In vivo expression and survival of gene-modified T lymphocytes in rhesus monkeys

Lymphocytes can be readily transduced with retroviral vectors and the gene-modified lymphocytes will stably express the inserted genes in vitro for long periods. As a prelude to studies in humans, we evaluated the survival of gene-modified T lymphocytes and the expression of the introduced genes in nonhuman primate T lymphocytes both in vitro and in vivo to determine if lymphocytes could be a potential cellular gene therapy vehicle. Rhesus peripheral blood T-lymphocytes and/or lymph node lymphocytes were transduced with a retroviral vector that contained a bacterial neomycin resistance (NeoR) gene or both NeoR and the human adenosine deaminase (hADA) genes. The cells were then selected for NeoR expression by growth in the neomycin analogue G418 and the autologous gene-modified T cells were reintroduced into the donor animals. T lymphocytes were periodically regrown from the blood and selected in G418. Gene-modified cells persisted in 1 animal for 727 days as detected by analysis for vector DNA by polymerase chain reaction (PCR). Evidence for expression of the human ADA or NeoR genes has also been detected up to 727 days after cell infusion. These findings suggest that gene-modified T lymphocytes can survive and circulate for long periods in vivo and can continue to express the introduced genes.