Genetically engineered CAR NK cells display selective cytotoxicity against FLT3‐positive B‐ALL and inhibit in vivo leukemia growth

• Published in: International journal of cancer Vol. 145; no. 7; pp. 1935 - 1945
• Main Authors: Oelsner, Sarah, Waldmann, Anja, Billmeier, Arne, Röder, Jasmin, Lindner, Aline, Ullrich, Evelyn, Marschalek, Rolf, Dotti, Gianpietro, Jung, Gundram, Große‐Hovest, Ludger, Oberoi, Pranav, Bader, Peter, Wels, Winfried S.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.10.2019; Wiley Subscription Services, Inc
• Subjects: Acute lymphoblastic leukemia; Acute myeloid leukemia; adoptive immunotherapy; Animals; Blast resistance; B‐ALL; Cancer; Cancer immunotherapy; Caspase; CD135; CD19 antigen; CD28 antigen; Cell Line, Tumor; chimeric antigen receptor; Chimeric antigen receptors; Cytotoxicity; Degranulation; Effector cells; Feasibility studies; FLT3; fms-Like Tyrosine Kinase 3 - immunology; Gene transfer; Genetic Engineering; Genetic modification; HL-60 Cells; Humans; Immunotherapy; Immunotherapy, Adoptive - methods; Interleukin 2 receptors; Interleukin Receptor Common gamma Subunit - genetics; Killer Cells, Natural - immunology; Killer Cells, Natural - transplantation; Leukemia; Lymphatic leukemia; Lymphocytes B; Medical research; Mice, Inbred NOD; Mice, SCID; Myeloid leukemia; Natural killer cells; Precursor B-Cell Lymphoblastic Leukemia-Lymphoma - immunology; Precursor B-Cell Lymphoblastic Leukemia-Lymphoma - therapy; Protein-tyrosine kinase; Receptors, Chimeric Antigen - metabolism; Suicide; Therapeutic applications; Treatment Outcome; Xenograft Model Antitumor Assays; Xenografts; B-ALL; natural killer cells; chimeric antigen receptor; FLT3; CD135; adoptive immunotherapy
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.32269

Chimeric antigen receptor (CAR)‐engineered natural killer (NK) cells represent a promising effector cell type for adoptive cancer immunotherapy. Both, genetically modified donor‐derived NK cells as well as continuously expanding NK‐92 cells are currently under clinical development. To enhance their therapeutic utility for the treatment of pre‐B‐cell acute lymphoblastic leukemia (B‐ALL), we engineered NK‐92 cells by lentiviral gene transfer to express a FMS‐like tyrosine kinase 3 (FLT3)‐specific CAR that contains a composite CD28‐CD3ζ signaling domain. FLT3 has primarily been described as a therapeutic target for acute myeloid leukemia, but overexpression of FLT3 has also been reported in B‐ALL. Exposure of FLT3‐positive targets to CAR NK‐92 cells resulted in conjugate formation between NK and leukemia cells, NK‐cell degranulation and selective cytotoxicity toward established B‐ALL cell lines and primary blasts that were resistant to parental NK‐92. In a SEM B‐ALL xenograft model in NOD‐SCID IL2R γnull mice, treatment with CAR NK‐92 but not parental NK‐92 cells markedly inhibited disease progression, demonstrating high antileukemic activity in vivo. As FLT3 is known to be also expressed on precursor cells, we assessed the feasibility of incorporating an inducible caspase‐9 (iCasp9) suicide switch to enhance safety of our approach. Upon addition of the chemical dimerizer AP20187 to NK‐92 cells coexpressing the FLT3‐specific CAR and iCasp9, rapid iCasp9 activation was observed, precluding further CAR‐mediated cytotoxicity. Our data demonstrate that B‐ALL can be effectively targeted by FLT3‐specific CAR NK cells which may complement CD19‐directed immunotherapies, particularly in cases of inherent or acquired resistance to the latter. What's new? Therapy‐induced selection of antigen‐loss variants can result in resistance of pre‐B‐cell acute lymphoblastic leukemia (B‐ALL) to CD19‐directed immunotherapies. To evaluate FLT3 as a target for B‐ALL, here the authors engineered NK‐92 cells to express an FLT3‐specific chimeric antigen receptor (CAR). The CAR NK cells displayed high and selective cytotoxicity against established and primary B‐ALL cells in vitro and markedly reduced leukemia burden in a human B‐ALL xenograft model in vivo. The findings suggest FLT3‐specific CAR NK cells as a promising alternative approach for adoptive immunotherapy of B‐ALL.