Cell Separation
Cell separation has become fundamental to biomedicine and life sciences since the first red and white blood cells were first reported in 1974. The ability of isolating cell variants – be it blood cell components, diseased or infected cells from healthy, and transformed cells from normal underpins new therapies, treatments and diagnostics across the sector, resulting in a market valued at approximately $4Bn today. In the overwhelming majority of cases, cell separation takes place using one of three separation methods, each taking approximately 1/3 of total market share by value.
Density gradients exploit differences in cell densities; centrifuging cells in the presence of a density gradient causes the cells to band, allowing retrieval. Fluorescently-activated cell sorting (FACS) uses fluorophore-conjugated antibodies as a discriminator; cells are launched in droplets, each containing one cell, through a fluorescence detection system to determine the cell type and are then electrostatically diverted into different output receptacles. Finally, magnetically-activated cell sorting (MACS) uses magnetic microbeads conjugated with antibodies. These bind to targets on cell surfaces, which then can be extracted by applying a magnetic field.
However, all three methods have drawbacks. Density gradient methods are simple to use and have high throughput, but are only amenable where cells with significant morphological differences, such as blood cell fractionation. High-throughput FACS can sort typically 20 million cells at rates of up to 50,000 cells per second, with higher rates achievable at the cost of purity. FACS is also very expensive to buy (>$100k for a device) and run (due to costs of antibodies and other fluorescent labels). MACS has a lower cost of entry (typically $2k), though the running costs remain; and it has higher throughput (up to 1 billion cells, with 10% in the target fraction). Separations take typically 2h including time for beads to attach to cells. Only density gradient does not require the use of chemical labels; the others use fluorescent chemicals or antibodies to indicate the target population. These are expensive and may have limited specificity; in the case of MACS, the target protein must be present on the surface of the cells. Following separation, the labels may also persist in the cells, limiting their usefulness. Cell losses in FACS and MACS can exceed half the population, particularly at high sorting rates. Furthermore, neither conventional FACS or MACS systems comply with good manufacturing practice (GMP) for cell therapies meaning separated cells cannot be used for therapeutic purposes.