Biomedical Engineering Reference
In-Depth Information
prepare clinically safe ESC-/iPSC-derived cells. Because specific
surface antigens of undifferentiated ESCs/iPSCs, such as SSEA-4 and
TRA-1-60, have been already identified, undifferentiated ESCs/iPSCs
can be removed by FACS or MACS [36]. Here, the advantages and
drawbacks of FACS and MACS should be mentioned. The advantage
of FACS is that it enables complicated fractionation of targeted cells
with high accuracy. On the other hand, the drawback of FACS is that
it requires high costs and troublesome procedures. Actually, the
apparatus itself is extremely expensive. Furthermore, FACS is still
exclusively used for basic research at present, and some additional
improvement of the apparatus is needed to fulfill the requirements
of clinical safety. In the case of MACS, it enables simpler, lower-
cost, and more scalable fractionation of targeted cells than FACS.
Furthermore, MACS has been already utilized clinically for the
treatment of leukemia [37]. On the other hand, the drawback of MACS
is that the accuracy of cell fractionation is not as high as that of FACS.
This drawback is crucial for the negative selection of undifferentiated
ESCs/iPSCs. Evading these drawbacks of FACS and MACS, Choo et
al
implemented the negative selection of undifferentiated hESCs
by using a cytotoxic antibody [38]. They generated a monoclonal
antibody against podocalyxin-like protein-1, which is the surface
antigen of undifferentiated hESCs. They found that this antibody not
only bound to undifferentiated hESCs selectively but also killed the
cells. It was confirmed that hESCs treated with this antibody did not
form teratomas when transplanted into SCID mice. This negative
selection method is certainly one of the hopeful solutions to evade
the drawbacks of FACS and MACS.
Next, technologies in the positive selection of ESC-/iPSC-derived
cardiomyocytes are mentioned. As one of the strategies to enrich
ESC-/iPSC-derived cardiomyocytes, genetic modification has been
utilized [39-41]. For example, Xu et al. introduced a neomycin-
resistance gene into hESCs, which was designed to express in
differentiated cardiomyocytes [41]. They demonstrated that the
geneticin treatment of differentiated hESCs killed cells other
than cardiomyocytes, and hESC-derived cardiomyocytes were
successfully enriched with a purity of more than 99%. Although
genetic modification methods are certainly valuable for the basic
research of ESC-/iPSC-derived cardiomyocytes, genetic modification
is not suitable for clinical use. Density-gradient centrifugation is
.
