Cancer immunotherapy is emerging as a powerful tool in the treatment of cancer. Multiple clinical trials have established that infusion of tumour-specific T cells can cause regression of advanced tumours and prevent tumour relapse. While tumour-specific T cells are typically rare, engineering methods have been developed to introduce tumour-specific receptors into T cells and engender peripheral blood T cells with the ability to kill tumour cells. These engineering successes notwithstanding, tumour cells demonstrate variable sensitivity to T cell attack. Therefore, to maximize the impact of the engineered T cells, it is necessary to develop therapeutic strategies that render tumour cells sensitive to immune attack. For my thesis research, I sought to develop a high throughput screening assay that would allow me to screen chemical libraries for agents that sensitize tumour cells to T cell attack. My ultimate goal is to define chemical agents that effectively sensitize tumour cells to T cell attack but display a better toxicity profile than existing chemotherapies. To this end, I developed a screen where resistant tumour cells were exposed to T cells engineered with chimeric antigen receptors and positive hits were defined as agents that could enhance killing of the tumour cells. My work explored both murine and human systems and I ultimately decided to use human cells for my screen. Multiple methods for measuring tumour cell killing were evaluated, many tumour lines were screened and I optimized the conditions for generating large numbers of engineered T cells for the screen. The net result of my thesis work is a miniaturized assay that is ready for high throughput screening. / Thesis / Master of Science in Medical Sciences (MSMS)

At least 10% of all cancer deaths are attributable to local tumor disease burden. In select cases, existing treatments such as surgery, chemotherapy, radiation, and immunotherapy demonstrate efficacy in halting or slowing cancer progression to improve survival. However, these strategies remain insufficient for most patients depending on cancer stage and histological characteristics, resulting in locoregional spread, locoregional recurrence, or progression to metastatic disease while also inducing dose-limiting toxicity. Biomaterials enable localized delivery of small molecules and proteins to improve safety and efficacy of cancer therapies. To leverage the safety and efficacy of biomaterials for local cancer treatment, we developed electrospun, hydrophobic nanofiber meshes that deliver small molecules and proteins. The meshes are biodegradable, biocompatible, and mechanically robust, making them ideal delivery vehicles for intraoperative care in the context of local tumor resection. We optimized the meshes to deliver the chemotherapeutic doxorubicin via drug encapsulation within the nanofibers and within hydrophobic coatings made of poly(glycerol mono-stearate-co-caprolactone) (PGC-C18). The meshes, called doxorubicin-eluting meshes (DoMs), prevent local sarcoma recurrence while avoiding cardiotoxicity associated with systemic doxorubicin therapy. We next utilized this mesh formulation to encapsulate grazoprevir (GZV), an FDA approved drug recently repurposed as an inducer molecule for a logic chimeric antigen receptor (CAR) T cell. Using the meshes, we can modulate release over time and control cytokine expression in vitro. Finally, we designed meshes that adsorb proteins and release them in a tunable manner through wetting modulation, named ZipCAR Adaptor Modulation using a BiOdegradable Nanofiber Implant (ZAMBONI). We used the meshes to deliver universal CAR T cell adaptor proteins, which connect CAR T cells to cancer cells in a modular fashion. We demonstrate improved safety and efficacy in models of ovarian carcinoma and mesothelioma without evidence of on-target, off-tumor toxicity, a common mechanism of CAR T cell toxicity. Together, these results demonstrate a novel and robust approach to improve safety and efficacy in local cancer therapy. / 2025-07-19T00:00:00Z

京都大学 / 新制・課程博士 / 博士(人間健康科学) / 甲第24292号 / 人健博第107号 / 新制||人健||8(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 藤井 康友, 教授 岡 昌吾, 教授 滝田 順子 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

