-induced neutrophil activation and involving eosinophils [26]. Development of bertilimumab in chemotaxis [32]. In preclinical studies, the antibody has been asthma and allergic rhinitis has been discontinued. However, shown to suppress tumor growth of primary sarcoma, bertilimumab is currently in development with iCo Therapeutics for the treatment of severe ocular allergies and melanoma and gastric tumors in immunocompromised mouse models (Genmab press release, November 16, 2007). Immune Pharmaceuticals have recently been granted a license option for systemic uses of bertilimumab. Palmoplantar pustulosis is a rare chronic inflammation of the skin characterized by intraepidermal accumulation of mAbs Targeting CXCL8 neutrophils and recurrent eruptions of pustules on hands or feet. CXCL8 is elevated in lesional skin biopies from PPP CXCL8 (interleukin-8) is expressed by various cell types patients [43]. A phase I/II trial of HuMax-IL8 in including monocytes, macrophages, neutrophils, palmoplantar pustulosis was conducted to prove the concept lymphocytes and endothelial cells. It binds two receptors, that abrogation of CXCL8 activity is a valid therapeutic CXCR1 and CXCR2, that are present on the surface of strategy for chronic inflammatory diseases associated with neutrophils, monocytes, mast cells and epithelial cells. CXCL8 overproduction. Results from the trial showed that CXCL8 is a potent neutrophil-recruiting and activating treatment with HuMax-IL8 was well tolerated and factor [33, 34]. In addition, receptor engagement by CXCL8 significantly reduced the formation of fresh pustules and triggers an increase in the adhesion of leukocytes to overall clinical disease activity [32]. Moreover, HuMax-IL8 endothelial cells and induces angiogenesis [35]. was readily detectable in washing fluid samples obtained form the affected hands or feet from the patients. The A key role for CXCL8 in human disease is supported by antibody concentration in the washing fluid correlated with the fact that CXCL8 levels are consistently elevated in affected tissues in various inflammatory diseases including the dose of antibody that was administered and in line with this observation, the average CXCL8 concentrations in the psoriasis, rheumatoid arthritis and inflammatory bowel washing fluid decreased with increasing HuMax-IL8 doses. disease. CXCL8 was also found to be increased in sputum of This indicates a rapid passage of mAb from the circulation COPD patients where CXCL8 concentrations correlated with through the skin in PPP lesions, which allows the antibody to disease severity [36]. In addition, expression levels of neutralize CXCL8 activity at the site of inflammation. CXCL8 have been shown to correlate with disease progression in human melanomas, which might be linked to In addition to these mAbs described above, a topical its potent angiogenic activities [37, 38]. A variety of formulation of an anti-CXCL8 antibody for the treatment of preclinical animal studies using neutralizing mAbs against psoriasis has been developed by Anogen (ABCream) IL-8 demonstrate a reduction of neutrophil infiltration and (http://www.yesbiotech.com/antibodies_abcream.htm). No IL-8 mediated tissue injury [39, 40]. details have been published on the clinical development of ABX-IL8 and MDX-018 (HuMax-IL8;10F8) are the product and no pharmacokinetic or biodistribution data are available. Apparently, it has proven beneficial effects as therapeutic mAbs directed against CXCL8 that have been ABCream is currently marketed in China. evaluated in clinical trials (Table 1). ABX-IL8 is a fully human IgG2 antibody developed by Abgenix that was generated using transgenic mice expressing human Ig genes mAbs Targeting CXCL10 and exhibits a high affinity for human CXCL8 (Kd=21 pM ) [31]. The antibody efficiently blocks CXCL8 binding to CXCL10 (IP-10) can be produced by a variety of cell types including endothelial cells, monocytes, neutrophils, neutrophils and inhibits CXCL8-induced neutrophil fibroblasts, keratinocytes, hepatocytes and astrocytes in activation and migration in vitro [31]. Moreover, ABX-IL8 response to proinflammatory stimuli such as IFN, TNF inhibits the growth and metastasis of human melanoma cells and LPS [44, 45]. CXCL10 as well as its co-ligands CXCL9 in nude mice [41]. and CXCL11 all bind to CXCR3, a receptor mainly present Therapeutic Targeting of Chemokines with Monoclonal Antibodies Current Immunology Reviews, 2012, Vol. 8, No. 2 145 on the surface of Th1 cells, cytotoxic CD8 cells, monocytes, antibodies in clinical trials, serum CXCL10 levels were NK cells and mast cells. Although the CXCR3 ligands have monitored in preclinical toxicology studies, after partially redundant functions, various in vivo studies have administration of multiple doses of NI-0801 to cynomolgus demonstrated that they can also collaborate or compete with monkeys as well as during the Phase I trial in healthy each other, depending on timing and/ or pattern of their volunteers. Total circulating CXCL10 levels abruptly raised expression [46]. As mentioned in the introduction, CXCL10 several hundred-fold upon antibody administration and has been shown to impair function and decrease viability CXCL10/ NI-0801 complexes remained detectable in serum when cultured with human pancreatic beta islet cells, for a prolonged period of time. Interestingly, the maximal suggesting a role in the pathogenesis of diabetes [6], whereas level of circulating complexed CXCL10 was dose dependent this role has not been attributed to the other two ligands. but was identical at the two highest doses, reaching 10 nM. Furthermore, CXCL10 is associated with This data suggests that a fixed pool of CXCL10 could be mobilized from the tissue into the circulation and was proinflammatory T-cell responses yet also has angiostatic saturated by 10 to 20 mg/kg of NI-0801. At all times, a large properties [47]. Several studies have demonstrated the molar excess of NI-0801 over CXCL10 was present in the upregulation of CXCL10 in serum and tissue in sera and no CXCL10 activity was detectable in the serum of inflammatory diseases such as rheumatoid arthritis, cynomolgus monkeys. Moreover, sera from healthy inflammatory bowel diseases, diabetes and autoimmune hepatitis [48-51]. Antagonism of CXCL10 lead to disease volunteers that were given NI-0801 were capable of neutralizing the chemotactic activity of additional attenuation in animal models of IBD, arthritis, type I exogenously added CXCL10 (manuscript in preparation). diabetes and liver fibrosis [52-55]. Currently, two mAbs These results suggest efficient neutralization of CXCL10 in targeting CXCL10 are in clinical trials (Table 1). circulation by NI-0801, despite the presence of long-lived MDX-1100 is a fully human, high affinity, neutralizing, chemokine/antibody complexes. NI-0801 is currently under IgG1 anti-CXCL10 mAb developed by Medarex which has development for treatment of autoimmune and inflammatory been used in clinical trials for treatment of ulcerative colitis diseases. and rheumatoid arthritis. Initially, a Phase I study was conducted to determine the safety, pharmacokinetics and WHAT LESSONS CAN WE LEARN FROM THERA- pharmacodynamic profiles of MDX-1100 in healthy PEUTIC ANTIBODIES TARGETING CHEMOKINES volunteers. Single doses of MDX-1100 up to 10 mg/kg were SO FAR? well tolerated and the t1/2 was 10 days for the highest dose tested. In addition, a phase I trial of single administration of Multiple clinical trials have now been conducted with MDX-1100 in ulcerative colitis demonstrated that the drug various anti-chemokine mAbs. From the available was well tolerated by UC patients. information common patterns are emerging. A Phase II trial in ulcerative colitis was recently conducted and it was reported that repeated dosing of MDX- Safety 1100 was effective in inducing response with modest efficacy in patients with moderate to severe UC at the test All antibodies have been well tolerated and no specific dose of 10 mg/kg. Interestingly, patients with higher MDX- safety risks have been reported, suggesting that chemokine 1100 plasma levels had greater clinical benefits, suggesting targeting is a relatively safe therapeutic approach. As the that efficacy might be linked to higher exposure. A Phase II targets of these antibodies are soluble proteins, no ADCC or trial of MDX-1100 in rheumatoid arthritis met its primary CDC activities are anticipated regardless of the isotype of endpoint as a statistically significant higher proportion of the antibody. The theoretical concern that antibodies capable patients in the drug-treated cohort achieved an ACR20 of binding chemokines in the context of GAGs could response as compared to the placebo group. These mediate ADCC of CDC is in contradiction with the lack of encouraging results demonstrate that the CXCL10-CXCR3 toxicity observed in toxicology studies conducted in non- pathway plays an important role in RA pathogenesis and human primates and in phase I and phase II studies in provide a rationale for the further development of humans using these antibodies. In addition, no change in the MDX-1100 in rheumatoid arthritis. pattern of circulating pro-inflammatory cytokines have been reported, indicating that these antibodies do not induce NI-0801 is a fully human IgG1 mAb against human abnormal lymphocyte activation or cytokine release both of CXCL10 developed by NovImmune. This antibody was which are features of ADCC/CDC related activity. generated using phage display technology. The antibody has a high affinity for CXCL10 (Kd=170 pM) and efficiently Target Levels and Accessibility inhibits CXCL10 induced calcium flux and chemotaxis. In addition, NI-0801 is capable of binding CXCL10 Many chemokines are readily detectable by ELISA, even sequestered on GAGs assuring neutralization of CXCL10 in in sera from healthy individuals. However, in addition to its physiological context (manuscript in preparation). circulating levels, a fraction of chemokines is sequestered Data from the first in human study in healthy volunteers within tissues and immobilized on GAGs at the surface of revealed that single doses of NI-0801 up to 20 mg/kg were endothelial cells (Fig. 1A). Oligomerization and binding to well tolerated. NI-0801 displayed a pharmacokinetic profile, GAGs are essential for chemokine activity [5]. As a typical for human IgG with a half-life of approximately 17 consequence, an