# Efficacy of 300 IR house dust mite immunotherapy as a function of disease activity: Tertile analysis in clinical trials

Philippe Devillier, Pascal Demoly, Catherine Gentil, Karl Christian Bergmann, Thomas B. Casale, Yoshitaka Okamoto, Oliver Pfaar

► To cite this version:

Philippe Devillier, Pascal Demoly, Catherine Gentil, Karl Christian Bergmann, Thomas B. Casale, et al. Efficacy of 300 IR house dust mite immunotherapy as a function of disease activity: Tertile analysis in clinical trials. Clinical and Experimental Allergy, 2024, 54 (5), pp.329-338. 10.1111/cea.14478. hal-04615578

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# Efficacy of 300 IR house dust mite immunotherapy as a function of disease activity: Tertile analysis in clinical trials

Philippe Devillier<fnref n="1" />

Pascal Demoly<fnref n="2" /> ID

Catherine Gentil<fnref n="3" />

Karl-Christian Bergmann<fnref n="4" />

Thomas B. Casale<fnref n="5" />

Yoshitaka Okamoto<fnref n="6" />

Oliver Pfaar<fnref n="7" /> ID

**Correspondence**

Philippe Devillier, VIM Suresnes, Foch Hospital, 11, rue Guillaume Lenoir, 92150 Suresnes, France.
Email: p.devillier@hopital-foch.com

**Funding information**

Stallergenes Greer

**Abstract**

**Background:** The symptoms of house dust mite (HDM)-induced allergic rhinitis (AR) vary with changes in exposure related to the weather or the domestic environment. In allergen immunotherapy (AIT) studies, a certain level of AR disease activity is necessary to demonstrate treatment efficacy; the latter can be underestimated if a substantial proportion of the patient population is weakly symptomatic.

**Objective:** To better estimate the real treatment effect of a HDM sublingual AIT (SLIT) tablet, we analysed the results of natural field studies in detail by applying a tertile approach.

**Methods:** We used data from three randomised, controlled trials (RCT) in a total of 2585 patients with AR treated with the 300 index of reactivity (IR) HDM SLIT-tablet or placebo. The study centres were grouped into tertiles according to the level of combined symptom and medication scores in patients in the placebo group. In each tertile, the difference between SLIT and placebo was assessed through an analysis of covariance.

**Results:** In the three RCTs, combined scores were found to be similar in the SLIT and placebo groups in the low tertiles. The treatment effect of the 300 IR HDM tablet increased in the medium and high tertiles, with notably significant differences versus placebo in the highest tertile and greater (ranging from -21% to -39%) than in the entire study population (-13% to -20%). The positive relationship between treatment efficacy and the combined score in each tertile was independent of the RCT and the score used.

**Conclusion and Clinical Relevance:** Application of the tertile approach to AIT studies in a field in which many variables interact strongly might provide more accurate and meaningful measurements of efficacy and benefit for patients, better reflecting their real-life condition.

**KEYWORDS**

allergic rhinitis, efficacy, house dust mite, sublingual immunotherapy, symptom and medication score

This is an open access article under the terms of the [Creative Commons Attribution License](https://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

© 2024 The Authors. *Clinical & Experimental Allergy* published by John Wiley & Sons Ltd.

<footnote n="1">¹VIM Suresnes - UMR_0892 & Clinical Research Unit, Foch Hospital, University Versailles Saint-Quentin, Suresnes, France</footnote>

<footnote n="2">²IDESP, UMR UA11 University Hospital of Montpellier - INSERM, Montpellier, France</footnote>

<footnote n="3">³Axiodis, Toulouse, France</footnote>

<footnote n="4">⁴Institute of Allergology, Charité - Universitätsmedizin Berlin, Berlin, Germany</footnote>

<footnote n="5">⁵Division of Allergy and Immunology, University of South Florida, Tampa, Florida, USA</footnote>

<footnote n="6">⁶Department of Otorhinolaryngology-Head and Neck Surgery, Graduate School of Medicine, Chiba University and Chiba Rosai Hospital, Chiba, Japan</footnote>

<footnote n="7">⁷Department of Otorhinolaryngology, Head and Neck Surgery, Section of Rhinology and Allergy, University Hospital Marburg, Philipps-Universität Marburg, Marburg, Germany</footnote>
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## GRAPHICAL ABSTRACT

The efficacy of a 300 IR HDM SLIT tablet in three RCTs was evaluated in a tertile analysis. The treatment efficacy increased with the placebo score level in each tertile, regardless of the RCT and the combined score used. In the tertile with the highest disease activity, the 300 IR HDM SLIT tablet was associated with greater treatment efficacy.