An important obstacle to a functional cure for HIV/AIDS is the persistence of viral reservoirs found throughout the body in various cells and tissues. Reservoirs can be latently infected cells, or in the case of follicular dendritic cells (FDC), non-infected cells that trap infectious virus on their surface through immune complexes (HIV-IC). Although several strategies have been employed to target and eliminate viral reservoirs, they are short-lived and ineffective. In an attempt to provide a long-term approach, chimeric antigen receptor T (CAR-T) cells were designed to eliminate native HIV on FDCs. Although effective at eliminating HIV-infected cells, and halting spreading infection, their ability to eliminate the viral reservoir found on (FDCs) remains unclear. We used a novel second-generation CAR-T cell expressing domains 1 and 2 of CD4 followed by the mannose binding lectin (MBL) to allow recognition of native HIV envelope (Env) to determine the capacity to respond to the viral reservoir found on FDCs. We employed a novel fluorescent lysis assay, the Carboxyfluorescein succinimidyl ester (CFSE) release assay, as well as flow cytometric based assays to detect functional CAR-T activation through IFN-γ production and CD107a (i.e., LAMP1) membrane accumulation to test cytolytic capacity and functional activation of CD4-MBL CAR-T cells, respectively. We demonstrated their efficacy at eliminating HIV-infected cells or cells expressing gp160. However, these CAR-T cells were unable to lyse cells bearing surface bound HIV-IC. We found that failed lysis was not a unique feature of a resistant target, but a limitation in the CAR-T recognition elements. CAR-T cells were inactive in the presence of free HIV or in the presence of concentrated, immobilized virus. Further experiments determined that in addition to gp120 recognition by the CAR-T, the adhesion molecule ICAM-1 was necessary for efficient CAR-T cell killing of HIV-infected cells. CAR-T cell activity and killing were inhibited in the presence of ICAM-1 blocking antibody. These results suggest that other factors, such as adhesion molecules, play a vital role in CAR-T responses to HIV-infected cells. In addition, our findings highlighted the necessity to consider all models of HIV reservoirs, including FDCs, when evaluating therapeutic efficacy.

An important obstacle to a functional cure for HIV/AIDS is the persistence of viral reservoirs found throughout the body in various cells and tissues. Reservoirs can be latently infected cells, or in the case of follicular dendritic cells (FDC), non-infected cells that trap infectious virus on their surface through immune complexes (HIV-IC). Although several strategies have been employed to target and eliminate viral reservoirs, they are short-lived and ineffective. In an attempt to provide a long-term approach, chimeric antigen receptor T (CAR-T) cells were designed to eliminate native HIV on FDCs. Although effective at eliminating HIV-infected cells, and halting spreading infection, their ability to eliminate the viral reservoir found on (FDCs) remains unclear. We used a novel second-generation CAR-T cell expressing domains 1 and 2 of CD4 followed by the mannose binding lectin (MBL) to allow recognition of native HIV envelope (Env) to determine the capacity to respond to the viral reservoir found on FDCs. We employed a novel fluorescent lysis assay, the Carboxyfluorescein succinimidyl ester (CFSE) release assay, as well as flow cytometric based assays to detect functional CAR-T activation through IFN-γ production and CD107a (i.e., LAMP1) membrane accumulation to test cytolytic capacity and functional activation of CD4-MBL CAR-T cells, respectively. We demonstrated their efficacy at eliminating HIV-infected cells or cells expressing gp160. However, these CAR-T cells were unable to lyse cells bearing surface bound HIV-IC. We found that failed lysis was not a unique feature of a resistant target, but a limitation in the CAR-T recognition elements. CAR-T cells were inactive in the presence of free HIV or in the presence of concentrated, immobilized virus. Further experiments determined that in addition to gp120 recognition by the CAR-T, the adhesion molecule ICAM-1 was necessary for efficient CAR-T cell killing of HIV-infected cells. CAR-T cell activity and killing were inhibited in the presence of ICAM-1 blocking antibody. These results suggest that other factors, such as adhesion molecules, play a vital role in CAR-T responses to HIV-infected cells. In addition, our findings highlighted the necessity to consider all models of HIV reservoirs, including FDCs, when evaluating therapeutic efficacy.

