Allergen-specific immunotherapy (AIT or desensitisation) for ‘prophylactic inoculation against hay fever’ was first administered by Dr L Noon in St Mary’s Hospital, London in 1911 (The Lancet 10 June 1911). AIT is now practised globally, and the British Society for Allergy and Clinical Immunology (BSACI) published its guidelines for AIT in Allergic Rhinitis and insect-sting allergy with an aim to standardise good and safe practice in the UK.
AIT alters the natural course of the disease, although the precise immune-mechanisms have not yet been fully elucidated. Broadly speaking, AIT can be described under the following headings:
AIT is currently offered via two modalities in the NHS including:
SLIT is more convenient for patients as it does not involve multiple hospital visits and patients are trained to self-administer with appropriate counselling. Furthermore, SLIT carries a superior safety profile. Whilst anaphylaxis and generalised allergic reactions may occur with SCIT, they are extremely rare with SLIT. A recent national survey showed considerable heterogeneity with respect to choice of AIT extracts used by NHS clinics across the UK. Currently, there are only two products licensed in the UK including Grazax and Pollinex.
Patients are carefully assessed for the nature of allergic symptoms, their severity and temporal association with the respective allergen. Evidence of sensitisation demonstrated by skin prick test or serum specific IgE to the respective allergen is mandatory prior to commencement of AIT.
AIT is considered in those patients with partial or no response to first line pharmacotherapy, and in whom allergic rhinitis has a significant adverse impact on health-related quality of life. AIT is also considered for cat and horse allergy under special circumstances (eg: occupational exposure).
AIT should not be used for the treatment of asthma. In the UK AIT is not administered in patients with moderate-severe asthma, uncontrolled asthma or brittle asthma. It can be administered to patients with seasonal asthma and may be considered in those with well controlled mild asthma. Asthma is an independent risk factor for anaphylaxis. A detailed description of indications and contraindications of AIT are discussed in BSACI guidelines.
The optimal duration of AIT in the UK is 3 years.
As with AIT, all patients must have demonstrable sensitisation to the respective venom prior to administration of VIT. Also, patients should be screened for an underlying mast cell disorder (skin lesions and baseline serum tryptase).
VIT is not recommended for large local reactions, or in patients with severe, uncontrolled or brittle asthma. A detailed description of indications and contraindications are discussed in BSACI guidelines.
VIT is administered via the subcutaneous route. Optimal duration of VIT is 3 years. The majority of clinics in the UK employ a 12 week up dosing regimen starting with a small dose, also called ‘conventional protocol’. Target maintenance dose of VIT is 100 mcg every 4-6 weeks and up to 8 weeks in the final year of treatment. Accelerated regimens such as ‘rush’ and ‘ultra-rush’ are seldom employed in the UK. The only licensed VIT product in the UK (Pharmalgen) has been approved by NICE.
Whilst wasp VIT carries a high success rate (95-100%), bee VIT may show failure rates of up to 20-25%. Rarely, longer periods of treatment are considered under special circumstances.