Figure 3.

Major steps involved in one cycle of cell-SELEX to isolate aptamer probes for cell tracking. Briefly, after the incubation of a random single-stranded aptamer library with target cells and subsequent washing steps, negative selection is performed to remove nonspecific binding sequences. Subsequently, the target-bound sequences are PCR-amplified prior to being subjected to the next cycle. The aptamers can then be attached to therapeutic cells ex vivo to track their biodistribution or differentiation in stem cell therapy following implantation into the host. Alternatively, the labeled aptamers can be used for specifically monitoring target cells. Images of the bone marrow and mice were modified from https://commons.wikimedia.org/wiki/File:Gray72.png by Henry Vandyke Carter and from https://www.stockvault.net/photo/126860/white-mouse by 2happy, respectively, with permissions.