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Peripheral blood T cells can be genetically targeted against cancer using fusion receptors known as chimeric antigen receptors (CARs). Many preclinical studies have provided great encouragement for this approach. However, pioneering clinical trials have been less successful and identified poor T-cell survival in patients as a crucial limiting factor. To address this, what is needed is a system to achieve selective expansion of tumour-specific effector T cells, both in vitro and in vivo. Here, we describe such an approach using IL-4, a pharmaceutical that has been tested in cancer patients and which is normally a poor mitogen for T cells. A chimeric cytokine receptor named 4αβ was engineered in which the IL-4 receptor α (IL-4Rα) ectodomain was fused to the shared βc subunit, used by IL-2/IL-15. Addition of IL-4 to 4αβ-expressing T cells resulted in selective phosphorylation of STAT3/STAT5/ERK, mimicking the actions of IL-2 or IL-15. Using receptor-selective IL-4 muteins, partnering of 4αβ with γc was implicated in these findings. Next, human T cells were engineered to co-express 4αβ with CARs specific for two breast cancer targets: MUC1 or the extended ErbB family. These T cells exhibited an unprecedented capacity to undergo IL-4-dependent expansion in vitro and repeatedly destroyed breast cancer cultures, greatly exceeding the performance of IL-2-stimulated cells. Importantly, 4αβ-expressing T cells retained cytolytic specificity for target antigen and dependence upon IL-4 (or IL-2) for survival. We have also used this system to achieve rapid IL-4-driven ex vivo expansion and enrichment of CAR+ human T cells in bags (T-bags). Experiments were performed under closed and pseudo-good manufacturing practice conditions, scaling up for phase 1 clinical trials. T cells expanded in this manner demonstrate Th1 polarisation and potent tumour destructive activity, both in vitro and in vivo, in tumour-bearing SCID Beige mice. Together, these findings provide proof of principle for the development of pharmacologically regulated T-cell immunotherapy for breast and other cancers.