Preclinical Development of CAR T Cells with Antigen-Inducible IL18 Enforcement to Treat GD2-Positive Solid Cancers

PURPOSE

Cytokine-engineering of chimeric antigen receptor-redirected T cells (CAR T cells) is a promising principle to overcome the limited activity of canonical CAR T cells against solid cancers.

EXPERIMENTAL DESIGN

We developed an investigational medicinal product, GD2IL18CART, consisting of CAR T cells directed against ganglioside GD2 with CAR-inducible IL18 to enhance their activation response and cytolytic effector functions in the tumor microenvironment. To allow stratification of patients according to tumor GD2 expression, we established and validated immunofluorescence detection of GD2 on paraffin-embedded tumor tissues.

RESULTS

Lentiviral all-in-one vector engineering of human T cells with the GD2-specific CAR with and without inducible IL18 resulted in cell products with comparable proportions of CAR-expressing central memory T cells. Production of IL18 strictly depends on GD2 antigen engagement. GD2IL18CART respond to interaction with GD2-positive tumor cells with higher IFNγ and TNFα cytokine release and more effective target cytolysis compared with CAR T cells without inducible IL18. GD2IL18CART further have superior in vivo antitumor activity, with eradication of GD2-positive tumor xenografts. Finally, we established GMP-compliant manufacturing of GD2IL18CART and found it to be feasible and efficient at clinical scale.

CONCLUSIONS

These results pave the way for clinical investigation of GD2IL18CART in pediatric and adult patients with neuroblastoma and other GD2-positive cancers (EU CT 2022-501725-21-00).

CAR T cells as micropharmacies against solid cancers: Combining effector T-cell mediated cell death with vascular targeting in a one-step engineering process

To enhance the potency of chimeric antigen receptor (CAR) engineered T cells in solid cancers, we designed a novel cell-based combination strategy with an additional therapeutic mode of action. CAR T cells are used as micropharmacies to produce a targeted pro-coagulatory fusion protein, truncated tissue factor (tTF)-NGR, which exerts pro-coagulatory activity and hypoxia upon relocalization to the vascular endothelial cells that invade tumor tissues. Delivery by CAR T cells aimed to induce locoregional tumor vascular infarction for combined immune-mediated and hypoxic tumor cell death. Human T cells that were one-vector gene-modified to express a GD2-specific CAR along with CAR-inducible tTF-NGR exerted potent GD2-specific effector functions while secreting tTF-NGR that activates the extrinsic coagulation pathway in a strictly GD2-dependent manner. In murine models, the CAR T cells infiltrated GD2-positive tumor xenografts, secreted tTF-NGR into the tumor microenvironment and showed a trend towards superior therapeutic activity compared with control cells producing functionally inactive tTF-NGR. In vitro evidence supports a mechanism of hypoxia-mediated enhancement of T cell cytolytic activity. We conclude that combined CAR T cell targeting with an additional mechanism of antitumor action in a one-vector engineering strategy is a promising approach to be further developed for targeted treatment of solid cancers.

Abstract 3182: CAR T cells as micropharmacies to induce locoregional tumor vascular infarction by antigen-specific delivery of tissue factor to the tumor microenvironment

CAR T cell therapy of solid tumors is challenged by the heterogeneity of target expression and by mechanical and immune-modulatory barriers in the tumor microenvironment (TME). To combine CAR-retargeted T cell effector functions with a second therapeutic mode of action, we designed an innovative cell-based combination strategy. CAR-engineered antitumor effector T cells are used as micropharmacies to produce and deliver a pro-coagulatory fusion protein, tTF-NGR, in the TME to induce locoregional tumor vascular infarction for combined T-cell mediated and hypoxic tumor cell death. tTF-NGR is a CD13-targeted tissue factor variant with coagulation activity upon relocalization into the phospholipid membranes of the CD13-expressing vascular endothelial cells that invade tumor tissues. Consequent thrombosis in tumor blood vessels induces tumor infarction, growth retardation and regression in preclinical in vitro and in vivo studies and selective reduction of tumor blood flow in a clinical phase I study. Human T cells were co-transduced by retroviral one-vector gene transfer to express genes encoding for a GD2-specific CAR and for tTF-NGR, the latter in an antigen-dependent CAR-mediated manner. The engineered T cells exerted potent GD2 antigen-specific effector functions, including secretion of IFN-γ and TNF-α, upregulation of CD107 and tumor cell lysis, comparable to control CAR T cells producing mutant tTF-NGR lacking pro-coagulatory function. They secreted recombinant tTF-NGR in a strictly antigen-dependent manner upon coincubation with the anti-idiotype antibody ganglidiomab, which selectively engages the extracellular scFv of the CAR, or with GD2-positive tumor cells, shown by ELISA. tTF-NGR produced by human T cells effectively activates the extrinsic coagulation cascade, thus it retains its pro-coagulatory activity. In a murine Ewing sarcoma xenograft model which expresses the CAR target GD2on tumor cells along with CD13 on tumor vascular endothelial cells, GD2-specific CAR T cells with inducible tTF-NGR had noticeably superior therapeutic activity compared with control cells excreting mutant tTF-NGR. Mechanistic evidence hints at hypoxia-induced higher CAR T cell cytolytic activity. We conclude that combined CAR-mediated T cell targeting of cancer cells with CD13-targeted vascular infarction of the TME in a one-vector engineering strategy is a promising approach to overcome limitations of both strategies for effective targeting and eradication of solid cancers.

Citation Format: Bianca Altvater, Sareetha Kailayangiri, Christian Spurny, Maike Flügge, Jutta Meltzer, Lea Greune, Christian Schwöppe, Caroline Brand, Christoph Schliemann, Wolfgang Hartmann, Hinrich Abken, Axel Schambach, Nicole Farwick, Wolfgang E. Berdel, Claudia Rossig. CAR T cells as micropharmacies to induce locoregional tumor vascular infarction by antigen-specific delivery of tissue factor to the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3182.

Relevance of Abnormal KCNN1 Expression and Osmotic Hypersensitivity in Ewing Sarcoma

Simple Summary

The main oncogene in Ewing sarcoma directly drives a high expression of a previously unknown variant KCNN1 (encoding the K_Ca2.1 channel) that we also verified in samples from >200 patients. Yet, we found that the channel is not functional and does not modulate Ewing sarcoma cell behavior. We could explain this lack of functional impact by the surprising absence of any K_Ca2.1-carried K⁺ current in Ewing sarcoma cells. However, we show in a proof-of-principle study that the essential lack of a K⁺ conductance can be exploited by applying hypoosmotic stress and effectively and selectively killing the Ewing sarcoma cells.

Abstract

Ewing sarcoma (EwS) is a rare and highly malignant bone tumor occurring mainly in childhood and adolescence. Physiologically, the bone is a central hub for Ca²⁺ homeostasis, which is severely disturbed by osteolytic processes in EwS. Therefore, we aimed to investigate how ion transport proteins involved in Ca²⁺ homeostasis affect EwS pathophysiology. We characterized the expression of 22 candidate genes of Ca²⁺-permeable or Ca²⁺-regulated ion channels in three EwS cell lines and found the Ca²⁺-activated K⁺ channel K_Ca2.1 (KCNN1) to be exceptionally highly expressed. We revealed that KCNN1 expression is directly regulated by the disease-driving oncoprotein EWSR1-FL1. Due to its consistent overexpression in EwS, KCNN1 mRNA could be a prognostic marker in EwS. In a large cohort of EwS patients, however, KCNN1 mRNA quantity does not correlate with clinical parameters. Several functional studies including patch clamp electrophysiology revealed no evidence for K_Ca2.1 function in EwS cells. Thus, elevated KCNN1 expression is not translated to K_Ca2.1 channel activity in EwS cells. However, we found that the low K⁺ conductance of EwS cells renders them susceptible to hypoosmotic solutions. The absence of a relevant K⁺ conductance in EwS thereby provides an opportunity for hypoosmotic therapy that can be exploited during tumor surgery.

The Cellular Tumor Immune Microenvironment of Childhood Solid Cancers: Informing More Effective Immunotherapies

Common pediatric solid cancers fail to respond to standard immuno-oncology agents relying on preexisting adaptive antitumor immune responses. The adoptive transfer of tumor-antigen specific T cells, such as CAR-gene modified T cells, is an attractive strategy, but its efficacy has been limited. Evidence is accumulating that local barriers in the tumor microenvironment prevent the infiltration of T cells and impede therapeutic immune responses. A thorough understanding of the components of the functional compartment of the tumor microenvironment and their interaction could inform effective combination therapies and novel engineered therapeutics, driving immunotherapy towards its full potential in pediatric patients. This review summarizes current knowledge on the cellular composition and significance of the tumor microenvironment in common extracranial solid cancers of childhood and adolescence, such as embryonal tumors and bone and soft tissue sarcomas, with a focus on myeloid cell populations that are often present in abundance in these tumors. Strategies to (co)target immunosuppressive myeloid cell populations with pharmacological anticancer agents and with selective antagonists are presented, as well as novel concepts aiming to employ myeloid cells to cooperate with antitumor T cell responses.

GMP-Compliant Manufacturing of TRUCKs: CAR T Cells targeting GD2 and Releasing Inducible IL-18

Chimeric antigen receptor (CAR)-engineered T cells can be highly effective in the treatment of hematological malignancies, but mostly fail in the treatment of solid tumors. Thus, approaches using 4^th advanced CAR T cells secreting immunomodulatory cytokines upon CAR signaling, known as TRUCKs (“T cells redirected for universal cytokine-mediated killing”), are currently under investigation. Based on our previous development and validation of automated and closed processing for GMP-compliant manufacturing of CAR T cells, we here present the proof of feasibility for translation of this method to TRUCKs. We generated IL-18-secreting TRUCKs targeting the tumor antigen GD₂ using the CliniMACS Prodigy^® system using a recently described “all-in-one” lentiviral vector combining constitutive anti-GD₂ CAR expression and inducible IL-18. Starting with 0.84 x 10⁸ and 0.91 x 10⁸ T cells after enrichment of CD4⁺ and CD8⁺ we reached 68.3-fold and 71.4-fold T cell expansion rates, respectively, in two independent runs. Transduction efficiencies of 77.7% and 55.1% was obtained, and yields of 4.5 x 10⁹ and 3.6 x 10⁹ engineered T cells from the two donors, respectively, within 12 days. Preclinical characterization demonstrated antigen-specific GD₂-CAR mediated activation after co-cultivation with GD₂-expressing target cells. The functional capacities of the clinical-scale manufactured TRUCKs were similar to TRUCKs generated in laboratory-scale and were not impeded by cryopreservation. IL-18 TRUCKs were activated in an antigen-specific manner by co-cultivation with GD₂-expressing target cells indicated by an increased expression of activation markers (e.g. CD25, CD69) on both CD4⁺ and CD8⁺ T cells and an enhanced release of pro-inflammatory cytokines and cytolytic mediators (e.g. IL-2, granzyme B, IFN-γ, perforin, TNF-α). Manufactured TRUCKs showed a specific cytotoxicity towards GD₂-expressing target cells indicated by lactate dehydrogenase (LDH) release, a decrease of target cell numbers, microscopic detection of cytotoxic clusters and detachment of target cells in real-time impedance measurements (xCELLigence). Following antigen-specific CAR activation of TRUCKs, CAR-triggered release IL-18 was induced, and the cytokine was biologically active, as demonstrated in migration assays revealing specific attraction of monocytes and NK cells by supernatants of TRUCKs co-cultured with GD₂-expressing target cells. In conclusion, GMP-compliant manufacturing of TRUCKs is feasible and delivers high quality T cell products.

