EGFR-Targeted Granzyme B Expressed in NK Cells Enhances Natural Cytotoxicity and Mediates Specific Killing of Tumor Cells
Robert A. Jabulowsky
Winfried S. Wels
- Natural killer (NK) cells are highly specialized effectors of the innate immune system that hold promise for adoptive cancer immunotherapy. Their cell killing activity is primarily mediated by the pro-apoptotic serine protease granzyme B (GrB), which enters targets cells with the help of the pore-forming protein perforin. We investigated expression of a chimeric GrB fusion protein in NK cells as a means to augment their antitumoral activity. For selective targeting to tumor cells, we fused the epidermal growth factor receptor (EGFR) peptide ligand transforming growth factor α (TGFα) to human pre-pro-GrB. Established human NKL natural killer cells transduced with a lentiviral vector expressed this GrB-TGFα (GrB-T) molecule in amounts comparable to endogenous wildtype GrB. Activation of the genetically modified NK cells by cognate target cells resulted in the release of GrB-T together with endogenous granzymes and perforin, which augmented the effector cells' natural cytotoxicity against NK-sensitive tumor cells. Likewise, GrB-T was released into the extracellular space upon induction of degranulation with PMA and ionomycin. Secreted GrB-T fusion protein displayed specific binding to EGFR-overexpressing tumor cells, enzymatic activity, and selective target cell killing in the presence of an endosomolytic activity. Our data demonstrate that ectopic expression of a targeted GrB fusion protein in NK cells is feasible and can enhance antitumoral activity of the effector cells.
Novel Phylogenetic Algorithm to Monitor Human Tropism in Egyptian H5N1-HPAIV Reveals Evolution toward Efficient Human-to-Human Transmission
Vladimir R. Perovic
Claude P. Muller
Henry L. Niman
Dusan D. Tosic
- Years of endemic infections with highly pathogenic avian influenza (HPAI) A subtype H5N1 virus in poultry and high numbers of infections in humans provide ample opportunity in Egypt for H5N1-HPAIV to develop pandemic potential. In an effort to better understand the viral determinants that facilitate human infections of the Egyptian H5N1-HPAIVvirus, we developed a new phylogenetic algorithm based on a new distance measure derived from the informational spectrum method (ISM). This new approach, which describes functional aspects of the evolution of the hemagglutinin subunit 1 (HA1), revealed a growing group G2 of H5N1-HPAIV in Egypt after 2009 that acquired new informational spectrum (IS) properties suggestive of an increased human tropism and pandemic potential. While in 2006 all viruses in Egypt belonged to the G1 group, by 2011 these viruses were virtually replaced by G2 viruses. All of the G2 viruses displayed four characteristic mutations (D43N, S120(D,N), (S,L)129Δ and I151T), three of which were previously reported to increase binding to the human receptor. Already in 2006–2008 G2 viruses were significantly (p<0.02) more often found in humans than expected from their overall prevalence and this further increased in 2009–2011 (p<0.007). Our approach also identified viruses that acquired additional mutations that we predict to further enhance their human tropism. The extensive evolution of Egyptian H5N1-HPAIV towards a preferential human tropism underlines an urgent need to closely monitor these viruses with respect to molecular determinants of virulence.
A functional yeast survival screen of tumor-derived cDNA libraries designed to identify anti-apoptotic mammalian oncogenes
Inga Maria Melzer
Ralf Joachim Rieker
David Lukas Wachter
- Yeast cells can be killed upon expression of pro-apoptotic mammalian proteins. We have established a functional yeast survival screen that was used to isolate novel human anti-apoptotic genes overexpressed in treatment-resistant tumors. The screening of three different cDNA libraries prepared from metastatic melanoma, glioblastomas and leukemic blasts allowed for the identification of many yeast cell death-repressing cDNAs, including 28% of genes that are already known to inhibit apoptosis, 35% of genes upregulated in at least one tumor entity and 16% of genes described as both anti-apoptotic in function and upregulated in tumors. These results confirm the great potential of this screening tool to identify novel anti-apoptotic and tumor-relevant molecules. Three of the isolated candidate genes were further analyzed regarding their anti-apoptotic function in cell culture and their potential as a therapeutic target for molecular therapy. PAICS, an enzyme required for de novo purine biosynthesis, the long non-coding RNA MALAT1 and the MAST2 kinase are overexpressed in certain tumor entities and capable of suppressing apoptosis in human cells. Using a subcutaneous xenograft mouse model, we also demonstrated that glioblastoma tumor growth requires MAST2 expression. An additional advantage of the yeast survival screen is its universal applicability. By using various inducible pro-apoptotic killer proteins and screening the appropriate cDNA library prepared from normal or pathologic tissue of interest, the survival screen can be used to identify apoptosis inhibitors in many different systems.
