The choice of molecular components in engineered immune cell therapies could dramatically impact both treatment success and patient safety in blood cancers. This comprehensive analysis reveals critical differences between competing CAR T-cell designs that may influence clinical decision-making for thousands of leukemia patients worldwide. Examining outcomes from 40 clinical trials encompassing 1,540 patients with treatment-resistant acute lymphoblastic leukemia, researchers identified significant performance variations between different CAR T-cell engineering approaches. Constructs incorporating the 4-1BB co-stimulatory domain achieved a 94.0% minimal residual disease-negative complete remission rate, compared to 84.4% for CD28-based alternatives. More importantly, 4-1BB constructs demonstrated reduced neurotoxicity—a potentially life-threatening side effect causing seizures and cognitive impairment. The analysis also confirmed that targeting CD19 alone or in combination with CD22 outperformed CD22-only approaches. These findings represent more than incremental improvements in cancer immunotherapy. The safety advantage of 4-1BB constructs could expand treatment eligibility to older or more fragile patients previously considered too high-risk for CAR T-cell therapy. However, the meta-analysis highlights a persistent challenge: while initial remission rates exceed 80%, durability remains problematic across all construct types. This suggests that optimizing the initial cellular product, while crucial, represents only one piece of the therapeutic puzzle. The field may need combination approaches or sequential treatments to convert these impressive short-term responses into lasting cures for relapsed leukemia patients.