Generation of an NFκB-Driven Alpharetroviral "All-in-One" Vector Construct as a Potent Tool for CAR NK Cell Therapy

Immune cell therapeutics are increasingly applied in oncology. Especially chimeric antigen receptor (CAR) T cells are successfully used to treat several B cell malignancies. Efforts to engineer CAR T cells for improved activity against solid tumors include co-delivery of pro-inflammatory cytokines in addition to CARs, via either constitutive cytokine expression or inducible cytokine expression triggered by CAR recognition of its target antigen-so-called "T cells redirected for universal cytokine-mediated killing" (TRUCKs) or fourth-generation CARs. Here, we tested the hypothesis that TRUCK principles could be expanded to improve anticancer functions of NK cells. A comparison of the functionality of inducible promoters responsive to NFAT or NFκB in NK cells showed that, in contrast to T cells, the inclusion of NFκB-responsive elements within the inducible promoter construct was essential for CAR-inducible expression of the transgene. We demonstrated that GD2CAR-specific activation induced a tight NFκB-promoter-driven cytokine release in NK-92 and primary NK cells together with an enhanced cytotoxic capacity against GD2⁺ target cells, also shown by increased secretion of cytolytic cytokines. The data demonstrate biologically relevant differences between T and NK cells that are important when clinically translating the TRUCK concept to NK cells for the treatment of solid malignancies.

Surface expression of the immunotherapeutic target GD2 in osteosarcoma depends on cell confluency

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy of pediatric sarcomas is challenged by the paucity of targetable cell surface antigens. A candidate target in osteosarcoma (OS) is the ganglioside GD2 , but heterogeneous expression of GD2 limits its value.

AIM

We aimed to identify mechanisms that upregulate GD2 target expression in OS.

METHODS AND RESULTS

GD2 surface expression in OS cells, studied by flow cytometry, was found to vary both among and within individual OS cell lines. Pharmacological approaches, including inhibition of the histone methyltransferase Enhancer of Zeste Homolog 2 (EZH2) and modulation of the protein kinase C, failed to increase GD2 expression. Instead, cell confluency was found to be associated with higher GD2 expression levels both in monolayer cultures and in tumor spheroids. The sensitivity of OS cells to targeting by GD2 -specific CAR T cells was compared in an in vitro cytotoxicity assay. Higher cell confluencies enhanced the sensitivity of OS cells to GD2 -antigen specific, CAR T-cell-mediated in vitro cytolysis. Mechanistic studies revealed that confluency-dependent upregulation of GD2 expression in OS cells is mediated by increased de novo biosynthesis, through a yet unknown mechanism.

CONCLUSION

Expression of GD2 in OS cell lines is highly variable and associated with increasing cell confluency in vitro. Strategies for selective upregulation of GD2 are needed to enable effective therapeutic targeting of this antigen in OS.

VEGFR2 as a target for CAR T cell therapy of Ewing sarcoma

BACKGROUND

T cells engineered to express chimeric antigen receptors (CARs) are a novel modality to treat refractory cancers. The development of CAR T cells against Ewing sarcoma (EwS) is limited by a lack of targetable surface antigens. We investigated vascular endothelial growth factor receptor 2 (VEGFR2) expressed on tumor-associated blood vessels as potential CAR target in this cancer.

METHODS

Expression of VEGFR2 was studied by immunohistochemistry in human EwS biopsies and in murine xenografts and by flow cytometry in EwS cell lines. CARs with short, medium, and long hinge domains against either human or murine VEGFR2 were generated and expressed in human T cells by retroviral gene transfer. The capacity of the individual CARs to activate T cells in response to VEGFR2-expressing cells was compared in vitro.

RESULTS

Tumor-associated endothelial cells in human EwS biopsies and in xenografts expressed VEGFR2. Tumor cells in the majority of EwS biopsies were also VEGFR2-positive. Following modification with anti-mouse or anti-human VEGFR2-specific CAR genes, T cells specifically lysed VEGFR2-expressing target cells of the respective species. CAR T cells with short-length or medium-length hinge domains were functionally superior over those with the long hinge region by in vitro parameters, including antigen-specific degranulation responses, lysis of tumor spheroids, tumor necrosis factor α secretion, sequential killing, and proliferation.

CONCLUSIONS

VEGFR2 is consistently expressed on endothelial cells of the tumor stroma in EwS and thus is a candidate target for CAR T cells in this cancer. Among various VEGFR2-specific CARs, a construct with a short hinge domain was chosen to be further developed toward clinical translation.

Abstract 4999: Evaluation of anti-Gr1 antibody for depletion of MDSC in preclinical NSG mouse models of pediatric sarcoma

Preclinical in vivo studies of chimeric antigen receptor (CAR) T cells often rely on NOD-scid gamma (NSG) mouse models which lack T cells, B cells and NK cells and thereby allow for reliable engraftment of human tumor xenografts. But murine myeloid cells present in the NSG mouse strain can affect the tumor microenvironment as well as the function of adoptively transferred human immune effector cells. Long et al. (Cancer Immunol Res. 2016 Oct;4(10):869-880) reported that pediatric sarcoma xenografts in NSG mice induce in vivo expansion of murine CD11b+ myeloid-derived suppressor cells (MDSC), and that this cell population suppresses human CAR T cell proliferation in vitro. We investigated a strategy to avoid inhibitory effects of murine MDSCs on Ewing sarcoma xenografts in NSG mice by in vivo pretreatment with murine antibody against two cell surface antigens, Ly6C/Ly-6G (granulocyte-differentiation antigen-1, Gr-1), expressed on murine MDSC. Analysis of the CD11b+ myeloid cell populations in NSG mice 17-37 days after subcutaneous transplantation of the Ewing sarcoma cell line TC-71 showed a noticeable increase of CD11b+ cells in the peripheral blood compared to non-tumor bearing NSG mice (median 3.4 × 103, range 0.7-15.5 × 103 cells/ml, n=8 vs median 2.1 × 103, range 1.2-4.0 × 103 cells/ml, n=7). The increase was even more pronounced in the spleens, with a median absolute number of 2.6 × 106 CD11b+ cells (range 0.2-21 × 106 cells) per spleen in sarcoma-bearing mice versus 0.5 × 106 CD11b+ cells (range 0.2-0.8 × 106 cells) per spleen in mice without tumors. The granulocytic MDSC subset coexpressing Ly6Gpos was the most prominent subpopulation in spleen and blood. To eliminate murine MDSCs, we treated sarcoma-bearing mice twice weekly with 200 µg anti-Gr1 antibody RB6-8C5 over a period of 2 weeks, starting at tumor volumes of 100-200 mm3. While the combined percentage of the Ly6Gpos and Ly6Cpos cell populations in the spleens decreased compared to untreated mice (median 55%, range 36-75%, n=9 versus median 74%, range 72-86%, n=8), the total numbers of CD11b+ cells further increased (median 3.1 × 106, range 0.4 × 106-11 × 106 cells/spleen). Our data suggest that anti-Gr1 antibody pretreatment leads to blockade of the Ly6C/Ly6G receptors rather than eliminating MDSC subsets. To optimize preclinical pediatric sarcoma models, other methods for depletion or functional inactivation of mouse MDSCs will need to be evaluated.

Citation Format: Sareetha Kailayangiri, Bianca Altvater, Katja Urban, Jutta Meltzer, Lea Greune, Nicole Farwick, Silke Jamitzky, Claudia Rossig. Evaluation of anti-Gr1 antibody for depletion of MDSC in preclinical NSG mouse models of pediatric sarcoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4999.

Overcoming Heterogeneity of Antigen Expression for Effective CAR T Cell Targeting of Cancers

Chimeric antigen receptor (CAR) gene-modified T cells (CAR T cells) can eradicate B cell malignancies via recognition of surface-expressed B lineage antigens. Antigen escape remains a major mechanism of relapse and is a key barrier for expanding the use of CAR T cells towards solid cancers with their more diverse surface antigen repertoires. In this review we discuss strategies by which cancers become amenable to effective CAR T cell therapy despite heterogeneous phenotypes. Pharmaceutical approaches have been reported that selectively upregulate individual target antigens on the cancer cell surface to sensitize antigen-negative subclones for recognition by CARs. In addition, advanced T cell engineering strategies now enable CAR T cells to interact with more than a single antigen simultaneously. Still, the choice of adequate targets reliably and selectively expressed on the cell surface of tumor cells but not normal cells, ideally by driving tumor growth, is limited, and even dual or triple antigen targeting is unlikely to cure most solid tumors. Innovative receptor designs and combination strategies now aim to recruit bystander cells and alternative cytolytic mechanisms that broaden the activity of CAR-engineered T cells beyond CAR antigen-dependent tumor cell recognition.

Design and Characterization of an "All-in-One" Lentiviral Vector System Combining Constitutive Anti-GD2 CAR Expression and Inducible Cytokines

Genetically modified T cells expressing chimeric antigen receptors (CARs) so far have mostly failed in the treatment of solid tumors owing to a number of limitations, including an immunosuppressive tumor microenvironment and insufficient CAR T cell activation and persistence. Next-generation approaches using CAR T cells that secrete transgenic immunomodulatory cytokines upon CAR signaling, known as TRUCKs (“T cells redirected for universal cytokine-mediated killing”), are currently being explored. As TRUCKs were engineered by the transduction of T cells with two separate vectors, we developed a lentiviral modular “all-in-one” vector system that combines constitutive CAR expression and inducible nuclear factor of activated T cells (NFAT)-driven transgene expression for more efficient production of TRUCKs. Activation of the G_D2-specific CAR via GD2⁺ target cells induced NFAT promoter-driven cytokine release in primary human T cells, and indicated a tight linkage of CAR-specific activation and transgene expression that was further improved by a modified NFATsyn promoter. As proof-of-concept, we showed that T cells containing the “all-in-one” vector system secrete the immunomodulatory cytokines interleukin (IL)12 or IL18 upon co-cultivation with primary human GD2⁺ tumor cells, resulting in enhanced effector cell properties and increased monocyte recruitment. This highlights the potential of our system to simplify application of TRUCK-modified T cells in solid tumor therapy.

Abstract 388: SS18-SSX modulates YAP/TAZ-TEAD transcriptional activity in synovial sarcoma

Introduction: Synovial sarcoma (SySa) is a rare soft-tissue malignancy characterized by a specific reciprocal translocation t(X;18). The resulting chimeric SS18-SSX fusion protein acts as transcriptional dysregulator representing the major oncogenic driver in SySa tumorigenesis. Since targeting the fusion protein itself remains a particular challenge, it appears reasonable to therapeutically address signaling pathways which are functionally dependent on the SS18-SSX fusion protein. As different tumor entities were recently shown to harbor aberrant Hippo signaling patterns leading to increased activity of the transcriptional coactivators YAP/TAZ, the aim of this study was to analyze the role of YAP/TAZ in SySa and to decipher the functional link to the SS18-SSX fusion protein.

Experimental procedures: YAP/TAZ expression was analyzed by immunohistochemistry in a large cohort of SySa tissue specimens (n=65). Five SySa cell lines and mesenchymal SCP-1 stem cells stably expressing the SS18-SSX fusion protein were employed for in vitro analyses. We set out to analyze whether YAP/TAZ-TEAD transcriptional activity is dependent on the SySa-specific fusion protein, if this dependency is mediated by IGF-IR signaling (known to be activated in SySa) and to understand the biological function of YAP/TAZ in SySa. To modulate YAP/TAZ-TEAD transcriptional activity, RNAi-mediated knockdown and the small molecule inhibitor verteporfin were applied. Finally, the therapeutic effect of YAP/TAZ inhibition was tested in vivo using SySa cell line-based and patient-derived xenografts.