## 1 | INTRODUCTION

House dust mites (HDM) emit indoor aeroallergens that are responsible for perennial respiratory allergies (such as allergic rhinitis (AR) and allergic asthma) in more than 65 million people worldwide.¹ In a survey performed in Europe, 49% of adult patients with a clinical diagnosis of AR were sensitised to HDM allergens.² Due to differences in climate, however, this sensitisation can vary considerably from one region of Europe to another, with higher rates observed in wet areas.³

HDM-induced AR can have a significant negative impact on a patient's quality of life (QoL) by affecting sleep, daily activities and social activities.⁴⁻⁶ Although the symptoms of HDM-induced respiratory allergy are usually always present to some extent, their intensity varies over time as a function of changes in exposure related to the weather or the domestic environment.⁷,⁸ A survey of adult patients with poorly controlled, moderate-to-severe HDM respiratory allergy in three European countries described a complex set of changing, troublesome symptoms (very or extremely bothersome in over 40% of the participants) throughout the year, with peaks in spring, early autumn and (for patients with HDM allergy alone) mid-winter.⁶,⁹ Between 14% and 46% of the participants (depending on the country) suffered from symptoms of HDM allergy every day or almost every day of the year.⁶ Overall, about a third of the participants reported a strong or very strong impact of HDM allergy on their daily activities, and a quarter to a half reported a strong or very strong impact on sleep.⁶ Taken as a whole, the results of this European survey emphasised the great heterogeneity in HDM allergy profiles and the variability over time in symptom intensity.

More than 90% of HDM allergies worldwide are triggered by two HDM species, namely *Dermatophagoides (D.) pteronyssinus* and *D. farinae*.¹⁰,¹¹ Standardised allergen extracts from these two HDM species are mixed with excipients to formulate subcutaneous immunotherapy (SCIT) products or sublingual immunotherapy (SLIT) solutions or tablets.¹⁰,¹¹ Reviews and meta-analyses of clinical studies

### Key messages

* The efficacy of the 300 IR HDM SLIT-tablet was evaluated by tertile analysis in 3 RCTs.

* Treatment efficacy increased with the placebo score in each tertile, regardless of RCT and combined score.

* 300 IR HDM SLIT-tablet was associated with greater efficacy in the tertile, showing the highest disease activity.

have revealed that the mean effect size is quite consistent between different classes of HDM AIT (i.e.; for SCIT and SLIT tablets and, to a lesser extent, for SLIT solutions), with significantly lower symptom scores, medication scores, combined symptom and medication scores and rhinoconjunctivitis-related QoL questionnaire scores, and less frequent asthma exacerbations, although there can be considerable heterogeneity between individual trials.¹²⁻¹⁹ There was a low degree of variability in the effect size on AR across the large, multicentre, randomised controlled trials (RCTs) of SLIT tablets performed under natural field conditions, with a relative mean difference in the active versus placebo scores of about -20%. In a one-year study, the difference in scores between the active treatment group and the placebo group was smaller and did not reach the threshold for statistical significance because the patients were not symptomatic enough during the evaluation period to enable assessment of the efficacy versus placebo.²⁰ It is noteworthy that the effect size in the placebo group (evaluated as the reduction in the efficacy score vs. baseline) can be as high as 39% in HDM AIT studies, which limits the room for improvement by the active treatment.²¹ Furthermore, the retrospective, subjective scoring of AR severity during a study inclusion visit is inherently unreliable because of recall bias: patients tend to remember their 'hell days' more than their 'well days'.²¹ Lastly, a short-term run-in (baseline) period – even with placebo – prior to treatment allocation does not recapitulate the natural history of the
disease over the following year and particularly when the treatment is evaluated during a few weeks only.²¹ If the level of disease activity (as measured by a symptom score and/or rescue medication use) is low during the evaluation periods in a substantial proportion of the patient population in AIT natural field studies, the efficacy of AIT can therefore be underestimated. To assess more precisely the benefit of AIT in patients with grass pollen AR, we previously reported the results of a tertile analysis of RCT data in which study sites were grouped together according to the symptom score recorded in placebo-treated patients during the pollen season.²² This placebo value was used as the reference level of disease activity during the evaluation period in the corresponding area. The greatest active versus placebo difference was observed in the tertiles, in which the symptom scores in the placebo group were high enough to show a clinically relevant difference in the active treatment group. Using a placebo score method based on the same principle, Frew et al. reported that the effect size of grass pollen AIT versus placebo was greater when examining the 4 weeks at each centre in which the placebo-treated patients had the highest efficacy endpoint scores (the 'peak placebo score' weeks rather than the 'peak pollen count' weeks).²³ This study and approach further demonstrate that the effects of AIT can be better discriminated against in patients who are more highly symptomatic. Such an analysis could be even more relevant in AIT studies in patients with fluctuating symptoms of HDM-induced AR since not all moderate-to-severe patients suffer from their allergy during the short evaluation period in a RCT, even if they have suffered from it in previous months.

To better estimate the real treatment effect of the 300 index of reactivity (IR) HDM SLIT-tablet in moderate-to-severe patients with HDM-related AR symptoms of various intensities, we applied a tertile analysis to the results of natural field RCTs of this AIT product.

