THE LEVEL OF MESSENGER-RNA ENCODING THE AMPHOTROPIC RETROVIRUS RECEPTOR IN MOUSE AND HUMAN HEMATOPOIETIC STEM-CELLS IS LOW AND CORRELATES WITH THE EFFICIENCY OF RETROVIRUS TRANSDUCTION

The low level of amphotropic retrovirus-mediated gene transfer into hu man hematopoietic stem cells (HSC) has been a major impediment to gene therapy for hematopoietic diseases, In the present study, we have exa mined amphotropic retrovirus receptor (amphoR) and ecotropic retroviru s receptor mRNA expression in highly purified populations of mouse and human HSC. Murine HSC with low to undetectable levels of amphoR mRNA and relatively high levels of ecotropic retrovirus receptor mRNA were studied, When these HSC were analyzed simultaneously for ecotropic and amphotropic retrovirus transduction, ecotropic provirus sequences wer e detected in 10 of 13 long-term repopulated animals, while amphotropi c proviral sequences were detected in only one recipient, A second dis tinct population of murine HSC were isolated that express 3-fold highe r levels of amphoR mRNA, When these HSC were analyzed simultaneously f or ecotropic and amphotropic retrovirus transduction, 11 of 11 repopul ated mice contained ecotropic provirus and 6 of 11 contained amphotrop ic provirus sequences, a significant increase in the amphotropic retro virus transduction (P = 0.018), These results indicate that, among the heterogeneous populations of HSC present in adult mouse bone marrow, the subpopulation with the highest level of amphoR mRNA is more effici ently transduced by amphotropic retrovirus, In a related study, we fou nd low levels of human amphoR mRNA in purified populations of human HS C (CD34(+) CD38(-)) and higher levels in committed progenitor cells (C D34(+) CD38(+)). We conclude that the amphoR mRNA level in HSC correla tes with amphotropic retrovirus transduction efficiency.