Super-resolution imaging reveals altered actin architecture at CAR-T cell immune synapses.

The actin cytoskeleton plays a key integrative role in immunological synapse (IS) formation during T cell activation, but how these dynamics are altered in chimeric antigen receptor (CAR)-T cells remains unclear. Here, we used stimulated emission depletion (STED) microscopy to perform the first super-resolution analysis of actin remodeling at the IS in single- and dual (CD19/CD22) CAR-T cells, activated on supported lipid bilayers across different time points. Quantitative imaging reveals that CAR-T cells form structurally distinct synapses to untransduced cells, characterized by reduced actin-depleted regions, fewer actin foci, and persistent microvilli-like protrusions. These features indicate incomplete cytoskeletal contraction and impaired actin network reorganization, leading to partial synapse maturation. Our findings highlight fundamental differences in actin dynamics between CAR- and TCR-mediated signaling and suggest that defective actin remodeling may contribute to unstable synapse formation, altered signaling integration, and dysregulated responses or off-target effects. These insights could inform future CAR-T engineering strategies to enhance safety and efficacy.