This uncommissioned systematic review was subject to full peer-review.
Systematic review: antibodies and anti-TNF-α levels in inflammatory bowel disease
Article first published online: 22 MAR 2012
© 2012 Blackwell Publishing Ltd
Alimentary Pharmacology & Therapeutics
Volume 35, Issue 9, pages 971–986, May 2012
How to Cite
Chaparro, M., Guerra, I., Muñoz-Linares, P. and Gisbert, J. P. (2012), Systematic review: antibodies and anti-TNF-α levels in inflammatory bowel disease. Alimentary Pharmacology & Therapeutics, 35: 971–986. doi: 10.1111/j.1365-2036.2012.05057.x
- Issue published online: 2 APR 2012
- Article first published online: 22 MAR 2012
- Manuscript Accepted: 21 FEB 2012
- Manuscript Revised: 20 FEB 2012
- Manuscript Revised: 4 MAY 2011
- Manuscript Received: 29 APR 2011
The associations between clinical efficacy and infusion reactions with anti-TNF-α drug levels and the presence of antibodies against the drug have been described. However, the clinical utility of these tests in routine clinical practice remains unclear.
To examine the clinical significance of the development of antibodies against anti-TNF-α drugs and the relationship between the efficacy of these drugs and their serum levels. We also studied the clinical utility of testing for anti-TNF-α antibodies and measuring drug serum levels to optimise treatment of patients with inflammatory bowel disease (IBD) receiving these agents.
A systematic review was undertaken based on electronic searches of the PubMed database from the earliest record to February 2012. The reference lists of all relevant articles and abstracts from meetings were also consulted.
We observed a close relationship between trough levels of anti-TNF-α drug and maintenance of response to these drugs. The role of antibodies in loss of response seems to be limited to their effect favouring the clearance of the drug. The risk of infusion reactions, but not of delayed hypersensitivity reactions, is higher in patients with antibodies against the anti-TNF-α drug. Testing anti-TNF-α drug and antibody levels, together with clinical and endoscopic or radiological assessment, seems useful when attempting to optimise therapy and prevent inappropriate management of IBD patients.
Measurement of serum anti-TNF-α trough levels and antibody titres could prove useful in therapeutic drug monitoring in IBD patients treated with anti-TNF-α agents.
Tumour necrosis factor alpha (TNF-α) plays a pivotal role in the pathogenesis of several chronic inflammatory disorders, such as inflammatory bowel disease (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC). The introduction of infliximab, a chimeric monoclonal immunoglobulin G1 antibody against TNF-α that induces and maintains clinical remission in patients with moderate to severe IBD created new perspectives for the management of these disorders.[2, 3] Unfortunately, up to 40% of patients who respond to infliximab need multiple dose adjustments to maintain a clinical response in the long term.[3, 4]
The development of antibodies against anti-TNF-α drugs and low serum concentrations of the drug have been implicated as predisposing factors for therapeutic failure. Although the associations between clinical efficacy and infusion reactions with anti-TNF-α drug levels and the presence of antibodies against the drug have been described, the clinical utility of these tests in routine clinical practice remains unclear.
This review aims to understand the clinical significance of the development of antibodies against anti-TNF-α drugs and the relationship between the efficacy of these drugs and their serum levels. It also investigates the clinical utility of testing anti-TNF-α antibodies and serum anti-TNF-α concentrations for optimising the treatment of IBD patients receiving these therapies.
Bibliographical searches were performed in PubMed from the earliest records to February 2012 using the following key words (all fields): (antibody OR antibodies OR immunogenicity OR ‘serum levels’) AND (anti-TNF OR TNF-alpha OR TNF-α OR infliximab OR adalimumab OR certolizumab). The references from the articles selected for the study were also examined in search of articles meeting the inclusion criteria. Relevant abstracts and other material from meetings were investigated. Studies on the use of anti-TNF-α drugs in other diseases were included if relevant information was reported.
Role of TNF-α in chronic inflammatory diseases
TNF-α is a cytokine that plays a major role in several chronic inflammatory disorders, including rheumatoid arthritis, ankylosing spondylitis, psoriasis, and IBD. An animal model based on dysregulated TNF-α release revealed chronic inflammatory arthritis and Crohn-like IBD.
TNF-α is generated as a 26-kDa transmembrane type II polypeptide precursor (tmTNF) that is expressed on activated macrophages, T-lymphocytes, natural killer cells, and, to a lesser extent, non-immune cells, such as endothelial cells, smooth muscle cells, keratinocytes, and neurons.[6-8] Cleavage of tmTNF-α by TNF-α converting enzyme releases soluble TNF-α (sTNF-α). TNF-α exerts its effects both as a transmembrane protein (tmTNF-α) and as a soluble homotrimeric cytokine (sTNF-α).
