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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Objective

To describe a new systemic lupus erythematosus (SLE) responder index (SRI) based on a belimumab phase II SLE trial and demonstrate its potential utility in SLE clinical trials.

Methods

Data from a randomized, double-blind, placebo-controlled study in 449 patients of 3 doses of belimumab (1, 4, 10 mg/kg) or placebo plus standard of care therapy (SOC) over a 56-week period were analyzed. The Safety of Estrogens in Lupus Erythematosus: National Assessment (SELENA) version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) and British Isles Lupus Assessment Group (BILAG) SLE disease activity instruments, the Short Form 36 health survey, and biomarker analyses were used to create a novel SRI. Response to treatment in a subset of 321 serologically active SLE patients (antinuclear antibodies ≥1:80 and/or anti–double-stranded DNA antibodies ≥30 IU/ml) at baseline was retrospectively evaluated using the SRI.

Results

SRI response is defined as 1) a ≥4-point reduction in SELENA–SLEDAI score, 2) no new BILAG A or no more than 1 new BILAG B domain score, and 3) no deterioration from baseline in the physician's global assessment by ≥0.3 points. In serologically active patients, the addition of belimumab to SOC resulted in a response in 46% of patients at week 52 compared with 29% of the placebo patients (P = 0.006). SRI responses were independent of baseline autoantibody subtype.

Conclusion

This evidence-based evaluation of a large randomized, placebo-controlled trial in SLE resulted in the ability to define a robust responder index based on improvement in disease activity without worsening the overall condition or the development of significant disease activity in new organ systems.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Randomized controlled trials (RCTs) of patients with systemic lupus erythematosus (SLE) are particularly challenging because of the heterogeneity of disease manifestations (1), the waxing and waning course of the disease, the variety of immunomodulating medications used to control disease activity (2, 3), and the lack of a standardized method for defining response. The American College of Rheumatology (ACR), the Food and Drug Administration (FDA), the Outcome Measures in Rheumatology Clinical Trials (OMERACT), the European League Against Rheumatism (EULAR), and clinical experts recommend that SLE clinical trials include outcome measures assessing cumulative organ damage, SLE disease activity, health-related quality of life (HRQOL), and adverse events (3–8). In 1987, members of the Systemic Lupus International Collaborating Clinics (SLICC) initiated an effort to develop a consensus for disease activity indices (DAIs) and outcome measures for RCTs of SLE. Since that time, numerous instruments have been used in SLE clinical studies, including but not limited to the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) (9), the modifications to the SLEDAI that were developed for the Safety of Estrogens in Lupus Erythematosus: National Assessment trial (SELENA–SLEDAI) (10), and the British Isles Lupus Assessment Group (BILAG) instrument (11, 12), their SLE flare indices (13, 14), as well as the SLICC/ACR damage index (15).

The SLEDAI, Systemic Lupus Activity Measure (SLAM), and BILAG have performed in effective and reliable manners in studies; furthermore, they correlate with one another (6, 16, 17). The SLEDAI, SELENA–SLEDAI, SLEDAI 2000 update (SLEDAI-2K) (18–21), and BILAG (11, 12, 22) have been successfully used in observational trials and case studies, although baseline DAI scores were not always predictors of subsequent damage or other outcomes (23, 24). These DAIs were validated in the context of long-term observational studies and not in RCTs (3, 6, 7, 9, 12, 22). The few RCTs conducted have shown that improvement in DAI scores correlated with response rates, disease remission, and flare prevention (3, 6, 25, 26). However, a threshold of clinically meaningful change has not been established in studies performed with the investigational agents anti–CD40 ligand antibody (27), dehydroepiandrosterone (28), abetimus sodium (29), mycophenolate mofetil (30), or rituximab (31). A responder index developed in collaboration with the FDA defined response as improvement and/or no deterioration in patient- and physician-reported outcomes (28).

