Chimeric T cell receptors (TCR) are provided that combine, in a single chimeric species, the intracellular domain of CD3 .zeta.-chain, a signaling region from a costimulatory protein such as CD28, and a binding element that specifically interacts with a selected target. When expressed, for example in T-lymphocytes from the individual to be treated for a condition associated with the selected target, a T cell immune response is stimulated in the individual to the target cells. The chimeric TCR's are able to provide both the activation and the co-stimulation signals from a single molecule to more effectively direct T-lymphocyte cytotoxicity against the selected target and T-lymphocyte proliferation.