Specific Immunotherapy With Mannan-Conjugated Allergoids for HDM-Allergic Rhinitis/Rhinoconjunctivitis. MM09-SIT-063.

Inclusion Criteria: 1. Subjects who have signed and dated Informed Consent Form (ICF). 2. Female or male aged 12 to 65 years, both included. 3. Subjects with confirmed clinical history of inhalation allergy with moderate-severe persistent rhinitis/ rhinoconjunctivitis according to the ARIA classification(1) of at least 1 year duration (treated with anti-allergic medication) with or without mild-moderate intermittent or persistent controlled asthma according to the definition of GINA 2023(2) caused by D. pteronyssinus and/or D. farinae. The asthma diagnosis will be valid up to 12 months prior to signing the informed consent. 4. Subjects with positive skin prick test to a standardized allergen extract of D. pteronyssinus and/or D. farinae. The wheal major diameter must be ≥ 5 mm and greater than or equal to the wheal major diameter of the positive control (histamine). The results will be valid up to 12 months prior to the signature of the informed consent. 5. Subjects with specific IgE against a complete extract of D. pteronyssinus and/or D. farinae or any of the molecular components of allergenic sources with a value ≥ 3.5 kU/L. The results will be valid up to 12 months prior to the signature of the informed consent. 6. Subjects shall preferably be monosensitised to the study allergens. In the case of subjects sensitised to other aeroallergens, only those with the following characteristics (results valid 12 months prior to signing the informed consent form) may be included in the study: 1. Subjects with a positive skin prick test for Blomia tropicalis, and/or Lepidoglyphus destructor and/or other mites. The specific IgE value for these allergens must be ≤ 3.5 kU/L. 2. Subjects with positive skin prick test for dander may be included, provided that they have occasional exposure and symptoms. Subjects with habitual exposure to dander or living with animals must have a negative prick test. 3. Subjects sensitised (positive prick test) to one or more pollens who must carry out the first symptom and medication collection (after baseline visit (BV) or additional baseline visit (ABV)) and last symptom and medication collection period (after visit 12), according to the following conditions: 1\. Both symptom and medication collection periods must be carried out outside the pollen season. 2\. Both symptom and medication collection periods must start at least one month before and one month after the pollen season. An individual assessment of each subject will be performed in conjunction with the pollen calendar established for each geographical region to check that symptom and medication collection can be carried out under the above conditions. If this is not possible, subjects cannot be included in the study. 7\. Subjects with negative skin prick test for moulds. 8. Women of childbearing age (i.e., following menarche and until postmenopause, defined as no menses for 12 months without an alternative medical cause, or non-subject to permanent sterilisation methods, such as hysterectomy, bilateral salpingectomy, and bilateral oophorectomy) must confirm menarche and have a urine pregnancy test negative result before enrolling the study. 9\. Women of childbearing age must commit to using a highly effective contraception method during the trial and up to 1 months after the end of the investigational medicinal product. Such methods include combined (estrogen and progestogen containing) hormonal, contraception associated with inhibition of ovulation (oral, intravaginal, or transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable, or implantable), intrauterine device (IUD), intrauterine hormone-releasing system (IUS), male condom, diaphragm used with spermicide, bilateral tubal occlusion, vasectomised partner, or sexual abstinence. 10\. Subjects capable of complying with dosage regimen. 11. Subjects must record symptoms and medication consumption in an electronic diary via smartphone (preferably) or in a paper diary. To be confirmed at visit 1 (V1) Only subjects who meet the following criteria will be eligible for randomization: 12\. Subjects with a rhinitis/rhinoconjunctivitis combined symptom and medication score (RCSMS) ≥ 2 out of 6, recorded for at least 10 days, corresponding to moderate-to-severe allergic rhinitis/rhinoconjunctivitis (See Section 6.2). Exclusion Criteria: 1. Subjects sensitised (positive prick test) to one or more pollens where the time interval between baseline visit (BV) and additional baseline visit (ABV) is more than 7 months. 2. Subjects who have received previous immunotherapy to allergens under study (D. pteronyssinus and D. farinae) during the last 5 years or currently receiving immunotherapy with any other allergen. 3. Subjects who have undergone any desensitisation process (e.g., oral immunotherapy \[OIT\], milk, or egg) except those in the maintenance phase since at least 12 months. 4. Those cases in which allergen-specific immunotherapy (AIT) would be a contraindication according to the criteria of European Allergy and Clinical Immunology Immunotherapy Subcommittee.(3) 5. Subjects with uncontrolled asthma, according to GINA 2023(2),asthma with poor symptom control (frequent symptoms or reliever use, activity limited by asthma, night waking due to asthma) and/or frequent exacerbations (≥2/year) requiring oral corticosteroids (OCS), or serious exacerbations (≥1/year) requiring hospitalization. 6. Asthmatic subjects with forced expiratory volume in the first second (FEV1) \<80% despite pharmacological treatment. The result shall be valid up to 12 months prior to signing of informed consent (See Section 9.2). 7. Subjects with severe asthma, according to GINA 2023(2), on Step 4 or 5 treatment, who had poor symptom control and had good adherence and inhaler technique. 8. Subjects on treatment with β-blockers, except those administered topically, or angiotensin-converting enzyme (ACE) inhibitors. 9. Subje