ClinicalTrials.gov identifier: NCT00430534.

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Background: The major house dust mite allergen Der p 1 is associated with allergic diseases such as asthma. Production of recombinant Der p 1 was previously attempted, but with limited success. The present study describes the expression of recombinant (rec) ProDer p 1, a recombinant precursor form of Der p 1, in CHO cells. Methods: As optimization of the codon usage may allow successful overexpression of protein in mammalian cells, a synthetic gene encoding ProDer p 1 was designed on the basis of the codon usage frequently found in highly expressed human genes. Gene synthesis was accomplished from a set of 14 mutually priming overlapping oligonucleotides and after two runs of polymerase chain reaction. Results: COS cells transiently transfected with the synthetic ProDer p 1 gene produced up to 5–10 times as much ProDer p 1 compared with the expression level obtained after transfection with the authentic gene. To stably express the recombinant allergen, CHO-K1 cells were transfected with the ProDer p 1 synthetic gene, and one amplified recombinant clone produced up to 30 mg of recProDer p 1 per liter in the culture medium before purification. recProDer p 1 was secreted as an enzymatically inactive single-chain molecule presenting three glycosylated immunoreactive forms of 41, 38 and 36 kD. When examined with respect to direct binding, recProDer p 1 and natural Der p 1 displayed very similar IgE reactivities. However, IgE inhibition and histamine release assays showed a much higher reactivity to natural Der p 1 compared to recProDer p 1. Conclusions: These data indicated that codon optimization represents an attractive strategy for high-level production of allergen in mammalian cells.