Active immunization to tumor necrosis factor-α is effective in treating chronic established inflammatory disease: a long-term study in a transgenic model of arthritis
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Passive blockade of tumor necrosis factor-alpha (TNF-α) has demonstrated high therapeutic efficiency in chronic inflammatory diseases, such as rheumatoid arthritis, although some concerns remain such as occurrence of resistance and high cost. These limitations prompted investigations of an alternative strategy to target TNF-α. This study sought to demonstrate a long-lasting therapeutic effect on established arthritis of an active immunotherapy to human (h) TNF-α and to evaluate the long-term consequences of an endogenous anti-TNF-α response.
hTNF-α transgenic mice, which spontaneously develop arthritides from 8 weeks of age, were immunized with a heterocomplex (TNF kinoid, or TNF-K) composed of hTNF-α and keyhole limpet hemocyanin after disease onset. We evaluated arthritides by clinical and histological assessment, and titers of neutralizing anti-hTNF-α antibody by enzyme-linked immunosorbent assay and L929 assay.
Arthritides were dramatically improved compared to control mice at week 27. TNF-K-treated mice exhibited high levels of neutralizing anti-hTNF-α antibodies. Between weeks 27 and 45, all immunized mice exhibited symptoms of clinical deterioration and a parallel decrease in anti-hTNF-α neutralizing antibodies. A maintenance dose of TNF-K reversed the clinical deterioration and increased the anti-hTNF-α antibody titer. At 45 weeks, TNF-K long-term efficacy was confirmed by low clinical and mild histological scores for the TNF-K-treated mice. Injections of unmodified hTNF-α did not induce a recall response to hTNF-α in TNF-K immunized mice.
Anti-TNF-α immunotherapy with TNF-K has a sustained but reversible therapeutic efficacy in an established disease model, supporting the potential suitability of this approach in treating human disease.
KeywordsInfliximab Antibody Titer Maintenance Dose Neutralize Antibody Clinical Score
analysis of variance
enzyme-linked immunosorbent assay
human tumor necrosis factor-alpha
keyhole limpet hemocyanin
tumor necrosis factor-alpha
tumor necrosis factor kinoid
human tumor necrosis factor-alpha transgenic.
Rheumatoid arthritis (RA) is a chronic autoimmune disease with an estimated prevalence of about 0.5% in the adult population. This disease, characterized by synovial membrane hyperplasia and immune cell infiltration, affects multiple peripheral joints and leads to destruction of bone and cartilage, inducing pain and disability. Although its precise etiology is still unknown, the pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-17, and more recently IL-23, have been shown to be critical mediators in the inflammatory process . It has also been demonstrated that TNF-α mediates a wide variety of effector functions in RA, including the release of pro-inflammatory cytokines and chemokines, leukocyte accumulation, angiogenesis, and the activation of endothelial cells, chondrocytes, and osteoclasts [2, 3]. Based on the pivotal role of TNF-α in the pathogenesis of RA , two classes of biologic drugs to block this cytokine have been developed: a soluble TNF-α receptor (etanercept) and TNF-binding monoclonal antibodies (mAbs) such as infliximab, adalimumab, golimumab, or certolizumab [5, 6]. Although they show a rapid and substantial therapeutic benefit in most patients, with a good safety profile, primary unresponsiveness and secondary escape phenomena are not uncommon . Nonetheless, the tremendous success of TNF-α blockade by mAbs has sparked interest in developing alternative strategies for antagonizing TNF-α, such as gene therapy by electrotransfer , short interfering RNA , or active anti-TNF-α immunotherapy [10, 11, 12, 13].
Active immunotherapy is based on the established principles of vaccination. The aim of such a strategy is to use immunization with a protein compound to generate high titers of neutralizing antibodies to a given antigen, which can be either a self-protein or an environmental non-infectious agent. Therapeutic immunization has produced promising results in several fields, and in the case of active immunotherapy against cytokines (AIC), the choice of the target cytokine is informed by the long-term experience with mAbs, receptors, or antagonists in inflammatory and autoimmune diseases . Over the last decade, several active anti-TNF-α immunotherapies using mTNF-α derivates as the immunogen have been developed and tested in murine experimental models of RA [10, 11, 13].