Results: SySa tissue specimens and cell lines strongly expressed nuclear YAP/TAZ. RNAi-mediated knockdown of SS18-SSX fusion protein led to significant reduction of YAP/TAZ-TEAD transcriptional activity while SS18-SSX overexpression in SCP-1 cells induced aberrant YAP/TAZ signals. This regulatory connection was at least partly realized through an IGF-II/IGF-IR loop, in which the SS18-SSX fusion protein drives IGF2 expression causing dysregulation of the Hippo effectors LATS1 and MOB1, eventually leading to YAP/TAZ activation. Inhibition of YAP/TAZ-TEAD transcriptional activity by RNAi or verteporfin resulted in a significant induction of apoptosis and significant reduction of SySa cell growth in vitro and in vivo.

Conclusions: Our study reveals SS18-SSX fusion protein-driven YAP/TAZ-TEAD signals to play an elementary role in SySa. Given the high efficacy of YAP/TAZ-directed pharmacological approaches in SySa xenografts, this preclinical study may constitute the basis for a novel therapeutic strategy to inhibit SS18-SSX-driven tumorigenesis.

Citation Format: Ilka Isfort, Magdalene Cyra, Sandra Elges, Sareetha Kailayangiri, Bianca Altvater, Claudia Rossig, Jan-Henrik Mikesch, Agnieszka Wozniak, Patrick Schöffski, Eva Wardelmann, Marcel Trautmann, Wolfgang Hartmann. SS18-SSX modulates YAP/TAZ-TEAD transcriptional activity in synovial sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 388.

Abstract 3437: Requirement for YAP1 signaling in myxoid liposarcoma

Myxoid liposarcomas (MLS) account for 20% of malignant adipocytic tumors and are characterized by a high rate of local recurrence and development of distant metastases in approximately 40% of patients. Most MLS are driven by the FUS-DDIT3 fusion gene encoding an aberrant transcription factor. The mechanisms whereby FUS-DDIT3 mediates sarcomagenesis are incompletely understood, and strategies to selectively target MLS cells remain elusive. In this study, we employed genome-scale RNA interference (RNAi) screening to uncover that human mesenchymal stem cells engineered to express FUS-DDIT3 and MLS cell lines are dependent on YAP1, a transcriptional co-activator and central effector of the Hippo pathway involved in tissue growth and tumorigenesis. Analysis of a large cohort of primary MLS specimens (n=223) revealed that nuclear YAP1 expression was significantly more prevalent in MLS compared to other liposarcoma subtypes. In support of the concept that increased YAP1-mediated transcriptional activity represents an essential feature of MLS development, RNAi-based YAP1 depletion in cultured MLS cells resulted in suppression of cell viability, cell cycle arrest, cellular senescence, and induction of apoptosis accompanied by decreased YAP1 target gene expression, and YAP1-positive primary MLS tumors showed strong expression of YAP1 downstream effectors such as FOXM1 and PLK1. Mechanistically, FUS-DDIT3 promotes YAP1 transcription, nuclear localization, and transcriptional activity and physically associates with YAP1 in the nucleus of MLS cells, pointing to the coordinate establishment of gene expression programs that promote MLS tumorigenesis. Consistent with the hypothesis that a YAP1-directed therapeutic approach could represent a rational strategy to selectively target FUS-DDIT3-expressing MLS cells, pharmacologic inhibition of YAP1 activity with verteporfin suppressed cell viability and YAP1 target gene expression in MLS cell lines, and the growth-inhibitory effects of YAP1 knockdown or verteporfin treatment could be recapitulated in MLS cell line-based xenograft models. Collectively, our data identify dependence on aberrant YAP1 activity as specific liability of FUS-DDIT3-expressing MLS cells, and provide preclinical evidence that YAP1-mediated signal transduction represents a candidate target for therapeutic intervention that warrants further investigation.

Citation Format: Marcel Trautmann, Ya-Yun Cheng, Patrizia Jensen, Ninel Azoitei, Ines Brunner, Jennifer Hüllein, Mikolaj Slabicki, Ilka Isfort, Magdalene Cyra, Eva Wardelmann, Sebastian Huss, Bianca Altvater, Claudia Rossig, Susanne Hafner, Thomas Simmet, Anders Ståhlberg, Pierre Åman, Thorsten Zenz, Undine Lange, Thomas Kindler, Claudia Scholl, Wolfgang Hartmann, Stefan Fröhling. Requirement for YAP1 signaling in myxoid liposarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3437.

Requirement for YAP1 signaling in myxoid liposarcoma

Myxoid liposarcomas (MLS), malignant tumors of adipocyte origin, are driven by the FUS-DDIT3 fusion gene encoding an aberrant transcription factor. The mechanisms whereby FUS-DDIT3 mediates sarcomagenesis are incompletely understood, and strategies to selectively target MLS cells remain elusive. Here we show, using an unbiased functional genomic approach, that FUS-DDIT3-expressing mesenchymal stem cells and MLS cell lines are dependent on YAP1, a transcriptional co-activator and central effector of the Hippo pathway involved in tissue growth and tumorigenesis, and that increased YAP1 activity is a hallmark of human MLS Mechanistically, FUS-DDIT3 promotes YAP1 expression, nuclear localization, and transcriptional activity and physically associates with YAP1 in the nucleus of MLS cells. Pharmacologic inhibition of YAP1 activity impairs the growth of MLS cells in vitro and in vivo These findings identify overactive YAP1 signaling as unifying feature of MLS development that could represent a novel target for therapeutic intervention.

EZH2 Inhibition in Ewing Sarcoma Upregulates GD2 Expression for Targeting with Gene-Modified T Cells

Chimeric antigen receptor (CAR) engineering of T cells allows one to specifically target tumor cells via cell surface antigens. A candidate target in Ewing sarcoma is the ganglioside G_D2, but heterogeneic expression limits its value. Here we report that pharmacological inhibition of Enhancer of Zeste Homolog 2 (EZH2) at doses reducing H3K27 trimethylation, but not cell viability, selectively and reversibly induces G_D2 surface expression in Ewing sarcoma cells. EZH2 in Ewing sarcoma cells directly binds to the promoter regions of genes encoding for two key enzymes of G_D2 biosynthesis, and EZH2 inhibition enhances expression of these genes. G_D2 surface expression in Ewing sarcoma cells is not associated with distinct in vitro proliferation, colony formation, chemosensitivity, or in vivo tumorigenicity. Moreover, disruption of G_D2 synthesis by gene editing does not affect its in vitro behavior. EZH2 inhibitor treatment sensitizes Ewing sarcoma cells to effective cytolysis by G_D2-specific CAR gene-modified T cells. In conclusion, we report a clinically applicable pharmacological approach for enhancing efficacy of adoptively transferred G_D2-redirected T cells against Ewing sarcoma, by enabling recognition of tumor cells with low or negative target expression.

Phosphatidylinositol-3-kinase (PI3K)/Akt Signaling is Functionally Essential in Myxoid Liposarcoma

Myxoid liposarcoma (MLS) is an aggressive soft-tissue tumor characterized by a specific reciprocal t(12;16) translocation resulting in expression of the chimeric FUS-DDIT3 fusion protein, an oncogenic transcription factor. Similar to other translocation-associated sarcomas, MLS is characterized by a low frequency of somatic mutations, albeit a subset of MLS has previously been shown to be associated with activating PIK3CA mutations. This study was performed to assess the prevalence of PI3K/Akt signaling alterations in MLS and the potential of PI3K-directed therapeutic concepts. In a large cohort of MLS, key components of the PI3K/Akt signaling cascade were evaluated by next generation seqeuncing (NGS), fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC). In three MLS cell lines, PI3K activity was inhibited by RNAi and the small-molecule PI3K inhibitor BKM120 (buparlisib) in vitro An MLS cell line-based avian chorioallantoic membrane model was applied for in vivo confirmation. In total, 26.8% of MLS cases displayed activating alterations in PI3K/Akt signaling components, with PIK3CA gain-of-function mutations representing the most prevalent finding (14.2%). IHC suggested PI3K/Akt activation in a far larger subgroup of MLS, implying alternative mechanisms of pathway activation. PI3K-directed therapeutic interference showed that MLS cell proliferation and viability significantly depended on PI3K-mediated signals in vitro and in vivo Our preclinical study underlines the elementary role of PI3K/Akt signals in MLS tumorigenesis and provides a molecularly based rationale for a PI3K-targeted therapeutic approach which may be particularly effective in the subgroup of tumors carrying activating genetic alterations in PI3K/Akt signaling components.

Carbohydrate Targets for CAR T Cells in Solid Childhood Cancers

Application of the CAR targeting strategy in solid tumors is challenged by the need for adequate target antigens. As a consequence of their tissue origin, embryonal cancers can aberrantly express membrane-anchored gangliosides. These are carbohydrate molecules consisting of a glycosphingolipid linked to sialic acids residues. The best-known example is the abundant expression of ganglioside G_D2 on the cell surface of neuroblastomas which derive from G_D2-positive neuroectoderm. Gangliosides are involved in various cellular functions, including signal transduction, cell proliferation, differentiation, adhesion and cell death. In addition, transformation of human cells to cancer cells can be associated with distinct glycosylation profiles which provide advantages for tumor growth and dissemination and can serve as immune targets. Both gangliosides and aberrant glycosylation of proteins escape the direct molecular and proteomic screening strategies currently applied to identify further immune targets in cancers. Due to their highly restricted expression and their functional roles in the malignant behavior, they are attractive targets for immune engineering strategies. G_D2-redirected CAR T cells have shown activity in clinical phase I/II trials in neuroblastoma and next-generation studies are ongoing. Further carbohydrate targets for CAR T cells in preclinical development are O-acetyl-G_D2, NeuGc-GM3 (N-glycolyl GM3), G_D3, SSEA-4, and oncofetal glycosylation variants. This review summarizes knowledge on the role and function of some membrane-expressed non-protein antigens, including gangliosides and abnormal protein glycosylation patterns, and discusses their potential to serve as a CAR targets in pediatric solid cancers.

Abstract 4631: Expression of ganglioside GD2 in Ewing sarcoma cells is not associated with specific functional characteristics or stem cell features

Safe and effective targeting of cancer with chimeric antigen receptor (CAR) engineered T cells relies on the presence of adequate tumor-associated surface antigens. We have found that Ewing sarcomas (EwS) express ganglioside GD2 and are recognized by T cells engineered with GD2-specific CARs. In an extended series of 97 EwS patient samples, 52 were GD2pos by immunohistochemistry. Based on reports that GD2 in breast cancer defines a malignant population with stem cell characteristics, we hypothesized that GD2 expression in EwS is associated with high capacity to self-renew and reinitiate tumor growth. Among 15 individual EwS cell lines with variable surface expression of GD2 by flow cytometry, GD2 expression levels were not associated with the capacities to proliferate and expand in vitro, form colonies in semi-solid medium, nor with their chemosensitivity, assessed by cell viabilities in the presence of increasing concentrations of the cytotoxic drug doxorubicin. Subpopulations with GD2hi phenotype selected from GD2pos and from GD2low EwS cell lines by cell sorting maintained their GD2hi and GD2low expression status during subsequent cultures over several weeks. The two subpopulations did not have different in vitro growth, colony-formation capacity, or chemosensitivity. In xenografting experiments, GD2hi and GD2low subpopulations of two EwS cell lines initiated tumors with comparable efficacies. To obtain direct evidence that GD2 surface expression is irrelevant for the biology of EwS cells, we performed genetic knockdown of the GD3S gene which drives biosynthesis of GD2 by CRISPR/Cas9 gene editing. GD3S gene editing resulted in effective elimination of GD2 surface expression in the GD2hi EwS cell lines TC-71, VH-64 and A4573. The knockdown did not affect the capacity of the cells to proliferate, form colonies in soft agar in vitro, nor their chemosensitivity compared to wild-type EwS cells from the individual cell lines. We conclude that GD2 expression in EwS cells, other than reported in breast cancer, is not associated with distinct functional features. Specifically, GD2 does not affect the growth characteristics, clono- and tumorigenicity and chemosensitivity of the tumor cells. Elimination of GD2pos subpopulations from heterogeneous tumors by CAR T cell targeting is therefore unlikely to eradicate the disease and will have to be combined with additional targeting strategies.

