Challenges and promises for the development of donor-independent platelet transfusions

Abstract

Platelet transfusions are often a life-saving intervention, and the use of platelet transfusions has been increasing. Donor-derived platelet availability can be challenging. Compounding this concern are additional limitations of donor-derived platelets, including variability in product unit quality and quantity, limited shelf life and the risks of product bacterial contamination, other transfusion-transmitted infections, and immunologic reactions. Because of these issues, there has been an effort to develop strategies to generate platelets from exogenously generated precursor cells. If successful, such platelets have the potential to be a safer, more consistent platelet product, while reducing the necessity for human donations. Moreover, ex vivo–generated autologous platelets or precursors may be beneficial for patients who are refractory to allogeneic platelets. For patients with inherited platelet disorders, ex vivo–generated platelets offer the promise of a treatment via the generation of autologous gene-corrected platelets. Theoretically, ex vivo–generated platelets also offer targeted delivery of ectopic proteins to sites of vascular injury. This review summarizes the current, state-of-the-art methodologies in delivering a clinically relevant ex vivo–derived platelet product, and it discusses significant challenges that must be overcome for this approach to become a clinical reality.

Platelet bioreactor-on-a-chip

“…Two major quantitative roadblocks persist in the development of donorindependent PLTs for therapeutic use: (1) generating sufficient numbers (;3 3 10 8 ) of human MKs to support the production of 1 PLT transfusion unit (;3 3 10 11 PLTs); and (2) generating physiological numbers of functional human PLTs (;10 3 ) per MK. 18 The development of human embryonic stem cell cultures (hESC), 44,46 and more recently, hiPSC 47 (Feng Q et al, manuscript submitted 2014) offer a physiologically relevant and potentially unlimited source of progenitor cells that can be differentiated into human MKs in vitro to address the first quantitative roadblock. 48 Indeed, because PLTs are anucleate, PLT bioreactor-derived units could be irradiated prior to infusion, addressing concerns that cellular products derived from hESC or hiPSCs could be oncogenic or teratogenic.…”

“…16 Although functional human PLTs were first grown in vitro in 1995, 17 to date only ;10% of human MKs initiate proPLT production in culture. This results in yields of 10 122 PLTs per CD34 1 cord blood-derived or embryonic stem cell-derived MK, 18 which are themselves of limited availability, constituting a significant bottleneck in the ex vivo production of a PLT transfusion unit. Although second-generation cell culture approaches have provided further insight into the physiological drivers of PLT release, they have been unable to recreate the entire BM microenvironment, exhibiting limited individual control of extracellular matrix (ECM) composition, 19,20 BM stiffness, 21 endothelial cell contacts, 22,23 and vascular shear stresses, 24,25 and have been unsuccessful in synchronizing proPLT production, resulting in nonuniform PLT release over a period of 6 to 8 days.…”

Megakaryocyte- and megakaryocyte precursor–related gene therapies

“…Thus, recent studies describing transfusion of platelets derived from iPSCs or HSCs modified with gene transfer vectors indicate the potential feasibility toward accomplishing this goal. 32,77,78 Current analysis of the field indicates that it is essential to achieve further improvement for in vitro production of platelets (especially to increase the number and quality of platelets for transfusion) to make this strategy clinically feasible. 79 The authors of that article surmised that it may be more advantageous to infuse megakaryocytes (rather than platelets) derived from iPSCs.…”

SCL/TAL1-mediated transcriptional network enhances megakaryocytic specification of human embryonic stem cells

“…Patients with these disorders require continued platelet transfusions, but unfortunately, the platelets that are obtained from blood donors are only accessible in limited quantities and have a very short half-life. 2,3 Thus, the generation of a donor-independent system capable of providing constant and sufficiently large numbers of functional platelets would be an important step forward in transfusion medicine. 3 Over the past two decades, several groups have generated MKs and platelets in vitro from CD34 + HSCs that were obtained from peripheral blood, umbilical cord, fetal liver, and bone marrow, but the limited expansion capacity of CD34 + HSCs restricts their use as an efficient source of platelets.…”

“…2,3 Thus, the generation of a donor-independent system capable of providing constant and sufficiently large numbers of functional platelets would be an important step forward in transfusion medicine. 3 Over the past two decades, several groups have generated MKs and platelets in vitro from CD34 + HSCs that were obtained from peripheral blood, umbilical cord, fetal liver, and bone marrow, but the limited expansion capacity of CD34 + HSCs restricts their use as an efficient source of platelets. 4,5 Conversely, human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) are characterized by an unlimited growth capacity and the ability to differentiate into any cell lineage.…”