The present invention relates to a chimeric antigen-receptor (CAR) signalling system comprising； (i) a targeting component comprising an antigen-binding domain, a transmembrane domain and a first heterodimerization domain； and (ii) an intracellular signalling component comprising a signalling domain and a second heterodimerization domain； wherein spontaneous heterodimerization between the first and second heterodimerization domains causes the targeting component and signalling component to form a functional CAR complex.