Novel therapeutic approaches against ovarian cancer (OC) are urgently needed because of its high rate of recurrence even after extensive surgery and multi-agent chemotherapy. We aimed to develop a novel anti-CD24 chimeric antigen receptor (CAR) as an immunotherapeutic approach against OC cells and cancer stem cells (CSC). CSC represents a subpopulation of the tumor characterized by enhanced chemoresistance as well as the increased capability of self-renewal and metastasis. We designed a codon-optimized third-generation CAR containing the highly active single chain variable fragment (scFv) “SWA11” against CD24. We equipped the human NK-cell line NK-92 with the anti-CD24 CAR and an anti-CD19 control CAR using lentiviral transduction. Engineered NK-92 cells showed high cytotoxic activity against CD24-positive OC cell lines (SKOV3, OVCAR3). This effect was restricted to CD24-expressing cells as shown after lentiviral transduction of CD24-negative cell lines (A2780, HEK-293T) with CD24 transmembrane proteins. Additionally, NK-92 cells equipped with our novel anti-CD24 CAR were highly effective against patient-derived primary ovarian cancer cells. The activation of NK cells was shown by specific IFN secretion upon antigen stimulation. To further reduce possible off-target effects in vivo, we applied a dual-CAR approach using an anti-CD24-CD28-41BB fusion protein linked via a 2A sequence to an anti-mesothelin-CD3-CAR. The dual-CAR was simultaneously active against CD24 and mesothelin expressing cells. Our novel anti-CD24-CAR showed a highly cytotoxic effect against OC cell lines and primary OC cells and will be evaluated in future in vivo trials as a promising immunotherapeutic approach against OC.

Glioblastoma (GBM) remains the most aggressive and prevalent malignant primary brain tumor in adults. Unchanged since 2005, standard of care (SoC) consists of surgical resection, followed by radiation therapy (RT) with concurrent and adjuvant chemotherapy with temozolomide (TMZ). Despite these therapeutic efforts, patients succumb to recurrent disease with a median overall survival of 14.6 months and a five-year survival rate of 5.5-6.8%. Therapeutic failure is largely explained by ITH and the presence of treatment-resistant GBM stem-like cells (GSCs). Given the lack of understanding of recurrent GBM and absence of second line therapies patients, I hypothesize that genome-scale functional genetic interrogation will unravel recurrent GBM-specific tumor biology and inform development of novel therapeutics. First, I compared primary and recurrent GBM at the genetic, transcriptomic, proteomic and functional genetic levels. These analyses map a multilayered genetic response to drive tumor recurrence, identifying protein tyrosine phosphatase 4A2 (PTP4A2) as a novel modulator of self-renewal, proliferation and tumorigenicity at GBM recurrence. Mechanistically, genetic perturbation and a small molecule inhibitor of PTP4A2 repress axon guidance activity through a dephosphorylation axis with roundabout guidance receptor 1 (ROBO1) and exploit a genetic dependency on ROBO signaling. Importantly, engineered anti-ROBO1 single-domain antibodies also mimic the effects of PTP4A2 inhibition. Given the genetic dependency on ROBO signaling and enrichment of ROBO1 expression in GBM tissues, I undertook a campaign to evaluate ROBO1 as a therapeutic target in recurrent GBM and develop anti-ROBO1 chimeric antigen receptor T (CAR-T) cells using camelid single-domain antibodies targeting human ROBO1. I optimized the design of anti-ROBO1 CAR-T cells and tested the anti-tumor activity of these modalities in in vitro using patient-derived recurrent GBM lines and orthotopic patient-derived xenograft models. I present data to expand the repertoire of GBM-enriched antigens suitable for effective CAR-T cell therapy. Given that resistance to SoC and disease relapse are inevitable for GBM patients, pre-clinical and clinical advancement of immunotherapeutic modalities, combined with recent insights into the tumor immune microenvironment, are poised to improve clinical outcomes for this patient population. / Thesis / Doctor of Philosophy (PhD) / Glioblastoma remains the most lethal and prevalent primary brain tumor in adults. Standard of care for patients remains unchanged since 2005, consisting of surgery to remove visible tumor at diagnosis (primary tumor), followed by radiation therapy and chemotherapy to treat remaining tumor