A new MD Anderson study reports that success with off-the-shelf CAR T therapies is shaped by pre-existing immune rejection and the intrinsic fitness of donor-derived CAR T cells. The work frames variability in clinical response as an interaction between host immune pressure and manufactured cell performance. Rather than treating “universal” CAR T as uniformly durable, the findings emphasize that immune clearance mechanisms may eliminate therapeutic cells before they can exert cytotoxic effects. The study also underscores that donor-derived cell quality—measured as fitness-related properties—can determine persistence. Industry implications include a sharper focus on patient selection and pre-treatment immune profiling, alongside tighter manufacturing QC metrics that better predict functional fitness post-infusion. The analysis supports development of next-generation strategies aimed at reducing rejection while preserving or boosting CAR T cell fitness for sustained activity.