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In vitro expansion of hematopoietic stem cells by recombinant TAT-HOXB4 protein


Hematopoietic stem cells (HSCs) can self-renew extensively after transplantation. The conditions supporting their in vitro expansion are still being defined. Retroviral overexpression of the human homeobox B4 (HOXB4) gene in mouse bone marrow cells enables over 40-fold expansion of HSCs in vitro. To circumvent the requirement for retroviral infection, we used recombinant human TAT-HOXB4 protein carrying the protein transduction domain of the HIV transactivating protein (TAT) as a potential growth factor for stem cells. HSCs exposed to TAT-HOXB4 for 4 d expanded by about four- to sixfold and were 8–20 times more numerous than HSCs in control cultures, indicating that HSC expansion induced by TAT-HOXB4 was comparable to that induced by the human HOXB4 retrovirus during a similar period of observation. Our results also show that TAT-HOXB4-expanded HSC populations retain their normal in vivo potential for differentiation and long-term repopulation. It is thus feasible to exploit recombinant HOXB4 protein for rapid and significant ex vivo expansion of normal HSCs.

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Figure 1: Biochemical properties of HOXB4 proteins.
Figure 2: TAT-HOXB4 promotes in vitro proliferation of bone marrow cells.
Figure 3: TAT-HOXB4 stimulates ex vivo expansion of Sca+Lin cells.

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The authors acknowledge N. Mayotte for her technical assistance, M. Frechette and S. Matte for their expertise and help with the maintenance and manipulation of the animals kept at the SPF facility, and E. Massicotte for help with flow cytometry. This work was supported by a grant from the National Institutes of Health to G.S. and R.K.H. G.S. is a Scholar of the Leukemia and Lymphoma Society of America.

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Correspondence to Guy Sauvageau.

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Krosl, J., Austin, P., Beslu, N. et al. In vitro expansion of hematopoietic stem cells by recombinant TAT-HOXB4 protein. Nat Med 9, 1428–1432 (2003).

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