cells. Despite these therapeutic efforts, tumor relapse (recurrent tumor) is inevitable with no standardized second-line therapy. Patients succumb to recurrent disease with a median overall survival of 14.6 months and only 5.5-6.8% of patients survive five years post diagnosis. Therapy failure and tumor relapse are explained by immense diversity among tumor cells at the DNA and protein levels, giving rise to a subset of tumor cells with abilities to resist therapy and seed the recurrent tumor. Previous studies have presented evolution of tumor cells through therapy, with recurrent tumor cells harboring novel changes at the DNA and protein levels. However, the impact of these changes on tumor cell function has not been evaluated. In this thesis, we developed and applied a genetic screening technique to determine the functional role of thousands of genes in primary and recurrent tumor cells from the same patient. This analysis revealed numerous genes that exhibit differential effects on survival of primary and recurrent tumor cells, including genes that drive recurrent tumor cell growth but are dispensable in primary tumor cells. Functional remodeling of these genes and pathways revealed a new functional role of multiple proteins belonging to a process called axonal guidance in recurrent tumor cells. To evaluate the therapeutic potential of these findings, we deeply interrogated the mechanism by which axonal guidance drives recurrent tumor cells and targeted crucial molecular players using chemical and immunological therapies. Using models that predict clinical effectiveness, we engineered and tested a novel therapy that redirects immune cells to target recurrent tumor cells driven by dysfunctional axonal guidance activity. The goal of this thesis was to discover the functional differences between primary and recurrent tumor cells, thereby leveraging this information to engineer candidate therapies for treatment of recurrent glioblastoma.

In this PhD thesis the potential of T-cells as therapy for disease are explored. The applications of genetically modified T-cells for treatment of cancer and autoimmune disease; the functionality and optimal activation of T-cells are discussed. Successful treatment of cancer with T-cell receptor (TCR)-modified T-cells was first reported in 2006, and is based on recognition of a specific peptide by the TCR in the context of the MHC molecule. As antigen presentation in tumors is often defective and to avoid MHC-restriction, chimeric antigen receptors (CAR) molecules containing an antibody part for recognition of cell surface antigens and TCR and co-receptor signaling domains have been developed. Activated T-cells mount an efficient immune response resulting in the killing of the cancer cell and initiating T-cell proliferation. The rationale for using genetically modified T-cells instead of isolating tumor infiltrating lymphocytes from the tumor and expanding them (TIL therapy) is that it is often very difficult to obtain viable lymphocytes that are able to expand enough in order to use them for therapy. This thesis explores the possibility of using prostate-specific antigens to target T-cells towards prostate cancer. The prostate has many unique tissue antigens but most patients with metastatic prostate cancer have undergone prostatectomy and consequently have “prostate antigen” expression only in cancer cells. We targeted the prostate antigens TARP and PSCA with a HLA-A2 restricted TCR and a CAR respectively. In both cases the tumor-specific T-cells were able to generate potent proliferative and cytotoxic responses in vitro. The PSCA CAR-modified T-cells delayed subcutaneous tumor growth in vivo. It is evident from our in vivo experiments that the PSCA CAR T-cells were unable to completely cure the mice. Therefore, we aimed to improve the quality of the transferred T-cells and their resistance to the immunosuppressive tumor microenvironment. Stimulation with allogeneic lymphocyte-licensed DCs improved the resistance to oxidative stress and antitumor activity of the T-cells. We further investigated the potential of genetically modified regulatory T-cells (Tregs) to suppress effector cells in an antigen-specific manner. Using a strong TCR we hypothesize that the phenotype of the TCR-transduced Tregs may be affected by antigen activation of those cells. We found that the engineered Tregs produced cytokines consistent with Th1, Th2 and Treg phenotypes.