## 2 | METHODS

### 2.1 | Clinical studies

Our post-hoc analysis covered data from 2585 patients suffering from moderate-to-severe HDM AR with or without controlled asthma and who were included in three RCTs with the 300 IR HDM SLIT-tablet: the European phase II/III study in adults (VO57, NCT00674700),²⁴ the international phase III study in adults and adolescents (SL75, NCT02443805),²⁵ and the Japanese phase II/III study in adults and adolescents (JP-D1731, JapicCTI-121917)²⁶ (Table S1).

From an ethical standpoint, the three RCTs were performed in accordance with good clinical practice defined by the International Council for Harmonisation and the principles that have their origin in the Declaration of Helsinki and local laws and regulations. All participants, parents or legal representatives (for participants 17 years of age or younger) gave their written consent to participation after having been informed of the trial objectives and procedures.

All three studies were multicentre, randomised, double-blind and placebo controlled. The two phase II/III studies evaluated the 500 IR dose along with the 300 IR dose. For consistency, the present work only considered the data obtained with the 300 IR HDM tablet, having received marketing authorisation in the European Union, Australia/New Zealand, South Korea and Japan. All three studies featured a 3-day dose escalation period, after which the 300 IR tablet or a matching placebo was given once daily for approximately 12 months.

Two different scores were used as primary endpoints. In the VO57 and JP-D1731 studies, the primary endpoint was the average adjusted symptom score (AASS) during the primary evaluation period. The AASS was calculated by adjusting the daily rhinitis total symptom score (RTSS, which is the sum of the four nasal symptoms: sneezing, rhinorrhoea, nasal congestion and nasal pruritus) for rescue medication use (scale: 0-12 in VO57 because each nasal symptom was scored on a 0-3 scale, and scale: 0-15 in JP-D1731 because nasal pruritus was scored on a 0-3 scale and the three other symptoms were scored on a 0-4 scale). In fact, AASS corresponded to the average of the daily 'highest RTSS carried forward'.²⁷ Briefly, the AASS took account of the highest RTSS score on the preceding day and applied it to the day on which the rescue medication was taken and the following day. In the SL75 study, the primary endpoint was the average of the daily total combined score (ATCS) during the 4-week primary evaluation period. The daily TCS (scale: 0-15) was the sum of the patient's RTSS over the previous 24 hours (scale: 0-12) and the rescue medication score (RMS), in which only the 'strongest' type of medication used on a given day was taken into account (scale: 0-3) (Table S1). In 2014, a European Academy of Allergy and Clinical Immunology task force recommended using a homogeneous combined symptom and medication score (CSMS, scale: 0-6) as a primary endpoint in AIT trials.²⁸ When used as a secondary endpoint in SL75, the RTSS and the RMS were even equal weights when calculating the CSMS. For the purposes of the present work and to enable comparison of the three studies, the average CSMS (ACSMS) was computed post hoc on a 0-6 scale from the data of the VO57 and JP-D1731 studies.

### 2.2 | Assessment of the treatment effect by disease activity: grouping the study centres into tertiles

As mentioned above, the tertile analysis was based on the efficacy observed in the placebo group at each study site. The sites were ranked from the lowest mean score considered (the ACSMS, AASS or ATCS) in the placebo group after one year of treatment to the highest and then grouped into three clusters (i.e. low, medium and high tertiles), each of which included approximately a third of the patients (details in Appendix S1: Methods). The tertile analysis was pre-specified for the AASS in the VO57 study and performed post hoc for the ACSMS in all three studies, for the AASS in SL75 and JP-D1731, and for the ATCS in SL75.
## 2.3 | Statistical methods

The endpoints were analysed by tertile during the primary evaluation period. The latter was defined as the autumn (October 1st to December 31st) in the VO57 study or the 4 weeks or 8 weeks preceding the last record for patients treated for at least 300 days in the SL75 and JP-D1731 studies, respectively. For each considered endpoint, an analysis of covariance (ANCOVA) was performed, with (i) treatment group as the main effect, (ii) sex, age, sensitisation status, asthma status, the endpoint tertiles and the baseline average RTSS as covariates, and (iii) treatment group x endpoint tertiles as an interaction (details in Appendix S1: Methods). We calculated a point estimate and its 95% confidence interval (CI) for the difference in the adjusted least squares (LS) means between the 300 IR HDM tablet and placebo groups. The relative LS mean difference (%) was calculated as follows: $100 \times (LS mean - 300 IR - LS mean placebo)/LS mean placebo$. For the SL75 study, the primary endpoint (ATCS) was also analysed by tertile for each of the planned interim evaluation periods: 2 weeks every 3 months (i.e. months 3, 6, 9 and 12). The analyses were performed on the modified full analysis set, which comprised all the patients who received at least one dose of the 300 IR HDM tablet or placebo and who had data on at least one primary efficacy evaluation during the primary period. All statistical analyses were performed using SAS® software (version 9.4, SAS Institute Inc., Cary, NC,

USA). The sample size required to reliably assess the presence of an interaction between the treatment arm and the tertile was calculated post hoc using the GLMPOWER procedure. All statistical tests were two-sided with a .05 significance level.

