Sustained retroviral gene marking and expression in lymphoid and myeloid cells derived from transduced hematopoietic progenitor cells.

The expression of antiviral genes in human hematopoietic stem or progenitor cells has been proposed as a strategy for gene therapy of AIDS. To be successful, this strategy requires safe and efficient transfer of the therapeutic gene into hematopoietic cells and gene expression has to be maintained in HIV susceptible cells following differentiation. We have used retroviral vectors to transfer the gene for a transdominant inhibitor of HIV replication (RevM10) into CD34+ stem/progenitor cells isolated from human umbilical cord blood (UCB). Following transduction, cells were allowed to differentiate either in vitro in clonogenic assays and long-term stromal cell cultures or in human thymus implanted in immunodeficient scid/scid mice in vivo (SCID-hu). Following differentiation and expansion, multiple lineages of cells were shown to carry the transgene. A higher percentage of gene-marked progenitor cells (10-30% in most cases) were detected in methylcellulose colony assays and in long-term stromal cell cultures (1-5%). In contrast, gene-marked T cells derived from transduced CD34+ cells in a SCID-hu model were detected at an even lower frequency (0.01-1%). RevM10 RNA expression was detected in CD34+ cells immediately after transduction and was maintained after in vitro differentiation of those cells into CD14+ myeloid cells. In T cells, the RevM10-specific RNA was detectable by RT-PCR and also by semiquantitative RNase protection. These findings demonstrate that LTR-driven gene expression is sustained in relevant cells derived from retrovirus-transduced hematopoietic progenitor cells after extensive differentiation in vitro and in vivo and suggest that stringent in vivo, rather than in vitro assays, may be a better preclinical system to improve gene marking and expression in hematopoietic cells.