Early ERT has also been previously described to improve immune function in these mice, twice weekly injections of PEG-ADA at high doses (1–5 units of PEG-ADA per gram body weight) from day 10 pp can normalize the percentages of CD4+CD8+ cells in the thymus of 7–8 weeks old ADA–/– mice and prevent the respiratory failure (24). This evidence concerns the gene ADA and respiratory failure.