## 3 | RESULTS

The three studies' populations have been described previously in detail.²⁴⁻²⁶ For each tertile in each study, the number of patients, the endpoint value over the primary evaluation period in each treatment group and the relative difference versus placebo are given in Table 1 for the ACSMS and Table 2 for the AASS.

In each study, there were substantial differences in the treatment effect between the low tertile on the one hand and the medium and high tertiles on the other. In the VO57, SL75 and JP-D1731 studies, the LS mean ACSMS in the placebo arm was close to 1 (0.92, 1.17 and 1.06, respectively) in the low tertiles and around 1.5 (1.38, 1.67 and 1.62, respectively) in the high tertiles. The relative reductions in the ACSMS for the 300 IR HDM tablet vs. placebo were, respectively, 29%, 21% and 33% in the high tertiles and 13%, 18% and 20% in the total population. Smaller relative reductions or even relative increases were observed in the low tertiles: an increase of 6% in VO57, a reduction of 3% in SL75 and an increase of 3% in JP-D1731 (Figure 1 and Table 1). The LS mean differences versus placebo were

<table><caption>TABLE 1 The average combined symptom and medication score (ACSMS, scale: 0–6) by tertile, for the three clinical trials.</caption><thead><tr><th>Study</th><th>Tertile</th><th>Treatment group</th><th>N</th><th>ACSMS LS mean [95%CI]</th><th>Relative difference vs. placebo [95% CI]</th><th>p-Value</th></tr></thead><tbody><tr><td rowspan="6">VO57</td><td rowspan="2">Low</td><td>Placebo</td><td>50</td><td>0.92 [0.69; 1.14]</td><td>+5.7% [-24.9; 49.3]</td><td>.743</td></tr><tr><td>300 IR</td><td>57</td><td>0.97 [0.75; 1.19]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>47</td><td>1.12 [0.88; 1.37]</td><td>-9.0% [-33.7; 22.3]</td><td>.572</td></tr><tr><td>300 IR</td><td>37</td><td>1.02 [0.75; 1.29]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>56</td><td>1.38 [1.17; 1.60]</td><td>-29% [-50.0; -3.5]</td><td>.0130</td></tr><tr><td>300 IR</td><td>47</td><td>0.98 [0.75; 1.22]</td><td></td><td></td></tr><tr><td rowspan="6">SL75</td><td rowspan="2">Low</td><td>Placebo</td><td>230</td><td>1.17 [1.04; 1.31]</td><td>-3.3% [-18.4; 14.1]</td><td>.691</td></tr><tr><td>300 IR</td><td>194</td><td>1.13 [0.99; 1.28]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>219</td><td>1.50 [1.35; 1.66]</td><td>-27.7% [-39.2; -14.8]</td><td>&lt;.0001</td></tr><tr><td>300 IR</td><td>194</td><td>1.08 [0.93; 1.25]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>227</td><td>1.67 [1.51; 1.83]</td><td>-21.3% [-32.2; -9.1]</td><td>.0014</td></tr><tr><td>300 IR</td><td>198</td><td>1.31 [1.16; 1.48]</td><td></td><td></td></tr><tr><td rowspan="6">JP-D1731</td><td rowspan="2">Low</td><td>Placebo</td><td>100</td><td>1.06 [0.90; 1.21]</td><td>+ 2.6% [-9.8; 16.6]</td><td>.736</td></tr><tr><td>300 IR</td><td>105</td><td>1.08 [0.93; 1.23]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>98</td><td>1.26 [1.11; 1.41]</td><td>-22.7% [-32.6; -12.0]</td><td>.0007</td></tr><tr><td>300 IR</td><td>95</td><td>0.97 [0.82; 1.13]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>99</td><td>1.62 [1.47; 1.77]</td><td>-32.7% [-41.2; -23.1]</td><td>&lt;.0001</td></tr><tr><td>300 IR</td><td>88</td><td>1.09 [0.93; 1.25]</td><td></td><td></td></tr></tbody></table>

Note: ANCOVA model with sex, age, sensitisation status, asthma status, endpoint tertiles and baseline average RTSS as covariates, and treatment group x endpoint tertiles as an interaction. p-Values of approximate t-tests obtained with PROC MIXED (SAS®). Bold values correspond to statistical significant results.

