RARE CELL SORTING
Circulating tumor cells (CTCs) are cancer cells that enter the circulatory system after escaping from the primary or metastatic tumors. CTCs in peripheral blood have been used as liquid biopsies that assist in prognosis, evaluation of therapeutic target and monitoring treatment response. Despite the importance of CTCs, due to the low abundance of CTCs among millions of peripheral blood cells, and their heterogeneous morphological and phenotypic profiles, the enrichment and subsequent characterization of CTCs remain technically challenging.
Fig. 1. (A) Enlarged images of the sorting area of the microfluidic chip at different sorting steps. (B) Three-step sorting of 8 mL peripheral blood from a healthy patient spiked with 60 PC9 cells. Red dots represent spiked PC9 cells and black dots represent blood cells.
On-chip Sort is capable of isolating CTCs with high purity via multi-step sorting for further downstream applications such as Next Generation Sequencing. Multi-step sorting works by deflecting liquid pulses to CTCs and their surrounding blood cells into the collection reservoir during the first sort. At the second sort, the isolated CTCs (and blood cells) are reintroduced into the sample reservoir and re-sorted further to reduce the number of blood cells and enrich the CTCs. This step is repeated until all the blood cells are removed (Fig. 1A).
Peripheral blood (8 mL) from a healthy patient was spiked with 60 PC9 cells. Prior to sorting, this sample underwent lysis to remove red blood cells, fixation and permeabilization, and was stained by FITC-conjugated anti-CK and PE/Cy7-conjugated anti-CD45. CK-positive and CD-45 negative cells were isolated on On-chip Sort for three sorts (Fig. 1B). The more the sample was sorted, the more purified the isolated sample became. After three sorts, the isolated sample achieved yield of ~70% and purity of ~80%. These results show that On-chip Sort can isolate highly purified rare cells to facilitate downstream analyses.