At Tuesday’s State-of-the-Art Session “Stem Cell Engineering”, Cedric Ghevaert, M.D., Ph.D. presented a new approach to the in vitro development of platelets.
- His research team has explored a different strategy to stem cell differentiation called forward programming which delivers high purity and high yield megakaryocyte cultures.
- His team has discovered a strategy to create “universal” platelets using β2 microglobulin as a knock-out target using CRISPR-Cas9 technology. This has exciting implications for patients who are alloimmunized to platelet antigens.
Demand for platelets is high; nearly 60% of administered platelets are used in prophylactic situations to prevent bleeding in settings such as chemotherapy support or inherited platelet disorders, while 40% are used therapeutically during surgery or following trauma. Medical care is dependent on donated platelets from healthy volunteers. However, donated platelets have only a very short shelf life of 5-7 days. Historically, there have been the additional concerns of biosafety and alloimmunization.
Ghevaert explained the traditional process for producing platelets in vitro, beginning with the differentiation of megakaryocytes from human induced pluripotent stem cells (hiPSCs). He described a variety of approaches to differentiation, including the classical approach of directed differentiation and a more recent approach with selective immortalisation of megakaryocyte (MK) progenitors from a progenitor pool.
In contrast, his research team has explored a new strategy to differentiation called forward programming, which relies on the forced expression of MK-specific transcription factors in stem cells to impose the MK identity more directly. This approach delivers high purity and high yield megakaryocyte cultures. But MKs are not the goal. The next step is to produce from these MKs, platelets of adequate number and function that would be required for clinical therapies.
Ghevaert then explained the potential of genome editing to make “universal” platelets. He noted that HLA Class I expression depends on expression of β2 microglobulin. He described how his team can knock-out β2 microglobulin expression and therefore create iPSC lines from which universal HLA Class I null platelets could be derived.
While progress has been made, in vitro platelet production for clinical application still has challenges to overcome and requires technological breakthroughs for further advancement.