Abbreviations: CI, confidence interval; IR, index of reactivity; LS, least squares; N, number of patients in the modified full analysis set.
<table><caption>TABLE 2 The average adjusted symptom score (AASS; a 0–12 scale in studies VO57 and SL75 and a 0–15 scale in the JP-D1731 study) by tertile, for the three clinical trials.</caption><thead><tr><th>Study</th><th>Tertile</th><th>Treatment group</th><th>N</th><th>AASS LS mean [95%CI]</th><th>Relative difference vs. placebo [95%CI]</th><th>p-Value</th></tr></thead><tbody><tr><td rowspan="6">VO57</td><td rowspan="2">Low</td><td>Placebo</td><td>46</td><td>3.08 [2.37; 3.79]</td><td>+4.1% [-26.1; 47.6]</td><td>.796</td></tr><tr><td>300 IR</td><td>52</td><td>3.21 [2.53; 3.88]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>47</td><td>3.38 [2.69; 4.08]</td><td>-9.2% [-33.6; 21.8]</td><td>.534</td></tr><tr><td>300 IR</td><td>47</td><td>3.07 [2.37; 3.77]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>60</td><td>4.76 [4.13; 5.39]</td><td>-39.1% [-52.2; -23.7]</td><td>.0002</td></tr><tr><td>300 IR</td><td>42</td><td>2.90 [2.16; 3.64]</td><td></td><td></td></tr><tr><td rowspan="6">SL75</td><td rowspan="2">Low</td><td>Placebo</td><td>232</td><td>3.46 [3.07; 3.86]</td><td>-5.4% [-20.3; 12.1]</td><td>.512</td></tr><tr><td>300 IR</td><td>198</td><td>3.28 [2.84; 3.73]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>221</td><td>4.21 [3.77; 4.67]</td><td>-17.1% [-29.7; -2.6]</td><td>.0188</td></tr><tr><td>300 IR</td><td>198</td><td>3.49 [3.04; 3.97]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>223</td><td>5.04 [4.61; 5.46]</td><td>-26.7% [-36.6; -15.8]</td><td>&lt;.0001</td></tr><tr><td>300 IR</td><td>190</td><td>3.69 [3.25; 4.15]</td><td></td><td></td></tr><tr><td rowspan="6">JP-D1731</td><td rowspan="2">Low</td><td>Placebo</td><td>101</td><td>5.18 [4.57; 5.79]</td><td>+2.4% [-9.4; 15.5]</td><td>.702</td></tr><tr><td>300 IR</td><td>108</td><td>5.31 [4.71; 5.91]</td><td></td><td></td></tr><tr><td rowspan="2">Medium</td><td>Placebo</td><td>97</td><td>6.33 [5.72; 6.93]</td><td>-20.3% [-28.8; -11.0]</td><td>.0002</td></tr><tr><td>300 IR</td><td>92</td><td>5.04 [4.42; 5.67]</td><td></td><td></td></tr><tr><td rowspan="2">High</td><td>Placebo</td><td>99</td><td>7.40 [6.79; 8.01]</td><td>-30.0% [-37.4; -21.9]</td><td>&lt;.0001</td></tr><tr><td>300 IR</td><td>88</td><td>5.18 [4.54; 5.82]</td><td></td><td></td></tr></tbody></table>

Note: ANCOVA model with sex, age, sensitisation status, asthma status, endpoint tertiles and baseline average RTSS as covariates, and treatment group × endpoint tertiles as an interaction. p-Values of approximate t-tests obtained with PROC MIXED (SAS®).

Abbreviations: CI, confidence interval; IR, index of reactivity; LS, least squares; N, number of patients in the modified full analysis set.

statistically significant in the high tertiles in all three studies and in the medium tertiles in two studies (SL75 and JP-D1731).

Similarly, the LS mean AASS in the placebo arm was about 50% higher in the high tertiles than in the low tertiles. The relative reductions in AASS with the 300 IR HDM tablet versus placebo in the high tertiles (39%, 27% and 30% in VO57, SL75 and JP-D1731, respectively) were greater than those observed in the whole study population (18%, 17% and 18%, respectively). Smaller relative reductions or even relative increases in the AASS were observed in the low tertiles, with an increase of 4% in VO57, a decrease of 5% in SL75 and an increase of 2% in JP-D1731 (Figure 2 and Table 2). Again, the LS mean differences versus placebo were all statistically significant in the high tertiles in all three studies and in the medium tertiles in two studies (SL75 and JP-D1731).

In the VO57 study, the AASS was also analysed by tertile and by confounding sensitisation status (multiple interactions) (Table S2 and Figure S1). Estimations in the subgroup without confounding sensitisations (84% of the study population) led to a treatment effect corresponding to a relative reduction in AASS of 21% versus placebo in the entire subgroup, a decrease of 39% in the high tertile and an increase of 8% in the low tertile.

We also analysed the primary endpoint of SL75 (the ATCS over the primary evaluation period) by tertile (Figure 3A and Table S3). As had been found with the ACSMS and AASS, the relative reduction in ATCS with the 300 IR HDM tablet versus placebo was greater (by

a factor of 1.6) in the high tertile than in the total population, and the relative reductions were statistically significant in the high and medium tertiles but not in the low tertile. In addition, the relative differences in ATCS means between the 300 IR and placebo groups at each evaluation period (months 3, 6, 9 and 12) are shown for the total population and by tertile in Figure 3B and Table S4. The treatment effect visibly increased over the 12-month treatment period in the medium and high tertiles and in the whole study population but was not apparent in the low tertile at any timepoint. The relative reductions versus placebo were similar in the total population and the medium tertile and were greater in the high tertile.