Chemical Chaperones Improve Protein Secretion and Rescue Mutant Factor VIII in Mice with Hemophilia A.
Stefanie D. Roth
Jeremy C. Simpson
- nefficient intracellular protein trafficking is a critical issue in the pathogenesis of a variety of diseases and in recombinant protein production. Here we investigated the trafficking of factor VIII (FVIII), which is affected in the coagulation disorder hemophilia A. We hypothesized that chemical chaperones may be useful to enhance folding and processing of FVIII in recombinant protein production, and as a therapeutic approach in patients with impaired FVIII secretion. A tagged B-domain-deleted version of human FVIII was expressed in cultured Chinese Hamster Ovary cells to mimic the industrial production of this important protein. Of several chemical chaperones tested, the addition of betaine resulted in increased secretion of FVIII, by increasing solubility of intracellular FVIII aggregates and improving transport from endoplasmic reticulum to Golgi. Similar results were obtained in experiments monitoring recombinant full-length FVIII. Oral betaine administration also increased FVIII and factor IX (FIX) plasma levels in FVIII or FIX knockout mice following gene transfer. Moreover, in vitro and in vivo applications of betaine were also able to rescue a trafficking-defective FVIII mutant (FVIIIQ305P). We conclude that chemical chaperones such as betaine might represent a useful treatment concept for hemophilia and other diseases caused by deficient intracellular protein trafficking.
The viral vector vaccine VSV-GP boosts immune response upon repeated applications
Lisa Mareike Egerer
Dorothee von Laer
- Poster presentation AIDS Vaccine 2012 Boston, MA, USA. 9-12 September 2012
Background: Vesicular stomatitis virus (VSV) is a potent candidate vaccine vector for various viral diseases (e.g. HIV, HCV, RSV). The biggest limitation of VSV, however, is its neurotoxicity, which limits application in humans. The second drawback is that VSV induces neutralizing antibodies rapidly and is thus ineffective as a vaccine vector upon repeated applications. Our group has recently shown that VSV pseudotyped with the glycoprotein (GP) of the lymphocytic choriomeningitis virus (LCMV), VSV-GP, is not neurotoxic. The aim of this project was to evaluate the potential of VSV-GP as a vaccine vector.
Methods: For this purpose, we used Ovalbumin (OVA) as a model antigen and analyzed immunogenicity of GP-pseudotyped and wildtype VSV containing OVA (VSV-GP-OVA and VSV-OVA) in vitro and in vivo in mouse models.
Results: We showed that both vectors infected murine bone marrow-derived dendritic cells (bmDCs) in vitro. These bmDCs were able to activate OVA specific CD8+ and CD4+ T cells. Immunization experiments in mice revealed that both VSV-OVA and VSV-GP-OVA induced functional OVA-specific cytotoxic T cells (CTLs) after a single immunization. In addition, with both viruses, mice generated antibodies against OVA. However, boosting with the same virus was only possible for the GP-pseudotyped virus but not for wild type VSV. The efficacy of repeated immunization with VSV-OVA was most likely limited by high levels of neutralizing antibodies, which we detected after the first immunization. In contrast, no neutralizing antibodies against VSV-GP were induced even after boosting.
Conclusion: Taken together, we showed that the non-neurotoxic VSV-GP is able to induce specific T cell and B cell responses against the model antigen OVA to the same level as the wild type VSV vector. However, in contrast to wild type VSV, VSV-GP-OVA boosted the immune response upon repeated applications. Thus, VSV-GP is a promising novel vaccine vector.
