Marking and gene expression by a lentivirus vector in transplanted human and nonhuman primate CD34(+) cells

Recently, gene delivery vectors based on human immunodeficiency virus (HIV) have been developed as an alternative mode of gene delivery. These vectors have a number of advantages, particularly in regard to the ability to infe ct cells which are not actively dividing. However, the use of vectors based on human immunodeficiency virus raises a number of issues, not the least o f which is safety; therefore, further characterization of marking and gene expression in different hematopoietic lineages in primate animal model syst ems is desirable. We use two animal model systems for gene therapy to test the efficiency of transduction and marking, as web as the safety of these v ectors. The first utilizes the rhesus animal model for cytokine-mobilized a utologous peripheral blood CD34(+) cell transplantation. The second uses th e SCID-human (SCID-hu) thymus/liver chimeric graft animal model useful spec ifically for human T-lymphoid progenitor cell reconstitution. In the rhesus macaques, detectable levels of vector were observed in granulocytes, lymph ocytes, monocytes, and, in one animal with the highest levels of marking, e rythrocytes and platelets. In transplanted SCID-hu mice, we directly compar ed marking and gene expression of the lentivirus vector and a murine leukem ia virus-derived vector in thymocytes. Marking was observed at comparable l evels, but the lentivirus vector bearing an internal cytomegalovirus promot er expressed less efficiently than did the murine retroviral vector express ed from its own long terminal repeats. In assays for infectious HIV type 1 (HIV-1), no replication-competent HIV-1 was detected in either animal model system. Thus, these results indicate that while lentivirus vectors have no apparent deleterious effects and may have advantages over murine retrovira l vectors, further study of the requirements for optimal use are warranted.