In 2005, the FDA released draft guidance on the development of drugs for the treatment of SLE that covered the use of DAIs, flares, and organ-specific outcomes (4). Based on the FDA, OMERACT, and EULAR recommendations, the ideal responder index should detect early as well as overall changes in disease activity. It should also be able to simultaneously identify improvement and worsening in the same and/or different organ systems, be validated by a long-term RCT, and be compatible with regulatory requirements of the FDA and European Medicines Evaluation Agency (4, 5, 8).

The largest phase II RCT in SLE completed to date examined the efficacy of belimumab in patients with active SLE who were receiving standard of care therapy (SOC) (32). Belimumab, a fully human monoclonal antibody to B lymphocyte stimulator (BLyS; trademark of Human Genome Sciences, Rockville, MD), was developed to selectively inhibit the biologic activity of soluble BLyS (33). Elevated levels of BLyS (a promoter of B cell survival, B cell differentiation, and Ig class switching) have been shown to correlate with increased SLE disease activity (32, 34). In this phase II trial, exploratory analyses identified a major subpopulation of SLE patients who were serologically active, indicative of B cell hyperactivity, and more responsive to belimumab therapy than to placebo as determined by DAIs of SLE and HRQOL (32, 35, 36).

Evidence-based exploratory analyses of this RCT led to the creation of a robust individual responder index, which not only could be used as a primary end point in SLE trials, but also could define a clinically meaningful change. The SLE responder index (SRI) utilizes the SELENA–SLEDAI score to determine global improvement, BILAG domain scores to ensure no significant worsening in heretofore unaffected organ systems, and physician's global assessment (PGA) to ensure that improvements in disease activity are not achieved at the expense of the patient's overall condition, which may have been missed by either DAI.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Study design and entry criteria.

The evidence base for the SRI evaluation came from a phase II dose-ranging RCT evaluating the safety, tolerability, biologic activity, and efficacy of belimumab combined with SOC in 449 SLE patients who had SELENA–SLEDAI scores of ≥4 at baseline (32). Patients with a diagnosis of SLE by ACR criteria (37) and a history of measurable autoantibodies who were receiving a stable SOC regimen (2) for at least 60 days prior to day 0 (first dose) were included; patients with active lupus nephritis or central nervous system disease were excluded. Concurrent corticosteroid and immunosuppressive agents could be changed throughout the protocol as clinically indicated. All patients gave informed consent for the study, and there was an independent data safety monitoring committee (32).

Patient population.

A major subset of patients (n = 321) identified as serologically active (antinuclear antibodies [ANA] ≥1:80 by HEp-2 cell immunofluorescence and/or anti–double-stranded DNA [anti-dsDNA] antibodies ≥30 IU/ml) at screening and baseline (day 0) were found to respond better to belimumab therapy than to placebo (32). Representing 71.5% of the original cohort, these patients were assessed to evaluate components of DAIs of SLE in developing the SRI.

SLE disease activity and efficacy measures: DAIs.

The SELENA–SLEDAI (10), SLE flare index (SFI) (13), PGA, BILAG (11, 22), and Short Form 36 (SF-36) (38) were determined every 4 weeks during the first 24 weeks of the study and then at weeks 32, 40, 48, and 52. A reduction of ≥4 points in the SELENA–SLEDAI score from baseline was considered to be a clinically meaningful improvement (39). PGA (10, 13) scores of 0, 1, 2–2.5, and 3 were benchmarks on a 10-cm visual analog scale (VAS) corresponding to no, mild, moderate, or severe life-threatening lupus disease activity, respectively. An increase in ≥1 unit from the last assessment was considered a mild/moderate flare, whereas an increase to >2.5 points was considered a severe flare (13). An increase of ≥0.3 points (>10% on the 3-point VAS) from baseline was considered clinically significant worsening (40). The SFI identifies mild/moderate flares or severe flares based on clinical activity, PGA, or the need for additional treatment (13). A severe flare by the classic BILAG is defined as a new organ domain score of A, whereas a moderate flare is defined as a new organ domain score of B (14). Biomarkers and laboratory parameters routinely measured with the SLE disease activity scales have been described (32).