TNF-α binds to the TNFR1 and TNFR2 receptors, which can be expressed both as transmembrane receptors and as soluble receptors. TNF-α receptors diverge in their cellular expression and, although they share structural homology in their extracellular TNF-binding domains, they induce different cytoplasmic signalling pathways. These receptors are expressed on the cell surface in response to various stimuli. At rest, they are shed from the cell surface or internalised into the cell (thus becoming inactivated).
sTNF-α preferentially binds TNFR1, which activates intracellular signalling pathways that mediate apoptosis. By contrast, tmTNF-α has a greater affinity for TNFR2, which is produced in larger amounts than TNFR1 and may serve to capture TNF-α for subsequent processing by TNFR1. TNFR2 activates NF-κβ and protects against caspase 8–mediated induction of apoptosis. TNFR2 or structurally similar receptors are promoted by mycobacteria to promote their survival, suggesting that TNFR2 plays an important in vivo role in maintaining cell life and preventing apoptosis of activated inflammatory cells. Anti-TNF-α drugs act by controlling inflammation in IBD and in other chronic inflammatory disorders in which TNF-α plays a major role through different mechanisms.
Structure of anti-TNF-α monoclonal antibodies
Recombinant monoclonal antibody technology was used to develop the first generation of anti-inflammatory biological agents directed at neutralising TNF-α, and, in 1998, the US Food and Drug Administration (FDA) approved the use of infliximab for the treatment of CD.
Infliximab (Remicade; Janssen Biotech Inc., Great Valley Parkway Malvern, PA, USA) is a recombinant monoclonal antibody of the IgG1 kappa subclass composed of 25% murine and 75% human sequences. It has a variable murine Fab′ region linked by bisulfide bonds to the human IgG1:κ constant region. The results of clinical trials in patients with rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis have revealed the presence of antibodies against the anti-TNF-α molecule, which could block the drug and thus decrease its clinical efficacy. These findings were confirmed in trials with CD patients and led to the creation of a fully human anti-TNF-α molecule that prevented immunogenicity and formation of antibodies that could interfere with the drug's clinical efficacy and safety. However, as all exogenous proteins have the potential to induce immunogenicity, the notion that fully human proteins might be non-inmunogenic is unfounded.
Adalimumab (Humira; Abbott Laboratories SP, Abbott Park, Chicago, IL, USA) is also a recombinant monoclonal antibody, although it is fully humanised, with human-derived variable regions and a human IgG:κ constant region.
Certolizumab pegol (Cimzia; Samera GmbH, Kundl, Austria) contains the Fab′ fragment of a humanised anti-TNF-α monoclonal antibody. To increase its plasma half-life and prevent interference, the Fab' fragment was attached to a polyethylene glycol moiety consisting of two 20-kDa branches at a free cysteine residue far removed from the antigen-binding site.
In addition to their direct TNF-α inhibitory effects, infliximab and adalimumab have a direct cytotoxic and apoptotic action. These effects have not been reported for certolizumab, which lack the constant region of human IgG1:κ Fc. Infliximab, adalimumab, and certolizumab have been approved for CD (certolizumab in the US but not in Europe). Infliximab is the only anti-TNF-α approved for the treatment of UC.
Anti-TNF-α drugs bind specifically to sTNF-α and tmTNF-α, thus preventing them from binding to their receptors, TNFR1 and TNFR2. Infliximab and adalimumab were shown to induce apoptosis by reverse signalling in peripheral blood monocytes, leukaemia cells, and lamina propria T cells, whereas certolizumab did not. Each of the antagonists is known to reduce TNF-α levels, whereas infliximab and adalimumab also decrease serum IL-6 and acute phase reactants, such as C-reactive protein.
Immunogenicity of anti-TNF-α monoclonal antibodies
Immunogenicity is the potential of an antigen to induce an immune response after being recognised by T and B lymphocyte receptors. Antibodies to anti-TNF-α may be released in genetically susceptible patients in response to the IgG1 human components. As previously described, the presence of antidrug antibodies can impede the clinical response by affecting the drug's bioavailability, pharmacokinetics, and pharmacodynamics. In some cases, the clinical efficacy of anti-TNF-α may not be affected by the presence of antibodies against the drug, probably because they have low affinity with the drug or fail to interact with it. Some studies have reported that concomitant treatment with immunosuppressive drugs, such as azathioprine or methotrexate, may decrease the formation of antibodies and increase levels of anti-TNF-α drugs, although the exact mechanism is not clearly understood.
Antibodies against anti-TNF-α drugs have been associated with acute infusion reactions, which occur within 1–2 h of administration and include fever, nausea, breathlessness, and headache. No association has been found between antibodies against anti-TNF-α drugs and delayed hypersensitivity reactions, which occur 3–12 days after infusion and are characterised by myalgia, arthralgia, pruritus, facial or peripheral oedema, sore throat, and headache.
