In gene therapy, in order to avoid serious side effects due to the unexpected expression of the transgene in non-target cells, transgenes have to be delivered only to the target cells. In response to this issue, many researchers have aimed at developing target cell-selective gene carriers using active targeting strategies. However, such methodology does not always work, because an ideal molecular marker, which is specific to the target disease cells, is not always available. In this study, we introduce a new concept regarding target disease cell-selective gene therapy (D-RECS). Here, we use intracellular signals, which are activated to an extraordinary degree only in the target disease cells, as a trigger for transgene expression using polymer-peptide conjugates. This strategy could actually activate gene expression in the target signal-activated cells only. Hyper-activation of certain intracellular signals has been reported in many diseases. Thus, this new strategy is expected to provide a powerful methodology for future gene therapy. In this review, the basic concept, some examples, and the molecular design of D-RECS carriers are introduced.