The invention relates to the field of stem cell engraftment and human ex vivo gene therapy.
Bone marrow transplantation is often accompanied by marrow cytotoxic therapy to create marrow space or niches. The usual method of creating such niches is by irradiation and/or chemotherapy treatment. This practice has been challenged by Brecher, Saxe and colleagues, who demonstrated that bone marrow cells (e.g., hematopoietic stem cells) engraft into normal non-myeloablated hosts (Brecher, G. et al. (1982) PNAS USA 79:5085; and Saxe, D. F. et al. (1984) Exp. Hematol. 12:277). These investigators showed varying levels of engraftment up to 25% after infusion of normal bone marrow into non-myeloablated hosts.
One theoretical approach to transplantation involves procurement of stem cells for transplantation followed by expansion of the stem cells to increase their number prior to infusion into the host. Cellular expansion and/or induction into active cell cycling is accomplished by contacting cytokines or other agents, such as 5-fluorouracil, with the stem cells in vivo, if expansion occurs prior to collection of stem cells; or in vitro, if expansion occurs following collection of stem cells. Long-term repopulation of bone marrow with cytokine-treated cells has been assessed in vivo (Bodine D. M., Blood, 79:913, 1992; Szilvassy S. J. and Cory, S., Blood 84:74, 1994; Li, C. L. and Johnson, G. R. Blood 84:408, 1994; and Ramshaw, H. S. et al., Experimental Hematology, 22:823, No. 548, 1994).
Additionally, cytokines have been used in various combinations to enhance retroviral integration into stem cells by increasing the percent of stem cells in the process of active cell cycle. In vitro cytokine incubations have been used to induce active cell cycling in hematopoietic cells to facilitate retroviral integration in various gene therapy approaches (Bodine D. M. et al., Exp Hematol 19:206, 1991; Szilvassy S. J. and Cory, S., Blood 84:74, 1994; and Kittler, E. L. W. et al., Blood 84:344, 1994 (abstr. suppl I)). Subsequent to retroviral integration, these actively cycling transfected stem cells are introduced into a mammal so that they engraft in the bone marrow of the mammal. Thus the success of ex vivo gene therapy is dependent not only on the efficiency of retroviral integration, but also on the efficiency of transfected stem cell engraftment.
There is a great need for methodologies to enhance engraftment of stem cells in a host mammal for the purpose of improved human bone marrow transplantation therapy as well as for improved human ex vivo gene therapy.