The variable murine region of infliximab is thought to be the antigenic component that induces the formation of antibodies to infliximab. The true incidence of antibody formation in IBD patients treated with infliximab remains unknown, because of the different administration schedules (episodic vs. scheduled therapy), as well as technical factors associated with timing of antibody determination. The incidence of antibody formation is very high in episodic treatment (36–61%) and low in maintenance schedules (5–18%). A subanalysis from the ACCENT I study showed that, at week 72, the proportion of patients with antibodies against infliximab was higher in the group treated with episodic infliximab than in the groups of patients on scheduled maintenance therapy with 5 and 10 mg/kg (30%, 10% and 7%, respectively), indicating that a single dose of infliximab generates more immunogenicity than scheduled treatment.
Much in the same way as infliximab, adalimumab can induce the formation of antibodies in some patients. As most clinical trials do not report the presence of antibodies to adalimumab, this rate is less frequently reported than that of infliximab. Karmiris et al. reported that 9.2% of CD patients receiving adalimumab developed antibodies against adalimumab and these were associated with lower trough serum levels of the drug. Additional clinically relevant data from three rheumatoid arthritis studies show that approximately 5% of patients developed antibodies to adalimumab that subsequently neutralised the in vitro adalimumab.
Approximately 12% of CD patients treated with certolizumab develop antibodies to the drug. The clinical impact of these antibodies remains unknown.
Patients who do not respond to or lose response to an anti-TNF-α drug may be successfully treated with a different anti-TNF-α drug. Of note, some studies have shown that the antibodies developed against one of the anti-TNF-α agents are very specific and do not affect the bioavailability of a subsequent anti-TNF-α drug. However, studies in patients with rheumatoid arthritis have shown that the risk of developing antibodies against one anti-TNF-α is higher in patients who have developed antibodies to a previous anti-TNF-α drug. Evidence suggests that this does not apply to IBD patients.
Determination of anti-TNF-α drug concentrations and antibody titers
The methods used to detect anti-TNF-α drug concentrations and anti-TNF-α antibody concentrations are based on enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay.
ELISA uses specific antibodies for capture and detection. The antibody binds to the antigen through one of its Fab arms and then binds to the conjugate (biotinylated anti-TNF-α drug) through its other Fab arm. ELISA has been used in most clinical trials due to its simplicity, which is its main advantage, although it is less specific. Both infliximab and adalimumab and antibodies against these drugs are predominantly IgG. Therefore, ELISA can detect other antibodies against human proteins, such as rheumatoid factor or antibodies against haplotypes, which interfere in the determination of quantification of anti-TNF-α drug concentrations and antibody titers. Kappa light chains of infliximab also interfere in measurement, thus increasing the likelihood of false-negative results. Antibodies to anti-TNF-α drugs bind with anti-TNF-α molecules in serum to form immunocomplexes that cannot be detected by ELISA. Under these circumstances, the test may show false-negative results.[26, 27] Some new methods are being developed to improv the accuracy of the ELISA, as fluid-phase enzyme immunoassay, but the experience with them is scarce.
Radioimmunoassay is more sensitive and specific than ELISA, and radioisotopes make it more complex; however, it offers greater sensitivity, does not interact with other immunoglobulins such as rheumatoid factor, can detect IgG4 that are functionally monovalent (only bound to an ‘antigen’), and is less susceptible to artefacts from neo-epitope formation. Its main drawback, besides its technical complexity, is the scarce information on its clinical potential, as it has not been assessed in clinical trials evaluating the efficacy and safety of anti-TNF-α drugs (only two small-scale studies have been performed[15, 29]).
Timing of measurement of concentrations of anti-TNF-α drugs and antibodies against anti-TNF-α drugs
The presence of detectable serum levels of anti-TNF-α drugs interferes with the determination of antibody titers using current methods. The drug binds to antibodies to form immune complexes that cannot be detected by ELISA. When antibody levels are detectable, we can be sure that they are positive regardless of the serum levels of the anti-TNF-α drug. However, when antibody levels are negative, it is necessary to know exactly what the levels of the anti-TNF-α drugs are: if anti-TNF-α serum levels are undetectable, the result is a true negative, but if anti-TNF-α serum levels are detectable and antibody levels are negative, the result is considered inconclusive, because it might be a true negative result or a false negative result if the antibodies have bound to the anti-TNF-α drug. Therefore, with current measuring methods, we should determine anti-TNF-α drug levels when antibody titres are measured to enable further interpretations.
