Our aim was to build on data from our previous comparisons of a L1CAM-specific CAR T cell constructs harboring either long or short spacers and the 4-1BB costimulatory domain, which showed functional discrepancies between preclinical evaluations in vitro and in mouse models, and are used in the ongoing clinical phase I trial for children with neuroblastoma (ClinicalTrials.gov Identifier: NCT02311621) (6). The gene discussed is L1CAM; the disease is neuroblastoma.