4 | DISCUSSION

In all three studies analysed here, the greatest relative improvements in AR clinical scores for moderate-to-severe patients receiving the 300 IR HDM SLIT-tablet (vs. placebo) were observed in the tertiles, wherein the placebo group reflects a higher disease activity (i.e. the high tertile in particular) (Figure 4). Conversely, the course of AIT did not show clinical benefit in the centres with a low AR score in the placebo group (i.e. the low tertile in particular) at the time of the evaluation period, the duration of which was limited compared to that of the entire study. The results were almost independent of the AR score used in the analysis: the ACSMS, AASS or ATCS. The
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**FIGURE 1** The treatment effect increases with greater disease activity in the placebo groups - the average combined symptom and medication score (ACSMS) by tertile and in the entire study population in the VO57 study (A), the SL75 study (B) and the JP-D1731 study (C). LS mean differences between groups were estimated over each study's primary evaluation period in an ANCOVA. \*p ≤ .05; \*\*p ≤ .01; \*\*\*p ≤ .001. HDM, house dust mite; IR, index of reactivity.</figcaption></figure>

treatment effect in the study population as a whole was driven by the tertiles in which placebo patients exhibited the highest level of AR disease activity during the evaluation period.

Interestingly, the LS mean AASS values (scale: 0-12) in the low tertile in studies VO57 and SL75 were 3.08 and 3.46, respectively. The AASS is calculated by adjusting the ARTSS for rescue medication use; hence, in patients not taking any rescue medication, the AASS is equal to the ARTSS. In a prospective study comparing HDM AR patients with control patients without AR (i.e.

<figure><img src="image_7.png" /></figure>

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /><figcaption>**FIGURE 2** The treatment effect increases with greater disease activity in the placebo groups - the average adjusted symptom score (AASS) by tertile and in the entire study population in the VO57 study (A), the SL75 study (B) and the JP-D1731 study (C). LS mean differences between groups were estimated over each study's primary evaluation period in an ANCOVA. \*p ≤ .05; \*\*p ≤ .01; \*\*\*p ≤ .001. HDM, house dust mite; IR, index of reactivity.</figcaption></figure>

not using AR medications) living in the same environment, the limit of the normal range (defined as the mean plus two standard deviations) of a three-symptom total nasal symptom score (nasal congestion, itching/sneezing and rhinorrhoea, scored from 0 to 3) in controls was 2.8 out of 9.²⁹ No treatment can push a score below the level observed in healthy patients; there is always a floor effect. Hence, there was little room for improvement in the AASS in the low tertiles, which were probably inadequate for showing the efficacy of the 300 IR HDM tablet. Moreover, in a one-year RCT²⁰ in which the LS mean AASS (2.84) in the placebo
<figure><img src="image_10.png" /></figure>

FIGURE 3 The treatment effect increases with greater disease activity in the placebo groups – (A) the average total combined score (ATCS) by tertile and in the entire study population in the SL75 study over the primary evaluation period. LS mean differences between groups were estimated in an ANCOVA (the data are shown as the LS mean and the upper bound of the 95%CI; \*p \le .05; \*\*p \le .01; \*\*\*p \le .001); (B) The change over time in the ATCS (at baseline and at months 3, 6, 9 and 12); descriptive data are shown as the relative difference (in %) in the mean value vs. placebo. HDM, house dust mite; IR, index of reactivity.

group (n = 211) was similar to that observed in the low tertile of the present studies, a lower AASS was not observed in the group treated with the 300 IR HDM tablet (n = 207; LS mean = 2.85). Understandably, these patients were not sufficiently symptomatic to enable assessment of the treatment efficacy, and the trial was terminated for 'futility'.

Furthermore, the AR scores in the patients treated with the 300 IR HDM tablet were similar in all three tertiles and also similar to the placebo scores in the low tertiles. In contrast, the placebo scores were about 50% higher in the high tertiles than in the low tertiles. This suggests the possibility that the final AR scores after 300 IR HDM tablet treatment may have been limited by the 'floor effect' discussed above: that is, the magnitude of AIT's effect may be mainly dependent on the level of AR disease activity. Hence, the tertile analysis highlights that the efficacy of the 300 IR HDM tablet in moderate-to-severe allergic patients subject to yearly climatic and/or regional variations in HDM exposure will be particularly beneficial during the periods when symptoms are most troublesome.

<figure><img src="image_11.png" /></figure>

FIGURE 4 The treatment effect (expressed as the absolute difference vs. placebo (A) and relative difference vs. placebo (B)) increases with greater disease activity in the placebo groups, as illustrated by the AASS by tertile in the natural field trials VO57 (with and without confounding sensitisations) and SL75. AASS, average adjusted symptom score; IR, index of reactivity; LS, least squares.

