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SIT with a depigmented, polymerized mite extract

. IT has been shown that allergen specific immunotherapy produces clinical benefit in mite allergic patients (1). In most studies, the threshold dose eliciting an immediate bronchial obstruction following immunotherapy was increased significantly using specific bronchial challenges as an objective criterion of efficacy (1). To achieve this goal, a series of injections over a long period of time is required. The time needed to achieve efficacy can be shortened by the use of higher doses, although this approach is more dangerous since a relationship between the dose administered and the appearance of adverse effects has been established. In an attempt to overcome this disadvantage, glutaraldehyde-modified allergenic extracts were developed, proving to be safer than unmodified vaccines while retaining their clinical efficacy (2,3). A further improved method, which includes, before polymerization, a depigmentation step in which the enzymatic activity is inactivated and the pigments are removed, has recently been developed. This process allows the administration of larger doses than of native extracts. Thirty-three patients were included in an open, controlled and parallel study. All the patients met the following criteria: mild or moderate bronchial asthma of more than two years of evolution, and sensitized to D. pteronyssinus and D. farinae. The exclusion criteria were those outlined in the WHO position paper on allergen immunotherapy (1). They were randomly assigned to receive treatment with a mixture of D. pteronyssinus and D. farinae modified allergen vaccine (Depigoid, CBF LETI, S.A., Madrid, Spain) (active group; n=22); or only pharmacological treatment (control group; n=11). The modified extracts showed a decrease in overall IgE binding potency .95% when compared with the native unmodified extracts. The potency for human IgG-antibody binding remained without modification. The native extract of D. pteronyssinus contained 20.35 mg of Der p1 and 12.30 mg of Der p2 per mg of freeze-dried extract, and D. farinae contained 19 mg of Der f 1. After the polymerization process, Der p 1, Der p 2 and Der f 1 were not detectable in the modified extract. The active group received five injections of build up and six maintenance doses. The total number of injections was 232, and only four local reactions with a diameter . 10 cm were recorded. Specific bronchial provocation test (BPT) was performed at baseline and after 6 months using native, standardized (in HEP units), unmodified extract of D. pteronyssinus. A significant difference in the amount of native extract of D. pteronyssinus needed to produce a drop of 20% in the FEV1 (p=0.0029, Wilcoxon test) in the active group was found (median at baseline was 0.6 HEP (35 mg) vs. 3.96 HEP (232 mg) at the end), whereas no difference (median 0.6 vs. 0.57 HEP) was found in the control group. After the treatment, 10 patients in the active group needed more than twice the amount of the native allergen to obtain a positive BPT, whereas only one did in the control group (p=0.028 by contingency table analysis). The results demonstrate that the modified vaccine-treated patients experience a significant clinical improvement after only 6 months of treatment in the objective outcome of specific bronchial provocation test. It is now accepted that an important feature of the efficacy of specific immunotherapy is the delivery of high doses of allergen. Commonly, monthly maintenance doses for mite immunotherapy ranges from 0.5 to 11.5 mg/ml (4–7). In the present study, the highest administered dose was 42.5 mg of freeze-dried modified extract of D. pteronyssinus and 32.5 mg D. farinae. Therefore, the combined highest dose was 75 mg in 0.5 ml. These doses are the equivalent of chemically modifying 10 times the usual dose of a nonmodified extract. The total accumulated dose was 296.65 mg of modified extract of D. pteronyssinus and 226.85 mg of D. farinae (523.5 mg of total extract). An important conclusion of this study is that the modified extract of D. pteronyssinus and D. farinae clearly protects against mite allergens present in the native extracts. It suggests that the clinically relevant epitopes are present in the polymer. These findings are in agreement with the specific IgG data, which demonstrates that both, native and polymer, retained IgG binding epitopes in the same proportion, while specific IgE binding epitopes were significantly reduced in the polymer.