SRI calculations.

The SRI was calculated any time the SLE disease activity scores were measured in individual patients. A responder was defined as having a ≥4-point reduction from baseline in SELENA–SLEDAI score and no new BILAG A organ domain scores or ≥2 new BILAG B organ domain scores compared with baseline and no worsening in PGA (<0.3-point increase from baseline). If all 3 criteria were met, the patient was considered a responder at that particular point in time; otherwise, the patient was considered a nonresponder.

Statistical methods.

An exploratory analysis limited to patients with serologic activity at screening and baseline was performed on all disease activity scales and efficacy parameters at the week 52 visit. Because of the general lack of a dose response observed in biomarkers, efficacy parameters, or safety measures, the 3 belimumab treatment groups were combined (n = 235) and compared with the placebo-treated patients (n = 86) (32). The SRI and all of the other categorical data were analyzed using the likelihood ratio chi-square test, and the percent change from baseline in PGA was analyzed using a Student's t-test. The absolute change from baseline in the SF-36 physical component summary (PCS) was analyzed using an analysis of variance, adjusting for the baseline PCS score. For other study end points, discrete variables were analyzed using a likelihood chi-square test and continuous variables were analyzed using a Student's t-test.

Missing data in the SELENA–SLEDAI, BILAG, and PGA were imputed using a last observation carried forward method. A sensitivity analysis of the SRI was also performed, in which discontinuation before the week 52 visit was considered to be a treatment failure. Analysis of the selected efficacy end points was performed in a modified intent-to-treat population, defined as all patients who were randomized and received at least 1 dose of study drug or placebo. The SRI analyses were retrospectively applied to the phase II data of all of the patients and the serologically active subset. The analyses were not subjected to multiple comparison adjustment.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Demographics and baseline characteristics of serologically active SLE patients.

There were no significant differences across treatment groups in any of the parameters, as shown in Table 1. The serologically active patients, representing 71.5% of the enrolled patient population, had baseline demographics similar to the entire cohort (32), except for a higher percentage with anti-dsDNA antibodies (69.5% versus 49.7%), ANAs ≥1:80 (95.3% versus 71.2%), a history of immunologic disorder per the ACR SLE criteria (84.4% versus 72.6%), and low C3 (39.3% versus 30.1%) or C4 (50.2% versus 40.1%) levels.

Table 1. Baseline demographic and clinical characteristics of serologically active patients (n = 321)*
 Placebo (n = 86)Belimumab
1.0 mg/kg (n = 78)4.0 mg/kg (n = 79)10.0 mg/kg (n = 78)All active (n = 235)
  • *

    Values are the percentage unless otherwise indicated. SELENA–SLEDAI = Safety of Estrogens in Lupus Erythematosus: National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index; BILAG = British Isles Lupus Assessment Group; PGA = physician's global assessment; BLyS = B lymphocyte stimulator; ALOD = above level of detection (0.350 ng/ml); ANAs = antinuclear antibodies; anti-dsDNA = anti–double-stranded DNA.

  • Excluding aminoquinolines (hydroxychloroquine, chloroquine, and quinacrine).