More recently, with the aim of addressing diseases mediated by human TNF-α (hTNF-α), we developed an anti-hTNF-α compound called TNF kinoid (TNF-K), which is composed of biologically inactive but immunogenic hTNF-α conjugated to a carrier, keyhole limpet hemocyanin (KLH). We have tested TNF-K in hTNF-α transgenic (TTg) mice, which overexpress hTNF-α and develop an erosive polyarthritis that shares many features with RA [14, 15]. This model is the only relevant model since anti-TNF antibodies generated by TNF-K target hTNF-α. Previously, we have shown that a prophylactic anti-hTNF-α immunization protected TTg mice OK from developing arthritis [12, 16]. To determine the potency of this compound against established arthritis, we immunized TTg mice after the onset of arthritis. We studied the animals for a long time period to evaluate the duration of the potential disease-modulating activity of TNF-K. We showed that TNF-K immunization is efficacious against established arthritis and induces a transient TNF blockade with reversible effects on arthritis in TTg mice.
Materials and methods
Six- to nine-week-old male hemizygous TTg mice (1006-T) were purchased from Taconic Farms (Germantown, NY, USA) . These mice are similar to Tg197 mice and develop a spontaneous arthritis at from 8 to 10 weeks of age . All procedures were approved by the Animal Care and Use Committee of the University of Paris 13.
We obtained hTNF-α kinoid (TNF-K), a protein complex of hTNF-α and KLH, as previously described . Dulbecco's phosphate-buffered saline (PBS) was purchased from Eurobio (Les Ulis, France). ISA-51 adjuvant was obtained from Seppic (Paris, France).
Therapeutic and long-term effect of TNF-K active immunization
All treatments were started after the onset of arthritis, when TTg mice reached an average clinical score of 3 out of 12. The experimental protocol was as follows (Additional file 1). The control group consisted of eight mice treated with PBS emulsified in ISA-51 adjuvant (PBS group) at 15, 16, and 19 weeks of age. This group was followed for 12 weeks and then euthanized for ethical reasons. A group of 23 TTg mice received three primary intramuscular (IM) injections of TNF-K (4 μg) emulsified in ISA-51 (TNF-K group) at 15, 16, and 19 weeks of age. They were then randomly subdivided into two subgroups of eight and one subgroup of seven TTg mice. The first eight mice were euthanized at 27 weeks of age to compare the TNF-K immunized group with controls. At 32 weeks of age, the subgroup of seven mice received a maintenance dose of TNF-K emulsified in ISA-51 adjuvant, whereas the second subgroup of eight mice received, as a control, an injection of PBS emulsified in ISA-51 at the same time; both were followed until 45 weeks of age. In parallel, another group of eight mice was given weekly intraperitoneal (IP) injections of infliximab (1 mg/kg) from week 15 to week 27. At this time, infliximab was discontinued.
From blood samples collected at different time points during the experiment and at sacrifice, sera were obtained and tested for anti-KLH and anti-TNF-α antibody titers and for anti-TNF-α antibody neutralizing capacity. Specific anti-hTNF-α and anti-KLH antibody titers were determined using direct enzyme-linked immunosorbent assay (ELISA) . Precoated ELISA plates with 100 ng per well hTNF-α or KLH were incubated with serial dilutions of sera from immunized and control mice. Specific IgGs were detected by using horseradish peroxidase-conjugated rabbit anti-mouse IgG (Zymed Laboratories Inc., now part of Invitrogen Corporation, Carlsbad, CA, USA). The optical density (OD) was measured at 490 nm for each well.
