The present invention relates to a chimeric antigen receptor (CAR) signalling system comprising； (i) a receptor component comprising an extracellular antigen-binding domain, a transmembrane domain and a intracellular first chemical inducer of dimerization binding domain 1 (CBD1)； and (ii) an intracellular signalling component comprising a signalling domain and a second chemical inducer of dimerization binding domain 2 (CBD2)； wherein CBD1 and CBD2 are capable of simultaneously binding to a chemical inducer of dimerization (CID)； wherein, in the absence of the CID, binding of the antigen-binding component to antigen does not result in signalling through the signalling component； whilst, in the presence of the CID, the receptor component and the signalling component heterodimerize and binding of the antigen-binding domain to antigen results in signalling through the signalling domain.
