CAR-Engineered Immune Cells as Programmable Living Therapeutics: Cell Sources, Engineering Routes, and Translational Bottlenecks

Chimeric Antigen Receptor (CAR)-engineered immune cells now extend well beyond autologous CAR-T therapy to span early-clinical NK, invariant natural killer T, gamma-delta T, and double-negative T platforms, clinical-stage regulatory T-cell programs, preclinical macrophage, neutrophil and dendritic-cell systems, and adjacent BCR/antibody-engineered B-cell approaches. This Perspective proposes a chassis-aware framework in which target biology and tissue location determine the required effector function, and this function in turn constrains cell source, receptor architecture and antigen logic, engineering route, developability assays, and safety controls, rather than allowing receptor design to be transferred unchanged from the CD19 CAR-T precedent. Each chassis requires a lineage-adapted signalling architecture, and ex vivo and in vivo programming are treated as distinct pharmacological strategies with different implications for expression duration, biodistribution, off-target transduction, redosing, and rescue. Clinical translation further requires chassis- and route-specific potency assays, predefined critical quality attributes, batch comparability, quantitative biodistribution and persistence measurements, and controls for lineage instability or suppressive polarization. Treating each chassis-route combination as a distinct therapeutic hypothesis, rather than a variant of CAR-T, provides a testable and generalizable route from molecular design to clinical and regulatory development.