Humanized VH4vκ1 CAR is effective against the Raji lymphoma tumor line expressing low CD19 antigen in vitro. (A) Variability of CD19 antigen expression is analyzed on the surface of ALL patient peripheral blood mononuclear cells (PBMCs; n = 10) as well as Raji WT and Raji CD19-low cell lines. (B) Histogram showing CD19 expression on Raji-WT, Raji CD19-KO, and Raji CD19-low clone. Raji CD19-low cell line was used for the following experiments. Tn/mem expressing the specified CAR constructs were analyzed for their ability to (C) degranulate and (D) produce IFN-γ in response to Raji CD19-KO, Raji WT, and Raji CD19-low by flow cytometry. Data are shown as mean of two experiments.