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 safety of Cat-PAD administered as increasing single doses.

This study is designed as a two centre, randomised, placebo-controlled, escalating single dose study in up to 88 cat allergic subjects. Cohorts of 8 subjects will be enrolled. Each cohort will undergo screening 14-28 days before treatment and a baseline challenge for EPSR and LPSR to cat allergen injected into the arm 7 days before treatment. On the treatment day, subjects will be injected either intradermally (into the skin) or subcutaneously (under the skin) with a single dose of Cat-PAD or placebo and safety observations made for 8 h. After 21 days, subjects will again have cat allergen injected into the arm and the EPSR and LPSR will be recorded. The dose of Cat-PAD will be increased in successive cohorts, provided that the previous dose tested was well tolerated.

Inclusion Criteria:

• A reliable history of rhinoconjunctivitis (sneezing, rhinorrhoea, nasal blockage, itchy/red/sore/watering eyes) or controlled asthma (GINA (2006) classification 1) on exposure to cats for at least 1 year.
• Late-Phase Allergic Skin Reaction (LPSR) to 0.010 HEP units Leti cat allergen eight hours after intradermal injection of greater than 25mm diameter response on single arm.

Exclusion Criteria:

• Subjects with asthma falling under GINA(2006) 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 normal.
• Subjects with an acute phase skin response to cat allergen with a weal diameter > 30mm.
• Subjects who suffer from hay fever, and cannot complete the clinical study outside the pollen season.
• Allergen immunotherapy during the last 5 years or Cat Dander immunotherapy ever.
• Use of the following therapies for the periods specified prior to the screening visit will make the subject ineligible for the study: corticosteroids: (depot: 90 days; systemic: 30 days; dermatological, intranasal, inhalational: 15 days); cromones (14 days); antihistamines other than loratadine (nasal and long-acting oral: 10 days; short-acting oral, ocular: 7 days); leukotriene inhibitors (10 days); anticholinergics (7 days); alpha-adrenergic agonists (7 days); tricyclic antidepressants (14 days). If it becomes a medical necessity for a subject to use one of these contraindicated medications during the study this will become an individual stopping criteria.
• 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