Modeling human hematopoietic stem cell gene therapy in nonhuman primates.

In the field of gene therapy, hematopoietic stem cells (HSCs) are attractive targets because of their self-renewal and multilineage differentiation potential. These properties make them suitable for treatment of many genetic and hematologic disorders (ie, hemoglobinopathies). The initial trials of gene therapy in humans using HSCs were adopted based on studies done in mice. Not surprisingly, the successful results achieved in the murine experiments almost 20 years ago were not translated into success in humans. This failure led to systematic studies in large animal models, including nonhuman primates, of different variables that are known to have an effect on overall gene transfer efficiency. These factors include increasing gene transfer efficiency by using an optimal combination of stimulatory growth factors in transduction media, use of improved retroviral vectors with different pseudotypes, and testing new vectors, such as lentiviral vectors and use of in-vivo/ex-vivo selection systems. In this review, progress and new developments achieved in nonhuman primates and their relevance to the field of human HSC gene therapy are discussed.