Post-transcriptional regulation of 5-lipoxygenase mRNA expression via alternative splicing and nonsense-mediated mRNA decay
Bernd Lothar Sorg
- 5-Lipoxygenase (5-LO) catalyzes the two initial steps in the biosynthesis of leukotrienes (LT), a group of inflammatory lipid mediators derived from arachidonic acid. Here, we investigated the regulation of 5-LO mRNA expression by alternative splicing and nonsense-mediated mRNA decay (NMD). In the present study, we report the identification of 2 truncated transcripts and 4 novel 5-LO splice variants containing premature termination codons (PTC). The characterization of one of the splice variants, 5-LOΔ3, revealed that it is a target for NMD since knockdown of the NMD factors UPF1, UPF2 and UPF3b in the human monocytic cell line Mono Mac 6 (MM6) altered the expression of 5-LOΔ3 mRNA up to 2-fold in a cell differentiation-dependent manner suggesting that cell differentiation alters the composition or function of the NMD complex. In contrast, the mature 5-LO mRNA transcript was not affected by UPF knockdown. Thus, the data suggest that the coupling of alternative splicing and NMD is involved in the regulation of 5-LO gene expression.
Einfluss des Transkriptionsfaktors Tal1 auf die Osteoklastogenese durch Regulation von DC-STAMP
- Das menschliche Knochengewebe unterliegt einem ständigen Auf- und Abbau. Der
Knochenumbau, die so genannte Knochenremodellierung, findet stetig statt und etwa 10 %
des gesamten Knochengewebes werden innerhalb eines Jahres erneuert (Lerner UH, 2006).
Während der Knochenremodellierung befindet sich die Zellaktivität der Knochenaufbauenden
Osteoblasten und der Knochen-abbauenden Osteoklasten in einem
empfindlichen Gleichgewicht (Karsenty G und Wagner EF, 2002; Teitelbaum SL, 2000).
Durch Störung des Gleichgewichts zwischen Osteoblasten und Osteoklasten kann es zu
Knochen-assoziierten Krankheiten wie Osteoporose oder Osteopetrose kommen (Helfrich
MH, 2003; Sambrook P und Cooper C, 2006).
Osteoklasten sind multinukleäre Zellen, die in der Lage sind die Knochenmatrix zu
resorbieren (Teitelbaum SL, 2000). Sie entstehen aus pluripotenten, hämatopoetischen
Stammzellen durch Differenzierung und Zellfusion von Monozyten/Makrophagen-
Vorläuferzellen (Menaa C et al., 2000, Yavropoulou MP und Yovos JG, 2008). Die
Osteoklasten-Differenzierung wird hauptsächlich durch die Zytokine M-CSF (macrophage
colony stimulating factor) und RANKL (receptor activator of nuclear factor k b ligand)
induziert. Sie initiieren ein spezifisches Expressionsmuster Osteoklasten-spezifischer Gene
und aktivieren die Zellfusion in Osteoklasten-Vorläuferzellen zur Bildung reifer Osteoklasten
(Boyle WJ et al., 2003; Asagiri M und Takayanagi H, 2007). Die RANKL-vermittelte Induktion
der Osteoklastogenese beruht auf der Initiierung eines streng regulierten Netzwerks aus
Transkriptionsfaktoren (Yang X und Karsenty G, 2002). Einige Transkriptionsfaktoren, die
während der Osteoklasten-Differenzierung induziert und exprimiert werden, sind nicht auf
Osteoklasten beschränkt. Sie erfüllen auch Aufgaben in anderen hämatopoetischen
Differenzierungsprozessen (Engel I und Murre C et al., 1999), so dass vermutlich die
Kombination der Transkriptionsfaktoren entscheidend für die Osteoklastogenese ist.
Der basic helix-loop-helix-Transkriptionsfaktor Tal1 (T-cell acute lymphocytic
leukemia 1, auch Scl1, stem cell leukemia 1) ist ein entscheidender Faktor in der primitiven
und der definitiven Hämatopoese (Bloor AJ et al., 2002; Shivdasani RA et al., 1996). Die
Expression von Tal1 konnte bisher in verschiedenen hämatopoetischen Zelllinien gezeigt
werden, u.a. in monozytischen Zellen (Elefanty AG et al., 1998; Green AR et al., 1992;
Pulford K et al., 1995; Dey S et al., 2010).
