Abstract: Provided are anti-idiotype antibodies that specifically recognize anti-ROR1 antibody moieties, in particular, anti-ROR1 antibody moieties present in recombinant receptors, including chimeric antigen receptors (CARs). The disclosure further relates to uses of anti-idiotype antibodies for specifically identifying and/or selecting cells expressing such recombinant receptors, such as anti-ROR1 CAR T cells. The disclosure further relates to uses of anti-idiotype antibodies for specifically blocking or activating such cells.

Abstract: The present disclosure provides compositions and methods for stimulating, enriching, expanding, and/or activating engineered cells that express a recombinant receptor, e.g., a chimeric antigen receptor. In some embodiments, the provided methods include ex vivo or in vitro stimulation, enrichment, expansion, and/or activation of cells by incubation with a particle, e.g., a bead particle, attached to a binding molecule, such as a polypeptide antigen or anti-idiotype antibody, that recognizes or binds to the recombinant receptor. Also provided herein are methods for transfecting or transducing cells that have not been previously incubated with an activating or stimulating agent, such as have not been incubated with anti-CD3/anti-CD28 antibodies and/or one or more recombinant cytokines, by transducing or transfecting the cells in the presence of the particles with attached binding molecules. In some embodiments, the provided compositions can be used in methods to prepare cells, e.g.

Abstract: Provided are receptor tyrosine kinase-like orphan receptor 1 (ROR1)-binding molecules, in particular, to human antibodies specific for ROR1, including antibody fragments. The present disclosure further relates to recombinant receptors, including chimeric antigen receptors (CARs) that contain such antibodies or fragments, and polynucleotides that encode the antibodies, antigen-binding fragments or receptors specific for ROR1. The disclosure further relates to genetically engineered cells, containing such ROR1-binding proteins and receptors, and related methods and uses thereof in adoptive cell therapy.