Women93.096.294.997.496.2
Race     
 White65.169.262.069.266.8
 African American24.423.131.626.927.2
Hispanic or Latino origin19.815.425.319.220.0
Age, mean ± SD years41.3 ± 11.339.8 ± 11.541.0 ± 10.540.1 ± 10.940.3 ± 10.9
Disease duration, mean ± SD years8.1 ± 7.59.2 ± 7.810.2 ± 9.38.5 ± 7.69.3 ± 8.3
SELENA–SLEDAI score, mean ± SEM9.7 ± 0.610.4 ± 0.69.5 ± 0.59.8 ± 0.59.9 ± 0.3
≥1 A or 2 B BILAG scores59.366.767.173.168.9
PGA, mean ± SEM1.3 ± 0.051.6 ± 0.061.5 ± 0.051.5 ± 0.061.5 ± 0.03
Daily prednisone use73.371.873.471.872.3
 >7.5 mg at baseline45.438.536.743.639.6
Immunosuppressive agent use47.746.259.550.051.9
BLyS ALOD47.756.450.650.052.3
ANAs ≥1:8094.297.497.592.395.7
Anti-dsDNA antibodies ≥30 IU/ml67.475.667.168.070.2
Low C3 (<90 mg/dl)30.247.438.042.342.6
Low C4 (<16 mg/dl)41.960.346.852.653.2

Efficacy.

Changes from baseline in SELENA–SLEDAI scores.

Three analyses compared week 52 belimumab treatment responses with placebo in the serologically active population (Figure 1): 1) percent change in SELENA–SLEDAI scores, 2) percentage of patients achieving a threshold of absolute change in SELENA–SLEDAI score by 1-point increments of improvement or worsening (range −5 to +5, respectively), and 3) percentage of patients with ≥4-point improvement. The percent reductions in SELENA–SLEDAI scores at week 52 were statistically greater in the belimumab group than in the placebo group (−28.8% versus −14.2%; P = 0.044) (Figure 1A). There were significantly more patients with >0 to ≤2–point improvements in the belimumab group than in the placebo group; a trend of belimumab-treated patients achieving ≥3 to ≤5–point improvements without reaching statistical significance was also observed (Figure 1B). Compared with placebo, significantly fewer patients treated with belimumab had worsening of SELENA–SLEDAI scores at all incremental changes of >0 to ≤5 points. A larger percentage of patients had a ≥4-point reduction in SELENA–SLEDAI score in the belimumab group than in the placebo group at all time points (not significant), with separation beginning at week 16 (Figure 1C and Table 2).

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Figure 1. The effect of belimumab on the Safety of Estrogens in Lupus Erythematosus: National Assessment (SELENA) version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) score at week 52 in serologically active patients (n = 321).A, Percent change in SELENA–SLEDAI score from baseline over time. B, Absolute changes from baseline in SELENA–SLEDAI score at week 52. C, Percentage of patients with a ≥4-point reduction in SELENA–SLEDAI score. a = statistically significant better response with all active belimumab vs. placebo (P = 0.04); b = statistically significant better response with all active belimumab vs. placebo (P < 0.05).

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Table 2. Summary of efficacy results for serologically active patients at week 52 (n = 321)*
 Placebo (n = 86)BelimumabP
1.0 mg/kg (n = 78)4.0 mg/kg (n = 79)10.0 mg/kg (n = 78)All active (n = 235)
  • *

    Serologically active patients are those with antinuclear antibodies ≥1:80 and/or anti–double-stranded DNA (anti-dsDNA) antibodies ≥30 IU/ml at screening and day 0. SRI = systemic lupus erythematosus responder index; SELENA–SLEDAI = Safety of Estrogens in Lupus Erythematosus: National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index; BILAG = British Isles Lupus Assessment Group; PGA = physician's global assessment.

  • From likelihood ratio test for pairwise comparison between combined all active belimumab vs. placebo.

  • Percentage of patients with a reduction in SELENA–SLEDAI score of ≥4, no worsening by BILAG index (no new A or 2B flares), and no worsening by PGA (<0.3-point increase).

  • §

    No new A or 2B BILAG flares.

  • Less than 0.3-point increase in PGA from baseline.

  • #

    Modified SRI by excluding both anti-dsDNA and low complement (C3/C4) levels from the determination of the SELENA–SLEDAI score. The number of patients with a minimum score of ≥4 at baseline and their mean baseline score are shown for each treatment group.

