ToleroMune House Dust Mite (HDM) Tolerability Study

Inclusion Criteria: * Male or female, aged 18-65 years. * Asthma controlled by Step 1 or Step 2 treatment as defined by GINA in the four weeks prior to randomisation. * Asthma controlled by Step 1 or Step 2 treatment as defined by GINA in the four weeks prior to randomisation. * No change in asthma controller treatment (dose, frequency) in the four weeks prior to randomisation. * A reliable history consistent with rhinoconjunctivitis on exposure to HDM for at least 1 year that has required symptomatic treatment on at least one occasion during the year prior to randomisation * Positive skin prick test to Dermatophagoides pteronyssinus with an average wheal diameter at least 5 mm larger than that produced by the negative control. * ImmunoCAP® Dermatophagoides pteronyssinus-specific Immunoglobulin E ≥ 0.35 kU/L. Exclusion Criteria: * History of life-threatening asthma * Asthma exacerbation in the 12 weeks prior to randomisation * Pre-bronchodilator Forced Expiratory Volume in 1 Second (FEV1) \< 80 % of predicted, regardless of the cause. * Post-bronchodilator FEV1/Forced Vital Capacity ratio of \< 0.7. * Concurrent respiratory disease that would confound study participation or affect subject safety. * Non-HDM allergy that may significantly interfere with the results of this study. 7\. Previous immunotherapy treatment with any HDM allergen for more than 1 month within 5 years prior to screening.