In this sense, determinations should be made when the drug level is expected to be lowest (trough level), namely, just before the following administration. As this determination is required to interpret antibody titres, trough level has been used in most studies and has proven to be a predictor of response to treatment.[20, 21]
Clinical significance of antibodies against anti-TNF-α drugs
Estimating the clinical significance of immunogenicity and serum levels of anti-TNF-α drugs is difficult, because of the many different ways of presenting and interpreting results. Data can be reported in terms of presence of antibody (positive, negative or indeterminate), concentration (high or low), threshold (above or below an arbitrary cut-off point such as 8 μg/mL), clinical effect (also heterogeneously defined), and safety (infusion reactions). In most cases, the threshold for drug levels is the lowest concentration that the testing method can detect. In the case of infliximab, the most common threshold is 1.4 μg/mL, which is the lowest detection limit of the kit manufactured by Prometheus Laboratories (San Diego, CA, USA). An antibody titre is considered positive if it is above the detection limit and negative if it is below the detection limit and infliximab serum levels are undetectable (antibody levels below 1.69 μg/mL with infliximab serum levels below 1.4 μg/mL, in the case of the Prometheus Laboratories kit). When infliximab serum levels are more than 1.4 μg/mL, the results are considered inconclusive, because the circulating infliximab interferes with the antibodies against the drug and, therefore, with measurement.
Tables 1, 2 and 3 summarise the studies assessing the impact of antibodies against anti-TNF-α drugs in efficacy and safety. Most trials with infliximab administered in episodic regimens to patients with IBD report that the presence of antibody is associated with secondary loss of response.[29-31] However, this has not been confirmed by studies with scheduled regimens, probably because when infliximab is administered in its scheduled regimen, circulating drug can interfere with the antibody assay. However, it is an important message to note that antibodies are not always associated with a loss of response.
|Authors||N||Regimen of administration||Follow-up (median)a||Patients with ATI||Infliximab serum levels||Impact of ATI on safety||Impact of ATI on efficacy||Impact of ATI oninfliximab levels||Impact of infliximab levels on efficacy|
43% IMM vs. 75% in patients without IMM
|Higher levels in patients with IMM (P < 0.01)|
More reactions in patients with ATI
(OR: 2.4, P < 0.01)
|Shorter duration or response in patients with ATI||Lower levels in patients with ATI||Higher efficacy in patients with levels higher than 12 μg/mL|
|Farrell||53||Episodic||24 months||36%; lower in patients with IMM||Not reported||Positive ATI in all patients with infusional reaction||Not reported||Not reported||Not reported|
|Farrell||80||Episodic||16 weeks||26 vs. 42% with and without premedication P > 0.05||Not reported||Not reported||Not reported||Not reported||Not reported|
|Farrell||44||Episodic||68 infusions||Not reported||Not reported||More infusional reaction in patients with ATI 40 vs. 4.7% P < 0.001||Lower response rate and shorter duration of response in patients with ATI||Not reported||Not reported|
|514||Scheduled (+episodic retreatment)||72 weeks|
10% 5 mg/kg
7% 10 mg/kg
Higher infusion reaction in patients with ATI (OR: 1.8)
No association with delayed reactions
|No association between ATI positivity and remission rate||Lower infliximab levels in ATI positive patients||Not reported|
46 vs. 73% with and without IMM
|IMM did not impact on drug level||Lower infusional reaction rate in patients with IMM||Shorter duration of response in patients with ATI without IMM. No impact on patients with IMM||Lower levels in patients with ATI 7.5 μg/mL vs. 11 μg/mL, P < 0.01||Not reported|
|Ainsworth||33||Episodic||8 weeks after the last infusion||54%||Not reported||Not reported||ATI positive in 100% of patients who lost response vs. 53% in patients who maintained it||Not reported||Not reported|
39% with episodic vs. 16% with scheduled
IMM impacted on ATI formation only in episodics
|IMM did not impact on drug level|
Higher infusional reaction rate in patients with ATI: 50 vs. 21%, P < 0.05
IMM did not impact on it
|No association between ATI positivity and endoscopic improvement||Not reported||Higher proportion of patients with detectable levels achieved clinical remission 82 vs. 6%. P < 0.001|
|Van Assche||80||Scheduled||2 years|
5 vs. 12.5% with and without IMM
P > 0.05
|Not reported||Not reported||No association between ATI positivity and clinical response||Not reported||Lower infliximab levels correlated with higher C reactive protein and higher CDAI score|
|338||Scheduled||30 weeks||0.9 vs. 14.6% with and without IMM||Higher levels with IMM 1.6 vs. 3.5 μg/mL P < 0.01||Not reported||Higher remission rate among patients with inconclusive ATI (due to high infliximab levels)||Not reported||Higher infliximab levels correlated with higher efficacy|
|Yamada||31||Scheduled||2.3 years||Not reported||Not reported||Not reported||Not reported|
Trough levels were similar between patients in remission and those who lost response, but the interval between infusions was significantly shorted in this group
Drug levels after infusion significantly correlated with the maintenance of response
|Afif||155||93% scheduled||50 weeks||14 vs. 29% with and without IMM P < 0.05||Therapeutic levels in 48 vs 21% patients with and without IMM, P < 0.001||No direct comparison|
No direct comparison
17% of ATI positive in patients with loss of response vs. 38% in patients with hypersentitive reactions
