Diagnostic criteria were based on recommendations by the Pan-American Group for Immunodeficiency and the European Society for Immunodeficiencies, which included failure to thrive, persistent diarrhea, respiratory symptoms, and oral candidiasis, or Pneumocystis pneumonia, severe bacterial infections, and disseminated Bacillus Calmette-Guérin (BCG) infection during the first 2 to 7 months of life. In addition, patients included in the study were <2 years of age, with either transplacentally acquired maternal T cells or <20 % CD3+ T cells, the absolute lymphocyte count (ALC) <3000/mm3. Exclusion criteria include HIV infection, congenital rubella, DiGeorge syndrome, Zap70 deficiency, Cartilage hair hypoplasia, PNP deficiency and MHC class II deficiency.