Molecular Analysis of T Lymphocyte-Directed Gene Therapy for Adenosine Deaminase Deficiency: Long-Term Expression In Vivo of Genes Introduced with a Retroviral Vector

Abstract

Peripheral blood lymphocytes from a patient with adenosine deaminase (ADA) deficiency were transduced in vitro with a replication-defective retroviral vector containing a human ADA-cDNA. Eighteen months after the last of a series of infusions of autologous retroviral vector-treated cells, vector sequences were detectable in DNA isolated from peripheral blood mononuclear cells (PBMCs), with an average copy number approaching one per cell. Increased ADA enzyme activity reaching approximately one-quarter normal levels was found in this population of cells. Other evidence of long-term retroviral vector expression in vivo included neomycin phosphotransferase (NPT) activity and demonstration of persistent vector mRNA by reverse transcriptase polymerase chain reaction (RT-PCR). No evidence of spontaneous reversion of either mutant endogenous ADA allele was found.

Overview summary

Children with severe combined immunodeficiency due to adenosine deaminase (ADA) deficiency have been treated with autologous T lymphocytes transduced in vitro with a retroviral vector containing both a normal human cDNA for ADA and a cDNA for neomycin phosprotransferase (neo). This report by Mullen et al. analyzes long-term expression of the retroviral vector genes in the first patient over a three and one-half year period of treatment and observation.