Not direct comparison
45% of non-therapeutic levels in patients with loss of response vs. 20% in patients with acute reactions
ATI do not have crossed reaction with adalimumab
|Higher hypersensitive reaction rate in patients with ATI 52 vs. 3%, P < 0.001||More frequency of ATI in patients with complete loss of response 78 vs. 17% P < 0.01||Not reported||Not reported|
|Authors||N||Regimen of administration||Follow-up (median)a||Patients with ATA||Adalimumab serum levels||Impact of ATA on safety||Impact of ATA on efficacy||Impact of ATA on adalimumab levels||Impact of adalimumab levels on efficacy|
|West et al.||30||Scheduled||318 days||17%; in patients without IMM 20% vs. 7.7% in patients with IMM (P > 0.05)||Not reported||Not reported||Presence of ATA related to a nonresponse to adalimumab (OR: 13)||Not reported||Not reported|
|Karmiris et al.||168||Scheduled||20 months||9.2%. The use of IMM had not impact on the ATA development||Higher levels with induction dose of 160/80 mg than with 80/40 mg||No relation was found||Patients with ATA had lower median trough serum concentrations of adalimumab (P < 0.001)|
Patients who discontinued adalimumab had lower adalimumab trough levels (short- and long-term)
Response to dose escalation correlated with the increase in serum levels
Dose escalation was longer among patients with IMM
|Authors||Regimen of administration||N||Follow-upa (median)||Patients with ATI||Anti-TNF serum levels||Impact of ATI on safety||Impact of ATI on efficacy||Impact of ATI onAnti-TNF serum levels||Impact of anti-TNF serum levels on efficacy|
ACT 1 trial
53 no IMM
55 no IMM
|Not reported||Not reported||Not reported||Not reported||Not reported|
ACT 2 trial
53 no IMM
57 no IMM
|Not reported||Not reported||Not reported||Not reported||Not reported|
41% no IMM
|39% detectable||59% patients with infusional reactions had ATI||Presence of ATI had no impact on the efficacy||77% with undetectable level had ATI|
Patients with detectable drug levels had significantly:
Higher clinical remission 69 vs.15%
Higher endoscopic remission 27 vs. 8%
Lower colectomy 7 vs. 55%
|Ferrante||Scheduled||30||35 months||Not reported||Not reported||Not reported||Not reported||Not reported||Higher rate of colectomy in patients with lower drug levels: 33 vs. 17%, P = 0.3 (small sample size)|
|Sandborn||Schedule||245||52 weeks||2.8%||Higher among responders, but no statistical comparison performed||Not reported||Not reported||Not reported||Not reported|
Baert et al. performed a study that included CD patients treated with episodically administered infliximab. Infliximab concentrations and anti-infliximab antibody titres were measured 4 weeks after the last infusion. The authors found that the serum anti-infliximab antibody concentration correlated inversely with the duration of response to infliximab (71 days in patients with anti-infliximab antibodies <8 μg/mL and 35 days in patients with anti-infliximab antibodies >8 μg/mL, P < 0.001). The minimum antibody concentration to be considered positive was a threshold arbitrarily chosen by the authors; therefore, the group with the larger duration of response included patients with both positive and negative anti-infliximab antibodies. This study showed an association between the concentration of anti-infliximab antibodies and the occurrence of infusion reactions – patients with >8 μg/mL had a relative risk of 2.4 – whereas delayed hypersensitivity reactions were unrelated to anti-infliximab antibodies.
Farrell et al. studied 53 CD patients treated with episodic infliximab and stratified them into ‘continuous response’, ‘secondary loss of response’, ‘partial response’, and ‘non-primary response’. The authors found an association between clinical response and the presence of anti-infliximab antibodies: none of the patients with a ‘continued response’ showed anti-infliximab antibodies, whereas 73% of patients with ‘secondary loss of response' developed them (P < 0.01). The predictive value of the presence of anti-infliximab antibodies was assessed in a subgroup of 44 patients. The authors found that the presence of anti-infliximab antibodies was a predictor of nonresponse to subsequent infusions; however, these results were from a post hoc analysis, so the clinical relevance of the findings remains unknown. Among these 44 patients, those who had anti-infliximab antibodies had a significantly higher incidence of infusion reactions (40% vs. 5%, P < 0.01). The presence of anti-infliximab antibodies >8 μg/mL before a subsequent infusion predicted a fourfold higher risk of serious infusion reactions.
As for scheduled maintenance regimens, the ACCENT I study did not stratify efficacy results according to the presence of anti-infliximab antibodies. The median infliximab trough concentration was lower in patients with anti-infliximab antibodies than in those with negative or inconclusive anti-infliximab antibodies. A subanalysis of the ACCENT I trial showed that the clinical response was similar in patients with and without anti-infliximab antibody (64% vs. 62%) and remission (41% vs. 39%) at week 54; therefore, no relationship was found between response to treatment and the presence of anti-infliximab antibodies. Among patients who were randomised to placebo, the response rate was slightly lower in those with anti-infliximab antibodies than in those who were anti-infliximab antibody–negative or –inconclusive, although the difference was not statistically significant. Regarding safety, the authors found that anti-infliximab antibodies were associated with a 12% absolute increase in infusion reactions, although the positive predictive value of anti-infliximab antibodies for an infusion reaction was only 36%.
