Natural killer (NK) cells are an important effector cell type for adoptive cancer immunotherapy. Similar to T cells, NK cells can be modified to express chimeric antigen receptors (CARs) to enhance antitumor activity, but experience with CAR-engineered NK cells and their clinical development is still limited. Here, we redirected continuously expanding and clinically usable established human NK-92 cells to the tumor-associated ErbB2 (HER2) antigen. Following GMP-compliant procedures, we generated a stable clonal cell line expressing a humanized CAR based on ErbB2-specific antibody FRP5 harboring CD28 and CD3ζ signaling domains (CAR 5.28.z). These NK-92/5.28.z cells efficiently lysed ErbB2-expressing tumor cells in vitro and exhibited serial target cell killing. Specific recognition of tumor cells and antitumor activity were retained in vivo, resulting in selective enrichment of NK-92/5.28.z cells in orthotopic breast carcinoma xenografts, and reduction of pulmonary metastasis in a renal cell carcinoma model, respectively. γ-irradiation as a potential safety measure for clinical application prevented NK cell replication, while antitumor activity was preserved. Our data demonstrate that it is feasible to engineer CAR-expressing NK cells as a clonal, molecularly and functionally well-defined and continuously expandable cell therapeutic agent, and suggest NK-92/5.28.z cells as a promising candidate for use in adoptive cancer immunotherapy.

Natural killer (NK) cells hold promise for adoptive cancer immunotherapy but are dependent on cytokines such as interleukin (IL)-2 for growth and cytotoxicity. Here, we investigated the consequences of ectopic expression of IL-15 in human NK cells. IL-2 and IL-15 belong to the common γ chain family of cytokines and have overlapping activities. Transduction of clinically applicable NK-92 cells with lentiviral vectors encoding human IL-15 resulted in predominantly intracellular expression of the cytokine, and STAT5 activation, proliferation and cytotoxicity of the producer cells in the absence of IL-2. Growth of non-transduced bystander cells was not supported, allowing rapid enrichment of gene-modified cells solely by IL-2 withdrawal. This was also the case upon transduction of NK-92 and NKL cells with a bicistronic lentiviral vector encoding IL-15 and a chimeric antigen receptor (CAR) targeting the pancarcinoma antigen EpCAM. Effector cells co-expressing CAR and IL-15 continued to proliferate in the absence of exogenous cytokines and displayed high and selective cell-killing activity against EpCAM-expressing breast carcinoma cells that were resistant to the natural cytotoxicity of unmodified NK cells. This strategy facilitates rapid isolation and continuous expansion of retargeted NK cells and may extend their potential clinical utility.

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In addition to primary natural killer (NK) cells, continuously growing cytotoxic cell lines such as NK-92 are being considered for adoptive cancer immunotherapy. High cytotoxicity of NK-92 has been shown against malignant cells of hematologic origin in preclinical studies, and general safety of infusion of NK-92 cells has been established in phase I clinical trials. To enhance their therapeutic utility, we genetically modified NK-92 cells to express chimeric antigen receptors (CAR) specific for different tumor-associated surface antigens including ErbB2 (HER2). Such CAR were composed of a tumor-specific scFv antibody fragment fused via hinge and transmembrane domains to intracellular signaling proteins such as CD3 zeta chain or a composite CD28-CD3 zeta fusion molecule. Glioblastoma multiforme (GBM) is the most common and severe intracranial malignant tumor in humans. Despite aggressive therapy, recurrence of GBM is very frequent, and the median survival of GBM patients is only 12 to 15 months. Since enhanced ErbB2 expression was found in up to 80% of GBM cases, adoptive ErbB2-targeted immunotherapy may represent a more efficient alternative to standard therapy. For development towards clinical applications, here we generated a lentiviral second generation CAR construct (5.28.z) specific for the ErbB2 antigen, and established GMP-compliant protocols for transduction and expansion of NK-92 cells. An ErbB2-specific single cell clone (NK-92/5.28.z) was isolated, which showed high and selective cytotoxicity towards different established ErbB2-expressing glioblastoma cells and tumor cells of various other origins in vitro, as well as specific tumor homing in murine in vivo models. Treatment with NK-92/5.28.z cells also resulted in marked inhibition of the growth of subcutaneous glioblastoma xenografts in NOD/SCID γc KO mice. Ongoing work now focuses on evaluating the feasibility and efficacy of intracranial application of NK-92/5.28.z cells in orthotopic xenograft models of ErbB2-positive glioblastoma cells as a basis for further development of these cells as an adoptive immunotherapy for glioblastoma patients. Citation Format: Concong Zhang, Kurt Schönfeld, Michael Burger, Sabrina Genßler, Christiane Sahm, Christian Brendel, Sonja Naundorf, Marcus Odendahl, Ulrike Köhl, Torsten Tonn, Manuel Grez, Joachim P. Steinbach, Winfried S. Wels. ErbB2/HER2-specific natural killer cells for adoptive immunotherapy of glioblastoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3967. doi:10.1158/1538-7445.AM2013-3967