Preclinical targeting of human acute myeloid leukemia and myeloablation using chimeric antigen receptor-modified T cells. Blood. 2014;123:2343-2354. [PMID: 24596416 DOI: 10.1182/blood-2013-09-529537]

The Fanconi anemia pathway controls oncogenic response in hematopoietic stem and progenitor cells by regulating PRMT5-mediated p53 arginine methylation

The Fanconi anemia (FA) pathway is involved in DNA damage and other cellular stress responses. We have investigated the role of the FA pathway in oncogenic stress response by employing an in vivo stress-response model expressing the Gadd45β-luciferase transgene. Using two inducible models of oncogenic activation (LSL-K-ras^G12D and Myc^ER), we show that hematopoietic stem and progenitor cells (HSPCs) from mice deficient for the FA core complex components Fanca or Fancc exhibit aberrant short-lived response to oncogenic insults. Mechanistic studies reveal that FA deficiency in HSPCs impairs oncogenic stress-induced G₁ cell-cycle checkpoint, resulting from a compromised K-ras^G12D-induced arginine methylation of p53 mediated by the protein arginine methyltransferase 5 (PRMT5). Furthermore, forced expression of PRMT5 in HSPCs from LSL-K-ras^G12D/CreER-Fanca^−/− mice prolongs oncogenic response and delays leukemia development in recipient mice. Our study defines an arginine methylation-dependent FA-p53 interplay that controls oncogenic stress response.

CAR T-cells targeting FLT3 have potent activity against FLT3-ITD+ AML and act synergistically with the FLT3-inhibitor crenolanib

FMS-like tyrosine kinase 3 (FLT3) is a transmembrane protein expressed on normal hematopoietic stem and progenitor cells (HSC) and retained on malignant blasts in acute myeloid leukemia (AML). We engineered CD8⁺ and CD4⁺ T-cells expressing a FLT3-specific chimeric antigen receptor (CAR) and demonstrate they confer potent reactivity against AML cell lines and primary AML blasts that express either wild-type FLT3 or FLT3 with internal tandem duplication (FLT3-ITD). We also show that treatment with the FLT3-inhibitor crenolanib leads to increased surface expression of FLT3 specifically on FLT3-ITD⁺ AML cells and consecutively, enhanced recognition by FLT3-CAR T-cells in vitro and in vivo. As anticipated, we found that FLT3-CAR T-cells recognize normal HSCs in vitro and in vivo, and disrupt normal hematopoiesis in colony-formation assays, suggesting that adoptive therapy with FLT3-CAR T-cells will require subsequent CAR T-cell depletion and allogeneic HSC transplantation to reconstitute the hematopoietic system. Collectively, our data establish FLT3 as a novel CAR target in AML with particular relevance in high-risk FLT3-ITD⁺ AML. Further, our data provide the first proof-of-concept that CAR T-cell immunotherapy and small molecule inhibition can be used synergistically, as exemplified by our data showing superior antileukemia efficacy of FLT3-CAR T-cells in combination with crenolanib.

Monoclonal Antibody Therapies for Hematological Malignancies: Not Just Lineage-Specific Targets

Today, monoclonal antibodies (mAbs) are a widespread and necessary tool for biomedical science. In the hematological cancer field, since rituximab became the first mAb approved by the Food and Drug Administration for the treatment of B-cell malignancies, a number of effective mAbs targeting lineage-specific antigens (LSAs) have been successfully developed. Non-LSAs (NLSAs) are molecules that are not restricted to specific leukocyte subsets or tissues but play relevant pathogenic roles in blood cancers including the development, proliferation, survival, and refractoriness to therapy of tumor cells. In consequence, efforts to target NLSAs have resulted in a plethora of mAbs-marketed or in development-to achieve different goals like neutralizing oncogenic pathways, blocking tumor-related chemotactic pathways, mobilizing malignant cells from tumor microenvironment to peripheral blood, modulating immune-checkpoints, or delivering cytotoxic drugs into tumor cells. Here, we extensively review several novel mAbs directed against NLSAs undergoing clinical evaluation for treating hematological malignancies. The review focuses on the structure of these antibodies, proposed mechanisms of action, efficacy and safety profile in clinical studies, and their potential applications in the treatment of hematological malignancies.