Le transfert adoptif de cellules T exprimant un récepteur chimérique reconnaissant un antigène (CAR), est un traitement qui génère des réponses impressionnantes dans les cancers hématologiques mais est beaucoup moins efficace pour le traitement de tumeurs solides. Les tumeurs solides modulent leur microenvironnement induisant des formes multiples d’immunosuppression qui inhibent l’efficacité des fonctions effectrices des cellules T ayant infiltrées la tumeur. Au cours de ma thèse, j’ai évalué le potentiel de deux stratégies pour améliorer les réponses anti-tumorales des cellules T CAR. La première se focalise sur l’étude du rôle potentiel des cellules immunes non T, exprimant un CAR sur la stimulation des fonctions et de la persistance de cellules T CAR+ dans le microenvironnement tumoral. Afin d’étudier la fonction des cellules CAR non T, nous avons généré un modèle de souris transgénique (vav-CAR) dans lequel les cellules immunes expriment un CAR reconnaissant l’antigène tumoral Her2 (ErbB2). Comme attendu, les cellules T CAR+ possèdent des fonctions anti-tumorales, mais nous avons aussi mis en évidence que les macrophages et les cellules NK exprimant le CAR montraient une réponse cytokinique, cytotoxique et phagocytiques spécifiques de l’antigène. De plus, en utilisant le modèle vav-CAR, nous avons démontré le potentiel des cellules immunes CAR+ dans le rejet des tumeurs et cela indépendamment des cellules T CD8+. Les cellules T CD4+ sont essentielles puisque leur élimination réduit considérablement les réponses anti-tumorales dans notre modèle vav-CAR. Il a été démontré que certaines sous-populations de cellules T auxiliaires participent aux réponses anti-tumorales avec les cellules Th1 et Th17 démontrant une efficacité plus robuste que les autres sous-populations. Notre deuxième stratégie s’est focalisée sur l’étude de l’impact du métabolisme au cours de la polarisation des cellules T CD4+ et plus particulièrement lors de la différenciation des cellules T CAR+ en cellules Th1. En effet, l’activation et différenciation des cellules T sont fortement associées à une augmentation des besoins métaboliques. Dans le microenvironnement tumoral, en raison de la forte demande en ressources de la tumeur, la déprivation en nutriments ainsi générée peut limiter l’accès aux nutriments d’autres types cellulaires et ainsi altérer le devenir et les fonctions des cellules immunes greffés infiltrant la tumeur. En conséquence, modifier les cellules immunes CAR+ afin qu’elles puissent résister à la compétition métabolique du microenvironnement tumoral pourrait leur permettre de conserver leurs fonctions effectrices. En étudiant l’impact de la déprivation en nutriments sur la différenciation des cellules T, nous avons trouvé que des concentrations limitantes en glutamine, l’acide aminé le plus abondant du plasma, inhibaient le potentiel des cellules T à se différencier vers la voie Th1 associée à la production d’IFNγ. Au contraire, cette condition favorisait la conversion de cellules T CD4 naïves en cellules régulatrices Foxp3+ ayant des fonctions suppressives (Tregs). De plus, nous avons montré que la présence d’un seul métabolite dérivé de la glutamine, l’α-ketoglutarate (αKG), suffisait à augmenter les fonctions effectrices anti-tumorales de plusieurs sous-types de cellules T auxiliaires CAR+, augmentant la production d’IFNγ et diminuant l’expression de FOXP3. Ainsi, durant ma thèse, j’ai développé un modèle murin vav-CAR, générant un outil permettant d’étudier et manipuler les fonctions de multiples populations de cellules immunitaires exprimant un CAR. Ce modèle permettra de promouvoir l’utilisation de cellules immunes optimisées exprimant un CAR dans le cadre d’immunothérapies dirigées contre des tumeurs solides. De plus, en utilisant ce modèle, nous avons identifié