In der vorliegenden Arbeit wurde der Einfluss des Transkriptionsfaktors Tal1 in
Monozyten und reifen Osteoklasten, vor allem in Bezug auf genregulatorische Prozesse
während der Osteoklasten-Differenzierung, untersucht. Der Transkriptionsfaktor Tal1 wird
in vitro und in vivo in Osteoklasten-Vorläuferzellen und reifen Osteoklasten exprimiert. Die
Proteinexpression von Tal1 wird durch die Inkubation der Zellen mit RANKL induziert, jedoch
wurde dies in Bezug auf die mRNA-Expression von Tal1 nicht beobachtet, so dass
vermutlich eine posttranskriptionelle Regulation von Tal1 vorliegt.
Die Überexpression von Tal1 sorgte für eine Blockade der Differenzierung von
Osteoklasten-Vorläuferzellen in reife Osteoklasten. Der Verlust von Tal1 in primären
Monozyten/Makrophagen-Zellen führte zur veränderten Expression von über 1200 Genen,
wobei jeweils etwa 600 Gene herauf- bzw. herabreguliert waren. Dies verdeutlicht, dass Tal1
sowohl an der Aktivierung als auch an der Reprimierung der Genexpression in Osteoklasten-
Vorläuferzellen beteiligt ist. Die Liste der herabregulierten Gene beinhaltete u.a. das
Osteoklasten-spezifische Enzym Acp5 (auch TRAP, tartrate resistant acid phosphatase), die
Liste der herauf regulierten Gene beinhaltete u.a. DC-STAMP (dendritic cell specific
transmembrane protein) und ATP6V0D2 (d2 isoform of vascuolar ATPase V0 domain), beide
werden im Zusammenhang mit der Zellfusion während der Osteoklasten-Differenzierung
beschrieben (Kim K et al., 2008; Kim T et al., 2010; Yagi M et al., 2005). Der Promotor von
DC-STAMP beinhaltet mehrere potentielle Bindestellen für Tal1 und Osteoklastenspezifische
Transkriptionsfaktoren. Es konnte gezeigt werden, dass Tal1, PU.1 und MITF im
Bereich um 343 bp vor dem Transkriptionsstartpunkt des DC-STAMP-Promotors binden und
dass Tal1 mit den Osteoklasten-spezifischen Transkriptionsfaktoren PU.1 und MITF
interagiert. Der inhibitorische Effekt von Tal1 auf die Osteoklasten-Differenzierung kommt
durch die Reprimierung der Aktivität der Osteoklasten-spezifischen Transkriptionsfaktoren
PU.1 und MITF auf dem DC-STAMP-Promotor in Osteoklasten-Vorläuferzellen zustande.
Während der Osteoklastogenese kommt es zu einer verringerten Tal1-Bindung auf dem DCSTAMP-
Promotor, wodurch die Tal1-vermittelte Inhibierung der Expression aufgehoben wird.
Die Bindung von PU.1 und MITF auf dem Promotor von DC-STAMP nimmt während der
Osteoklasten-Differenzierung zu. Die Expression von DC-STAMP wird im Verlauf der
Osteoklastogenese induziert, wodurch es zur Zell-Zell-Fusion kommt.
Die Analyse des transkriptionellen Netzwerks, das die Fusion mononukleärer Zellen
in reife Osteoklasten reguliert, vertieft das molekulare Verständnis der Osteoklasten-
Differenzierung und kann zur Entwicklung neuer therapeutischer Ansätze beitragen, die in
der Behandlung von Osteoporose, Riesenzelltumoren und anderen Osteoklastenassoziierten
Krankheiten verwendet werden können.
Next generation of antiretroviral agents targeting the RNA binding site of the HIV-1 cellular cofactor DDX3: an innovative therapeutic approach
- Introduction: Efficacy of currently approved anti-HIV drugs is hampered by mutations of the viral enzymes, leading invariably to drug resistance and chemotherapy failure. Recent data suggest that cellular co-factors also represent useful targets for anti-HIV therapy. We have recently provided evidence for the possibility to block HIV-1 replication by targeting its cellular cofactor DDX3.
Material and methods: Molecular modeling and in silico technologies were applied to rationally design small molecules specifically targeting the RNA binding site of human DDX3. Biochemical studies of mutated DDX3 enzymes were also used to identify additional potential drug binding sites.
Optimization of compounds identified by application of a high-throughput docking approach afforded a promising lead compound which proved to inhibit both the helicase and ATPase activity of DDX3 and to reduce the viral load of peripheral blood mononuclear cells (PBMC) infected with HIV-1. A novel interaction site has been also identified in DDX3, which, when blocked, can reduce viral replication, representing an additional target for small molecules inhibitors.
