T-cell lines from 2 patients with adenosine deaminase (ADA) deficiency showed the restoration of ADA activity resulted from the reversion of an inherited mutation

Abstract

IntroductionAdenosine deaminase (ADA) is an enzyme of the purine salvage pathway that catalyses the deamination of adenosine and 2Ј-deoxyadenosine to inosine and 2Ј-deoxyinosine, respectively. Inherited deficiency of ADA was serendipitously found to result in one of the autosomal recessive forms of severe combined immunodeficiency (SCID). 1 Evaluation of a genotype-phenotype relationship revealed a deficiency of ADA results in varied impairment of immune status as well as clinical course. 2 Residual ADA enzyme activity of each mutant correlated closely with biochemical and clinical phenotypes of patients. 3 In 1990, the first clinical trial of gene therapy was performed in a patient with ADA deficiency. 4 Since then, more than 10 patients with ADA deficiency have been treated by gene therapy. Although beneficial effects of the gene therapy were reported in some cases, 4,5 complete cure of the disease by stem cell gene therapy has not yet been realized. [6][7][8] Such results may suggest that inevitable ADA enzyme replacement interferes with growth advantage of gene-introduced cells compared with recent successful gene therapy of X-SCID patients. 9 Here we report data on 2 patients with ADA deficiency from different families, in whom possible reverse mutation had occurred as reported previously. 10 We detected the reversion in the patients' T-cell lines, and at least one of them seemed to possess the revertant cells in vivo; however, mutant cells might overcome the revertant after receiving ADA enzyme replacement therapy. Study design PatientsPatient 1, now a 13-month-old girl, is the first child of a healthy unrelated couple. She had an episode of respiratory infection at age 15 days, and after 5 days, she was admitted to a hospital with progressive respiratory distress and failure to thrive. Because the number of her peripheral blood lymphocytes was very low (200/L), she was suspected to have SCID, and screening of ADA enzyme activity revealed a trace level of ADA. The patient is now being treated with ADA polyethylene glycol-modified bovine ADA (PEG-ADA).Patient 2, now an 11-month-old girl, is the second child of a healthy couple without consanguinity. When she was 1 month old, she had a bacterial skin infection on her thigh. The episode was temporally controlled; however, she was hospitalized after a few days because the infection recurred. Laboratory examination revealed a very low number of white blood cells (700-1700/L) and hypogammaglobulinemia (IgG, 162 mg/dL; IgA, Ͻ6.0 mg/dL; IgM, 13.5 mg/dL). Her red blood cells (RBC) were examined by ADA screening assay, and the results showed a trace level of the enzyme activity. During this study, she received bone marrow transplantation from her healthy brother when she was 5 months old. Cell linesThe T-cell lines from the patients were established using herpesvirus saimiri as described elsewhere. 11 B-cell lines were also established with EpsteinBarr virus. Because of the low number of peripheral lymphocytes, it took 2 to 3 months to establish both the patients' l...

Spontaneous In Vivo Reversion of an Inherited Mutation in the Wiskott-Aldrich Syndrome

“…Both the patients were characterized with their progressive mild clinical course probably due to the reverse mutation in some lineage cells. Recently, we also detected reverse mutation in T cell lines from two patients with adenosine deaminase deficiency (31). In this study, the patient could survive Ͼ30 years without receiving bone marrow transplantation.…”

A reversion of an IL2RG mutation in combined immunodeficiency providing competitive advantage to the majority of CD8+ T cells

“…9 To date, spontaneous gene reversions have been reported in several patients suffering from ADA-SCID. [10][11][12][13][14] This form of SCID that causes a metabolic disease is due to defective adenine deaminase (ADA) activity in all cells. It has been found that lymphocytes are particularly sensitive to the toxic effects of the accumulating purine metabolites in ADA deficiency.…”

Molecular Basis for Paradoxical Carriers of Adenosine Deaminase (ADA) Deficiency That Show Extremely Low Levels of ADA Activity in Peripheral Blood Cells Without Immunodeficiency

“…The level of total dAXP in RBC of the mother and brother was only slightly elevated to about 1% of total adenine nucleotides (normal Ͻ0.2%) compared with dAXP levels of 0.1% in RBC of the father and 14% in RBC of the child with SCID. As shown in Table I, established patient's T cell line, not B cell line, showed significant ADA activity due to reversion of the maternal mutation (20). In family II, ADA activity in PBMC and granulocytes from the patient's mother was also about 1% of normal.…”

“…We have reported the mutations in family I previously (20). The SCID proband had inherited an ADA allele with the R235Q mutation in exon 8 from her mother and an allele with a 1-bp deletion in exon 4 from her father; her brother also carried the paternal allele.…”

“…We have reported the proband with SCID previously (20). The diagnosis (at age of 3 mo) was based on evaluation of ADA activity in PBMC.…”