The primary objective of this clinical trial is to quantify the loss of in vivo biological potency of a depigmented polymerized (DPP) allergenic cat epithelial extract versus the native allergenic extract (N).

This is an open-label, non-randomized phase II clinical trial.

Three different concentrations of three different cat epithelial allergenic extracts, together with a positive and negative control, using 10 mg/ml histamine dihydrochloride and a glycerated phenol saline solution, respectively, will be tested in every subject on the volar surface of the forearm.

Inclusion Criteria:

A subject will be eligible for inclusion in the study only if all of the following criteria are met:

• The subject (and/or legal representative, where applicable) has given written, signed and dated informed consent.
• Subjects of either sex and of any race or ethnic group.
• Age > 18 years and < 60 years on the day of inclusion in the study.
• Positive clinical history of allergy to cat epithelia (i.e., rhinitis, conjunctivitis, rhinoconjunctivitis, asthma, urticaria, etc. ).
• A positive prick-test (mean diameter of papule ≥ 3 mm or area of papule ≥ 7 mm2) with a commercial extract of cat epithelium. The results of the prick-test will be valid if they were obtained in the year prior to inclusion of the subject in the study.
• A positive specific IgE test (> 0.70 KU/l) for cat epithelium. The results of the IgE test will be valid if they were obtained in the year prior to inclusion of the subject in the study.

Exclusion Criteria:

A subject will NOT be eligible for inclusion in the study if any of the following criteria are met:

• Immunotherapy in the last 5 years involving allergens known to be able to interfere with the test allergen (e.g., cat extract).
• Use of drugs that can interfere with the skin response before and during the study (e.g., antihistamines), within the intervals established in section 9.1 and appendix 1.
• Treatment with any of the following medicines: tricyclic or tetracyclic antidepressants or MAOIs (Monoamine oxidase inhibitors), beta-blockers or chronic use of oral corticosteroids or use of corticosteroids via either the oral or the parenteral route in repeated and intermittent dosing regimens (> 10 mg/day of prednisone or equivalent).
• Pregnant or nursing women and women with a positive pregnancy test in visit 2.
• Dermographism affecting the skin of the test site, in either of the two visits to the study centre.
• Atopic dermatitis affecting the skin of the test site, in either of the two visits to the study centre.
• Urticaria affecting the skin of the test site, in either of the two visits to the study centre.
• Clinically relevant immune system diseases (both autoimmune disorders and immune deficiencies). (Hashimoto's thyroiditis with hypothyroidism well controlled through thyroid hormone therapy does not necessarily represent a contraindication. Graves' disease (hyperthyroidism) would be an exclusion criterion due to the potential risk in the event adrenaline must be used.)
• Serious uncontrolled diseases that may increase the safety risk of the subjects participating in the study, including but not limited to the following: heart failure, serious or uncontrolled respiratory diseases, endocrine disorders, clinically relevant liver or kidney diseases, or haematological disorders.
• Patents with diseases or conditions that limit adrenaline use (coronary disease, severe arterial hypertension, etc.).
• Serious psychiatric, psychological or neurological problems.
• Medication, alcohol or illegal drug abuse in the last year.
• Participation in any other clinical trial during the 30 days (or 5 times the biological half-life of the investigational product - whichever is longest) prior to inclusion of the subject in this study.