Transient Inhibition of Endogenous Transforming Growth Factor- β1 (TGFβ1) in Hematopoietic Stem Cells Accelerates Engraftment and Enhances Multi-Lineage Repopulating Efficiency

We show that ex vivo transient inhibition of endogenous transforming growth factor-β1 (TGFβ1) in highly enriched and partially enriched murine hematopoietic stem cells (HSC): (1) accelerates engraftment of long-term repopulating HSC (“LTR-HSC”), (2) increases donor stem cell chimeras in competitive bone marrow repopulation studies, (3) permits transplant of as few as sixty LTR-HSC to rescue mice from hematopoietic death after lethal irradiation using direct (non-competitive) transplants and (4) promotes extended survival in vitro of single or multiple LTR-HSC in the absence of growth factors. Our approach to inhibit TGFβ1 involved use of either neutralizing monoclonal antibodies (“TGFβ-MAB”) or antisense phosphorodiamidate morpholino oligomers (“TGFβ1-PMO”) prior to iv transplant. Our previous studies showed that TGFβ1 is a potent reversible inhibitor of LTR-HSC proliferation. Unexpectedly, LTR-HSC treated with TGFβ-MAB and transplanted 1-2 hr later, or treated with TGFβ1-PMO for 16hr then transplanted, rapidly engrafted and produced relatively high levels of donor chimeras that persisted for >6-10 months. Early post-transplant, donor neutrophils predominated but only if TGFβ1 was inhibited in the LTR-HSC. Finally, we tested the ability of LTR-HSC to rescue mice from hematopoietic death after lethal irradiation: as few as 250 LTR-HSC treated with TGFβ-MAB or TGFβ1-PMO rescued essentially 100% of mice and produced a durably graft. In contrast, control treated LTR-HSC (untreated, isotype control MAB, or control-PMO) essentially could not rescue lethally irradiate mice. In cases where donor stem cell numbers are limiting, these methods could prove to be clinically useful. Our more recent studies have demonstrated that human specific TGF-β1-PMO can reverse the dysfunctions of diabetic lin-CD34+CD45+ stem cells to be able to repair endothelium in the retina.