Maser et al. performed a study on CD patients, most of whom were on scheduled maintenance treatment with infliximab. They found no difference in the duration of clinical response in patients with detectable infliximab serum levels with or without anti-infliximab antibodies (66% vs. 67%).
Steenhold et al. evaluated the potential usefulness of measurements of anti-infliximab antibodies to predict infusion reactions. They included 315 patients, 8% had had acute infusion reactions. The authors found that acute severe infusion reactions to infliximab were associated with circulating anti-infliximab IgG antibodies and therefore resemble a type 3 hypersensitivity reaction. Risk of reaction was particularly high at second infusion in retreatment series. However, negative anti-infliximab antibodies before retreatment did not rule out acute severe infusion reactions. The authors pointed out that it remains to be tested if anti-IFX antibodies measurements following first infusion in a new series can identify patients at risk.
In conclusion, the presence of antibodies against anti-TNF-α drugs does not seem to directly affect the duration of the response to therapy. The risk of infusion reactions, but not the risk of delayed hypersensitivity reactions, is higher in patients with antibodies against the anti-TNF-α drug.
Clinical significance of serum trough levels of anti-TNF-α drugs
Serum drug levels are monitored at regular intervals to optimise treatment and avoid adverse events in the case of drugs, such as cyclosporin, tacrolimus, and, more controversially, the metabolites of 6-tioguanine. Here, we review the clinical significance of trough levels of anti-TNF-α in relation with clinical response (Tables 1, 2 and 3).
In the study by Baert et al., infliximab serum levels were measured 4 weeks after infusion (as patients were on episodic treatment, trough levels could not be measured). Patients with an infliximab concentration >12 μg/mL (threshold for the therapeutic range, as established by the authors) had a significantly longer duration of response after infusion than patients with lower concentrations (81.5 days vs. 68.5 days, P < 0.01).
The multivariate analysis by Maser et al. confirmed this finding, showing that a detectable trough serum concentration of infliximab alone was a significant positive predictor of clinical remission [odds ratio (OR), 38; 95% confidence interval (CI), 9–60, P < 0.001] and endoscopic improvement (OR, 23; 95% CI, 4–124, P < 0.001). An analysis of the COMMIT study found similar results, showing that patients with detectable infliximab concentration at trough were more likely to achieve treatment success than patients with undetectable trough levels, although this difference was not statistically significant.
An association between infliximab trough concentrations and mucosal healing was seen in an analysis of 210 CD patients. Patients with mucosal healing had the highest trough levels followed by those with partial healing. Patients without healing had the lowest median trough levels.
Ainsworth et al. used radioimmunoassay to assess the relationship between serum levels of anti-infliximab antibodies, functional infliximab levels (capable of binding to TNF-α), and clinical response in 33 CD patients treated with infliximab and found that functional levels of infliximab were significantly higher in patients with sustained response than in those who lost response over time (2.9 μg/mL vs. 0 μg/mL, P < 0.01). Interestingly, patients who did not initially respond to infliximab had negative antibody titres and high functional infliximab concentrations (30 μg/mL), suggesting that TNF-α did not play a major role in the maintenance of inflammation in these patients.
Yamada et al. studied 31 CD patients on scheduled maintenance treatment with infliximab. The median trough levels were not significantly different between patients who maintained response and patients who lost response and, therefore, had shorter intervals between infusions. This might suggest faster infliximab clearance in patients with loss of response. In a novel approach, these authors also measured serum infliximab levels immediately after infusion and found that the group who had lost response had lower infliximab levels than those who remained in remission (126 vs. 149, P = 0.04), even though the intervals between infusions had been shortened.
Drastich et al. published a study in abstract form, including 100 CD patients (52 under infliximab and 48 under adalimumab therapy) to determinate the association between infliximab and adalimumab trough levels and the presence of deep remission. They found that infliximab but not adalimumab serum trough level was good predictor of deep remission in CD patients.
An analysis of adalimumab trough concentrations from the CLASSIC I and II studies found slightly higher mean concentrations in patients who achieved remission after induction and during maintenance treatment than dose who did not. However, the analysis of remission status at different serum concentration threshold values was not able to find a concentration that would distinguish patients by remission status.
