Glutaraldehyde-modified recombinant Fel d 1: A hypoallergen with negligible biological activity but retained immunogenicity

Background: Recombinant allergens are under investigation for replacing allergen extracts in immunotherapy. Site-directed mu-tagenesis has been suggested as a strategy to develop hypoallergenic molecules that will reduce the risk of side effects. For decades, chemically modified allergen extracts have been used for the same reason. Aim: To evaluate whether glutaraldehyde modification is a good strategy to produce hypoallergenic recombinant allergens with retained immunogenicity. Methods: Fel d 1 was cloned as a single construct linking both chains of the molecule and expressed in Escherichia coli and Pichia pastoris. After physicochemical purification, recombinant (r) Fel d 1 was chemically modified using glutaraldehyde. The effect of modification on immune reactivity was evaluated using radioallergosor-bent test, CAP inhibition, competitive radioimmunoassay, enzyme-linked immunosorbent assay, basophil histamine release, and T-cell proliferation assays. Both natural and recombinant unmodified Fel d 1 were used as controls. Results: rFel d 1 demonstrated similar IgE binding and biologic activity as its natural counterpart. Upon modification, IgE-binding potency decreased > 1000-fold, translating into a >10⁶-fold reduction in biologic activity assessed by basophil histamine release. In contrast, the modified recombinant did not show a decreased but even a moderately increased capacity (1.5-fold) to stimulate proliferation of T cells (P < 0.01). Finally, it induced specific IgG antibodies in rabbits that recognized the unmodified allergen. Conclusions: Chemical modification is a practical and highly effective approach for achieving hypoallergenicity of recombinant allergens with retained immunogenicity.