Artificial extracellular matrices (ECM) based on 3D biohybrid hydrogels consisting of covalently crosslinked polyethylene(glycol) and heparin have been developed, which can easily be loaded with positively charged biomolecules through electrostatic interactions.1 To finely control both the structural and mechanical properties of these 3D hydrogels, we have used different manufacturing procedures, such us the inverse opal technique2 or 3D printing.3 These PEG-heparin hydrogels have been designed to mimic the ECM of healthy secondary lymphoid organs, in particular the lymph nodes, with the objective of improving the current CAR T cell manufacturing technologies. In particular, we aim at obtaining in vivo persistent CAR T cells; a current limitation of the adoptive cellular (immuno)therapies. Indeed, we have been able to increase the proliferation of primary human T cells as well as CAR expression, when compared with state-of-the-art expansion systems, while maintaining therapeutically desired phenotypes.1,2,4 Additionally, we tailored our 3D hydrogels to mimic the ECM of malignant tissues with the aim of creating well-controlled and reproducible patient-derived tumoroids.