The present disclosure provides compositions and methods for stimulating,enriching, expanding, and/or activating engineeredcells that express a recombinant receptor, e.g., a chimeric antigen receptor.In some embodiments, the provided methods includeex vivo or in vitro stimulation, enrichment, expansion, and/or activation ofcells by incubation with a particle, e.g., a bead particle,attached to a binding molecule, such as a polypeptide antigen or anti-idiotypeantibody, that recognizes or binds to the recombinantreceptor. Also provided herein are methods for transfecting or transducingcells that have not been previously incubated with an activatingor stimulating agent, such as have not been incubated with anti-CD3/anti-CD28antibodies and/or one or more recombinant cytokines,by transducing or transfecting the cells in the presence of the particles withattached binding molecules. In some embodiments, theprovided compositions can be used in methods to prepare cells, e.g.,genetically engineered T cells, for of adoptive immunotherapy.