Conclusions: We have identified the first inhibitors of HIV-1 replication targeting the RNA binding site of the cellular cofactor human DDX3. These compounds may offer superior selectivity over the ATP-competitive inhibitors previously developed. In addition, a novel RNA interacting motif specific to DDX3 has been identified, opening new venues for HIV-1 drug development.
Cytotoxic capacity of IL-15-stimulated cytokine-induced killer cells against human acute myeloid leukemia and rhabdomyosarcoma in humanized preclinical mouse models
Winfried S. Wels
- Allogeneic stem cell transplantation (allo-SCT) has become an important treatment modality for patients with high-risk acute myeloid leukemia (AML) and is also under investigation for soft tissue sarcomas. The therapeutic success is still limited by minimal residual disease (MRD) status ultimately leading to patients’ relapse. Adoptive donor lymphocyte infusions based on MRD status using IL-15-expanded cytokine-induced killer (CIK) cells may prevent relapse without causing graft-versus-host-disease (GvHD). To generate preclinical data we developed mouse models to study anti-leukemic- and anti-tumor-potential of CIK cells in vivo. Immunodeficient mice (NOD/SCID/IL-2Rγc−, NSG) were injected intravenously with human leukemic cell lines THP-1, SH-2 and with human rhabdomyosarcoma (RMS) cell lines RH41 and RH30 at minimal doses required for leukemia or tumor engraftment. Mice transplanted with THP-1 or RH41 cells were randomly assigned for analysis of CIK cell treatment. Organs of mice were analyzed by flow cytometry as well as quantitative polymerase chain reaction for engraftment of malignant cells and CIK cells. Potential of CIK cells to induce GvHD was determined by histological analysis. Tissues of the highest degree of THP-1 cell expansion included bone marrow followed by liver, lung, spleen, peripheral blood (PB), and brain. RH30 and RH41 engraftment mainly took place in liver and lung, but was also detectable in spleen and PB. In spite of delayed CIK cell expansion compared with malignant cells, CIK cells injected at equal amounts were sufficient for significant reduction of RH41 cells, whereas against fast-expanding THP-1 cells 250 times more CIK than THP-1 cells were needed to achieve comparable results. Our preclinical in vivo mouse models showed a reliable 100% engraftment of malignant cells which is essential for analysis of anti-cancer therapy. Furthermore our data demonstrated that IL-15-activated CIK cells have potent cytotoxic capacity against AML and RMS cells without causing GvHD.
Retargeted natural killer cells for adoptive cancer immunotherapy
- NK cells are part of the innate immune system, and are important players in the body’s first defence line against virus-infected and malignantly transformed cells. While T cells recognize neoplastic cells in an MHC-restricted fashion, NK cells do not require prior sensitization and education about the target. In leukemia and lymphoma patients undergoing allogeneic hematopoietic stem cell transplantation not only T cells but also NK cells have been found to mediate potent graft-versus-tumor effects. Hence, autologous or donor-derived NK cells hold great promise for cancer immunotherapy. Since the generation of highly purified NK cell products for clinical applications is labor-intensive and time consuming, established human NK cell lines such as NK-92 are also being considered for clinical protocols. NK-92 cells display phenotypic and functional characteristics similar to activated primary NK cells. While NK-92 cells are highly cytotoxic towards malignant cells of hematologic origin, they do not affect healthy human tissues. NK-92 cells can be expanded under GMP-compliant conditions, and can therefore be provided in sufficient numbers with defined phenotypic characteristics for clinical applications. Safety of NK-92 cells for adoptive immunotherapy was already shown in two phase I/II clinical trials. In contrast to malignant cells of hematologic origin, most solid tumor cells are not sensitive to unmodified NK-92 cells. Hence, to overcome resistance mechanisms of tumor cells and to broaden the target spectrum of NK-92 cells, gene-modified variants have been generated which express chimeric antigen receptors (CARs) that specifically target tumor surface antigens. The expression of these CARs is sufficient to redirect their cytotoxic activity towards otherwise NK cell-resistant target cells. Extending these earlier approaches, in the framework of this work optimized CAR constructs that target the pancarcinoma antigen epithelial cell adhesion molecule (EpCAM) were derived and functionally