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 look at the efficacy, safety and tolerability of two doses of Cat-PAD in cat allergic subjects following challenge to cat allergen in an EEC.

This study is designed as a randomised, double-blind, placebo-controlled, parallel group study to evaluate the safety and tolerability of Cat-PAD in cat allergic subjects with allergic rhinoconjunctivitis,subjects may also have controlled asthma. The efficacy of Cat-PAD will be explored in subjects using an(Environmental Exposure Chamber)EEC.

The study will consist of 3 study periods. In Period 1, Screening will be performed up to a maximum of 12 weeks before randomisation and may consist of one or two visits to the clinic, at the Investigator's discretion. Baseline Challenge will consist of 4 visits to the EEC at least 3 days before randomisation.

In Period 2, subjects in each cohort complying with the inclusion/exclusion criteria will be randomised to one of three groups and will receive treatment every 2 weeks (±2 days) for 14 weeks.

In Period 3, Post Treatment Challenge will consist of 4 visits to the EEC 18-22 weeks after the first administration in the treatment period and assessments will be performed identical to those at the baseline challenge. Follow-up will be conducted 3-10 days after PTC.

Inclusion Criteria:

• Male or female, aged 18-65 years
• Minimum 1-year history of rhinoconjunctivitis on exposure to cats. (Subjects may also have controlled asthma)
• Positive skin prick test to cat allergen with a wheal diameter at least 3mm larger than that produced by the negative control
• Minimum qualifying rhinoconjunctivitis symptom scores

Exclusion Criteria:

• "Partly controlled" and "uncontrolled" asthma
• History of anaphylaxis to cat allergen
• FEV1 of less than 70% of predicted
• Subjects who cannot tolerate baseline challenge in the EEC
• Treatment with beta-blockers,Alpha-adrenoceptor blockers, Tranquillizers or psychoactive drugs
• A history of any significant disease or disorder (e.g. cardiovascular, pulmonary, gastrointestinal, liver, renal, neurological, musculoskeletal, endocrine, metabolic, neoplastic/malignant, psychiatric, major physical impairment)