SRI response rate, %29.148.743.046.246.00.006
 ≥4-point reduction in SELENA– SLEDAI score39.552.648.147.449.40.117
 No worsening by BILAG§81.488.594.991.091.50.015
 No worsening by PGA76.789.788.692.390.20.003
Modified SRI, no.#74706768205 
 Baseline SELENA–SLEDAI score, mean8.28.18.28.18.2 
Modified SRI response rate, %#32.448.646.347.147.30.025
PGA and SF-36 PCS.

Among the serologically active patients, the PGA scores in the belimumab-treated patients were significantly lower than the scores observed in the placebo-treated patients, both early (weeks 4, 8, and 16) and late (weeks 48 and 52) in the study. A 32.7% reduction in PGA score at week 52 in the belimumab group was observed versus a 10.7% reduction with placebo treatment (P = 0.001) (Figure 2A). Similarly, the PCS score of the SF-36 improved significantly more in the belimumab group than in the placebo group at weeks 12, 24, 48, and 52 (+3.0 versus +1.2 points at week 52; P = 0.041) (Figure 2B). A 2.5-point increase is considered the minimum clinically important difference in the SF-36 PCS from baseline (35, 36), which was observed only in the belimumab group from week 24 onward.

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Figure 2. The effect of belimumab on the physician's global assessment (PGA) and Short Form 36 (SF-36) scores at week 52 in serologically active patients (n = 321). A, Percent change in PGA. B, Absolute point change in SF-36 physical component summary (PCS) scores. a = statistically significant better response with all active belimumab vs. placebo (P < 0.05).

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BILAG organ domain flares.

There were no significant differences between the belimumab and placebo groups in the percentages of patients who developed new A or B organ domain scores at week 52 (29.4% versus 39.5%; P = 0.087) (34). However, focusing on specific organ domains (Figure 3), significantly fewer belimumab-treated patients than placebo-treated patients had new BILAG A or B flares in the renal (P = 0.034), neurologic (P = 0.035), and musculoskeletal (P = 0.008) domains. A favorable trend was seen in the cardiorespiratory (P = 0.060) organ domain. Incorporating a higher threshold for SLE flares, there were fewer new 1 A or ≥2 B organ domain flares at week 52 in the belimumab group than in the placebo group (8.5% versus 18.6%; P = 0.015) (Table 2).

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Figure 3. The effect of belimumab on British Isles Lupus Assessment Group (BILAG) domain scores at week 52 (new A or B scores). The percentages of serologically active patients with new 1 A or 1 B BILAG organ domain scores at week 52 are shown. a = statistically significant better response with all active belimumab vs. placebo (P < 0.05).

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SRI.

In serologically active patients, the week 52 response rates for the SRI and its 3 components are shown in Table 2. No dose response was evident across the 3 belimumab dosing groups. Higher SRI response rates over time occurred in the belimumab-treated group than in the placebo group, with separation after week 12. Statistical significance was reached at week 52 (46% with belimumab versus 29% with placebo; P = 0.006) (Figure 4A) and week 56 (49% with belimumab versus 35% with placebo; P = 0.029) (data not shown). A greater percentage of patients who received belimumab achieved a ≥4-point improvement in SELENA–SLEDAI score at week 52 than in the placebo group (49.4% versus 39.5%; P = 0.117). Patients who received belimumab were more likely to have no worsening (<0.3-point increase) in PGA at week 52 (90.2% versus 76.7%; P = 0.003) and have no new A or 2 B BILAG flares (91.5% versus 81.4%; P = 0.015) than those in the placebo group. More patients receiving belimumab treatment achieved sustained SRI responses (weeks 40–52) than those receiving placebo (26.8% versus 17.4%; P = 0.076) (data not shown).

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Figure 4. A, Systemic lupus erythematosus responder index over 52 weeks in serologically active patients (n = 321). B, Response rate at week 52 in belimumab-treated patients with different autoantibody subtypes at baseline. a = statistically significant better response with all active belimumab vs. placebo (P = 0.006); anti-dsDNA = anti–double-stranded DNA.