Citation Format: Sareetha Kailayangiri, Bianca Altvater, Silke Jamitzky, Stefanie Lesch, Jan-Henrik Mikesch, Sonja Schelhaas, Schaefers Michael, Jutta Meltzer, Nicole Farwick, Wolfgang Hartmann, Eva Wardelmann, Petra Fischer, Jendrik Hardes, Claudia Rossig. Expression of ganglioside GD2 in Ewing sarcoma cells is not associated with specific functional characteristics or stem cell features [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4631.

Abstract B04: Functional characterization of IGF-IR/PI3K/Akt signaling in myxoid liposarcoma

Introduction: Myxoid liposarcoma (MLS) is the second most common type of liposarcoma and an aggressive disease with particular propensity to develop hematogenic metastases. Ninety percent of MLS are characterized by a reciprocal translocation t(12;16) (q13;p11), leading to the pathogenic gene fusion of FUS and DDIT3. The resulting chimeric FUS-DDIT3 fusion protein is suggested to play a crucial role in MLS pathogenesis, although the specific mechanism of action remains to be substantiated. Aiming at the preclinical identification of novel therapeutic options, we here investigate the functional relevance of FUS-DDIT3 in IGF-IR/PI3K/Akt signal transduction.

Experimental Procedures: Immunohistochemical analyses of IGF-IR/PI3K/Akt signaling effectors and modulators were performed in a comprehensive cohort of clinical MLS specimens. FUS-DDIT3-dependent activation of the IGF-IR/PI3K/Akt signaling cascade was analyzed by siRNA and immunoblotting in vitro. Cell proliferation and FACS assays were performed in multiple tumor-derived MLS cell lines. An established MLS chorioallantoic membrane model (CAM) was employed for in vivo confirmation of the preclinical in vitro data.

Results: In a significant subset of MLS specimens, immunohistochemical staining revealed elevated phosphorylation levels of various signaling components, representing a strong indication of activated IGF-IR/PI3K/Akt signaling to be a frequent feature in MLS. IGF-IR inhibition significantly suppressed the IGF-IR/PI3K/Akt signaling cascade, associated with impairment of MLS cell viability and induction of apoptosis in vitro and in vivo. Furthermore, siRNA-mediated knockdown of FUS-DDIT3 led to dephosphorylation of IGF-IR/PI3K/Akt signaling components, implying that the FUS-DDIT3 fusion protein is involved in the IGF-IR regulated signaling cascade.

Conclusions: Our preclinical study emphasizes the pivotal role of the IGF-IR/PI3K/Akt signaling pathway in MLS pathogenesis and indicates its functional dependence on the MLS-specific FUS-DDIT3 fusion protein. Furthermore, our in vitro and in vivo results demonstrate that targeting the IGF-IR/PI3K/Akt signaling pathway provides a rational, molecularly founded therapeutic strategy in the treatment of MLS.

Citation Format: Marcel Trautmann, Magdalene Alice Cyra, Christian Bertling, Ilka Isfort, Jasmin Menzel, Konrad Steinestel, Inga Grünewald, Bianca Altvater, Claudia Rossig, Pierre Åman, Eva Wardelmann, Sebastian Huss, Wolfgang Hartmann. Functional characterization of IGF-IR/PI3K/Akt signaling in myxoid liposarcoma [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr B04.

Programmed cell death ligand 1 (PD-L1) expression is not a predominant feature in Ewing sarcomas

BACKGROUND

Programmed cell death 1 (PD-1) receptor engagement on T cells by its ligand programmed cell death ligand 1 (PD-L1) is a key mechanism of immune escape, and antibody blockade of the interaction has emerged as an effective immunotherapeutic strategy in some cancers. The role and relevance of the PD-1 checkpoint in Ewing sarcoma (EwS) is not yet understood.

PROCEDURE

Here, we investigated expression of PD-L1 and PD-1 in EwS by immunohistochemistry analysis of pretherapeutic tumor biopsies and in tumor xenografts following treatment with human T cells engineered to express a chimeric antigen receptor (CAR) against the tumor-associated antigen G_D2 . PD-L1 surface expression in EwS cell lines was assessed by flow cytometry.

RESULTS

PD-L1 expression was not detectable on tumor cells in any of the 60 EwS biopsies. Infiltrating PD-L1 positive T cells were found in one tumor, and four biopsies contained PD-1-positive T cells. Of 13 EwS cell lines, none constitutively expressed PD-L1 on the cell surface. Interferon-γ cytokine stimulation induced upregulation of the ligand on all cell lines. Adoptive therapy with CAR gene-modified T cells in a mouse model did not induce PD-L1 expression in EwS xenografts despite tumor infiltration with PD-1+ CD3+ T cells.

CONCLUSIONS

EwS cells can upregulate PD-L1 under inflammatory conditions, but do not express the ligand in the pretherapeutic tumor microenvironment or postexposure to CAR T cells. PD-1 checkpoint blockade alone is thus unlikely to evoke potent immune responses against EwS. Identification of the relevant immune evasion strategies in EwS will be vital for the development of effective immune targeting strategies.

T cell infiltration into Ewing sarcomas is associated with local expression of immune-inhibitory HLA-G

Ewing sarcoma (EwS) is an aggressive mesenchymal cancer of bones or soft tissues. The mechanisms by which this cancer interacts with the host immune system to induce tolerance are not well understood. We hypothesized that the non-classical, immune-inhibitory HLA-molecule HLA-G contributes to immune escape of EwS. While HLA-G^pos suppressor T cells were not increased in the peripheral blood of EwS patients, HLA-G was locally expressed on the tumor cells and/or on infiltrating lymphocytes in 16 of 47 pretherapeutic tumor biopsies and in 4 of 12 relapse tumors. HLA-G expression was not associated with risk-related patient variables or response to standard chemotherapy, but with significantly increased numbers of tumor-infiltrating CD3+ T cells compared to HLA-G^neg EwS biopsies. In a mouse model, EwS xenografts after adoptive therapy with tumor antigen-specific CAR T cells strongly expressed HLA-G whereas untreated control tumors were HLA-G^neg. IFN-γ stimulation of EwS cell lines in vitro induced expression of HLA-G protein. We conclude that EwS cells respond to tumor-infiltrating T cells by upregulation of HLA-G, a candidate mediator of local immune escape. Strategies that modulate HLA-G expression in the tumor microenvironment may enhance the efficacy of cellular immunotherapeutics in this cancer.

Vaccination to improve the persistence of CD19CAR gene-modified T cells in relapsed pediatric acute lymphoblastic leukemia

Trials with second generation CD19 chimeric antigen receptors (CAR) T-cells report unprecedented responses but are associated with risk of cytokine release syndrome (CRS). Instead, we studied the use of donor Epstein-Barr virus-specific T-cells (EBV CTL) transduced with a first generation CD19CAR, relying on the endogenous T-cell receptor for proliferation. We conducted a multi-center phase I/II study of donor CD19CAR transduced EBV CTL in pediatric acute lymphoblastic leukaemia (ALL). Patients were eligible pre-emptively if they developed molecular relapse (>5 × 10-4) post first stem cell transplant (SCT), or prophylactically post second SCT. An initial cohort showed poor expansion/persistence. We therefore investigated EBV-directed vaccination to enhance expansion/persistence. Eleven patients were treated. No CRS, neurotoxicity or graft versus host disease (GVHD) was observed. At 1 month, 5 patients were in CR (4 continuing, 1 de novo), 1 PR, 3 had stable disease and 3 no response. At a median follow-up of 12 months, 10 of 11 have relapsed, 2 are alive with disease and 1 alive in CR 3 years. Although CD19CAR CTL expansion was poor, persistence was enhanced by vaccination. Median persistence was 0 (range: 0-28) days without vaccination compared to 56 (range: 0-221) days with vaccination (P=0.06). This study demonstrates the feasibility of multi-center studies of CAR T cell therapy and the potential for enhancing persistence with vaccination.

Targeting Ewing sarcoma with activated and GD2-specific chimeric antigen receptor-engineered human NK cells induces upregulation of immune-inhibitory HLA-G

Activated and in vitro expanded natural killer (NK) cells have substantial cytotoxicity against many tumor cells, but their in vivo efficacy to eliminate solid cancers is limited. Here, we used chimeric antigen receptors (CARs) to enhance the activity of NK cells against Ewing sarcomas (EwS) in a tumor antigen-specific manner. Expression of CARs directed against the ganglioside antigen G_D2 in activated NK cells increased their responses to G_D2+ allogeneic EwS cells in vitro and overcame resistance of individual cell lines to NK cell lysis. Second-generation CARs with 4-1BB and 2B4 co-stimulatory signaling and third-generation CARs combining both co-stimulatory domains were all equally effective. By contrast, adoptive transfer of G_D2-specific CAR gene-modified NK cells both by intratumoral and intraperitoneal delivery failed to eliminate G_D2-expressing EwS xenografts. Histopathology review revealed upregulation of the immunosuppressive ligand HLA-G in tumor autopsies from mice treated with NK cells compared to untreated control mice. Supporting the relevance of this finding, in vitro co-incubation of NK cells with allogeneic EwS cells induced upregulation of the HLA-G receptor CD85j, and HLA-G1 expressed by EwS cells suppressed the activity of NK cells from three of five allogeneic donors against the tumor cells in vitro. We conclude that HLA-G is a candidate immune checkpoint in EwS where it can contribute to resistance to NK cell therapy. HLA-G deserves evaluation as a potential target for more effective immunotherapeutic combination regimens in this and other cancers.

