Collection and expansion of single cells and colonies released from a micropallet array.

The ability to selectively grow out individual cells possessing unique characteristics from within a mixed population is of widespread importance for biomedical investigations. Generation of genetically engineered cell lines, transformation studies, cell-based assays, and stem cell studies are examples where single-cell cloning is of immense value. The vast majority of mammalian cells grow adherent to a surface; therefore, positive selection followed by cloning of cells while the cells remain adherent to their growth surface is an important goal. We recently demonstrated a microfabricated cell array combined with laser-based release of individual array elements for positive selection of single cells. In the current work, a strategy to collect single cells for clonal expansion is described. The system enabled cloning of individual cells with 80-90% efficiency. Single cells were selected and cloned from small populations of fewer than 10,000 cells. Strategies used by cells to migrate from the pallets to form colonies on the surface of the collection device were examined. Implementation of encoded array elements made it possible to follow specific cells throughout the selection, collection, and cloning procedure. Thus, a particular cell can be identified by any number of imaging techniques, isolated, and clonally expanded to generate a homogeneous cell line or a pure sample for genetic or biochemical analysis.