A novel serum-based assay of functional IgG inhibitory activity is predictive of the clinical response to immunotherapy

Hayfever affects 12 million people in UK and may ruin what for most of us is the best time of the year. Hayfever impairs concentration at work and may reduce performance in school exams. Many sufferers respond to antihistamines and nasal steroid sprays. There remains a hard core who may benefit from allergy vaccination (desensitisation injections). Discovered in UK 100 years ago, this treatment is highly effective but requires specialist supervision . We have developed in partnership with a company, ALK Abello, an alternative, effective and safer vaccine containing grass extract that is taken daily as a rapidly dissolving tablet under the tongue (GRAZAX). Based on our understanding of how vaccination works, we now wish to develop a test that measures ‘protective’ antibodies in the bloodstream that will allow us to predict those patients who are likely to respond best to desensitisation and to monitor the effects of treatment.

Hayfever affects 12 million people in UK, of whom 4 million remain uncontrolled by medical therapy. For such individuals, subcutaneous allergen immunotherapy is effective and involves weekly then monthly injections of grass pollen extract, usually continued for 3-4 years. The subcutaneous route is associated with a small risk of systemic reactions and requires specialist supervision. The alternative sublingual route, using high dose allergen in liquid/tablet form under the tongue, is also effective and safe for home use. We are currently undertaking a definitive 5 year trial to address whether sublingual immunotherapy, like subcutaneous treatment, induces long-term remission after 3 years therapy.
Immunotherapy deviates B cell responses towards production of allergen-specific IgG, particularly IgG4, which has the potential to block IgE-mediated responses. Although IgG4 levels have historically shown poor correlations with treatment response, ?functional? assays reflecting antibody avidity/affinity could be more predictive of efficacy. Pollen-specific IgG4 induced by immunotherapy inhibits IgE-facilitated allergen presentation (IgE-FAP), possibly a rate-limiting process in Th2 cell-driven allergic responses at the low allergen concentrations encountered during the pollen season. We have replaced this complex technique with a simple flow cytometric assay (IgE-FAB) detecting allergen-IgE complex binding to B cells expressing CD23 (low affinity IgE receptor). Binding is inhibited by IgG within sera of immunotherapy-treated subjects. Remarkably, in a small double-blind withdrawal trial of immunotherapy, continuing clinical remission was associated with persistence of IgE-FAB inhibitory activity despite a marked reversal of absolute IgG4 concentrations. Thus our ?functional? assay is distinct from serum IgG as detected by ELISA. The detailed technical validation of this assay is now published (Dec 06).

We are now seeking validation of this assay as a biomarker in a wider context. Inhibitory activity for IgE-FAB will be measured in 2 recent large multi-centre immunotherapy trials in severe hayfever: (1) the UK Subcutaneous Immunotherapy study (n=410) - a one year double-blind placebo-controlled dose-response study, and (2) the International Sublingual Immunotherapy study (n=634) - an ongoing 5 year double-blind placebo-controlled study of sublingual grass allergen tablets, with the final 2 years comprising a double-blind withdrawal of therapy. Published results for year one confirm good efficacy.
These definitive studies will help determine whether simple immunoreactive IgG or ?functional? IgG are predictive biomarkers of the clinical response in individual patients. Moreover, we aim to provide the basis for a predictive assay to identify the responder population, when to discontinue therapy and to predict relapse after treatment discontinuation.