This association between clinical efficacy and anti-TNF-α drug serum levels has also been confirmed in UC. Seow et al. studied 115 active UC patients who received at least three induction infusions of infliximab; patients responding to induction received infliximab at scheduled intervals of 8 weeks. Infliximab concentrations and anti-infliximab antibody titres were evaluated in 108 patients from serum samples drawn immediately before the infusion of infliximab or 8 weeks after the last dose of infliximab in the event of early discontinuation. The authors analysed the relationship between trough infliximab levels and clinical outcome and found that patients with a detectable serum infliximab concentration had higher rates of clinical remission and endoscopic improvement and a lower rate of colectomy than those in whom trough serum infliximab was undetectable. However, the authors did not find differences in the rate of remission, endoscopic response, or colectomy between patients with positive anti-infliximab antibody titres and patients with negative anti-infliximab antibody titres. However, the rate of remission and response was higher and the percentage of colectomy lower among patients with inconclusive antibody titres, probably as a result of the higher serum infliximab levels in this group.
The multivariate analysis revealed an undetectable level of infliximab and a baseline Mayo score ≥10 to be predictors of colectomy. These results highlight the impact of having undetectable infliximab serum levels on the outcome of UC patients.
Data on the significance of anti-adalimumab antibody titres and adalimumab serum levels are scarce, and the pivotal studies provide little information. Studies from patients with psoriatic arthritis and rheumatoid arthritis show that observations with this drug are similar to those with infliximab. Van Kuijk et al. performed a study of 22 patients with psoriatic arthritis treated with adalimumab. Four patients (18%) developed anti-adalimumab antibodies and had lower adalimumab trough levels, suggesting that anti-adalimumab antibodies may partly explain the greater clearance of the drug through the formation of immune complexes. The authors concluded that a proportion of patients develop antibodies against adalimumab and that these antibodies are associated with lower drug concentrations and diminished response to treatment.
Karmiris et al. analysed the effect of trough serum concentrations and anti-adalimumab antibodies on the clinical outcome of 168 CD patients and found that discontinuation of adalimumab due to loss of response was directly related to low adalimumab trough serum concentration, which was observed more frequently in patients who developed anti-adalimumab antibody titres, suggesting that the antibodies could favour clearance of the drug. In patients who lost response, the dose was escalated to 40 mg/week. After escalation, adalimumab trough concentrations increased (4.8–9.4 μg/mL, P < 0.01), and this increase correlated well with the clinical response to escalation (5.9 μg/mL in responders vs. 0 μg/mL in non-responders, P < 0.001).
Similar findings were observed by Vermeire et al. The authors included 86 CD patients who had lost response to maintenance infliximab and underwent dose adjustments. The median infliximab trough level when patients were in remission was 1.34 μg/mL, and this decreased to 0.95 μg/mL when they lost response. After adjustment, the median trough levels increased significantly throughout the group. The dose adjustment was clinically successful in 55% of patients and was correlated with a significant increase in trough levels (2.25 μg/mL vs. 3.43 μg/mL, P < 0.01), whereas no increase was observed in patients with no clinical response. The authors concluded that there is large inter-individual variability in infliximab levels, so the therapeutic threshold concentration cannot be established. The loss of response to infliximab was associated with a decrease in infliximab trough levels and the dose escalation led to a significant increase in infliximab serum levels only among patients who recovered response after application of this strategy.
Three recent studies published in abstract form have tried to estimate the optimal trough concentration of infliximab in both CD and UC. The first one, by Lamblin et al., included 44 CD patients and estimated, based on a concentration-effect relationship model, that the optimal trough concentration might be around 5 μg/mL. The second one, by Arias et al., included 135 UC patients. The authors calculated the area under the ROC curve of infliximab trough level after 14 weeks of treatment, that was 0.6. The best cut-off value was 7.19 μg/mL, with 80% specificity and 57% sensitivity for sustained benefit under infliximab therapy. The third one, by Bortlik et al., included 84 CD patients; in the multivariate analysis only the trough levels of infliximab had impact in the sustained response. The best cut-off point estimated by these authors was 3 μg/mL, with a positive and negative predictive values of 85% and 45%, respectively.
In conclusion, the aforementioned data demonstrate a close relationship between trough levels of anti-TNF-α drugs and maintenance of response. However, the threshold for therapeutic concentration cannot be established yet. The role of antibodies against the drug in the loss of response seems to be limited to its effect favouring the clearance of the drug.
Utility of measuring anti-TNF-α drug concentrations and antibody titres in clinical practice
Only one study has evaluated the usefulness of measuring drug and antibody levels in clinical practice in IBD patients treated with anti-TNF-α drugs. In their retrospective study, Afif et al. examined 155 IBD patients (78% CD) who had been treated with infliximab and had undergone testing at their physicians' discretion to determine the association between infliximab and anti-infliximab antibody concentration. The authors retrospectively evaluated the reason for testing, the rationale for changing treatment after testing, the response to treatment changes, and the clinical utility of testing.