Abstract 2314: Different stimulation conditions affect the immune phenotype of GD2-specific chimeric antigen receptor-expressing T cells

The in vivo persistence of chimeric antigen receptor (CAR) modified T cells is a major prerequisite for their antitumor activity and was found to be associated with a less differentiated immune phenotype. Here, we compared two in vitro T cell stimulation conditions: coated anti-CD3/CD28 antibodies [3/28], and Dynabead stimulation of enriched CD3+ T cells [DB]. Peripheral blood T cells from three healthy donors were stimulated with either of the two methods, retrovirally transduced with the GD2-specific CAR GD2-BBz on day 2 or 3, and expanded in RPMI/AIMV medium with 50 IU/ml recombinant human interleukin-2 for 13 days. T cell expansion rates were comparable between the two stimulation conditions and independent of CAR gene expression. Transduction efficiencies, determined by staining with the GD2-CAR-specific antibody Ganglidiomab, were also comparable. The immune phenotype by expression of CD3, CD4, CD8, CD45RO and CD197 was determined by flow cytometry analysis on day 13 or 14 after initial stimulation. The proportions of central memory (TCM), effector memory (TEM) or naïve T cells (TN) within the two types of cultures were noticeably different (Table 1), with a higher proportion of non-transduced CD8+ T cells with a TCM phenotype after DB compared to CD3/CD28 stimulation (p = 0.005 for DB d2, p = 0.01 for DB d3). Compared to non-transduced T cells, CAR-expressing cells of all types of cultures had higher proportions of TCM cells (p = 0.02 for CD4+ T cells, p<0.01 for CD8+ T cells). In conclusion, we found that the stimulation conditions have a strong impact on the T cell phenotype and that retroviral CAR gene transduction can also affect T cell differentiation. The optimal T cell culture conditions for a product with sustained persistence in vivo will ultimately emerge from clinical trials. Table 1:Proportions of T cell subpopulations on day 13 or 14 (medians and ranges)xyTN: CD45RO-/CD197+TCM: CD45RO+/CD197+TEM: CD45RO+/CD197-3/28NT37.9% CD4+ (31.8-41.3) 53.0% CD8+ (20.9-72.9)20.2% CD4+ (20.2-27.0) 6.1% CD8+ (3.7-6.9)35.2% CD4+ (32.8-45.4) 35.5% CD8+ (17.0-66.3)CAR d224.4% CD4+ (15.1-28.8) 32.9% CD8+ (23.9-48.9)33.6% CD4+ (29.9-49.3) 27.7% CD8+ (17.7-38.8)37.3% CD4+ (22.4-47.2) 27.1% CD8+ (25.4-32.7)DBNT33.1% CD4+ (15.0-45.6) 53.8% CD8+ (46.8-53.8)32.6% CD4+ (29.9-45.2) 19.6% CD8+ (17.8-26.3)23.3% CD4+ (16.6-51.7) 12.1% CD8+ (10.6-15.2)CAR d211.5% CD4+ (10.9-27.7) 37.1% CD8+ (24.7-41.860.7% CD4+ (53.0-69.7) 48.0% CD8+ (34.4-65.2)16.5% CD4+ (16.1-26.6) 8.7% CD8+ (5.7-10.3)DBNT33.2% CD4+ (26.5-55.2) 51.6% CD8+ (34.2-62.5)23.0% CD4+ (21.9-40.2) 14.2% CD8+ (11.2-16.9)19.1% CD4+ (17.6-48.6) 15.2% CD8+ (13.0-19.6)CAR d317.5% CD4+ (13.4-34.5) 36.6% CD8+ (28.5-46.5)45.7% CD4+ (36.6-57.5) 38.0% CD8+ (22.2-55.1)22.0% CD4+ (21.4-32.6) 10.8% CD8+ (8.5-19.6)

Citation Format: Laurin Ochs, Bianca Altvater, Sareetha Kailayangiri, Christian Spurny, Claudia Rossig, Silke Jamitzky. Different stimulation conditions affect the immune phenotype of GD2-specific chimeric antigen receptor-expressing T cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2314.

Optimized human CYP4B1 in combination with the alkylator prodrug 4-ipomeanol serves as a novel suicide gene system for adoptive T-cell therapies

Engineering autologous or allogeneic T cells to express a suicide gene can control potential toxicity in adoptive T-cell therapies. We recently reported the development of a novel human suicide gene system that is based on an orphan human cytochrome P450 enzyme, CYP4B1, and the naturally occurring alkylator prodrug 4-ipomeanol. The goal of this study was to systematically develop a clinically applicable self-inactivating lentiviral vector for efficient co-expression of CYP4B1 as an ER-located protein with two distinct types of cell surface proteins, either MACS selection genes for donor lymphocyte infusions after allogeneic stem cell transplantation or chimeric antigen receptors for retargeting primary T cells. The U3 region of the myeloproliferative sarcoma virus in combination with the T2A site was found to drive high-level expression of our CYP4B1 mutant with truncated CD34 or CD271 as MACS suitable selection markers. This lentiviral vector backbone was also well suited for co-expression of CYP4B1 with a codon-optimized CD19 chimeric antigen receptor (CAR) construct. Finally, 4-ipomeanol efficiently induced apoptosis in primary T cells that co-express mutant CYP4B1 and the divergently located MACS selection and CAR genes. In conclusion, we here developed a clinically suited lentiviral vector that supports high-level co-expression of cell surface proteins with a potent novel human suicide gene.

Insulin-like growth factor-1 receptor (IGF-1R) inhibition promotes expansion of human NK cells which maintain their potent antitumor activity against Ewing sarcoma cells

BACKGROUND

Patients with primary metastatic or relapsed Ewing sarcomas (EwS) have a poor prognosis. While inhibitory insulin-like growth factor 1 receptor (IGF-1R)-specific antibodies have shown single agent activity in some patients with refractory disease, effective therapeutic targeting will rely on optimal combinations with conventional or innovative therapies. Specifically, combination of inhibitory IGF-1R antibodies with adoptive transfer of activated natural killer (NK) cells may have therapeutic benefit in EwS without adding toxicity.

PROCEDURE

We investigated the in vitro effects of IGF-1R targeting on the immunological profile of EwS cells and on the survival and tumor targeting capacity of K-562-activated NK cells.

RESULTS

IGF-1R inhibition reliably reduced EwS cell viability without affecting expression of immune-modulatory and MHC molecules. In NK cells, we observed a significant superior expansion following in vitro activation in the presence of IGF-1R-specific antibodies, while expression of differentiation markers and activating receptors remained unaffected. Activated NK cells coincubated with EwS cells showed potent degranulation responses unaffected by IGF-1R inhibition. These findings were reproducible in a stimulator cell-free NK cell expansion system, suggesting that direct effects of IGF-R1 antibodies on the IGF-R1 pathway in NK cells induce their activation and expansion.

CONCLUSIONS

Activated human NK cells respond to IGF-1R inhibition with superior expansion kinetics while maintaining potent antitumor responses against EwS. Combination of adoptive NK cell transfer with IGF-1R targeting may be an efficient means to eliminate minimal residual disease after conventional therapy and thereby rescue patients at the highest risk of relapse.

Abstract 458: Immune-inhibitory HLA-G is expressed in the tumor microenvironment of Ewing Sarcomas

Ewing Sarcoma (EwS) is an aggressive malignancy of bone and soft tissue which still lacks efficient treatment in case of metastases and relapse. Cellular immunotherapies for EwS are under development, but inhibitory molecules in the tumor microenvironment may counteract antitumor immune responses by preexisting or therapeutic immune effector cells. Here we hypothesized that the non-classical HLA-molecule HLA-G may contribute to immune escape of EwS. HLA-G is a potent inhibitor of both T cells and NK cells. It is naturally expressed on trophoblast cells during pregnancy as well as on mesenchymal stem cells from which EwS cells are thought to originate. We analyzed expression of membrane-bound HLA-G1 by flow cytometry and expression of shedded HLA-G1 and soluble HLA-G5 by ELISA in 14 EwS cell lines with and without stimulation with interferon-γ (IFN-γ). Whereas all cell lines failed to express HLA-G1 both before and after IFN-γ stimulation, and none secreted HLA-G without stimulation, 1 of 14 cell lines (TC-32) responded to IFN-γ stimulation by significant upregulation of soluble HLA-G (p = 0.004). To study HLA-G expression in EwS within their tumor microenvironment, we analyzed paraffin-embedded pretherapeutic tumor biopsies from 35 patients by IHC using the HLA-G specific antibody clone 4H84 and detected HLA-G expression in 12 cases (34%), either on the tumor cells (10/35) and/or on infiltrating lymphocytes (7/35). We further studied the presence of soluble HLA-G and HLA-G+ T cells in the peripheral blood of 19 EwS patients and 15 healthy donors. Serum HLA-G was not increased in the EwS patients compared to healthy controls. Moreover, no significant difference in the proportions of naturally occurring HLA-G+CD4+ (Mean 0.9±0.8% vs. 0.9±0.6%, p = 0.627) or HLA-G+CD8+ (Mean 1.2±1.2% vs. 1.7±1.0%, p = 0.134) suppressor T cells among peripheral blood lymphocytes was found between EwS patients and healthy donors by flow cytometry. Thus, systemic HLA-G secretion and expression is unlikely to have a major role in EwS, but the presence of HLA-G+ cells found in EwS biopsies in a substantial proportion of patients deserves further exploration. To address the potential functional relevance of HLA-G+ cells in the tumor microenvironment, we expressed HLA-G1 in 2 EwS cell lines by retroviral gene transfer. Coincubation of HLA-G-expressing EwS cells with freshly isolated allogeneic NK-cells resulted in suppression of EwS cell lysis by NK cells in 3 of 6 NK cell donors in a flow cytometry based cytotoxicity assay. In detail, HLA-G+ EwS cells suppressed NK-cell cytotoxicity up to 47.0±14.8%, (VH-64, p = 0.001) and up to 87.0±16.0% (WE-68, p = 0.002) compared to mock transduced control.

We conclude that local expression of HLA-G within the tumor microenvironment in EwS is a candidate mediator of immune escape and a potential barrier to cellular immunotherapeutics. Strategies that modulate HLA-G expression may be effective to overcome local immune suppression in this cancer.

Citation Format: Christian Spurny, Bianca Altvater, Sareetha Kailayangiri, Silke Landmeier, Martina Ahlmann, Uta Dirksen, Andreas Ranft, Heinz Wiendl, Wolfgang Hartmann, Eva Wardelmann, Claudia Rossig. Immune-inhibitory HLA-G is expressed in the tumor microenvironment of Ewing Sarcomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 458. doi:10.1158/1538-7445.AM2015-458

Targeting interleukin-2 to the bone marrow stroma for therapy of acute myeloid leukemia relapsing after allogeneic hematopoietic stem cell transplantation

The antibody-based delivery of IL2 to extracellular targets expressed in the easily accessible tumor-associated vasculature has shown potent antileukemic activity in xenograft and immunocompetent murine models of acute myelogenous leukemia (AML), especially in combination with cytarabine. Here, we report our experience with 4 patients with relapsed AML after allogeneic hematopoietic stem cell transplantation (allo-HSCT), who were treated with the immunocytokine F16-IL2, in combination with low-dose cytarabine. One patient with disseminated extramedullary AML lesions achieved a complete metabolic response identified by PET/CT, which lasted 3 months. Two of 3 patients with bone marrow relapse achieved a blast reduction with transient molecular negativity. One of the 2 patients enjoyed a short complete remission before AML relapse occurred 2 months after the first infusion of F16-IL2. In line with a site-directed delivery of the cytokine, F16-IL2 led to an extensive infiltration of immune effector cells in the bone marrow. Grade 2 fevers were the only nonhematologic side effects in 2 patients. Grade 3 cytokine-release syndrome developed in the other 2 patients but was manageable in both cases with glucocorticoids. The concept of specifically targeting IL2 to the leukemia-associated stroma deserves further evaluation in clinical trials, especially in patients who relapse after allo-HSCT.

Abstract 3974: Insulin-like growth factor-1 receptor (IGF-1R) inhibition promotes expansion of human NK cells with potent antitumor activity against Ewing sarcoma cells

Despite optimization of modern treatment strategies, patients with primary metastatic Ewing sarcomas or with relapsed disease have a poor prognosis. The insulin-like growth factor 1 receptor (IGF-1R) pathway is a target of the disease-defining translocations and important for the biology of Ewing sarcomas. IGF-1R antagonists have shown activity in some patients with refractory disease. More effective therapeutic IGF-1R targeting will rely on optimal combinations of IGF-1R mAbs with conventional or innovative therapies. Specifically, adoptive transfer of activated NK cells may have therapeutic benefit in Ewing sarcoma without adding toxicity. Modulatory or synergistic interactions between novel drugs and cellular therapies as a basis for potent combinations have only started to be explored.