The neutralizing capacity was assessed by using the L929 cytotoxicity assay, reflecting neutralizing antibodies . Briefly, mouse fibroblast L929 cell line (CCL 1) (American Type Culture Collection, Manassas, VA, USA) was cultured in Dulbecco's modified Eagle's medium containing 10% fetal calf serum. The cells were seeded in flat-bottomed 96-well plates and grown to 95% confluence. After 21 hours of incubation at 37°C, serial dilution of serum with a 100% toxic hTNF-α dose was added on L929 cells with 1 μg/mL of actinomycin D. After 20 hours of incubation at 37°C, the medium was removed and replaced with MTS/PMS during 4 hours at 37°C. The OD at 490 nm was measured for each well. The neutralization titer was expressed as the reciprocal of the serum dilution that neutralizes 50% of hTNFα activity.
Evaluation of B-memory response after TNF-K immunization
Thirty-six TTg mice received three IM injections of TNF-K emulsified in ISA-51 adjuvant at 7, 8, and 11 weeks of age. They were then randomly subdivided in two subgroups of ten and two subgroups of eight TTg mice. Neutralizing anti-hTNF-α antibody titers were monitored every month. When a decrease of 50% of the neutralizing capacity of these antibodies was observed, mice were intraperitoneally injected with native hTNF-α (10 ng), native hTNF-α (100 ng), KLH (10 μg), or PBS (equivalent volume) 24 weeks after the primary injection. Four weeks later, these mice received IM injections of the same compound with the same doses. The mice were further followed for 10 weeks. The native hTNF-α doses were chosen based on previous results we obtained in a TNF-α-dependent lethal shock experiment, in which we showed that 1 μg of native hTNF-α injections in TTg mice sensibilized with D-galactosamine was enough to kill the mice .
Clinical and histological assessments
Blinded weekly monitoring of body weight and arthritis scores in all four limbs was started from the reception of the animals (9 weeks of age). Clinical severity of arthritis for each paw (fingers, tarsus, and ankle) was quantified by attributing a score ranging from 0 to 3: 0, normal; 1, slight redness and swelling; 2, pronounced edematous swelling of the entire foot; 3, joint deformity and rigidity . The scores of each paw were summed, resulting in an arthritis score ranging from 0 to 12. The mean arthritis score on each clinical observation day was calculated for each treatment group.
For histological assessment of arthritis, all animals were sacrificed after 18-week or 36-week follow-up. Left forelimbs and right hind paws were collected, fixed with formol, decalcified, dehydrated, and included in paraffin blocks. Slides of 5 μm in thickness were made using a microtome. At least four serial sections were realized for each paw in order to obtain a reliable spatial evaluation of articular hints. Slides were then stained with hematoxylin and eosin or with safranin-O before microscopic observation (optical microscope). Synovitis and bone erosions were defined on slides stained with hematoxylin and eosin. Lesions were evaluated quantitatively on each slide using a 3-point scale ranging from 0 to 3, where 0 = normal articulation; 1 = slight inflammation and thickening of the synovium; 2 = mild thickening of the synovium and mild inflammation with invasion of the subsynovial area by inflammatory cells; 3 = severe inflammation and massive invasion of adjacent tissues by pannus . Other sections were scored for loss of safranin-O staining as a measure of cartilage proteoglycan depletion using a scale from 0 to 3, where 0 = no depletion; 1 = depletion of staining and thinning down of the lateral superficial layer; 2 = depletion of staining and thinning down of the central superficial layer; 3 = severe and mostly complete depletion of staining in the superficial layer .
Data distribution was preliminarily checked by the Kolmogorov-Smirnov test. Serial measurements of clinical scores, body weight, antibody titers, and antibody neutralizing capacity were analyzed considering the area under the curve for each subject as a summary measure; these measures were then analyzed as raw data . According to data distribution and number of groups, a parametric (analysis of variance [ANOVA], t test) or non-parametric (Kruskal-Wallis, Mann-Whitney) test was then performed. Post hoc comparisons were performed with the appropriate test according to data distribution (Student-Newman-Keuls for parametric data and Dunn test for non-parametric data). Clinical score time trend was analyzed by Spearman rho, and 95% confidence intervals (CIs) were given. Histological scores were compared with ANOVA or Kruskal-Wallis and their appropriate post hoc analysis according to data distribution. Differences in antibody titer at different time points were analyzed with repeated measures ANOVA due to normal distribution of data. Incidences of arthritis were compared using Fisher exact test with Yates correction. All statistics were performed with MedCalc statistical software version 10.4.8 (MedCalc Software bvba, Mariakerke, Belgium).