Precision therapy for acute myeloid leukemia

Acute myeloid leukemia (AML) is a molecularly and clinically heterogeneous disease. Despite advances in understanding the pathogenesis of AML, the standard therapy remained nearly unchanged over the past three decades. With the poor survival for older patients and high relapse rate, multiple studies are ongoing to address this important issue. Novel therapies for AML, including the refinements of conventional cytotoxic chemotherapies and genetic and epigenetic targeted drugs, as well as immunotherapies, have been developed in recent years. Here, we present a mechanism-based review of some promising new drugs with clinical efficacy, focus on targeted drugs that are most potential to pave the road to success, and put forward the major challenges in promoting the precision therapy for AML.

AML: exposed and exploited?

In this issue of Blood, Gillissen and colleagues characterize donor-derived cytotoxic antibodies, isolated from allogeneic hematopoietic cell transplant (HSCT) patients with acute myelogenous leukemia (AML) in sustained remission, that targeted the spliceosome U5 snRNP200 complex expressed on the cell membrane of AML blasts. Mechanistically, in vitro antibody-dependent cytotoxicity did not cause leukemia cell apoptosis, but rather destabilization of the cell membrane cytoskeleton and subsequent pore formation, resulting in cellular swelling and extravasation of intracellular contents (oncosis). In addition, in vivo reduction in AML burden using a U5 snRNP200–specific antibody was demonstrated in a murine SCID xenograft model. Collectively, the authors’ work suggests a potential role for donor-derived antibodies in mediating graft-versus-leukemia (GVL) activity following allogeneic HSCT.1

Anticancer cellular immunotherapies derived from umbilical cord blood

INTRODUCTION

The lack of highly effective drugs in many malignancies has prompted scientific interest in the development of alternative treatment strategies. Cellular immunotherapy involving the adoptive transfer of immune cells that potently recognize and eliminate malignantly transformed cells has become a promising new tool in the anticancer armory. Studies suggest that the unique biological properties of umbilical cord blood (UCB) cells could precipitate enhanced anticancer activity; hence, UCB could be an optimal source for immunotherapy with the potential to provide products with 'off-the-shelf' availability.

AREAS COVERED

In this review, the authors summarize data on the transfer of naturally occurring or genetically modified UCB cells to treat cancer. The focus within is on the phenotypic and functional differences compared to other sources, the alloreactive and anticancer properties, and manufacturing of these products. Therapies utilizing cytokine-induced killer (CIK) cells, natural killer (NK) cells and chimeric antigen receptor (CAR) T-cells, are discussed.

EXPERT OPINION

The cellular immunotherapy field has become a growing, exciting area that has generated much enthusiasm. There is evidence that anticancer immunotherapy with UCB-derived products is feasible and safe; however, considering the limited number of clinical trials using UCB-derived products, further studies are warranted to facilitate translation into clinical practice.

SLAMF7-CAR T cells eliminate myeloma and confer selective fratricide of SLAMF7+ normal lymphocytes

SLAMF7 is under intense investigation as a target for immunotherapy in multiple myeloma. In this study, we redirected the specificity of T cells to SLAMF7 through expression of a chimeric antigen receptor (CAR) derived from the huLuc63 antibody (elotuzumab) and demonstrate that SLAMF7-CAR T cells prepared from patients and healthy donors confer potent antimyeloma reactivity. We confirmed uniform, high-level expression of SLAMF7 on malignant plasma cells in previously untreated and in relapsed/refractory (R/R) myeloma patients who had received previous treatment with proteasome inhibitors and immunomodulatory drugs. Consequently, SLAMF7-CAR T cells conferred rapid cytolysis of previously untreated and R/R primary myeloma cells in vitro. In addition, a single administration of SLAMF7-CAR T cells led to resolution of medullary and extramedullary myeloma manifestations in a murine xenograft model in vivo. SLAMF7 is expressed on a fraction of normal lymphocytes, including subsets of natural killer (NK) cells, T cells, and B cells. After modification with the SLAMF7-CAR, both CD8⁺ and CD4⁺ T cells rapidly acquired and maintained a SLAMF7^- phenotype and could be readily expanded to therapeutically relevant cell doses. We analyzed the recognition of normal lymphocytes by SLAMF7-CAR T cells and show that they induce selective fratricide of SLAMF7^+/high NK cells, CD4⁺ and CD8⁺ T cells, and B cells. Importantly, however, the fratricide conferred by SLAMF7-CAR T cells spares the SLAMF7^-/low fraction in each cell subset and preserves functional lymphocytes, including virus-specific T cells. In aggregate, our data illustrate the potential use of SLAMF7-CAR T-cell therapy as an effective treatment against multiple myeloma and provide novel insights into the consequences of targeting SLAMF7 for the normal lymphocyte compartment.

