In vivo generation of human CD19‐CAR T cells results in B‐cell depletion and signs of cytokine release syndrome

Chimeric antigen receptor (CAR) T cells brought substantial benefit to patients with B‐cell malignancies. Notwithstanding, CAR T‐cell manufacturing requires complex procedures impeding the broad supply chain. Here, we provide evidence that human CD19‐CAR T cells can be generated directly in vivo using the lentiviral vector CD8‐LV specifically targeting human CD8(+) cells. Administration into mice xenografted with Raji lymphoma cells and human peripheral blood mononuclear cells led to CAR expression solely in CD8(+) T cells and efficacious elimination of CD19(+) B cells. Further, upon injection of CD8‐LV into mice transplanted with human CD34(+) cells, induction of CAR T cells and CD19(+) B‐cell depletion was observed in 7 out of 10 treated animals. Notably, three mice showed elevated levels of human cytokines in plasma. Tissue‐invading CAR T cells and complete elimination of the B‐lymphocyte‐rich zones in spleen were indicative of a cytokine release syndrome. Our data demonstrate the feasibility of in vivo reprogramming of human CD8(+) CAR T cells active against CD19(+) cells, yet with similar adverse effects currently notorious in the clinical practice.