Effect of modification of peanut conglutin on IgE and T cell reactivity in adults with peanut allergy

Abstract

Background: Peanut allergy has a strong impact on the daily life of patients. Because curative therapy is still not available, patients need to follow life-long elimination diets. Specific immunotherapy (SIT) using peanut extract has been shown to be associated with significant side effects. Chemically modified allergens may provide a safer alternative. Method(s): Purified native conglutin, containing Ara h 2 and Ara h 6, and two modifications thereof, one being reduced and alkylated (RA), and one with additional glutaraldehyde treatment (RAGA), were generated by HAL Allergy BV. Serum of 14 peanut allergic patients (proven by DBPCFC) was analyzed for IgE binding on immunoblot, and for IgE, IgG1 and IgG4 binding by ELISA. Allergeninduced basophil degranulation was analyzed by direct basophil activation test (BAT). T cell lines specific for native conglutin were generated and analyzed for proliferation (stimulation index, SI) and cytokine production (IL-13, IFN-gamma, IL-10, TNF-alpha). Result(s): The 14 patients reflected the peanut-allergic population, with a range of clinical severity from mild to severe, a positive skin prick test to Ara h 2 and Ara h 6, and IgE-binding to these proteins on immunoblot. As compared to native conglutin, IgE binding to RA and RAGA on immunoblot was reduced significantly. The reduction was stronger for RAGA than for RA, and stronger for Ara h 6 than for Ara h 2. In ELISA, median binding to RA was reduced by 78% for IgE, 56% for IgG1, 78% for IgG4. Binding to RAGA was reduced by 87% for IgE, 82% for IgG1, 96% for IgG4. The median allergeninduced basophil degranulation was reduced by 82% for RA and by 91% for RAGA. In contrast to the reduction of IgE and IgG reactivity, T cell reactivity was largely retained: proliferation to RA was unchanged (SI 2.0-26.4, median 18.3), and proliferation to RAGA was reduced but still strong (SI 1.2-19.6, median 8.3) as compared to native conglutin (SI 9.9-18.4, median 12.7). Levels of IL-13, IFN-gamma and TNF-alpha correlated with proliferation. No IL-10 production was observed. Conclusion(s): Chemical modification of peanut conglutin overall reduces allergenicity, as measured by IgE binding and allergeninduced basophil degranulation, with the strongest reduction observed for RAGA. In contrast, T cell immunogenicity to both modified variants, and especially to RA, is retained. This shows that chemical modification may be a promising approach for the development of immunotherapy for peanut allergy.