To provide a proof-of-principle that CAR T cell-mediated killing can be observed in zebrafish embryos within a 24 hour assay, which is a typical time-span for in vitro tests, we decided to use a well-established pair in the CAR T cell field, a CD19-specific CAR already applied in the clinics for treatment of B cell malignancies and the CD19 expressing pre-B leukemia cell line Nalm-6 as target tumor cells [22]. The gene discussed is CD19; the disease is neoplasm.