**Acknowledgements**

expansion of UCB CD34+ cells with SR 1 and cytokines. The median time to neutrophil recovery for 17 patients has been reported as being 15 days. Further studies are planned based on infusion of the expanded unit only. Recent in vitro studies [153] indicate that SR 1 promotes the production of megakaryocyte precursors from CD34+ cells with 90% reaching the proplatelet stage with TPO addition, thereby potentially contributing to the ex vivo production of platelets from normal cells for transfusion.

produced in a fed-batch culture system is recruiting patients with hematological

**vi.** A Phase I/II clinical trial (NCT02668315) involving UM171-expanded UCB HSCs

With most of these clinical studies, the common denominator is that it is possible to reduce the time to neutrophil engraftment to 15–17 days and possibly down to 10–11 days. Thus, improved early neutrophil engraftment is possible with current expansion protocols and the key question going forward relates to whether it is possible to maintain or promote long-term hematopoietic engraftment, particularly where genome editing is applied and where there is

The key considerations in expanding human UCB HSC include (i) cost to health providers of GMP cell products and clinical trials, (ii) the number of clinical trials that UCB recipients can be entered into and alternative protocols for HSCT, (iii) restrictions in the use of some compounds or protocols related to intellectual property rights, (iv) defining which UCB units will engraft long term and why 1 UCB unit will engraft in preference to another, (v) addressing variability in donor cell response, particularly related to platelet engraftment and long-term reconstitution of the expanded UCB unit, (vi) the availability of licensed facilities in which to expand cells, and (vii) the optimal development of the best and cheapest protocols to allow rapid engraftment of neutrophils and platelets, longer-term lymphoid reconstitution, and expansion of the HSCs without their differentiation for long-term hemopoietic reconstitution

Clinical trials to date have demonstrated improved homing or retention in the bone marrow niche and improved early neutrophil engraftment. Further research and development is required to regulate the self-renewal of the HSC without significant differentiation in order to facilitate novel genome engineering studies and the development of this into a cost-effective GMP-grade process. Ensuring that the cells can effectively home to and engraft in the bone marrow after this manipulation may require the addition of small molecules (e.g., fucTVI, dmPGE2) for a short period prior to transplant after expansion with specific growth factor cocktails. In the short term, better characterization and refinement of newer and existing UCB products will result in shorter hospital stays and improved prognosis for HSC transplant recipients as to-time-to-hematological-reconstitution shortens, the incidence of graft failure reduces and treatment of residual malignant or cure for acquired or inherited disease improves. Better characterization of UCB self-renewal and differentiation should also ex-

malignancies from January 2016.

154 Umbilical Cord Blood Banking for Clinical Application and Regenerative Medicine

**6. Conclusions**

a need to expand blood cells ex vivo for difficult-to-transfuse patients.

at affordable costs to the healthcare provider and for transplant recipients.

The authors have no conflicts of interest to declare. We would like to acknowledge NHS Blood and Transplant, a University of Oxford RDM award, and Innovate UK for their support. We would like to thank Mrs Wendy Slack for proof reading the manuscript.