Here, we investigated the effects of IGF-1R-specific mAbs on the in vitro activation and expansion of human NK cells and their cytolytic activity against Ewing sarcoma cells. Freshly isolated PBMCs from 6 healthy donors were stimulated with irradiated K-562 in the presence or absence of two different inhibitory IGF-1R mAbs and expanded for up to 23 days. 7 of 8 NK cell cultures expanded in vitro at superior rates (3.3+/-1.2 fold) when IGF-1R mAbs were present in the cultures. These findings were reproduced in a stimulator cell free system based on magnetic cell sorting and subsequent stimulation of NK cells. Thus, IGF-1R-induced increases of NK cell expansion do not rely on interactions with bystander cells. Non-specific Fc-mediated NK cell stimulation was excluded by experiments using whole IgG as control. NK cells were found to surface-express IGF-1R and respond to coincubation with IGF-1R mAb with receptor downregulation (n=3). We conclude that direct effects of IGF-1R mAbs on the IGF-1R pathway in NK cells are likely to induce their activation and expansion. The expression of differentiation markers and activating receptors by in vitro activated and expanded NK cells was unaffected by IGF-1R antagonists. Upon coincubation with the Ewing sarcoma cell lines TC-71, TC-32 and VH-64 and with the newly established, low-passage cell culture DC-ES-6, NK cells that were activated and expanded in the presence and absence of IGF-1R antibody showed comparable, potent and reproducible degranulation responses by CD107a upregulation. Twenty-four hour preincubation of the Ewing sarcoma cell lines with IGF-1R mAb or presence of the mAbs during coculture also did not affect Ewing-sarcoma induced NK cell degranulation responses.

We conclude that human NK cells respond to IGF-1R mAb inhibition with superior expansion kinetics while maintaining potent antitumor responses against Ewing sarcoma. Combining adoptive NK cell transfer with IGF-1R targeting may be an efficient means to eliminate minimal residual disease after conventional therapy and thereby rescue patients at highest risk of relapse.

Citation Format: Silke Landmeier, Andrea-Caroline Krueger, Stephanie Piepke, Saskia Janneschuetz, Bianca Altvater, Sareetha Kailayangiri, Christian Spurny, Heribert Juergens, Claudia Rossig. Insulin-like growth factor-1 receptor (IGF-1R) inhibition promotes expansion of human NK cells with potent antitumor activity against Ewing sarcoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3974. doi:10.1158/1538-7445.AM2014-3974

Common Ewing sarcoma-associated antigens fail to induce natural T cell responses in both patients and healthy individuals

Disseminated or relapsed Ewing sarcoma (EwS) has remained fatal in the majority of patients. A promising approach to preventing relapse after conventional therapy is to establish tumor antigen-specific immune control. Efficient and specific T cell memory against the tumor depends on the expansion of rare T cells with native specificity against target antigens overexpressed by the tumor. Candidate antigens in EwS include six-transmembrane epithelial antigen of the prostate-1 (STEAP1), and the human cancer/testis antigens X-antigen family member 1 (XAGE1) and preferentially expressed antigen in melanoma (PRAME). Here, we screened normal donors and EwS patients for the presence of circulating T cells reactive with overlapping peptide libraries of these antigens by IFN-γ Elispot analysis. The majority of 22 healthy donors lacked detectable memory T cell responses against STEAP1, XAGE1 and PRAME. Moreover, ex vivo detection of T cells specific for these antigens in both blood and bone marrow were limited to a minority of EwS patients and required nonspecific T cell prestimulation. Cytotoxic T cells specific for the tumor-associated antigens were efficiently and reliably generated by in vitro priming using professional antigen-presenting cells and optimized cytokine stimulation; however, these T cells failed to interact with native antigen processed by target cells and with EwS cells expressing the antigen. We conclude that EwS-associated antigens fail to induce efficient T cell receptor (TCR)-mediated antitumor immune responses even under optimized conditions. Strategies based on TCR engineering could provide a more effective means to manipulating T cell immunity toward targeted elimination of tumor cells.

Anchorage-independent growth of Ewing sarcoma cells under serum-free conditions is not associated with stem-cell like phenotype and function

Novel treatment strategies for Ewing sarcoma aim to eliminate residual tumor cells that have maintained the capacity to reinitiate tumor growth after intensive conventional therapy. Preclinical models that more closely mimic in vivo tumor growth than standard monolayer cultures are needed. Sphere formation under anchorage-independent, serum-free conditions has been proposed to enrich for cells with tumor-initiating, stem cell-like properties in various solid cancers. In the present study, we assessed the phenotype and functional stem cell characteristics of Ewing sarcoma spheres. Spheres were generated under serum-free culture conditions from four Ewing sarcoma cell lines and four relapse tumor biopsies. Standard monolayer cultures were established as controls. Median levels of surface expression of the Ewing sarcoma marker CD99 as well as the supposed stem cell marker CD133 and the neural crest marker CD57 were comparable between spheres and monolayers. Ewing sarcoma spheres from individual tumors failed to continuously self-renew by secondary sphere formation. They contained variable proportions of side populations (SPs). Sphere culture did not enhance the in vivo tumorigenicity of Ewing sarcoma cells in a murine xenograft model. We conclude that sphere formation under serum-free conditions is not a reliable tool to enrich for cells with stem cell characteristics in Ewing sarcoma. By mimicking the anchorage-independent, multicellular growth of Ewing sarcoma micrometastases, in vitro sphere growth may still add value as a preclinical tool to evaluate the efficacy of novel therapeutics.

High proportions of CD4⁺ T cells among residual bone marrow T cells in childhood acute lymphoblastic leukemia are associated with favorable early responses

Residual nonmalignant T cells in the bone marrow of patients with acute leukemias may be involved in active immune responses to leukemic cells. Here, we investigated the phenotypic signature of T cells present at diagnosis in 39 pediatric patients with acute lymphoblastic leukemia (ALL) treated within standardized ALL-BFM study protocols. Previously described age associations of lymphocyte subpopulations in the peripheral blood of healthy children were reproduced in leukemic bone marrow. Analysis of individual lymphocyte parameters and risk-associated variables using univariate linear regression models revealed a correlation of higher CD4/CD8 ratios at diagnosis with a favorable bone marrow response on day 15. Separate analysis of CD4⁺ cells with the CD4⁺CD25(hi)FoxP3⁺ T(reg) cell phenotype showed that the association was caused by non-T(reg) CD4⁺ cells. The association of higher CD4/CD8 ratios with a favorable bone marrow response on day 15 of treatment persisted in a cohort extended to 69 patients. We conclude that CD4⁺ non-T(reg) cells in leukemic bone marrow at diagnosis may have a role in early response to treatment. Prospective analysis of the CD4/CD8 ratio in a large cohort of pediatric patients is now needed. Moreover, future experiments will establish the functional role of the individual T cell subsets in immune control in pediatric ALL.

Abstract 3980: The immunomodulatory agent L-MTP-PE induces activation and expansion of human γδ T cells capable of lysing osteosarcoma cells

The outcome of patients with metastatic osteosarcoma remains poor despite aggressive multimodality therapy. Liposomal Muramyl Tripeptide Phosphatidyl Ethanolamine (L-MTP-PE) is a non-specific immune modulator that activates monocytes and macrophages and has shown antitumor activity in osteosarcoma. The mechanism of action of L-MTP-PE remains unresolved. Here we investigated the effects of the agent on lymphocyte subpopulations.

Whole peripheral blood from 9 healthy donors were stimulated with L-MTP-PE for 24 hours. Compared to non-stimulated controls, a proliferative response of CD3+ lymphocytes was found (1.77±0.06 fold expansion, p=<0.001). The strongest effect was observed on the γδ TCR+ CD3+ T cell subpopulation which expanded 5.0±1.0 fold. To further evaluate the effects of L-MTP-PE on γδ T cell proliferation, mononuclear cells were isolated from peripheral blood of 5 healthy donors and cultured in the presence of L-MTP-PE. On day 11, γδ T cells had expanded 4.6±0.6 fold compared to medium-controls. Addition of interleukin-2 (IL-2) to the cultures increased expansion of γδ T cells up to 9.8±1.6. In comparison, the known γδ T-cell stimulatory aminobisphosphonate agent zoledronic acid (ZA) combined with IL-2 induced 25.8±7.2-fold expansion. γδ T cell stimulation by ZA was previously shown to involve inhibition of the mevalonate pathway enzyme farnesyl diphosphate synthase and subsequent increase of isopentyl pyrophosphate levels. To explore the mechanism of γδ T cell expansion by L-MTP-PE, coincubation experiments were repeated in the presence of the HMG-CoA reductase inhibitor mevastatin. Addition of mevastatin resulted in a 5.1±1.8-fold reduction of L-MTP-PE induced γδ T cell expansion, confirming a critical role of the mevalonate pathway in γδ T cell expansion and thus a mechanism comparable to ZA. To explore the in vitro antitumor activity of L-MTP-PE activated γδ T cells, 24 hour coincubation experiments were performed with the osteosarcoma cell lines HOS and SAOS on day 6 of cultures. In a flow-cytometry based cytotoxicity assay, substantial cytolysis of osteosarcoma cells from both cell lines was observed after coincubation with both L-MTP-PE- and L-MTP-PE/IL-2-stimulated γδ T cells. At an effector-to-target-ratio of 1:1, L-MTP-PE-stimulated γδ T cells reduced viable cell counts of HOS and SAOS to 41.4±2.7% and 54.0±7.6%, respectively, and L-MTP-PE/IL-2-stimulated γδ T cells decreased cell counts to 33.7±2.0% and 23.0±0.9%. In comparison, ZA/IL-2-stimulated γδ T cells resulted in reduced viability to 46.2±1.0% (HOS) and 38.9±3.8% (SAOS).

We conclude that L-MTP-PE induces effective in vitro expansion of γδ T cells via a mechanisms involving the mevalonate pathway, in a manner similar to aminobisphosphonate agents. L-MTP-PE-activated γδ T cells have the potential to lyse osteosarcoma cells and may thus be involved in the antitumor effects of this agents.