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Sensitivity analyses of a modified SRI were performed, in which the minimum requirement for improvement in SELENA–SLEDAI score was 5, 6, or 7 points. At a threshold of a ≥5-point improvement, 35.9% (n = 206) of those in the belimumab group achieved a response compared with 22.5% in the placebo group (n = 71; P = 0.034). More stringent requirements of 6- or 7-point improvements reduced the number of evaluable patients with higher baseline scores, but the treatment effect remained favorable, although not statistically significant (P ≤ 0.242) (data not shown). To address the impact of laboratory values on the SRI, analyses were performed following removal of both the anti-dsDNA and complement components of the SELENA–SLEDAI score. SRI response rates (47.3% all active belimumab versus 32.4% placebo; P = 0.025) (Table 2) without the serologic components remained statistically different, confirming the clinical relevance of the SRI.

The percentage of patients with a ≥4-point improvement in SELENA–SLEDAI score defined as nonresponders (not achieving 1 or both of the other response criteria, PGA or BILAG) in the SRI was >3-fold greater in the placebo group than in the belimumab group (10.3% versus 3.4%). Of 34 placebo-treated patients who had a ≥4-point improvement in SELENA–SLEDAI score at week 52, 9 patients (26%) did not meet SRI criteria because of worsening disease activity (2 PGA, 3 BILAG, and 4 PGA plus BILAG). In comparison, of 116 belimumab-treated patients with a ≥4-point improvement in SELENA–SLEDAI score at week 52, 8 patients (7%) did not meet SRI criteria because of worsening disease activity (2 PGA, 4 BILAG, and 2 PGA plus BILAG). Even if dropouts before week 52 were assumed to be nonresponders at 52 weeks, a greater percentage of serologically active patients treated with belimumab achieved a response as defined by the SRI (40.9% versus 27.9% with placebo; P = 0.031) (data not shown).

An analysis of all belimumab-treated patients stratified by autoantibody subtype (anti-dsDNA, anti-RNP, anti-Ro, anticardiolipin, and anti-Sm; n = 63–165 per subgroup) at baseline revealed that the week 52 SRI responses were comparable (40–51%) across the 5 different autoantibody subtypes and the serologically active (46%) group (n = 235) (Figure 4B). An analysis of all of the patients (n = 449) irrespective of baseline autoantibody status demonstrated a significantly higher SRI response rate at week 52 in the combined belimumab treatment group than in the placebo group (45.9% versus 35.4%; P = 0.045) (data not shown).

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

The lack of a gold standard to measure SLE disease activity or a surrogate marker endorsed by international rheumatology societies or national health authorities has impeded the development of SLE therapies. Several DAIs such as the SLEDAI, SELENA–SLEDAI, BILAG, SLAM, and European Consensus Lupus Activity Measure (3, 7) have been validated based on the concordance of scores with expert opinion, acceptable interobserver variability among trained evaluators, correlation between individual patients' scores on different indices, and correlation between increases in scores and clinical decisions to increase therapy. Although each DAI has its unique strengths and weaknesses, all have demonstrated sensitivity to changes (7) in disease activity in cohort studies, and therefore are suitable for use in clinical trials. The draft FDA guidance document recommended analyzing the results of clinical trials to verify “that an improvement in a disease activity score represents clinical benefit to the patient and to assess the generalizability of the results” and “that the improvement in disease activity is not accompanied by worsening in other disease manifestations” (4).