An important finding to note is the greater effect observed in the subpopulation without potentially confounding sensitisations from the VO57 study (21% reduction in AASS vs. placebo) compared to that of the overall population (18%), with the highest reduction in AASS observed in the high tertile (39%). This study counted 52% of polysensitised patients. Although HDM allergic patients co-sensitised to allergens likely to significantly impact the symptoms were to be excluded, 16% of the patients enrolled had a positive skin prick test to ragweed or mugwort pollen, mould, *Aspergillus* or *Parietaria* and were classified as a subgroup with potentially confounding sensitisations. The efficacy of the 300 IR HDM tablet was shown to be independent of polysensitisation status.²⁴ Nevertheless, limiting confounding factors in the analysis reinforces the demonstration of a particularly better treatment effect in the higher tertiles, where the efficacy of HDM AIT can be fully expressed.
In environmental exposure chamber (EEC) studies, patients are recruited on the basis of their symptom level (e.g. RTSS threshold ≥6 in two studies of HDM tablets<sup>30,31</sup>) during controlled, optimised exposure to HDM allergens; this procedure avoids variations in natural exposure and circumvents the confounding effects of other allergens.<sup>32,33</sup> However, interactions between the EEC trial participants (i.e. seeing the exacerbation of allergic symptoms in other participants) might create a nocebo effect and thus partially mask the true difference between AIT-treated and placebo-treated scores.<sup>32</sup> In an EEC, patients do not use rescue medication, and so the AASS equals the ARTSS. In the two studies of HDM tablets conducted in different EECs,<sup>30,31</sup> the LS mean ARTSS (scale: 0-12) in the placebo arm during the plateau phase of the allergen challenge (i.e. after the first 2h of HDM exposure) after 6 months of AIT were respectively 7.45<sup>30</sup> and 5.51<sup>31</sup> (unpublished data). In one EEC study<sup>31</sup> where the symptom score in the placebo group was similar to that observed in the high tertiles in the VO57 and SL75 natural field studies, the relative reduction in the ARTSS for the marketed dose of HDM tablet vs. placebo was in the same range as in the high tertiles. In the other EEC study, where the symptom score in placebo patients was 2 points higher than in the high tertiles of the natural field studies, the relative reduction reached 49%.<sup>30</sup> These results further emphasise that the magnitude of the treatment effect of HDM AIT is related to the level of AR disease activity.

Another way of taking account of allergen exposure involves measuring the baseline content of *D. pteronyssinus* and *D. farinae* group 1 allergen per g of dust collected at the patients' residence. In the SL75 study,<sup>25</sup> the dust's allergen content could be assessed in 76% of the patients in the full analysis set (see Appendix S1: Methods). During the primary evaluation period, the treatment effect versus placebo was consistently greater in patients exposed to a HDM level equal to or greater than 2, 5 and 10 µg of mite group 1 allergen/g of dust than in patients exposed to less than 2, 5 and 10 µg, respectively. A higher level of HDM exposure was associated with a greater treatment effect versus placebo, with a relative reduction in the primary endpoint of 24.6% in the 38.1% of patients with exposure ≥2 µg/g, 27.4% in the 20.3% of patients with exposure ≥5 µg/g and 40% in the 8.9% of patients with exposure ≥10 µg/g (Table S5). However, these data came from a small proportion of the overall study population: two-thirds of the 76% of patients with data for HDM content in dust had a relatively low level of exposure (<2 µg/g).

In another approach for more precisely assessing treatment benefit as a function of disease activity, one can analyse the difference versus placebo according to the patients' mean AR score at baseline (see Appendix S1: Methods). To be eligible for inclusion in the SL75 study, the patients had to have a baseline ATCS ≥5.<sup>25</sup> A post hoc analysis showed that the beneficial effect of the 300 IR dose was larger in patients with the highest baseline ATCS. With respect to the study population evaluated at month 12 (n=1262), significant differences in ATCS with the 300 IR HDM tablet versus placebo were observed in patients with an ATCS at baseline >6 (n=981, 77.7%; p=.001), >8 (n=502, 39.8%; p=.014), >10 (n=183, 14.5%; p=.026) and >12

(n=42, 3.3%; p=.015), with relative differences of -14.5%, -15.4%, -23.6% and -57.7%, respectively (Table S6). However, these results were derived from small proportions of the study population, that is around a third of the patients with a baseline ATCS >8 and much less for those with a baseline ATCS >10 or >12. Again, the AR score at baseline (prior to treatment allocation) was not absolutely predictive of the treatment effect during the evaluation periods since a relative difference versus placebo equal to or higher than the difference in the total population (-17%) was observed in the small proportion of patients with a baseline AR score >10 (14.5% of the study population), while it was observed in a large proportion of the patients in the medium and high tertiles (i.e. two thirds of the population).

