Expression of human adenosine deaminase using a transmissable murine retrovirus vector system

Human adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4) was expressed at high levels in cultured mouse cells using a transmissable murine retrovirus vector system. A cDNA clone encoding ADA has been inserted into a plasmid vector containing retroviral transcription and packaging signals as well as a selectable gene for G418 resistance. The constructions were transfected into psi 2 cells, which package the recombinant retroviral genomes into replication-defective virus particles. Isoenzyme analysis for ADA in G418-selected psi 2 cells showed at least 20-fold more human ADA activity than endogenous mouse ADA activity. A mouse T-cell lymphoma line, BL/VL3, was cocultured with transformed psi 2 cells producing human ADA, and some of the cocultured cells were selected for resistance to G418. Both G418-selected and unselected cocultured cells expressed human ADA activity at 25%-50% the level of the endogenous enzyme. Thus, efficient retroviral transduction of ADA expression was obtained.