Development of A Chimeric Antigen Receptor Targeting C-Type Lectin-Like Molecule-1 for Human Acute Myeloid Leukemia

The treatment of patients with acute myeloid leukemia (AML) with targeted immunotherapy is challenged by the heterogeneity of the disease and a lack of tumor-exclusive antigens. Conventional immunotherapy targets for AML such as CD33 and CD123 have been proposed as targets for chimeric antigen receptor (CAR)-engineered T-cells (CAR-T-cells), a therapy that has been highly successful in the treatment of B-cell leukemia and lymphoma. However, CD33 and CD123 are present on hematopoietic stem cells, and targeting with CAR-T-cells has the potential to elicit long-term myelosuppression. C-type lectin-like molecule-1 (CLL1 or CLEC12A) is a myeloid lineage antigen that is expressed by malignant cells in more than 90% of AML patients. CLL1 is not expressed by healthy Hematopoietic Stem Cells (HSCs), and is therefore a promising target for CAR-T-cell therapy. Here, we describe the development and optimization of an anti-CLL1 CAR-T-cell with potent activity on both AML cell lines and primary patient-derived AML blasts in vitro while sparing healthy HSCs. Furthermore, in a disseminated mouse xenograft model using the CLL1-positive HL60 cell line, these CAR-T-cells completely eradicated tumor, thus supporting CLL1 as a promising target for CAR-T-cells to treat AML while limiting myelosuppressive toxicity.

Integrating Proteomics and Transcriptomics for Systematic Combinatorial Chimeric Antigen Receptor Therapy of AML

Chimeric antigen receptor (CAR) therapy targeting CD19 has yielded remarkable outcomes in patients with acute lymphoblastic leukemia. To identify potential CAR targets in acute myeloid leukemia (AML), we probed the AML surfaceome for overexpressed molecules with tolerable systemic expression. We integrated large transcriptomics and proteomics datasets from malignant and normal tissues, and developed an algorithm to identify potential targets expressed in leukemia stem cells, but not in normal CD34⁺CD38^- hematopoietic cells, T cells, or vital tissues. As these investigations did not uncover candidate targets with a profile as favorable as CD19, we developed a generalizable combinatorial targeting strategy fulfilling stringent efficacy and safety criteria. Our findings indicate that several target pairings hold great promise for CAR therapy of AML.

Overcoming the Immunosuppressive Tumor Microenvironment of Hodgkin Lymphoma Using Chimeric Antigen Receptor T Cells

Patients with otherwise treatment-resistant Hodgkin lymphoma could benefit from chimeric antigen receptor T-cell (CART) therapy. However, Hodgkin lymphoma lacks CD19 and contains a highly immunosuppressive tumor microenvironment (TME). We hypothesized that in Hodgkin lymphoma, CART should target both malignant cells and the TME. We demonstrated CD123 on both Hodgkin lymphoma cells and TME, including tumor-associated macrophages (TAM). In vitro, Hodgkin lymphoma cells convert macrophages toward immunosuppressive TAMs that inhibit T-cell proliferation. In contrast, anti-CD123 CART recognized and killed TAMs, thus overcoming immunosuppression. Finally, we showed in immunodeficient mouse models that CART123 eradicated Hodgkin lymphoma and established long-term immune memory. A novel platform that targets malignant cells and the microenvironment may be needed to successfully treat malignancies with an immunosuppressive milieu.Significance: Anti-CD123 chimeric antigen receptor T cells target both the malignant cells and TAMs in Hodgkin lymphoma, thereby eliminating an important immunosuppressive component of the tumor microenvironment. Cancer Discov; 7(10); 1154-67. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1047.