All in all, the tertile approach used in the present exploratory analysis appears to be a valuable proxy measure of disease activity in the context of HDM allergy, where exposure to allergens remains difficult to assess with accuracy. It provides a better understanding of the true impact of the treatment when patients are suffering from their HDM allergy but should not be considered as an assessment of the proportion of patients who have benefited from AIT. Indeed, in RCTs, the treatment effect is evaluated over a relatively limited period compared to the duration of the study. During this limited period, a proportion of patients may be less symptomatic or asymptomatic depending on the variability of geographical, meteorological and domestic conditions, whereas they present more symptoms during other periods in which they will benefit from AIT. Although a tertile analysis takes into account the overall study population (regardless of the individual response to AIT), a number of assumptions must hold. Firstly, high AR scores in placebo-treated patients are assumed to reflect local allergen exposure. Secondly, each centre or cluster of centres geographically close to each other must have equivalent numbers of patients on placebo and patients on active treatment. Tertile analyses have some limitations: for example, a natural field study must have sufficient statistical power for a pre-specified, post-hoc analysis by tertile. The sample size calculation for adding a tertile analysis to the SL75 study statistical plan (n=1434, taking into account the ANCOVA model and the CSMS results) indicated that the planned number of patients for the primary analysis (n=1478) was sufficient to perform a proper tertile analysis.

5 | CONCLUSIONS

In order to facilitate the interpretation of clinical trial data, floor effects for the symptom and/or medication scores used in AR trials should be specifically assessed. Application of the tertile approach based on the placebo group's AR symptom and/or medication scores provides a more accurate picture of the patient benefit actually obtained with AIT in natural field studies with many strongly interacting variables and is more likely to reflect real life. We suggest that RCTs of AIT should include a pre-specified tertile analysis as a secondary endpoint to evaluate the real treatment effect.
## AUTHOR CONTRIBUTIONS

All authors have made substantial contributions to the analysis or interpretation of data critically reviewed the manuscript for important intellectual content. The first draft of the manuscript was written by Pr. Philippe Devillier. Post hoc statistical analyses were conducted by Catherine Gentil. All authors approved the final version of the manuscript for publication. These authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

## ACKNOWLEDGEMENTS

The authors thank Dr Silvia Scurati and Dr Josiane Cognet-Sicé (Stallergenes Greer, Antony, France) for reviewing the manuscript and Dr David Fraser (Biotech Communication SARL, Ploudamézeau, France) for providing editorial assistance, which was funded by Stallergenes Greer.

## FUNDING INFORMATION

This work was funded by an educational grant from Stallergenes Greer.

## CONFLICT OF INTEREST STATEMENT

P. Devillier reports personal fees and non-financial support from ALK-Abelló, AstraZeneca, Boehringer-Ingelheim, Chiesi, GlaxoSmithKline, Menarini, Procter & Gamble, Stallergenes Greer and Viatris. P. Demoly reports grants from ALK-Abelló, AstraZeneca, GlaxoSmithKline, Menarini, Stallergenes Greer, ThermoFisherScientific and Viatris. C. Gentil reports fees to her institution for conducting statistical analyses from Stallergenes Greer. K.C. Bergmann has no conflicts of interest to declare. T.B. Casale reports grants to his institution from ALK-Abelló and Stallergenes Greer, and consulting fees from ThermoFisher. Y. Okamoto reports lecture fees from Shionogi Pharmaceutical Co., Ltd and Stallergenes Greer and non-financial supports/participation to Advisory Board from Stallergenes Greer. O. Pfaar reports grants and/or personal fees from ALK-Abelló, Allergopharma, Stallergenes Greer, HAL Allergy Holding B.V./HAL Allergie GmbH, Bencard Allergie GmbH/Allergy Therapeutics, Lofarma, ASIT Biotech Tools S.A., Laboratorios LETI/LETI Pharma, GlaxoSmithKline, from ROXALL Medizin, Novartis, Sanofi-Aventis and Sanofi-Genzyme, Med Update Europe GmbH, streamedup! GmbH, Pohl-Boskamp, Inmunotek S.L., John Wiley and Sons, AS, Paul-Martini-Stiftung (PMS), Regeneron Pharmaceuticals Inc., RG Aerztefortbildung, Institut für Disease Management, Springer GmbH, AstraZeneca, IQVIA Commercial, Ingress Health, Wort&Bild Verlag, Verlag ME, Procter & Gamble, ALTAMIRA, Meinhardt Congress GmbH, Deutsche Forschungsgemeinschaft, Thieme, Deutsche AllergieLiga e.V., AeDA, Alfried-Krupp Krankenhaus, Red Maple Trials Inc., Königlich Dänisches Generalkonsulat, Medizinische Hochschule Hannover, ECM Expro & Conference Management, Technical University Dresden, all outside the submitted work and within the last 36 months; and he is a member of EAACI Excom, member of the ext. board of directors of DGAKI; coordinator, main- or co-author

of different position papers and guidelines in rhinology, allergology and allergen-immunotherapy.

## DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.

## ORCID

Pascal Demoly https://orcid.org/0000-0001-7827-7964

Oliver Pfaar https://orcid.org/0000-0003-4374-9639

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## SUPPORTING INFORMATION

Additional supporting information can be found online in the Supporting Information section at the end of this article.

**How to cite this article:** Devillier P, Demoly P, Gentil C, et al. Efficacy of 300 IR house dust mite immunotherapy as a function of disease activity: Tertile analysis in clinical trials. *Clin Exp Allergy*. 2024;54:329-338. doi:10.1111/cea.14478