Effect of TNF-K immunization in TTg mice on established arthritis
Histological evaluation of arthritis in human tumor necrosis factor (TNF)-alpha transgenic mice immunized with TNF kinoid
Number of mice
TNF-K (3 injections, sacrifice at week 27)
0.1 ± 0.1a
0.0 ± 0.0a
TNF-K (3 injections without maintenance dose, sacrifice at week 45)
0.6 ± 0.2d
0.2 ± 0.1d
TNF-K (3 injections with maintenance dose, sacrifice at week 45)
0.5 ± 0.1d
0.3 ± 0.1d
Intermittent infliximab (sacrifice at week 45)
1.4 ± 0.1
0.9 ± 0.2
Phosphate-buffered saline (sacrifice at week 27)
1.6 ± 0.1
0.9 ± 0.2
Reversibility of TNF-α blockade
Effect of a maintenance dose
We next investigated whether this flare in arthritis disease could be ameliorated by the administration of a maintenance dose (late boost) of TNF-K. Therefore, seven TTg mice that had received a primary course of three injections of TNF-K were administered a maintenance dose of TNF-K at 32 weeks of age. As a control, the remaining eight TTg mice that had received the primary course were injected with PBS emulsified in ISA-51 adjuvant. The arthritis clinical score curves decreased for mice that received the maintenance dose and increased for the controls (Figure 1a). The differential in clinical scores between the two groups did not reach statistical significance, and this was due to the small sample size related to effect size. (With an alpha error of 0.05 and a beta error of 0.2, a sample size of 22 mice would have been necessary for the detected difference to be statistically significant.) Nevertheless, clinical score time-trend analysis with Spearman rho showed a reduction of the scores for maintenance-dosed mice (ρ = -0.249, 95% CI -0.448 to -0.026, P < 0.05) and a deterioration for controls (ρ = 0.405, 95% CI 0.214 to 0.567, P < 0.05), supporting the efficacy of a maintenance dose of TNF-K in treating the late flare of arthritis (Figure 3b, c).
Histological inflammation and destruction were assessed at 45 weeks of age (Table 1). All of the immunized animals exhibited mild signs of histological inflammation and destruction of ankle and knee joints. As with the clinical scores, the differences between immunized animals that received the maintenance dose and those that did not were not statistically significant (Table 1).
We also compared the clinical efficacy of TNF-K active immunization with infliximab intermittent treatment on arthritis of TTg mice over this 18-week extension period. No statistically significant difference was detected between the two treatments (Figure 1a). However, as would be expected, the clinical scores of the infliximab group deteriorated over time since treatment was withdrawn at 27 weeks of age (Figure 3d).
We further examined the histology of infliximab intermittent-treated TTg mice sacrificed at 45 weeks of age. All of the mice from this group, treated with infliximab during 12 weeks, had developed severe inflammation and exhibited mild cartilage destruction of the joints 18 weeks after the infliximab withdrawal (Table 1 and Additional file 1). By comparison, TNF-K immunized animals, receiving or not receiving the maintenance dose, showed lesser inflammation and cartilage destruction compared with the infliximab group (P < 0.05) (Table 1).
Anti-TNFα antibodies after TNF-K immunization
B-memory response against TNF-α after TNF-K immunization
In the present study, we show in a long-term follow-up that TNF-K immunization dramatically improves the disease status of clinically established arthritis. When the active immunization was administered after the onset of active disease, its beneficial effect, mediated by the production of a high titer of neutralizing anti-hTNF-α antibodies, was evident both in clinical symptoms and in the histological indicators for arthritis. Additionally, in these experiments, we evaluated the effect of TNF-α blockade over a long-term period and showed the long-lasting efficacy and the reversible effect of TNF-K immunization. Moreover, we present evidence that no B-cell memory response to native hTNF-α was induced by TNF-K immunization.
