Soft Synthetic Cells with Mobile Membrane Ligands for Ex Vivo Expansion of Therapy‐Relevant T Cell Phenotypes

The expansion of T cells ex vivo is crucial for effective immunotherapy but currently limited by a lack of expansion approaches that closely mimic in vivo T cell activation. Taking inspiration from bottom‐up synthetic biology, a new synthetic cell technology is introduced based on dispersed liquid‐liquid phase‐separated droplet‐supported lipid bilayers (dsLBs) with tunable biochemical and biophysical characteristics, as artificial antigen presenting cells (aAPCs) for ex vivo T cell expansion. These findings obtained with the dsLB technology reveal three key insights: first, introducing laterally mobile stimulatory ligands on soft aAPCs promotes expansion of IL‐4/IL‐10 secreting regulatory CD8+ T cells, with a PD‐1 negative phenotype, less prone to immune suppression. Second, it is demonstrated that lateral ligand mobility can mask differential T cell activation observed on substrates of varying stiffness. Third, dsLBs are applied to reveal a mechanosensitive component in bispecific Her2/CD3 T cell engager‐mediated T cell activation. Based on these three insights, lateral ligand mobility, alongside receptor‐ and mechanosignaling, is proposed to be considered as a third crucial dimension for the design of ex vivo T cell expansion technologies. This study introduces a novel synthetic cell technology utilizing dispersed liquid–liquid phase‐separated droplet‐supported lipid bilayers for ex vivo T cell expansion. By incorporating mobile ligands on soft synthetic cells, the technology enhances the expansion of regulatory CD8+ T cells with reduced immune suppression susceptibility. These findings highlight the importance of ligand mobility and mechanosignaling in T cell activation, proposing a third dimension for T cell expansion.