un métabolite de la glutamine, qui orchestre les réponses immunitaires au moyen d’une reprogrammation métabolique des cellules T CD4. / The adoptive transfer of T cells expressing a chimeric antigen receptor (CAR) as a treatment for cancer has achieved impressive responses in haematological malignancies, but has been less successful in the treatment of solid tumors. The tumor microenvironment of solid tumors presents multiple forms of immunosuppression, inhibiting the efficient effector function of infiltrating anti-tumor T cells. During my PhD, we assessed the potential of two strategies to enhance the anti-tumor function of CAR T cells. The first focuses on the potential of other CAR-expressing immune subsets to stimulate CAR T cell function and persistence in the tumor microenvironment. To elucidate the function of CAR-expressing non-T lymphocytes, we generated a transgenic mouse model (vav-CAR) in which immune cells express a CAR against the Her2 (ErbB2) tumor antigen. As expected, CAR T cells harboured anti-tumor function but we also found that CAR-modified macrophages and natural killer cells (NKs) exhibited significant antigen specific cytokine secretion, cytotoxicity and phagocytosis. Moreover, using the vav-CAR model, we demonstrated the potential of CAR immune cells to mediate tumor rejection independently of CD8+ T cells. CD4+ T cells were critical for this response as their deletion severely abrogated the anti-tumor responses in our vav-CAR model. Distinct T helper subsets have been shown to participate to anti-tumor responses, with Th1 and Th17 cells demonstrating a more robust efficacy as compared to other T helper subsets. Our second strategy was focused on the impact of metabolism in the polarisation of CD4+ T cells, in particular the differentiation of CAR T cells to Th1 lineage. T cell activation and polarisation is highly associated with increased metabolic needs. Given that nutrient deprivation in the tumor microenvironment, due to a high demand of the tumor for resources, can limit the nutrients available for other cell types, the fate and function of adoptively transferred immune cells may be altered upon entering the tumor. Therefore, modifying CAR immune cells to resist metabolic suppression in the tumor microenvironment may help retain their effector functions. Upon assessing the effects of nutrient deprivation on T cell differentiation, we found that limiting concentrations of glutamine, the most abundant amino acid in the plasma, inhibited the potential of T cells to undergo Th1 differentiation with associated IFNγ secretion. Rather, this condition resulted in the conversion of naïve CD4+ T cells into suppressive Foxp3+ regulatory T cells (Tregs). Furthermore, we determined that a single glutamine-derived metabolite, α-ketoglutarate (αKG), enhanced the anti-tumor effector functions of multiple CAR T helper subsets, increasing the production of IFNγ and reducing FOXP3 expression.Thus, during my PhD, I generated a vav-CAR model, providing a platform in which the function of multiple CAR-bearing immune subsets can be studied and manipulated. This model will promote the utilisation of optimized CAR-bearing immune cells in adoptive immunotherapy for solid tumors. Furthermore, using the CAR model, we have identified a glutamine metabolite that orchestrates immune responses through the metabolic reprogramming of CD4 T cells.