Active immunization has previously shown its efficacy in several experimental models of human autoimmune diseases, as well as other pathologies, using cytokines cross-linked to virus-like particles of the bacteriophage Qβ [13, 20, 21] or complexed with KLH (kinoids) [16, 22, 23]. The numerous clinical trials that have been performed or that are under way support both the feasibility and the safety of the use of active immunization against self-proteins in humans [24, 25, 26, 27].
Major questions with our active anti-cytokine immunotherapy targeting TNF-α, a pleiotropic cytokine, are the depth and the duration of the TNF-α inhibition . In contrast with the previous studies, the present one has been performed with a long-term clinical follow-up (over a 36-week period). Importantly, our present data show a decrease in anti-hTNF-α neutralizing antibodies after a peak 8 weeks after immunization. At the same time, comparisons of histological scores of TNF-K-treated animals at week 27 and week 45 showed a slight progression over time of arthritides. These data support the hypotheses of both residual hTNF-α activity and the reversibility of the blockade of hTNF-α in vaccinated animals. Furthermore, a maintenance dose given 17 weeks after treatment initiation both increased the anti-hTNF-α neutralizing antibodies and ameliorated the course of disease, demonstrating that the immune system remains responsive to TNF-K immunization.
In the present study, we have also demonstrated the B-memory response to hTNF-α after TNF-K vaccination. When we stimulated the immune system of TNF-K immunized transgenic mice, we demonstrated that IP injection of KLH dramatically induced the production of new anti-KLH antibodies. This B-cell memory response to KLH was not accompanied by any increase of anti-hTNF-α neutralizing antibody titers. Furthermore, injections of native autoantigen hTNF-α after active immunization with TNF-K against hTNF-α did not induce the production of new neutralizing anti-hTNF-α autoantibodies, demonstrating no B-cell memory response to native hTNF-α. These data suggest that in physiopathological situations in which native hTNF-α production would be stimulated (for example, infections), it would not be thwarted by an immunization with TNF-K performed a long time before. Taken together, these data are consistent with the transient production and effect of neutralizing anti-hTNF-α antibodies after TNF-K immunization.
Finally, we demonstrated that TNF-K and infliximab have comparable efficacy measured by clinical parameters in our model. Moreover, once infliximab weekly injections were discontinued (at 27 weeks of age), infliximab-treated mice exhibited a worsening of arthritides over time following the withdrawal of infliximab. Histopathological scores of these animals were significantly higher than those of TNF-K immunized mice, with or without late maintenance dose.
Our data show that active immunotherapy with TNF-K induced a long-lasting improvement in an RA model. The occurrence of a disease flare in previously immunized mice, the bell-shaped neutralizing anti-hTNF-α antibody curve, the increase of anti-hTNF-α neutralizing antibodies after a maintenance dose, and the absence of evidence of in vivo B-cell memory response to native hTNF-α are all elements supporting a favorable benefit-risk ratio for such a strategy and a transient response against hTNF-α after TNF-K immunization. Further studies should be performed to evaluate the risk of infections or tumors under TNF-K treatment in dedicated models since their occurrences are a matter of debate in patients treated with passive immunotherapies against TNF-α [28, 29].
We thank Gaelle Clavel for her invaluable help with histological interpretation and Monique Etienne and Simone Béranger (University of Paris 13), Stéphane Chambris (animal facilities, University of Paris 13), and Moufida Mahmoud Bacha (EA4222, Li2P, University of Paris 13) for their outstanding technical assistance. LD was the recipient of a studentship from Arthritis-Foundation and from Fondation pour la Recherche Médicale. This work also received financial support from Neovacs SA (Paris, France), Debiopharm SA (Lausanne, Switzerland), Agence Nationale de la Recherche (ANR), Institut National de la Santé et de la Recherche Médicale (INSERM), the Paris 13 University, and the Société Française de Rhumatologie (SFR).
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