Citation Format: Sibylle Mellinghoff, Bianca Altvater, Uta Dirksen, Heribert Juergens, Claudia Rossig, Martina Ahlmann. The immunomodulatory agent L-MTP-PE induces activation and expansion of human γδ T cells capable of lysing osteosarcoma cells. [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 3980. doi:10.1158/1538-7445.AM2013-3980

Abstract 458: High proportions of CD4+ T cells among residual bone marrow T cells in childhood acute lymphoblastic leukemia are associated with favorable early responses

Residual non-malignant T cells in the bone marrow of patients with acute leukemias may be involved in active immune responses to leukemic cells or contribute to immune evasion. Here, we investigated the phenotypic signature of T cells present at diagnosis in 39 pediatric patients with acute lymphoblastic leukemia (ALL) treated at our institution within standardized ALL-BFM study protocols. All patients are alive in first (n=35) or second (n=4) remission with a median follow-up of 79 months. Mononuclear cells were isolated from bone marrow, stained with fluorescein-conjugated monoclonal antibodies and analyzed by 6-color flow cytometry. Median CD4/CD8 ratios in our patient cohort were 1.22 (range 0.42 to 2.63). A median of 4.8% (0.6 to 24.0%) of T cells coexpressed HLA-DR, and a median of 4.4% (range 0.8 to 10.7%) of CD4+ T cells had the Treg cell phenotype CD25hiFoxP3+. A median of 6.5% (range 0.4 to 15.5%) of T cells were TCRγδ+. NK cell/T cell ratios were highly variable (range 2.5 to 40.2). Previously described age associations of lymphocyte subpopulations in peripheral blood of healthy children were also found in leukemic bone marrow. Specifically, among CD4+ T cells, an increase of antigen-experienced T cells (CD45RA-CCR7-) was found in older children (p=0.03). Analysis of individual lymphocyte parameters and patient related variables by univariate linear regression models revealed noticeable differences between patients with T and B lineage ALL: Patients with T-ALL had lower CD4/CD8 ratios (0.05) and higher proportions of CD4+CD25hiFoxP3+ Treg cells (p=0.03) and HLA-DR+ T cells (p=0.008) than patients with B lineage ALL. We further investigated potential associations with leukemia response to treatment. Higher CD4/CD8 ratio at diagnosis correlated with favorable bone marrow response (≤5% blasts) on day 15 (p=0.012). Separate analysis of CD4+ cells with CD4+CD25hiFoxP3+ Treg cell phenotype revealed that the association was caused by non-Treg CD4+ cells. No correlation of the CD4/CD8 ratio with other response parameters or with relapse was found. To further validate this finding, we retrospectively analyzed CD4/CD8 cell ratios in routine diagnostic immunophenotypings of 32 further pediatric patients with ALL, all treated according to ALL-BFM 2000 protocol in our institution. An association of higher CD4/CD8 ratios with favorable bone marrow response on day 15 of treatment persisted in the total cohort of 71 patients (p=0.05). We conclude that CD4+ nonTreg cells in leukemic bone marrow at diagnosis may have a role in early response to treatment. Prospective analysis of the CD4/CD8 ratio in a large cohort of pediatric patients is now needed. Moreover, future experiments will establish the functional role of the individual T cell subsets in immune control or escape in pediatric ALL.

Citation Format: Imke Lustfeld, Bianca Altvater, Martina Ahlmann, Sandra Ligges, Peter Brinkrolf, Christel Katerkamp, Annegret Rosemann, Anja Moericke, Claudia Rossig. High proportions of CD4+ T cells among residual bone marrow T cells in childhood acute lymphoblastic leukemia are associated with favorable early responses. [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 458. doi:10.1158/1538-7445.AM2013-458

Abstract 3978: Assessment of therapeutic responses of disseminated Ewing sarcoma xenografts to adoptive therapy with chimeric receptor gene-modified T cells in mice by whole body magnetic resonance imaging

Novel treatment strategies in Ewing sarcoma include molecularly targeted drugs and antibodies as well as cellular therapies. Preclinical in vivo models are needed that recapitulate the biology of multifocal disease and reflect the activity of novel therapies against systemic (micro)metastatic disease. Here, we used whole body magnetic resonance imaging techniques to monitor the engraftment and metastatic spread of human Ewing sarcoma xenografts in mice and to address the therapeutic efficacy of adoptive T cell transfer. Of 18 mice receiving intravenous injections of 2x106 VH-64 cells, all developed disseminated tumor growth detectable by whole-body MRI within 31 days. All mice had lung tumors, with a median of 19 tumors (range 1 to 60) per mouse. Sixteen mice had additional tumor manifestations, including bone and/or bone marrow (n=10), soft tissues (n=5), and kidney (n=13). Interobserver agreement was high, with an intraclass correlation of 0.929 for tumor numbers. Dissection and histological analysis confirmed the presence of CD99+ small blue round cell tumors in bones, lungs and kidneys in all examined specimens. Sequential whole body T2 MRI scans at weekly intervals following an initial scan 3 weeks after tumor inoculation revealed in vivo growth of tumors at all sites. To add further tissue information, we performed parallel diffusion weighted whole body imaging with background signal suppression (DWIBS). DWIBS effectively visualized metastatic Ewing sarcoma growth in bones, retroperitoneal organs, and soft tissues, whereas, as expected, susceptibility artifacts in air-filled spaces prevented effective detection of lung tumors. To assess the therapeutic efficacy of adoptive T cell transfer against disseminated Ewing sarcomas in this model, further cohorts of 9 mice each received transfusions of 1x107 14.G2a-28ζ gene-modified human GD2-specific T cells following tumor inoculation. Control mice received non-transduced T cells. The numbers of mice developing tumors and the numbers of tumors at extrapulmonary localizations sites were not noticeably different between treated and control mice. However, animals receiving GD2-targeted gene-modified T cell therapy had lower numbers of pulmonary tumors than controls (p<0.0001). Moreover, the median volumes of soft tissue tumors at first detection were lower in the treatment cohort (p=0.019). Mice treated with GD2-redirected T cells had a growth delay of their lung tumors, with both smaller volumes (p=0.023) and lower numbers of tumors (p=0.024) at 4 weeks after tumor inoculation. Thus, GD2-retargeted T cells cannot prevent disseminated tumor growth in this aggressive systemic disease model, but are active to reduce pulmonary Ewing sarcoma manifestations. Optimized strategies now aim to enhance the efficacy of chimeric T cell receptor therapies.

Citation Format: Lennart Liebsch, Sareetha Kailayangiri, Laura Beck, Bianca Altvater, Raphael Koch, Marc Hotfilder, Janine Ring, Cornelius Faber, Volker Vieth, Claudia Rossig. Assessment of therapeutic responses of disseminated Ewing sarcoma xenografts to adoptive therapy with chimeric receptor gene-modified T cells in mice by whole body magnetic resonance imaging. [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 3978. doi:10.1158/1538-7445.AM2013-3978

Abstract 2503: Multicellular Ewing sarcoma spheres are efficiently targeted by activated NK cells

The outcome of disseminated Ewing sarcoma remains poor despite intensive multimodal treatment regimens. The disease often responds well to chemotherapy, but systemic relapses occur in the majority of patients. Targeting of residual disease by cellular immunotherapy may sustain remission and improve outcome. Specifically, Ewing sarcoma cells have been shown to be exquisitely sensitive to targeting by activated NK cells. To further explore the value of cellular strategies, preclinical models are needed that mimic the anchorage-independent, multicellular growth of Ewing sarcoma micrometastases. Here, we generated Ewing sarcoma spheres from cell lines (VH-64, TC-32, TC-71, A4573) and from four low-passage cell cultures established from Ewing sarcoma biopsies at primary diagnosis or at relapse under serum-free growth conditions. Standard monolayer cultures were used for comparisons. Phenotypic analysis revealed considerable heterogeneity among individual Ewing sarcomas and between spheres and monolayers. While the Ewing sarcoma marker CD99 as well as CD133 were expressed at comparable densities, spheres had significantly higher expression of the neural crest marker CD57 (HNK-1) and of MHC class I than monolayers, whereas CD117 (c-kit) expression was lower. Side populations characterized by Hoechst dye exclusion and previously associated with cancer stem cell function were identified in one of two primary sphere cultures and in VH-64 spheres but were absent or reduced in monolayer cultures. However, cells resuspended from spheres did not form subcutaneous tumors in immunodeficient (NOD/scid) mice at higher efficiencies than monolayer cultures, arguing against higher tumorigenicity of sphere-cultured cells. VH64 spheres were significantly more resistant towards doxorubicine than monolayers, and resuspended cells from sphere cultures remained less susceptible to lysis than monolayer cultures, but among primary tumor cells, consistent differences in chemosensitivity were not observed between the two culture systems. In vitro activated allogeneic NK cells were uniformly capable to lyse single cells derived from both monolayer and sphere cultures from established cell lines and primary cell cultures. Moreover, NK cells efficiently eliminated intact Ewing sarcoma spheres. Thus, cultured Ewing sarcoma cells are highly heterogenous. Their phenotype, function and susceptibility to both chemo- and immunotherapy differs among individual cell lines and primary cultures and under variable in vitro growth conditions. Activated NK cells efficiently target Ewing sarcoma cells both as monolayers and as spheres. The sphere model may provide a useful tool to analyze the contribution of micrometastatic architecture and serum-free niches to immune evasion. Experiments with autologous NK cells and with NK cells engineered to express tumor antigen-specific chimeric receptors are ongoing.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2503. doi:1538-7445.AM2012-2503

Activated human γδ T cells induce peptide-specific CD8+ T-cell responses to tumor-associated self-antigens

Specific cellular immunotherapy of cancer requires efficient generation and expansion of cytotoxic T lymphocytes (CTLs) that recognize tumor-associated self-antigens. Here, we investigated the capacity of human γδ T cells to induce expansion of CD8+ T cells specific for peptides derived from the weakly immunogenic tumor-associated self-antigens PRAME and STEAP1. Coincubation of aminobisphosphonate-stimulated human peripheral blood-derived γδ T cells (Vγ9+Vδ2+), loaded with HLA-A*02-restricted epitopes of PRAME, with autologous peripheral blood CD8+ T cells stimulated the expansion of peptide-specific cytolytic effector memory T cells. Moreover, peptide-loaded γδ T cells efficiently primed antigen-naive CD45RA+ CD8+ T cells against PRAME peptides. Direct comparisons with mature DCs revealed equal potency of γδ T cells and DCs in inducing primary T-cell responses and peptide-specific T-cell activation and expansion. Antigen presentation by γδ T-APCs was not able to overcome the limited capacity of peptide-specific T cells to interact with targets expressing full-length antigen. Importantly, T cells with regulatory phenotype (CD4+ CD25hiFoxP3+) were lower in cocultures with γδ T cells compared to DCs. In summary, bisphosphonate-activated γδ T cells permit generation of CTLs specific for weakly immunogenic tumor-associated epitopes. Exploiting this strategy for effective immunotherapy of cancer requires strategies that enhance the avidity of CTL responses to allow for efficient targeting of cancer.

Abstract 1927: Induction of memory CD8+ T-cell responses to STEAP-1 specific peptides for immunotherapy of Ewing sarcoma

High-risk Ewing sarcoma is still fatal in many cases. Cellular immunotherapy is a promising approach for preventing relapse by eliminating residual disease after conventional treatment. A critical prerequisite is the availability of an adequate tumor target antigen. STEAP-1 is a surface protein aberrantly expressed in various cancers. Potential obstacles to the use of STEAP-1 as a tumor target are the limited immunogenicity of STEAP-1 epitopes, clonal deletion of STEAP-1-reactive T cells, and poor presentation of STEAP-1 peptides by MHC class I on tumor cells. Here we investigated whether functional and Ewing-tumor reactive STEAP-1-specific cytotoxic T cells (CTLs) can be expanded from the repertoire of normal donors by peptide stimulation.

STEAP-1 was confirmed to be expressed in 10 of 10 Ewing sarcoma cell lines by PCR. To expand STEAP-1-specific CTLs, CD8+ T cells from HLA-A2-positive healthy donors were stimulated with autologous dendritic cells pulsed with a pool of 4 STEAP-1 peptides (5 µM each), in the presence of rhIL-7, rhIL-12 and rhIL-15. Weekly restimulations were performed with peptide-pulsed K562 cells gene-modified to express human HLA-A2, CD80, CD40L and OX40L (K562aAPCs). CTLs with a predominant CD8+ effector memory CTL phenotype (CD45RA-, CCR7-) were successfully generated from 6 healthy donors. Their epitope specificity was confirmed by ELISPOT analysis after 2 to 6 rounds of restimulation. Pooled STEAP-1 peptides directly added to the CTLs induced specific secretion of IFN-γ (70 to 487 spot forming cells (SFC)/105 cells, mean 297.5±138.7 SFC/105 cells), in the absence of relevant background responses to a control peptide (0 to 50 and mean of 16.2±19.9 SFCs/105 cells). Restimulation of CTLs with individual STEAP-1 peptides demonstrated donor-dependent reactivity with one to four of the peptides, while neither one emerged as immunodominant. The CTLs specifically lysed STEAP-1 peptide pulsed target cells (52.9±4.3% at an effector-to-target ratio of 20:1), but not cells pulsed with control peptides (0.0±3.8%). In contrast, STEAP-1 specific CTLs failed to functionally interact with the HLA-A2+/STEAP-1+ Ewing sarcoma cell lines as measured by cytolysis and cytokine secretion, even after upregulation of MHC class I molecules by pretreatment with IFN-γ.

