Retroviral transduction of enriched hematopoietic stem cells allows lifelong Bcl-2 expression in multiple lineages but does not perturb hematopoiesis

Transduction of hematopoietic stem cells with a novel retrovirus has allowed long-term expression of human Bcl-2 in multiple hematopoietic lineages. Thy-1.2lo Sca-1+ H-2Khi stem cells enriched from the bone marrow of 5-fluorouracil–treated (Ly5-2) mice were infected with the bcl-2 retrovirus and injected into (Ly5-1) irradiated recipients. Analysis at 5 months indicated that reconstitution of hematopoiesis occurred predominantly from donor-derived (Ly5-2+) stem cells and that, in half the mice (18 of 35), most blood cells derived from virally transduced stem cells. The level of Bcl-2 expression achieved with the retroviral vector approached that of a well-characterized transgenic vector and could be sustained for life in several blood cell lineages. In the 25 mice assessed at 10 months, human Bcl-2 was readily detectable in 62 ± 22% of Ly5-2+ peripheral blood leukocytes. More detailed analysis of a cohort killed between 14 and 20 months established that human Bcl-2 protein could be detected in B and T lymphocytes, granulocytes, macrophages, and some immature erythroid cells. Furthermore, hematopoietic stem cells from the bone marrow of these mice maintained Bcl-2 expression in hematopoietic tissues of secondary recipients for at least another 19 months. These data provide clear evidence for efficient infection of primitive hematopoietic stem cells and for maintenance of proviral expression for over 2.5 years, the lifespan of mice. The level of exogenous Bcl-2 was sufficient to enhance survival of B and T lymphoid cells, granulocytes, and myeloid colony-forming cells cultured under suboptimal conditions, but hematopoiesis in the mice was not notably perturbed.