The aim of this drug trial is to evaluate the annualized asthma exacerbation rate under treatment with Acarizax versus placebo. The trial is intended for adults aged 18 to 65 with severe uncontrolled asthma and a house dust mite allergy. The study will involve 32 patients (up to 38 with study dropouts) recruited from French hospitals, in pulmonology and allergology departments.

Initially, all participants will receive Tezepelumab for 3 to 6 months (M-3/-6) to control asthma symptoms. If asthma is not controlled after 6 months, the participant will be excluded from the study and will continue on standard treatment.

Once their asthma is controlled, patients will be randomized in two groups:

• Group A: Tezepelumab + Acarizax®
• Group B: Tezepelumab + Placebo After 6 months of treatment with Acarizax or placebo (M6), Tezepelumab will be stopped and participants will continue treatment with Acarizax or placebo alone for a further 12 months (up to M18/End of search).

The study will include 5 visits during regular consultations (M-3/M-6, D0, M6, M12 and M18), as well as 2 follow-up telephone calls M3 and M9).

The TEZEPAIT study is a prospective, multicentre, 2-parallel-arms, placebo-controlled, double-blind, randomized (1:1) trial.

PHASE 1: Patients will be included in the study after verification of eligibility criteria and signing of informed consent. All patients will be treated with Tezepelumab for 3-6 months and randomized in two groups:

• Group A: Tezepelumab + Acarizax®
• Group B: Tezepelumab + Placebo If patients are not controlled (ACT ≥ 20/25) after 3 months of Tezepelumab, they will be re-assessed monthly, for 3 consecutive months, until asthma symptoms are controlled or they will be excluded from the rest of the study. If they are not controlled after 6 months, they will be excluded from the study.

PHASE 2: After the phase 1, if asthma symptoms are controlled (Asthma Control Test, ACT ≥20/25), patients in Group A will start Acarizax®, in addition to Tezepelumab, while patients in Group B will continue Tezepelumab plus a placebo. Patients will all receive a 6-month treatment of Acarizax® or placebo, before stopping Tezepelumab (M6), to assure an optimal effect of AIT, as shown in Phase 3 trials.

Patients will all receive an additional 6 months of Tezepelumab starting at D0 (Start of Acarizax®/placebo), before stopping it.

PHASE 3: After stopping Tezepelumab, patients will receive an additional 12-month treatment of Acarizax® or placebo. Patients will receive an 18-month course of Acarizax® or placebo.

For safety and ethical reasons, between M6 and M18 (Tezepelumab treatment will be suspended), in case of reappearance of uncontrolled severe asthma, Tezepelumab will be re-prescribed to patients.

At the end of the study, patients on placebo, if their asthma is controlled, will be offered Acarizax® treatment (as a regular prescription and paid / reimbursed as proposed by the National French HealthCare system) and patients on Acarizax® treatment and controlled will be able to continue it as routine care.

Inclusion Criteria:

• Patients aged ≥ 18 years and ≤ 65 years.
• Patient followed by a specialist in allergy and/or respiratory diseases working at one of the investigating sites in France.
• Patient allergic to HDM and with a clinical history of HDM-allergic asthma.
• Positive specific IgE (≥ 0.35 kUA/L, ImmunoCAP®) and positive skin prick test for Dermtophagoides pteronyssinus and/or Dermtophagoides farinae at screening.
• Patients satisfying diagnostic criteria for severe asthma, according to GINA international guidelines.
• A clinical history of asthma exacerbations in the past two years.
• A history of at least 2 asthma exacerbations during the previous 12 months.
• Uncontrolled asthma (ACT <20/25)
• Lung function measured by FEV1 ≥ 70% of predicted value or according to local requirements.
• Patients with persistent severe asthma who meet the Marketing Authorization criteria for Tezspire® (Tezepelumab) and Acarizax® prescriptions.

Exclusion Criteria:

• Patients sensitized and regularly exposed to animal dander, molds, and/or cockroach or any another perennial allergen.
• Patients treated with a monoclonal antibody for asthma within the previous 3 months or 5 half-lives.
• Patients who have received Sublingual immunotherapy (SLIT) or Sub-Cutaneous Immunotherapy (SCIT) treatment with DermatophagoIdes pteronyssinus and/or Dermatophagoïdes farinae within the previous 5 years.
• Patients received any education provided by a medical indoor environment counselor during the 12 months before the study, or and educational program is programmed during the study.
• Patients with acute respiratory tract infections.
• The patient who have performed any specific measure for mites' avoidance during the 12 months before the study or plan to implement such measures during the study.
• Pregnant, breastfeeding or lactating women.
• Patients with a history of tumor, autoimmune, or immune deficiency pathology.
• Patients with hematological pathology (coagulation disorders, anemia) that could interfere with the blood test.
• The patient reports any previous hypersensitivity reaction to the active substance or excipients present in Tezspire® or Acarizax®.
• Patients unable to read and/or write French language.
• Absence of signed consent.
• Patients who are not beneficiaries of the French social security system.
• Presence of any condition (physical, psychological or other) that might, in the investigator's opinion, hinder study performance.
• The patient is unavailable or unwilling to participate in future visits or is unable to comply with trial protocol.
• Women of childbearing potential and fertile men not using effective contraception.
• The patient is participating in another study for asthma and/or allergy treatment.
• Patients in an exclusion period determined by a previous study or is currently participating to any other allergy/asthma trial.
• Patients under legal protection (guardianship or curatorship)
• Patients with a business or personal relationship with trial staff or sponsor who is directly involved with the conduct of the trial.

Acarizax and placebo tablets will be reconstituted in the same shape.