Thus, while the induction of STEAP-1 peptide-specific CTLs is feasible, these CTLs do not efficiently recognize endogenously expressed antigen on Ewing sarcoma cells. Higher-avidity CTLs are likely needed for exploiting STEAP-1 as a target for adoptive immunotherapy in this disease. To define the critical requirements for recognition and lysis of STEAP-1 expressing target cells in an autologous setting, we are currently exploring activated autologous γδ T-APCs expressing full-length STEAP-1 protein by retroviral gene transfer as targets and stimulator cells for STEAP-1 specific CTLs.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1927.

2B4 (CD244) signaling via chimeric receptors costimulates tumor-antigen specific proliferation and in vitro expansion of human T cells

Regulatory NK cell receptors can contribute to antigen-specific adaptive immune responses by modulating T cell receptor (TCR)-induced T cell activation. We investigated the potential of the NK cell receptor 2B4 (CD244) to enhance tumor antigen-induced activation of human T cells. 2B4 is a member of the CD2 receptor subfamily with both activating and inhibitory functions in NK cells. In T cells, its expression is positively associated with the acquisition of a cytolytic effector memory phenotype. Recombinant chimeric receptors that link extracellular single-chain Fv fragments specific for the tumor-associated surface antigens CD19 and G(D2) to the signaling domains of human 2B4 and/or TCRzeta were expressed in non-specifically activated peripheral blood T cells by retroviral gene transfer. While 2B4 signaling alone failed to induce T cell effector functions or proliferation, it significantly augmented the antigen-specific activation responses induced by TCRzeta. 2B4 costimulation did not affect the predominant effector memory phenotype of expanding T cells, nor did it increase the proportion of T cells with regulatory phenotype (CD4+CD25(hi)FoxP3+). These data support a costimulatory role for 2B4 in human T cell subpopulations. As an amplifier of TCR-mediated signals, 2B4 may provide a powerful new tool for immunotherapy of cancer, promoting sustained activation and proliferation of gene-modified antitumor T cells.

A high proportion of bone marrow T cells with regulatory phenotype (CD4+CD25hiFoxP3+) in Ewing sarcoma patients is associated with metastatic disease

Immunosuppressive CD4+CD25(hi)FoxP3+ T cells (T(reg) cells) have been found at increased densities within the tumor microenvironment in many malignancies and interfere with protective antitumor immune responses. Osseous Ewing sarcomas (ESs) are thought to derive from a bone marrow (BM) mesenchymal cell of origin, and microscopic marrow involvement defines a subpopulation of patients at a high risk of relapse. We hypothesized that BM-resident T cells may contribute to a permissive milieu for immune escape of ESs. Using 6-color-flow cytometry, we investigated the pattern of immune cell subset distribution including NK cells, gammadelta T cells, central and effector memory CD8+ and CD4+ T cells as well as T cells with regulatory phenotype (T(reg) cells) in BM obtained at diagnosis from 45 primary or relapsed ES patients treated within standardized protocols. Although patients at relapse had an inverted CD4:CD8 T-cell ratio, neither CD8+ effector/memory T-cell subsets nor T(reg) cells significantly differed from patients at diagnosis. No significant associations of innate and effector/memory T-cell subpopulations with known risk factors were found, including age, gender, tumor site, primary metastases and histological tumor response. By contrast, T(reg) cells were found at significantly higher frequencies in patients with primary metastatic disease compared with localized ESs (5.0 vs. 3.3%, p = 0.01). Thus, increased BM T(reg) cells in patients with metastasized ES may reflect an immune escape mechanism that contributes to the development of metastatic disease. Immunotherapeutic strategies will have to adequately consider the regulatory milieu within areas of Ewing tumor-immune interactions.

2B4 (CD244) signaling by recombinant antigen-specific chimeric receptors costimulates natural killer cell activation to leukemia and neuroblastoma cells

PURPOSE

Novel natural killer (NK) cell-directed strategies in cancer immunotherapy aim at specifically modulating the balance between NK cell receptor signals toward tumor-specific activation. The signaling lymphocyte activation molecule-related receptor 2B4 (CD244) is an important regulator of NK cell activation. We investigated whether 2B4-enhanced activation signals can redirect the cytolytic function of human NK cells to NK cell-resistant and autologous leukemia and tumor targets.

EXPERIMENTAL DESIGN

In vitro-stimulated NK cells from healthy donors and pediatric leukemia patients were gene modified with CD19 or G(D2)-specific chimeric receptors containing either the T-cell receptor zeta or 2B4 endodomain alone or combined.

RESULTS

Chimeric 2B4 signaling alone failed to induce interleukin-2 receptor up-regulation and cytokine secretion but triggered a specific degranulation response. Integration of the 2B4 endodomain into T-cell receptor zeta chimeric receptors significantly enhanced all aspects of the NK cell activation response to antigen-expressing leukemia or neuroblastoma cells, including CD25 up-regulation, secretion of IFN-gamma and tumor necrosis factor-alpha, release of cytolytic granules, and growth inhibition, and overcame NK cell resistance of autologous leukemia cells while maintaining antigen specificity.

CONCLUSION

These data indicate that the 2B4 receptor has a potent costimulatory effect in NK cells. Antigen-specific 2B4zeta-expressing NK cells may be a powerful new tool for adoptive immunotherapy of leukemia and other malignancies.

Gene-engineered varicella-zoster virus reactive CD4+ cytotoxic T cells exert tumor-specific effector function

T cells with grafted specificities for surface antigens provide an avenue for rapidly producing immune effector cells with tumor specificity. However, the function of chimeric receptor (chRec) gene-modified T cells is limited by lack of T-cell expansion and persistence. We propose to use varicella zoster virus (VZV)-reactive T cells as host for the chRec because these cells can be expanded both in vitro and in vivo by stimulation of their native receptor during endogenous reexposure to the virus or by administration of VZV vaccine. We obtained human T cells reactive with VZV from the peripheral blood of seropositive donors by stimulation with VZV lysate and evaluated their characteristics after genetic modification with two tumor-specific model chRecs. Cultures dominated by cytolytic CD4(+) T cells (VZV-CTL) could be expanded and maintained in vitro. Gene-modified VZV-CTL recognized and lysed tumor targets in a MHC-independent manner while maintaining functional, MHC-restricted interaction with VZV antigen through their native receptor. Thus, chRec-transduced VZV-CTL may provide a source of potent tumor-reactive cells for adoptive immunotherapy of cancer. The availability of a safe and effective VZV vaccine provides the option of repeated in vivo stimulation to maintain high T-cell numbers until the tumor is eliminated.

CD28 co-stimulation via tumour-specific chimaeric receptors induces an incomplete activation response in Epstein-Barr virus-specific effector memory T cells

Expression of tumour antigen-specific chimaeric receptors in T lymphocytes can redirect their effector functions towards tumour cells. Integration of the signalling domains of the co-stimulatory molecule CD28 into chRec enhances antigen-specific proliferation of polyclonal human T cell populations. While CD28 plays an essential role in the priming of naive CD4(+) T cells, its contribution to effector memory T cell responses is controversial. We compared the function of the chRec with and without the CD28 co-stimulatory domain, expressing it in peripheral blood T cells or Epstein-Barr virus (EBV)-specific T cell lines. The chimaeric T cell receptors contain an extracellular single-chain antibody domain, to give specificity against the tumour ganglioside antigen G(D2). The transduced cytotoxic T lymphocytes (CTL) maintained their specificity for autologous EBV targets and their capacity to proliferate after stimulation with EBV-infected B cells. Intracellular cytokine staining demonstrated efficient and comparable antigen-specific interferon (IFN)-gamma secretion by CTL following engagement of both the native and the chimaeric receptor, independent of chimaeric CD28 signalling. Furthermore, tumour targets were lysed in an antigen-specific manner by both chRec. However, while antigen engagement by CD28 zeta chRec efficiently induced expansion of polyclonal peripheral blood lymphocytes in an antigen-dependent manner, CD28 signalling did not induce proliferation of EBV-CTL in response to antigen-expressing tumour cells. Thus, the co-stimulatory requirement for the efficient activation response of antigen-specific memory cells cannot be mimicked simply by combining CD28 and zeta signalling. The full potential of this highly cytolytic T cell population for adoptive immunotherapy of cancer requires further exploration of their co-stimulatory requirements.

Target antigen expression on a professional antigen-presenting cell induces superior proliferative antitumor T-cell responses via chimeric T-cell receptors

Human T cells expressing tumor antigen-specific chimeric receptors fail to sustain their growth and activation in vivo, which greatly reduces their therapeutic value. The defective proliferative response to tumor cells in vitro can partly be overcome by concomitant CD28 costimulatory signaling. We investigated whether T-cell activation via chimeric receptors (chRec) can be further improved by ligand expression on antigen-presenting cells of B-cell origin. We generated Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTLs) expressing a CD19-specific chRec. These CTLs are provided with native receptor stimulation by autologous EBV-transformed B-lymphoblastoid cell lines (LCLs) but exclusively with chRec (CD19-specific) stimulation by allogeneic, human leukocyte antigen (HLA)-mismatched CD19+ LCLs. CD19zeta-transduced EBV-specific CTLs specifically lysed both allogeneic EBV targets and CD19+ tumor cells through the chRec in a major histocompatibility complex-independent manner, while maintaining their ability to recognize autologous EBV targets through the native T-cell receptor. The transduced CTLs failed to proliferate in response to CD19+ tumor targets even in the presence of CD28 costimulatory signaling. By contrast, CD19 expressed on HLA-mismatched LCL-induced T-cell activation and long-term proliferation that essentially duplicated the result from native receptor stimulation with autologous LCLs, suggesting that a deficit of costimulatory molecules on target cells in addition to CD28 is indeed responsible for inadequate chRec-mediated T-cell function. Hence, effective tumor immunotherapy may be favored if engagement of the chRec on modified T cells is complemented by interaction with multiple costimulator molecules. The use of T cells with native specificity for EBV may be one means of attaining this objective.

Adoptive Cellular Immunotherapy with CD19-Specific T Cells

BACKGROUND

No effective therapeutic modalities exist for the treatment of relapsed high risk acute lymphoblastic leukemia (ALL). Adoptive cellular immunotherapy by transfusion of polyclonal donor lymphocytes is not always effective and is limited by cellular cross-reactivity with normal tissues, leading to development of clinical graft-versus-host disease (GVHD).

METHOD

To develop an immunotherapeutic strategy for targeted elimination of residual leukemic blasts, human T cells were gene-modified to express CD19-specific chimeric receptors.

RESULTS

Gene-modified T cells specifically lyse CD19-expressing lymphatic blast cells, however, they show a limited proliferative response to stimulation with CD19. Integration of the signal transduction domain of the costimulatory molecule CD28 enhances the proliferative properties of the gene-modified T cells.

CONCLUSIONS

Adoptive transfer of gene-modified virus-specific T cells may provide a useful strategy for prevention and early treatment of ALL relapses following allogeneic stem cell transplantation.