characterized. In collaboration with Heike Daldrup-Link’s laboratory (University of California San Francisco, USA) non-invasive imaging modalities to analyze biodistribution and tumor homing properties of retargeted NK-92 cells were evaluated. To enhance the persistence of adoptively transferred NK-92 cells in vivo, means to overcome NK-92 cells’ dependence on exogenous IL-2 for survival and cytolytic activity were investigated. EpCAM is expressed on a variety of tumors of epithelial origin including ovarian, gastric, colorectal, pancreatic, breast, lung and endometrial cancers. In epithelial cells EpCAM is mainly expressed at basolateral membranes, and EpCAM is involved in calcium-independent homotypic cell-cell adhesions. In tumor cells high and de novo EpCAM expression is not only restricted to basolateral membranes but can also be found on apical membranes. Tumor cells retain EpCAM expression throughout tumorigenesis and metastasis formation. Due to its surface expression and immunogenicity EpCAM has been exploited as target for immunotherapy. In earlier work in our group a prototypic, first generation EpCAM-specific CAR construct (31.z) harboring a murine flexible hinge region and murine CD3 ζ as signaling domain was derived and functionally characterized in NK-92 cells. To reduce the immunogenicity for their potential clinical application, this CAR construct was humanized by exchanging the hinge region and the intracellular signaling domain with corresponding sequences of human origin. In T cells incorporation of additional co-stimulatory domains derived from CD28 and 4-1BB significantly enhanced persistence and anti-tumor effects of adoptively transferred cells. Based on these findings a modified, second generation CAR construct encompassing transmembrane and intracellular regions of CD28 in addition to CD3 ζ intracellular signaling domains was derived (31.28.z). Both CAR constructs were stably expressed in NK-92 cells, and furthermore, expression of both CAR variants promoted antigen-specific lysis of antigen-expressing prostate and breast cancer cell lines. In competition experiments the cytotoxic activity of NK-92/31.z and NK-92/31.28.z cells towards antigen-expressing tumor cells was significantly reduced in the presence of parental MOC31 monoclonal antibody, indicating that binding of the EpCAM-specific CAR to its antigen on tumor cells is necessary to trigger antigen-specific cytotoxicity. At high effector to target ratios NK-92/31.28.z cells displayed slightly higher cytotoxic activity towards EpCAM-expressing target cell lines than NK-92/31.z cells, suggesting that incorporation of co-stimulatory domains had beneficial effects on the cytotoxic activity. For clinical applications the development of non-invasive imaging methods is necessary to follow the biodistribution of adoptively transferred cells and guide the identification of responders and non-responders at an early time point. In collaboration with Heike Daldrup-Link’s laboratory the homing properties of EpCAM-specific NK-92 cells to prostate tumor xenografts in rodent models was analyzed (University of California San Francisco, USA). At that time NK-92 cells expressing the second generation EpCAM-specific CAR 31.28.z were not yet available, and thus homing experiments were performed with NK-92 cells expressing the first generation CAR 31.z. For magnetic resonance imaging studies parental and EpCAM-specific NK-92 cells were labeled with clinical applicable ferumoxide particles. Labeled, gene-modified NK-92 cells displayed reduced CAR expression and reduced cytotoxic activity towards EpCAM-expressing DU145 prostate cancer cells in vitro. Nevertheless, MRI revealed specific accumulation of ferumoxide labeled EpCAM-specific NK-92 cells in DU145 tumor xenografts in athymic rats. In tumor sections of treated animals the presence of EpCAM-specific NK-92 cells was verified by Prussian blue and CD57 staining of tumor sections. In another study homing of DiD-labeled EpCAM-specific NK-92 cells to DU145 tumor xenografts was shown by optical imaging. These findings imply that specific targeting of NK-92 cells is retained in vivo, and that non-invasive imaging strategies can be employed to analyze biodistribution of NK-92 cells. Enhanced persistence of adoptively transferred cytotoxic effector cells has a major impact on the effectiveness of immunotherapy. Primary cytotoxic effector cells as well as NK-92 cells require IL-2 for their proliferation and to gain full activity of their effector functions. To bypass the need of exogenously supplied cytokines, the expression of chimeric cytokine receptors (CCR) harboring IL-2R β