antibody only recognizing the chemokine in days for the highest dose studied. Following the reports of a soluble or monomeric form is unable to neutralize its target elevated total CCL2 levels upon administration of anti-CCL2 146 Current Immunology Reviews, 2012, Vol. 8, No. 2 de Graaf et al. in a physiologically relevant context and thus is expected to Signs of efficacy have been reported both in RA and UC have limited efficacy (Fig. 1B). patient treated with the neutralizing anti-CXCL10 antibody MDX-1100. These findings demonstrate that the apparent These chemokine pools can be mobilized into the redundancy frequently invoked as a major hurdle when circulation and detected following injection of GAG-like structure such as heparin [56, 57]. As the affinity of an antagonizing the chemokine system, can be overcome. This is further supported by the positive outcome for the antibody for its target is generally much higher than the treatment of palmoplantar pustulosis using HuMax-IL8. affinity of chemokines for GAGs, administration of an anti- Interestingly, it was reported that in MDX-1100 UC trial, chemokine antibody might equally be expected to mobilize significantly higher response rates were observed in patients GAG-bound chemokines into the circulation (Fig. 1C, D). that had more exposure to the drug. This observation in our This aspect has only been addressed and reported in three programs so far: ABN 912 and CNTO 888, both targeting opinion further underscores the importance of target saturation to achieve efficacy (Fig. 1D). CCL2, as well as NI-0801 which targets CXCL10. Administration of these antibodies invariably lead to a concomitant rise in circulating total levels of the targeted CONCLUDING REMARKS chemokine up to 2000 times higher than the level of free The initial clinical trials evaluating anti-chemokines chemokine present at baseline. These observations indicate that the bulk part of chemokine in the body is sequestered mAbs were disappointing. In particular, the lack of efficacy observed when antagonizing a prominent and well and that the total amounts of chemokine present in the characterized pro-inflammatory chemokine such as CCL2, organism are higher than anticipated even under non- contributed to the general perception that achieving clinical inflammatory conditions. Therefore the target level in a benefit via chemokine targeting is difficult. The sharp disease setting and achieving sufficient target coverage are increase in circulating chemokine levels further raised important parameters to consider for therapeutic intervention. concerns although this phenomenon is generally observed and expected for soluble targets that acquire a long serum As the major fraction of the chemokine is immobilized, half-life once complexed to an antibody. Although the the ability to recognize its target in the context of GAGs, is complexity of the chemokine signaling network remains a an important requirement for a therapeutic effect (Fig. 1D). challenge, other factors linked to the antibody itself and to This characteristic has unfortunately not been systematically target level in a given disease setting might have reported for the different antibodies discussed here. compromised these trials. More recent programs have demonstrated that mAbs can be successfully used to Efficacy ameliorate inflammatory conditions in patients. This raises the hope that novel antibodies with appropriate The ABN 912 anti-CCL2 and the ABX-IL8 anti-CXCL8 characteristics will further demonstrate the potential of programs have been discontinued. The reasons for failure of chemokines as a promising class of therapeutic targets. these programs have been the scope of other reviews and included arguments which are generally raised in the context ACKNOWLEDGEMENTS of all programs targeting chemokines or their receptors, such as redundancy of the chemokine system and the limited This work was supported financially in part by the EU relevance of many of the animal models which have been Sixth Framework Programme INNOCHEM (Innovative used to validate a target for human disease [58, 59]. In Chemokine-based Therapeutic Strategies for Autoimmunity general, very little information is available on the antibodies and Chronic Inflammation). that have been used in animal models and how their characteristics (such as binding to the chemokine in the CONFLICT OF INTEREST context of GAG) compare with the corresponding therapeutic candidate. Additional efforts are required to Declared none. generate and properly characterize surrogate antibodies to validate targets as well as potential indications. REFERENCES However, other factors than target relevance might have [1] Chan AC, Carter PJ. Therapeutic antibodies for autoimmunity and contributed to the lack of efficacy, such as target levels and inflammation. Nat Rev Immunol 2010; 10: 301-16. accessibility that were discussed above. In the case of ABX- [2] Weiner LM, Surana R, Wang S. Monoclonal antibodies: versatile IL8, the paper describing the generation of the original platforms for cancer immunotherapy. 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Received: September 21, 2010 Revised: June 24, 2011 Accepted: July 8, 2011