A targeted T-cell engaging agent for treating a condition characterized by the presence of unwanted cells includes (a) a targeting moiety that is capable of targeting the unwanted cells； (b) a first T-cell engaging domain capable of T-cell engaging activity when binding a second T-cell engaging domain, wherein the second T-cell engaging domain is not part of the agent； (c) at least one inert binding partner capable of binding to the first T-cell engaging domain such that the first T-cell engaging domain does not bind to the second T-cell engaging domain unless the inert binding partner is removed； and (d) at least one cleavage site separating the first T-cell engaging domain and the inert binding partner, wherein the cleavage site is: (i) cleaved by an enzyme expressed by the unwanted cells； (ii) cleaved through a pHsensitive cleavage reaction inside the unwanted cell； (iii) cleaved by a complementdependent cleavage reaction.
