Additionally, a recent survey across several pediatric phase I/II clinical trials utilizing multiple CD19-redirected CAR constructs showed that up to 25% of children with B-ALL treated with a CD19 CAR T cell product ultimately suffered a CD19-negative relapse, accounting for a majority of the recorded relapses (Majzner & Mackall 2018). Here, CD19 is linked to acute lymphoblastic leukemia.