One hundred and seventy-seven determinations were performed, and the results had an impact on clinical decisions in 130 cases. Among patients with detectable antibody titres, changing to another anti-TNF-α drug led to response or remission in 92% of cases. By contrast, dose escalation produced a response in only 17% of patients with detectable antibodies, and none reached therapeutic levels of infliximab in successive determinations.
Among patients with sub-therapeutic levels of infliximab, 86% responded after dose escalation, while only 33% responded after switching to another anti-TNF-α drug. Among patients with clinical symptoms despite having detectable levels of infliximab, endoscopic or radiological examinations did not show evidence of inflammation in 62% of cases, and 76% continued the same treatment. Thirty-eight per cent (eight patients) showed inflammatory activity despite having detectable levels of infliximab.
This study was limited by its retrospective nature and lack of standard assessments of disease activity. The investigators selected the cohort according to their own criteria. The study lacked a control group to know whether the outcome of patients would have been different – worse – in the case of having made decisions without knowing drug levels or antibody titres. Therefore, the results should be interpreted with caution. Nonetheless, these results represent a first step towards individualised treatment of IBD patients.
The TAXIT trial, ‘A prospective controlled trough level adapted infliximab treatment trial’, which is currently ongoing, aims to investigate the value of the invidualised treatment with infliximab based on therapeutic drug monitoring. The results of this controlled study will show whether the long-term adjustment of the treatment based on infliximab levels is a superior strategy.
Optimising anti-TNF-α therapy in patients with IBD
Up to 40% of patients who initially respond to treatment with anti-TNF-α drugs will subsequently lose response. Management of these patients remains largely empiric, and strategies include dose escalation or shortening of infusion intervals, changing to another anti-TNF-α drug, or switching to another treatment group with a different therapeutic target.[48-51] A decision analysis based on a theoretical model suggested that dose escalation yields more quality-adjusted life years than switching to another anti-TNF-α drug; however, the cost is considerable. This empiric strategy likely leads to intensification of therapy in patients with antibodies against the drug who would have obtained a greater benefit by switching to another anti-TNF-α drug. The information provided by the determination of trough levels of the drug and antibodies could aid decision making in the case of loss of response and perhaps in preventing it in the future.
Figure 1 shows three clinical scenarios depending on the serum levels of antibodies and drugs in IBD patients who do not show an initial response, patients with a partial response, and patients with a loss of response.
Low drug trough levels with detectable antibodies
Antibodies can prevent the drug from entering the bloodstream, enhance clearance through immune complex formation with precipitation in vessels and clearance in the spleen, prevent the drug from entering sites of inflammation, or neutralise the ability of the drug to inhibit TNF-α. All result in an insufficient capacity to block TNF-α and control disease activity. Afif et al. showed that switching to another anti-TNF-α drug was more effective than dose escalation (92% vs. 17%, P < 0.004). This finding suggests that escalation in patients who have antibodies against an anti-TNF-α drug is less likely to succeed than switching to another anti-TNF-α drug.
Low drug trough levels without antibodies
The low drug trough levels can result from altered kinetics due to low bioavailability or decreased half-life in the bloodstream, for example, due to high consumption in severe disease. In such cases, dose escalation has been associated with a greater response than switching to another anti-TNF-α drug. Consequently, patients would theoretically benefit from administration of an increased amount of the currently used anti-TNF-α drug. This seems to be a more rational approach than switching to another anti-TNF-α drug.
High drug trough levels
If the patient has clinical symptoms, radiological and endoscopic examinations could confirm that symptoms are related to the presence of inflammation. If therapeutic anti-TNF-α drug concentrations are present and there is persistent disease, then increasing the dose of the anti-TNF-α or switching to another drug with the same mechanism of action (anti-TNF-α) would provide little benefit, and consideration should be given to switching to a medication with a different mechanism of action.
Anti-TNF-α drugs are increasingly used in the treatment of patients with IBD. A significant proportion of patients lose response to treatment over time, and this is a cause of concern for physicians, since in most cases, these agents are a ‘last resort’. Several strategies can be undertaken in cases of loss of response, for example, dose escalation (increasing the dose or shortening the interval), switching to another anti-TNF-α drug, or changing to another treatment group. The decision as to which is the best option for the management of these patients remains largely empiric. Evidence from studies suggests that measurement of anti-TNF-α trough serum levels and antibody titres could prove useful in therapeutic drug monitoring in IBD patients. The best treatment strategy is prevention based on early assessment of pharmacokinetic parameters and immunogenicity. Future strategies in difficult-to-treat patients will be based on a combination of immunosuppressants, pretreatment with hydrocortisone when antibodies are present, endoscopic and radiological examinations when necessary, and biological and genetic studies.
Declaration of personal interests: Dr M. Chaparro has served as a speaker and has received research funding from MSD and Abbott. Dr I. Guerra and P. Muñoz have nothing to declare. Dr P. Gisbert has served as a speaker, a consultant and advisory member for, and has received research funding from MSD and Abbott. Declaration of funding interests: None.
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