High-Level Expression from a Cytomegalovirus Promoter in Macrophage Cells

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Abstract
To identify vectors that provide optimal gene expression in human hematopoietic cells, we investigated retroviruses containing the adenosine deaminase (ADA) gene under the transcriptional control of the promoters/enhancers of Moloney murine leukemia virus and the human cytomegalovirus (CMV) immediate-early gene. ADA expression was monitored in transduced human multipotential promyelocytic leukemic HL-60 cells and human monocytic leukemic THP-1 cells. HL-60 cells can be induced by phorbol ester to differentiate into macrophage lineage cells and by retinoic acid into granulocytic cells. THP-1 cells undergo phorbol ester-induced differentiation to macrophage cells. In LNCA-transduced HL-60 derived macrophage cells, ADA controlled by the CMV promoter was expressed at 100.0 μmol/hr·mg, in contrast to 1.2 μmol/hr·mg from LN-transduced control cells. LNCA-transduced THP-1 macrophage cells showed a similar increase in ADA activity over control cells. These elevated enzyme activities were confirmed by Northern blots, which showed substantial increases in ADA mRNA derived from the CMV promoter. This suggests use of the CMV promoter for gene therapy targeted at macrophages, as, for example, in the treatment of lysosomal storage disorders such as Gaucher disease. These inducible cell lines have allowed the evaluation of transduced gene expression in proliferating and differentiating hematopoietic cells that may serve as an in vitro model of bone marrow-targeted gene therapy. Human hematopoietic cells that can be induced to differentiate into macrophage lineage cells or granulocytic cells were used to investigate vectors containing the adenosine deaminase (ADA) gene under the transcriptional control of the promoters/enhancers of Moloney murine leukemia virus and the human cytomegalovirus (CMV) immediate-early gene. In transduced macrophage lineage cells, ADA controlled by the CMV promoter was expressed at 80-fold higher levels than in uninduced controls. These elevated enzyme activities were confirmed by Northern blots that showed substantial increases in ADA mRNA derived from the CMV promoter. This suggests that gene therapy targeted at macrophages, as, for example, in treatment of lysosomal storage disorders such as Gaucher disease, would benefit from vectors containing the CMV promoter.