Emerging therapies for acute myeloid leukemia: translating biology into the clinic

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a poor outcome; overall survival is approximately 35% at two years and some subgroups have a less than 5% two-year survival. Recently, significant improvements have been made in our understanding of AML biology and genetics. These fundamental discoveries are now being translated into new therapies for this disease. This review will discuss recent advances in AML biology and the emerging treatments that are arising from biological studies. Specifically, we will consider new therapies that target molecular mutations in AML and dysregulated pathways such as apoptosis and mitochondrial metabolism. We will also discuss recent advances in immune and cellular therapy for AML.

Chimeric antigen receptors for adoptive T cell therapy in acute myeloid leukemia

Currently, conventional therapies for acute myeloid leukemia (AML) have high failure and relapse rates. Thus, developing new strategies is crucial for improving the treatment of AML. With the clinical success of anti-CD19 chimeric antigen receptor (CAR) T cell therapies against B-lineage malignancies, many studies have attempted to translate the success of CAR T cell therapy to other malignancies, including AML. This review summarizes the current advances in CAR T cell therapy against AML, including preclinical studies and clinical trials, and discusses the potential AML-associated surface markers that could be used for further CAR technology. Finally, we describe strategies that might address the current issues of employing CAR T cell therapy in AML.

Recent developments in immunotherapy of acute myeloid leukemia

The advent of new immunotherapeutic agents in clinical practice has revolutionized cancer treatment in the past decade, both in oncology and hematology. The transfer of the immunotherapeutic concepts to the treatment of acute myeloid leukemia (AML) is hampered by various characteristics of the disease, including non-leukemia-restricted target antigen expression profile, low endogenous immune responses, and intrinsic resistance mechanisms of the leukemic blasts against immune responses. However, considerable progress has been made in this field in the past few years.Within this manuscript, we review the recent developments and the current status of the five currently most prominent immunotherapeutic concepts: (1) antibody-drug conjugates, (2) T cell-recruiting antibody constructs, (3) chimeric antigen receptor (CAR) T cells, (4) checkpoint inhibitors, and (5) dendritic cell vaccination. We focus on the clinical data that has been published so far, both for newly diagnosed and refractory/relapsed AML, but omitting immunotherapeutic concepts in conjunction with hematopoietic stem cell transplantation. Besides, we have included important clinical trials that are currently running or have recently been completed but are still lacking full publication of their results.While each of the concepts has its particular merits and inherent problems, the field of immunotherapy of AML seems to have taken some significant steps forward. Results of currently running trials will reveal the direction of further development including approaches combining two or more of these concepts.

Treatment of Acute Myeloid Leukemia with T Cells Expressing Chimeric Antigen Receptors Directed to C-type Lectin-like Molecule 1

The successful immunotherapy of acute myeloid leukemia (AML) has been hampered because most potential antigenic targets are shared with normal hematopoietic stem cells (HSCs), increasing the risk of sustained and severe hematopoietic toxicity following treatment. C-type lectin-like molecule 1 (CLL-1) is a membrane glycoprotein expressed by >80% of AML but is absent on normal HSCs. Here we describe the development and evaluation of CLL-1-specific chimeric antigen receptor T cells (CLL-1.CAR-Ts) and we demonstrate their specific activity against CLL-1⁺ AML cell lines as well as primary AML patient samples in vitro. CLL-1.CAR-Ts selectively reduced leukemic colony formation in primary AML patient peripheral blood mononuclear cells compared to control T cells. In a human xenograft mouse model, CLL-1.CAR-Ts mediated anti-leukemic activity against disseminated AML and significantly extended survival. By contrast, the colony formation of normal progenitor cells remained intact following CLL-1.CAR-T treatment. Although CLL-1.CAR-Ts are cytotoxic to mature normal myeloid cells, the selective sparing of normal hematopoietic progenitor cells should allow full myeloid recovery once CLL-1.CAR-T activity terminates. To enable elective ablation of the CAR-T, we therefore introduced the inducible caspase-9 suicide gene system and we show that exposure to the activating drug rapidly induced a controlled decrease of unwanted CLL-1.CAR-T activity against mature normal myeloid cells.

