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Background Immune checkpoint inhibitors and immune-activating cytokines constitute a valuable resource to activate immune responses in tumors. However, their immune-activating capacity is associated with several adverse events, if not controlled spatio-temporally. Powerful gene regulation tools often include foreign proteins, which can trigger immune responses in nonhuman primates. We sought to exploit inducible genetic systems to activate the immune system in tumors in a safe and spatiotemporally regulated manner. While lentiviral vectors (LVs) usually enable constitutive transgene expression, we aimed at advancing towards a fully reversible system to control of transgene delivery, thus favoring adaptive immunity with minimal toxic effects linked to long term exposure.Methods We designed LVs to express synthetic intramembrane proteolysis receptors composed by: (i) a single-chain variable fragment extracellular domain (ECD); (ii) a transcriptionally active intracellular domain that can translocate to the nucleus; (iii) a fluorescent reporter; (iv) an inducible transgene. We assembled the synthetic receptors using a variety of ECDs and set co-cultures for the recognition of specific tumor ligands.Results Synthetic receptor-ligand recognition led to activation in distinct cell types independently of the localization of the ligand at the cell membrane or in the culture medium. Moreover, synthetic receptors drove transgene expression in a reversible and repeatable manner, with target recognition that strictly depended on antigen presence. We also engineered fusion proteins composed by an immune-activating cytokine and a cell-targeting domain, to be employed as inducible therapeutic payloads. We tested a variety of linkers between the cytokine and cell-targeting domain. We identified fusion proteins that enabled recognition and activation of immune cells upon targeting in vitro and in vivo.Conclusions Our findings demonstrate that synthetic receptors can efficiently and specifically recognize target cancer cell ligands, exhibiting robust ligand-dependent activation. This supports their potential as a promising inducible platform for in vivo applications. Moreover, the ability to spatially and dose-dependently control the expression of engineered cytokines may offer a novel therapeutic strategy for liver metastases. Further studies in preclinical models will be essential to assess the translational potential and therapeutic impact of this platform.