Adoptive immunotherapy using chimeric antigen receptor (CAR)-modified T cells targeting CD19 has shown remarkable therapeutic efficacy against B cell leukemia and lymphoma, and provided proof of concept for therapeutic potential in other hematologic malignancies. Acute myeloid leukemia (AML) is an entity with an unmet medical need for effective and curative treatments. Therefore, there is a strong desire for development of potentially curative CAR-T cell immunotherapy for AML treatment. FMS-like tyrosine kinase 3 (FLT3) is a homodimeric transmembrane protein expressed uniformly by AML blasts. FLT3 plays a vital role in the survival of AML blasts and is a key driver of leukemia-genesis in AML cases with internal tandem duplication (FLT3ITD) and tyrosine kinase domain (TKD) mutations. These attributes suggest that FLT3 could be an excellent target for CAR-T cell immunotherapy. Here, we engineered human CD4+ and CD8+ T cells to express FLT3-specific CARs and demonstrate that they confer potent reactivity against AML cell lines and primary AML blasts that express either wild-type FLT3 or FLT3-ITD. Further, we show that FLT3 CAR-T cells exert potent antileukemia activity in xenograft models of AML and induce complete remissions. We also demonstrate that FLT3-expression on FLT3-ITD+ AML cells can be augmented by FLT3 inhibitors, which lead to increased recognition by CARs and improved efficacy of FLT3 CAR-T cells. We confirmed this principle with three different FLT3 inhibitors which are at distinct stages of clinical development i.e. Phase II/III clinical trial (crenolanib, quizartinib) and clinically approved (midostaurin). Further, we observed the strongest anti-leukemia activity of FLT3 CAR-T cells in combination with crenolanib in vivo. FLT3 is known to be expressed by normal hematopoietic stem and progenitor cells. We evaluated FLT3-expression on normal hematopoietic stem cells (HSCs) using flow cytometry and confirmed lower level of FLT3-expression on HSCs and progenitors compared to AML cells. As anticipated, we found that FLT3 CAR-T cells recognize normal HSCs in vitro and in vivo, and compromise normal hematopoiesis, suggesting that adoptive therapy with FLT3 CAR-T cells will require successive CAR-T cell depletion and allogeneic HSC transplantation (HSCT) to reconstitute the hematopoietic system. Moreover, an FLT3 inhibitor treatment does not increase FLT3-expression on HSCs. Accordingly, we demonstrate that the depletion of FLT3 CAR-T cells is possible with inducible Caspase 9 (iCasp9) safety switch. Collectively, our data establish FLT3 as a novel CAR target in AML with particular relevance in high-risk FLT3-ITD+ AML. Our data demonstrate that FLT3 CAR-T cells act synergistically with FLT3 inhibitors in FLT3-ITD+ AML. i.e. FLT3 inhibitors-induced upregulation of FLT3 in FLT3-ITD+ AML cells enhances their recognition and elimination by FLT3 CAR-T cells. Due to recognition of normal HSCs, the clinical use of FLT3 CART cells is likely restricted to a defined therapeutic window and must be followed by CART cell depletion and allogeneic HSCT for hematopoietic reconstitution. The data provide rational to use FLT3 CAR-T cells in combination with FLT3 inhibitors to augment the anti-leukemia efficacy of FLT3 CAR-T cells in high-risk FLT3-ITD+ AML patients, and to mitigate the risk of relapse with FLT3-negative AML variants, which could otherwise develop under therapeutic pressure. The data provide proof of concept for synergistic use of CAR-T cell immunotherapy and small molecule targeted therapy and encourage the clinical evaluation of this combination treatment in high-risk patients with FLT3-ITD+ AML. / Adoptive Immuntherapie, die Chimäre- Antigenrezeptor (CAR) –modifizierte, gegen CD19 gerichtet T-Zellen verwendet, hat eine bemerkenswerte therapeutische Wirksamkeit gegen B-Zell-Leukämien und -Lymphome und großes therapeutisches Potenzial für die Behandlung anderer hämatologischer Erkrankungen gezeigt. Die Akute Myeloische Leukämie (AML) ist hierbei eine Entität, für die es bisher an wirksamen und kurativen Therapien fehlt und für die die Entwicklung einer potentiell kurativen CAR-T-Zellimmuntherapie von großer Bedeutung ist. FMS-like tyrosine kinase 3 (FLT3) ist ein