and IL-2R γ chains instead of CD3 ζ as signaling domains might initiate cytokine-like signals upon contact with the respective antigen. These interactions might support growth and survival of NK-92 cells in the absence of exogenous IL-2. As a starting point, a codon-optimized ErbB2-specific CAR consisting of the scFv(FRP5) single chain antibody fragment, a human CD8 α hinge region and human CD3 ζ transmembrane and intracellular domains was used. Transmembrane and intracellular domains of IL-2R β and IL-2R γ chains were amplified from NK-92 cell-derived cDNA, and were used to exchange the CD3 ζ domain in the ErbB2-specific construct. In human primary tumors EpCAM and ErbB2 overexpression are frequently found, and often correlate with poor prognosis. Hence, co-expression of ErbB2-specific CCRs with an EpCAM-specific CAR may provide NK cells with antigen-specific killing via EpCAM recognition and with antigen-dependent growth via binding to ErbB2. However, attempts to activate CCRs in NK-92 cells via co-incubation with antigen-expressing cells or cross-linking of the CCRs with recombinant antigen did not result in cytokine-independent but antigen-dependent growth. Likewise, no triggering of signal transducer and activator of transcription 5 (STAT5) was observed, which is a hallmark of IL-2 mediated signal transduction. The interactions between CCRs and their antigen might not be strong enough to trigger cytokine-like signals supporting the growth of cells in the absence of exogenous cytokines, and furthermore, might not lead to a significant up-regulation of STAT5-mediated signal transduction. An alternative approach to circumvent the need of exogenous cytokines is ectopic expression of homeostatic cytokines IL-2 and IL-15 in lymphocytes. In T cells expression of these cytokines is sufficient to render cells independent from exogenously supplied cytokines. In this work a lentiviral expression vector encoding IL-15 (SIEW-IL15) was generated, and used for transduction of NK-92 cells. This resulted in ectopic expression of IL-15 and cellular proliferation in the absence of exogenously supplied cytokines. Even after prolonged culture without exogenous IL-2, NK-92/IL15 cells retained their cytotoxic activity towards NK-sensitive target cells. Although expression of IL-15 in HC11 and COS-7 cells using the same vector led to secretion of bioactive IL-15 into culture supernatants, neither secreted nor surface-bound IL-15 was detected in NK-92/IL15 cells, implying that IL-15 promotes survival of gene-modified cells in a strictly autocrine fashion. In addition, NK-92 cells that were freshly transduced with SIEW-IL15 could be efficiently enriched by cytokine withdrawal. NK-92/IL15 cells that were co-transduced with an EpCAM-specific CAR retained their ability to grow in the absence of exogenously supplied cytokines and their antigen-specific cytotoxic activity. Based on these results, a bicistronic vector construct was generated allowing the simultaneous expression of a CAR construct and IL-15 as selection marker. EpCAM-specific CAR constructs (31.28.z and 31.TM) were inserted into the bicistronic expression cassette. NK-92 cells were transduced with these bicistronic expression constructs and selected by cytokine withdrawal. After 14 to 21 days of culture in the absence of IL-2 transduced cells grew out from which CAR-expressing NK-92 cells with high and homogenous surface expression were further enriched by FACS sorting. NK-92/31.28.z.IL15 cells displayed high cytotoxic activity towards EpCAM-expressing breast cancer cell lines, while EpCAM-negative melanoma cells were not lysed. The results of this work demonstrate that the expression of first (31.z) and second (31.28.z) generation CARs in NK-92 cells is sufficient to induce antigen-specific cytotoxicity. Furthermore, a specific accumulation of NK-92/31.z cells but not unmodified NK-92 cells was detected in EpCAM-expressing prostate carcinoma xenografts in athymic rats, indicating that specific targeting of these cells is retained in vivo. Ectopic expression of IL-15 renders the cells independent from exogenous cytokines, while they retain their cytotoxic activity even after prolonged culture without IL-2. Furthermore, ectopic expression of IL-15 in NK-92 cells can be used for selective enrichment of gene-modified cells by cytokine withdrawal. Subsequently, bicistronic expression constructs that allow simultaneous expression of a CAR construct and IL-15 as selection marker were generated. Expression of these bicistronic expression vectors in NK-92 cells is feasible, and might facilitate enrichment of gene-modified cells for clinical applications.