Immunotherapy, including checkpoint inhibitors and CAR-T cell therapy, has revolutionized oncology. While these mount durable antitumor responses in some patients, the overall response rate remains modest. Hence, an unmet medical need exists to increase the overall efficacy of immunotherapy. Cytokines, including IL-2 and IL-12, can achieve this. However, poor pharmacokinetics and systemic toxicities hamper clinical translation. The current tumor-targeted cytokine therapies rely on specific receptors on the tumor cell surface, limiting their effectiveness for tumors lacking these signature markers. In this project, we will investigate whether the acidic pH in the tumor microenvironment (TME) can be leveraged for tumor-targeted cytokine delivery. Hereto we will develop Membrane Anchoring CYtokine Chimeras (MACYCs). MACYCs are fusion proteins of a cytokine and the diphtheria toxin translocation domain. The latter anchors to membranes when transitioning from a neutral to a mildly acidic pH, as found in the TME. MACYCs will be designed to mediate ternary complex formation between cytokine receptor and cell membrane in acidic TME. IL-2 and IL-12 MACYCs will be produced by recombinant synthesis. We will investigate in vitro how MACYCs-mediated ternary complex formation depends on the pH of the environment. In vivo, in preclinical mouse tumor models, we will assess the biodistribution, safety, immune stimulation and antitumor activity of MACYCs in vivo.