homodimeres Transmembranprotein, das von AML-Blasten uniform exprimiert wird. FLT3 spielt eine wichtige Rolle beim Überleben von AML-Blasten und ist ein Schlüsselfaktor in der Leukämie-Genese bei AML-Fällen mit interner Tandem-Duplikation (FLT3-ITD) und Tyrosinkinase-Domänen (TKD)-Mutationen. Diese Eigenschaften legen die Vermutung nahe, dass FLT3 ein ausgezeichnetes Target für die CAR-T-Zell-Immuntherapie darstellen könnte. Daher setzten wir dort an und modifizierten humane CD4+ und CD8+ T-Zellen, um FLT3-spezifische CARs zu exprimieren, und konnten nachweisen, dass diese eine starke Reaktivität gegen AML-Zelllinien und primäre AML-Blasten besitzen, die entweder den FLT3-Wildtyp oder FLT3-ITD exprimieren. Weiterhin konnten wir zeigen, dass FLT3 CAR-T-Zellen in AML-Xenograft-Modellen eine starke anti-Leukämie-Aktivität besitzen und vollständige Remissionen hervorrufen können. Zudem gelang der Nachweis, dass die FLT3-Expression auf FLT3-ITD+ AML-Zellen durch FLT3-Inhibitoren verstärkt werden kann, was zu einer erhöhten Erkennung durch die CARs und einer verbesserten Wirksamkeit von FLT3-CAR-T-Zellen führt. Wir konnten dieses Prinzip mit drei verschiedenen FLT3-Inhibitoren belegen, die sich in unterschiedlichen Stadien der klinischen Entwicklung befinden, d. h. aus einer Klinischen Phase II / III-Studie (Crenolanib, Quizartinib) und einem klinisch zugelassenen Inhibitor (Midostaurin). Darüber hinaus beobachteten wir die stärkste anti-Leukämie-Aktivität von FLT3 CAR-T-Zellen in einer Kombination mit Crenolanib in vivo. Es ist bekannt, dass FLT3 von normalen hämatopoetischen Stamm- und Vorläuferzellen exprimiert wird. Wir untersuchten die FLT3-Expression in normalen hämatopoetischen Stammzellen (HSCs) mittels Durchflusszytometrie und bestätigten im Vergleich zu AML-Zellen eine niedrigere FLT3-Expression auf HSCs und Vorläuferzellen. Wie erwartet, zeigte sich, dass FLT3 CAR-T-Zellen normale HSCs in vitro und in vivo erkennen und die normale Hämatopoese beeinträchtigen, was darauf hindeutet, dass eine adoptive Therapie mit FLT3 CAR-T-Zellen eine sukzessive CAR-T-Zell-Depletion und allogene HSC-Transplantation erfordert, um das hämatopoetische System wiederaufzubauen. Darüber hinaus erhöht die Behandlung mit einem FLT3-Inhibitor nicht die FLT3-Expression auf den HSCs. Dementsprechend konnten wir aufzeigen, dass die Depletion von FLT3 CAR-T Zellen mit einer induzierbaren Caspase 9 (iCasp9) als „Sicherheitsschalter“ möglich ist. Zusammenfassend etablieren unsere Daten FLT3 als ein neuartiges CAR-Target in der Behandlung von AML mit besonderer Relevanz für die Hochrisiko-FLT3-ITD+ AML. Unsere Daten zeigen, dass FLT3 CAR-T-Zellen synergistisch mit FLT3-Inhibitoren in FLT3-ITD+ AML wirken, d.h. eine FLT3-Inhibitoren-induzierte Hochregulation von FLT3 in FLT3-ITD+ AML-Zellen bewirkt und dies die Erkennung und Eliminierung durch FLT3-CAR-T-Zellen verstärkt. Durch ihre Eigenschaft der Erkennung von normalen HSCs ist die klinische Verwendung von FLT3 CAR-T-Zellen wahrscheinlich auf ein definiertes therapeutisches Fenster beschränkt und muss durch eine anschließende CAR-T-Zell-Depletion und eine allogene HSCT zur Rekonstitution des hämatopoetischen Systems ergänzt werden. In Anbetracht der Daten scheint es sinnvoll, FLT3-CAR-T-Zellen in Kombination mit FLT3-Inhibitoren zu verwenden, um die anti-leukämische Wirksamkeit von FLT3-CAR-T-Zellen bei Hochrisiko-FLT3-ITD+ AML-Patienten zu erhöhen und das Risiko eines Rückfalls mit FLT3-negativen AML-Varianten zu verringern, die sich sonst therapiebedingt entwickeln könnten. Die Daten stellen ein Proof-of-Concept für den synergistischen Einsatz von CAR-T-Zell-Immuntherapie und niedermolekularen Inhibitoren dar, der eine klinische Evaluation dieser Kombinationsbehandlung bei Hochrisikopatienten mit FLT3-ITD+ AML erstrebenswert macht.