Abstract: The invention features a substrate and compositions, kits, devices, and methods employing the substrate that produces an isolated population of cells from a general population. The isolated population is enriched for one or more target populations. Substrate is can be liquefied and allows recovery of unlabeled, viable, and functional cells.

Abstract: The invention features a complex that binds to, stimulates, and expands a desired T cell population and facilitates separation of the target population from a sample. The complex can be gently dissociated from the binding unit after separating the desired T cell population, representing a safe and efficient approach for processing T cells for clinical use. Invention also provides methods of using such complexes as part of adoptive T cell therapy systems.