4 - Stem cell separation

Abstract

Separation methods have been applied to the stem cell field for many years for the isolation and/or enrichment of rare subpopulations from specific tissues for clinical applications. One typical example is the isolation of CD34+ hematopoietic stem cells (HSCs) or progenitor cells from umbilical cord blood or bone marrow using density gradient centrifugation integrated with magnetic-activated cell sorting (MACS) for the treatment of hematooncological diseases. Since that time many important advances have been made in stem cell research and the therapeutic potential of other adult stem cell populations has been highlighted. Moreover, the breakthrough of human induced pluripotent stem cell (iPSC) derivation through reprograming has also paved the way for the large-scale production of all types of patient-specific cells for regenerative medicine, tissue engineering and drug screening applications, as well as for studies in developmental biology. These are really important breakthroughs but their translation to clinical practice and other applications is delayed by the lack of efficient and high-resolution cell separation techniques. For example, the development of high-resolution methods to separate heterogeneous populations of human mesenchymal stem cells (MSCs) into specific subpopulations is crucial for studying their specific biological and therapeutic features with respect to their clinical role. Also, the depletion of tumorigenic cells from pluripotent stem cell derivatives, such as iPSCs, is essential for safe clinical application. This chapter critically assesses the main cell separation techniques presently available, their basic principles, their advantages and limitations, and examples of their application in the stem cell field. The techniques are grouped according to the basic principles that govern cell separation, related to the main physical, affinity and biophysical characteristics of cells. Novel trends in cell separation are also highlighted, including the use of novel ligands (e.g. aptamers) for affinity targeting of cells, the application of “tag-less” methods to avoid cell labeling, and the use of microfluidics and other microscale devices.