A Prospective, Randomized, Open-label, Multicentre Study to Compare the Safety of PURETHAL Mites Mixture 50,000 AUeq/mL Rush Up-Dosing Regimen with the Conventional Up-Dosing Regimen in Adult Participants with Allergic House Dust Mite Rhinitis/Rhinoconjunctivitis with or without Asthma.

Prior treatment

• Nasal surgery and/or severe nasal or severe oral disease within 6 months prior to Screening.
• Any immunosuppressive treatment or anti-IgE therapy within the last 6 months prior to the first dosing of the trial drug and during the trial.
• Any treatment with β-adrenergic blockers unless prescribed as per treatment standards to the participant if the medical benefit will prevail the risks upon Investigators discretion.
• Active acute respiratory infection within 2 weeks prior to Screening or at Screening.
• Use of prohibited medication and/or not being able to discontinue medications that are prohibited during the specified trial periods.
• Alcohol, drug, or medication abuse within the past year and during the trial.
• Uncontrolled asthma, as defined by any of the following: a. Asthma Control Test (ACT) ≤19, b. FEV1 ≤70% of predicted value, c. Emergency room visit for asthma attack/exacerbation within 6 months prior to screening, d. At least 1 hospitalization due to asthma within the last year, e. History of intubation/mechanical ventilation due to asthma, f. More than 2 courses of oral steroids used for treatment of asthma within the last 6 months prior to Screening, g. Daily use of inhaled corticosteroids >400mcg budesonide or equivalent.
• Previous treatment with AIT with HDM allergen or a cross-reacting allergen for more than 1 month at the maintenance level within the last 5 years. Initiation of HDM SCIT is acceptable, if treatment has been discontinued before reaching maintenance dose.
• AIT (subcutaneous, sublingual or oral) with other allergens than HDM within the last 3 months prior to screening or planned during the trial period.
• Participation in a clinical trial within the last 3 months prior to screening (e.g. new investigational drug or biological) or during the trial.
• Any vaccination (including COVID-19) less than 1 week prior to screening, during screening and the up-dosing phase (unless strongly medically demanded).

Other illness

• Hypersensitivity to any of the other components of the investigational product.
• Severe immune disorders (including autoimmune diseases) and/or diseases requiring immunosuppressive medication.
• Active malignancies or any malignant disease in the last 5 years.
• A chronic or acute disease that in the opinion of the Investigator might place the participant at an additional risk, including but not limited to the following: cardiovascular insufficiency, any severe or unstable lung diseases, endocrine disorders, clinically significant renal or hepatic diseases, haematological disorders, severe atopic dermatitis, other relevant skin diseases (affecting SPT testing areas).
• Diseases with a contraindication for the use of adrenaline/epinephrine (e.g. hyperthyroidism, glaucoma).
• Moderate to severe nasal obstructive disease such as polyps, septum deviation.
• Clinically significant chronic sinusitis or ocular infection.
• Severe psychiatric, psychological, or neurological disorders.
• History of anaphylaxis with cardio-respiratory symptoms (food allergy, drugs or an idiopathic reaction).

Other

• Participants not able to adhere to the e-Diary procedure and e-Diary completion.
• Female participants of childbearing potential who are pregnant or lactating.
• Any (expected) lack of cooperation or compliance upon the discretion of the Investigator.
• Employees of the Sponsor, CRO, clinical trial site and/or who are 1st grade relatives, or partners of the Investigator.
• Known commitment to an institution by virtue of an order issued either by the judicial or the administrative authorities
• Severe asthma (GINA 2025 treatment steps 4 - 5).

• Prior to screening, participant need to have signed the current approved Informed Consent Form (ICF).
• Male or female participant age 18-65 years at the time of informed consent.
• Clinical history consistent with HDM allergic rhinitis (with or without asthma) according to the ARIA classification (Allergic Rhinitis and its Impact on Asthma) (Bousquet J- et al. 2008) for at least one year prior to the first dosing.
• Participant should be able and willing to complete an e-Diary for a period of 24h after each injection.
• If a participant is asthmatic, the condition must be classified as mild to moderate and be clinically controlled for at least three months before the screening using inhaled steroids and / or Long Acting Beta Agonists (corresponding to GINA 2025 treatment steps 1 - 3) and inhaled steroid use should be on a stable, not higher dose than of ≤400 µg budesonide per day or dose-equivalent (≤500 µg beclometasone dipropionate; ≤160 µg ciclesonide; ≤250 µg fluticasone propionate; ≤200 µg mometasone furoate). Participants with asthma should use their standard asthma medication throughout the whole study period to ensure their asthma remains controlled.
• Positive SPT to D. pter and/or D. far (mean wheal diameter ≥ 3 mm, negative control should be < 2 mm, histamine positive control should be ≥ 3 mm), assessed at Screening.
• Participants with a positive NPT for D. pter extract at Screening (Lebel score ≥6 at 10,000 AU/mL). The test should be postponed, if baseline score is ≥ 3 or if negative control score is > 3.
• Allergen specific serum IgE level for D. pter and/or D. far of > 0,7 U/mL, assessed at Screening at local laboratory.
• Negative pregnancy test at Screening for women of childbearing potential. Females of childbearing potential must use a highly effective method of contraception (in accordance with Clinical Trials Facilitation Group recommendations) to prevent pregnancy and must continue using such a method throughout their participation in the trial. Contraceptive measures considered adequate are: a. combined (oestrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation (oral, intravaginal, transdermal) b. progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable, implantable) c. intrauterine device (IUD) d. intrauterine hormone releasing system (IUS) e. bilateral tubal occlusion f. vasectomised partner g. sexual abstinence.