A reduction from baseline in SELENA–SLEDAI score by ≥4 points has been defined as clinically meaningful (39). As a validated instrument requiring the unambiguous elimination or normalization of SLE signs, symptoms, or laboratory abnormalities, the SELENA–SLEDAI sets a high threshold for response. With the exception of laboratory values, it is not easily triggered by normal variations in disease activity. Increased disease activity using the SLEDAI or SELENA–SLEDAI has been defined as an increase of ≥3 points (10, 13). The SLEDAI, SLEDAI-2K, and SELENA–SLEDAI scores have been validated in observational studies, large RCTs (3, 7, 10, 41), and across populations with different ethnicities and races (16, 17). In addition, recent correlations of the classic BILAG and BILAG 2004 index (42) with the SLEDAI-2K indicated that a ≥3-point reduction in SELENA–SLEDAI score correlated with a clinically meaningful change in BILAG and an associated reduction in therapy, whereas a ≥3-point increase in the score was associated with disease worsening and new or increased therapy (43). In contrast, an ACR expert panel reviewing 15 case vignettes over 2 to 3 visits thought that a minimum of a 7-point reduction in the SELENA–SLEDAI score was clinically meaningful (44). The variations in defining a clinically meaningful threshold could be due to dissimilar sample sizes or baseline disease severity.

It is vital that improvement in SLE disease activity is not accompanied by worsening of other disease manifestations. The choice of the BILAG to evaluate worsening provided a sensitive measure of flare, because it assesses changes in organ-specific disease activity between points in time and was specifically developed with the tenet of intent-to-treat. It is thought that the development of either 1 A or ≥2 B organ system scores represents an increase in disease activity sufficient to add new therapy consisting of steroids and/or immunosuppressive agents (11, 14, 22), underscoring this definition as an important anchor of clinically meaningful change. The flare component of the SELENA–SLEDAI was not included in the measure of worsening because it was found to be particularly problematic in situations where patients with high disease activity at baseline triggered a severe flare based on modest increases in the SELENA–SLEDAI from scores close to 12 to a score of >12.

The PGA component is included in the SRI to ensure that improvement in the SELENA–SLEDAI score was not achieved at the expense of worsening of the patient's overall condition, which might not have been detected by the BILAG or SELENA–SLEDAI. PGA has been shown to correlate with SLEDAI or SELENA–SLEDAI scores (9, 10) and other DAIs (3, 7, 10, 13, 17, 20, 41). In a study performed by SLICC, SLE experts compared BILAG and SLEDAI scores with a physician-generated VAS in 80 cases evaluated at baseline and at 3 and 6 months. The 2 DAIs correlated well over time, but less so with the physician VAS, indicating that the VAS detects factors not reflected in the DAIs (45). In addition, OMERACT and EULAR recommend that outcome measures in clinical trials include disease activity with global and organ system scores, as well as biomarkers, HRQOL, and damage scores (5, 8).

In other diseases where manifestations are heterogeneous, combined responder instruments have been used to assess disease activity. In fact, the accepted primary regulatory end point for most rheumatoid arthritis RCTs, the ACR criteria for 20% improvement in disease activity, includes measures of signs, symptoms, and laboratory values. It incorporates several VAS scores that assess physician and patient global status of disease activity (46), as well as patient-reported pain. Furthermore, the primary end point for Crohn's disease, the Crohn's Disease Activity Index, includes measures of organ involvement, signs, symptoms, laboratory values, an assessment of patient global status, and use of medications (47).

The BILAG composite score or reduction of A and/or B organ domain scores were considered for inclusion in the SRI as measures of assessing improvement. However, in the phase II belimumab trial, both of these BILAG measures failed to show consistent improvement for either belimumab or placebo treatment because new or recurrent C or B scores, especially in the musculoskeletal and mucocutaneous domains, were frequently triggered through minor fluctuations of disease activity or laboratory values. Whereas BILAG scoring, which is anchored with definitions, was more sensitive to change than the SELENA–SLEDAI, the variability was so great using the primary outcome definitions that improvement or worsening were often not sustained for more than 1 to 3 months at a time. This suggested that defining one new B score as the cutoff for flare is too sensitive if the goal is to restrict flares to those that represent clinically meaningful changes. BILAG is a comparison with the prior month and is not anchored to baseline values; therefore, a patient could improve from the last visit but still be worse than they were at baseline. Conversely, a flare could be triggered despite the patient being better than at baseline.

