The invention provides a modified T lymphocyte for use in a method of treating a tumor or cancer in an individual comprising a first polypeptide comprising a first extracellular antigen binding domain that binds a first antigen, and a first intracellular signaling domain, wherein said first polypeptide does not comprise a co-stimulatory domain； and a second polypeptide comprising a second extracellular antigen binding domain binding a second antigen, or a receptor that binds said second antigen； and a second intracellular signaling domain, wherein said second polypeptide comprises one or more co-stimulatory domains, wherein said modified lymphocyte becomes maximally cytotoxic only when said first intracellular signaling domain and said second intracellular signaling domain are both activated by said first antigen and said second antigen, respectively.
