Cat allergy is an increasingly prevalent condition, affecting 10-15% of patients with allergic rhinoconjunctivitis and/or asthma. Cat-PAD is a novel, synthetic, allergen-derived peptide desensitising vaccine, currently being developed for the treatment of cat allergy. This study will investigate the efficacy of 4 treatment regimens of Cat-PAD in cat allergic subjects following challenge to cat allergen in an environmental exposure chamber (EEC).

This study is designed as a multicentre, randomised, double-blind, placebo-controlled study of 4 treatment regimens in up to 120 cat allergic subjects. A total of 24 subjects will be randomised into each treatment group. Each subject will undergo screening up to 4 weeks before treatment. Baseline challenge will consist of exposure to cat allergen for 3 hours in an EEC on 4 visits on successive days a week before the first administration of Cat-PAD or placebo. Treatment will be administered as intradermal injections into the flexor surface of alternate forearms. There are 5 treatment regimens involving administration of Cat-PAD or placebo. Post-treatment challenge (PTC) will consist of exposure to cat allergen for 3 hours in an EEC on 4 visits on successive days 18 weeks after the first administration of study medication.

Inclusion Criteria:

• Minimum 1-year documented history of rhinoconjunctivitis (Nasal symptoms: sneezing, itching, rhinorrhoea, blockage; Ocular symptoms: itching, redness, soreness, watering) on exposure to cats. [Subjects may also have controlled asthma (GINA classification 1)].
• Positive skin prick test to cat allergen with a wheal diameter at least 3mm larger than that produced by the negative control.
• Subjects must achieve minimum qualifying symptom scores on at least one Symptom Diary Card during EEC exposure on the third and fourth day during the Baseline Challenge. Minimum qualifying symptom scores are defined as a TRSS of at least 10 out of a possible 24 and a TNSS of at least 6 out of a possible 12.

Exclusion Criteria:

• Subjects with asthma falling under GINA classification 2 (partly controlled) and 3 (uncontrolled).
• A history of anaphylaxis to cat allergen.
• Subjects with a cat specific IgE >100 kU/L.
• Subjects with an FEV1 <80% of predicted.
• Subjects with an acute phase skin response to cat allergen with a mean wheal diameter > 50mm.
• Subjects who suffer from seasonal allergic rhinoconjunctivitis, and cannot complete the clinical study outside the local pollen season or who have significant allergy to other animal dander that cannot be avoided during the study period.
• Subjects who cannot tolerate baseline challenge in the EEC.
• Allergen immunotherapy during the last 12 months or any history of Cat Dander immunotherapy.
• Subjects for whom administration of adrenaline is contra-indicated (e.g. subjects with acute or chronic symptomatic coronary heart disease or severe hypertension).
• Subjects being treated with beta-blockers.
• History of immunopathological diseases.
• Positive test for Hepatitis B, Hepatitis C or HIV at screening.
• Have a history of severe drug allergy or anaphylactic reaction to food.
• A known allergy to thioglycerol.