A >2.5-point improvement in the SF-36 PCS (value of the minimum clinically important difference) (35, 36) was evaluated as an additional response criterion in the SRI. The SF-36 PCS median score was significantly improved in the group treated with belimumab compared with the placebo group. Significant differences were noted as early as 12 weeks, and sustained increases of >2.5 points were observed from weeks 24 through 52. The SF-36, a generic measure of HRQOL that has been validated in RCTs of SLE, offers the ability to compare SLE with other chronic rheumatic and nonrheumatic conditions (35, 36). Incorporating the SF-36 PCS as a fourth component of the SRI reduced the overall percentage of responders but increased the separation between active and placebo treatment (48). Although OMERACT (8), FDA (4), and EULAR (5) guidance recommend that HRQOL be measured in RCTs of SLE, the SF-36 was not included in the SRI because it is not a measure of SLE disease activity. Therefore, SF-36 data will be a major secondary end point in subsequent RCTs to assess the impact of treatment from the patient's perspective and to correlate responses with the SRI.

Treatment of serologically active SLE patients with belimumab resulted in greater SRI response rates at all time points, especially after week 12, in comparison with patients treated with placebo. Differences became statistically significant at weeks 52 and 56. SRI response detects improvements in both clinical disease manifestations and SLE-related laboratory abnormalities. Removal of the 2 serologic components of the SELENA–SLEDAI score did not diminish the belimumab treatment effect compared with the unmodified SRI. Interestingly, anti-Sm or anti-RNP antibodies have been associated with poorer responses or quicker times to relapse with rituximab therapy in SLE (49); however, in the belimumab trial, the SRI response rates were similar at 1 year, irrespective of autoantibody subtype at baseline. Reductions in activated or plasmacytoid B cells, a ≥50% reduction in anti-dsDNA antibodies, and/or normalization of low C4 concentrations were predictive of an SRI response in this trial (50).

Serologically active SLE patients who achieved a ≥4-point reduction in SELENA–SLEDAI score receiving belimumab treatment for 1 year compared with those receiving placebo were 2- to 3-fold less likely to develop increased SLE disease activity as defined by BILAG (new BILAG A score or ≥2 B scores) or PGA (≥0.3-point worsening). These results suggest that belimumab has the ability to improve and stabilize disease activity, as well as reduce flare rates in this population. In serologically active patients, there was a significant reduction in the time to new flares between weeks 24 and 52 as defined by the SFI (34), and there were significantly fewer new BILAG flares at week 52. The significant reductions in renal, neurologic, and musculoskeletal BILAG flares at week 52 suggest that belimumab may have a greater impact on some SLE disease manifestations than on others.

Retrospective application of the SRI to data from a large phase II RCT of belimumab in patients with active SLE demonstrated that belimumab treatment resulted in a statistically larger percentage of responders than treatment with placebo. This SRI, based on a responder analysis of a large phase II study, has been accepted as the 52-week primary efficacy end point for 2 ongoing global phase III studies, which will be carried out in serologically active SLE patients receiving SOC with baseline SELENA–SLEDAI scores of ≥6 points, and will compare treatment with belimumab (1 or 10 mg/kg) with placebo (ClinicalTrials.gov identifiers: NCT00424476 and NCT00410384).

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Furie had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Furie, Petri, Wallace, Chatham, Weinstein, Chevrier, Zhong, Freimuth.

Acquisition of data. Furie, Petri, Wallace, Ginzler, Merrill, Stohl, Chatham, Chevrier, Zhong, Freimuth.

Analysis and interpretation of data. Furie, Petri, Wallace, Ginzler, Stohl, Strand, Weinstein, Chevrier, Zhong, Freimuth.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES
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