The Flipside of the Power of Engineered T Cells: Observed and Potential Toxicities of Genetically Modified T Cells as Therapy

Autologous T cells modified to recognize novel antigen targets are a novel form of therapy for cancer. We review the various potential forms of observed and hypothetical toxicities associated with genetically modified T cells. Despite the focus on toxicities in this review, re-directed T cells represent a powerful and highly effective form of anti-cancer therapy; we remain optimistic that the common toxicities will become routinely manageable and that some theoretical toxicity will be exceedingly rare, if ever observed.

CD123 target validation and preclinical evaluation of ADCC activity of anti-CD123 antibody CSL362 in combination with NKs from AML patients in remission

Despite the heterogeneity of acute myeloid leukemia (AML), overexpression of the interleukin-3 receptor-α (CD123) on both the more differentiated leukemic blast and leukemic stem cells (LSCs) provides a therapeutic target for antibody treatment. Here we present data on the potential clinical activity of the monoclonal antibody CSL362, which binds to CD123 with high affinity. We first validated the expression of CD123 by 100% (52/52) of patient samples and the correlation of NPM1 and FLT3-ITD mutations with the high frequency of CD123 in AML. In vitro studies demonstrated that CSL362 potently induced antibody-dependent cell cytotoxicity (ADCC) of AML blasts including CD34⁺CD38⁻CD123⁺ LSCs by natural killer cells (NKs). Importantly, compared with healthy donor (HD) NKs, NKs drawn from AML patients in remission had a comparable ADCC activity against leukemic cells; of note, during remission, immature NKs were five times higher in AML patients than that in HDs. Significantly, we report a case where leukemic cells were resistant to autologous ADCC; however, the blasts were effectively lysed by CSL362 together with donor-derived NKs after allogeneic hematopoietic stem cell transplantation. These studies highlight CSL362 as a promising therapeutic option following chemotherapy and transplant so as to improve the outcome of AML patients.

Effective control of acute myeloid leukaemia and acute lymphoblastic leukaemia progression by telomerase specific adoptive T-cell therapy

Telomerase (TERT) is a ribonucleoprotein enzyme that preserves the molecular organization at the ends of eukaryotic chromosomes. Since TERT deregulation is a common step in leukaemia, treatments targeting telomerase might be useful for the therapy of hematologic malignancies. Despite a large spectrum of potential drugs, their bench-to-bedside translation is quite limited, with only a therapeutic vaccine in the clinic and a telomerase inhibitor at late stage of preclinical validation. We recently demonstrated that the adoptive transfer of T cell transduced with an HLA-A2-restricted T-cell receptor (TCR), which recognize human TERT with high avidity, controls human B-cell chronic lymphocytic leukaemia (B-CLL) progression without severe side-effects in humanized mice. In the present report, we show the ability of our approach to limit the progression of more aggressive leukemic pathologies, such as acute myeloid leukaemia (AML) and B-cell acute lymphoblastic leukaemia (B-ALL). Together, our findings demonstrate that TERT-based adoptive cell therapy is a concrete platform of T cell-mediated immunotherapy for leukaemia treatment.

Balance of Anti-CD123 Chimeric Antigen Receptor Binding Affinity and Density for the Targeting of Acute Myeloid Leukemia

Chimeric antigen receptor (CAR)-redirected T lymphocytes are a promising immunotherapeutic approach and object of pre-clinical evaluation for the treatment of acute myeloid leukemia (AML). We developed a CAR against CD123, overexpressed on AML blasts and leukemic stem cells. However, potential recognition of low CD123-positive healthy tissues, through the on-target, off-tumor effect, limits safe clinical employment of CAR-redirected T cells. Therefore, we evaluated the effect of context-dependent variables capable of modulating CAR T cell functional profiles, such as CAR binding affinity, CAR expression, and target antigen density. Computational structural biology tools allowed for the design of rational mutations in the anti-CD123 CAR antigen binding domain that altered CAR expression and CAR binding affinity without affecting the overall CAR design. We defined both lytic and activation antigen thresholds, with early cytotoxic activity unaffected by either CAR expression or CAR affinity tuning but later effector functions impaired by low CAR expression. Moreover, the anti-CD123 CAR safety profile was confirmed by lowering CAR binding affinity, corroborating CD123 is a good therapeutic target antigen. Overall, full dissection of these variables offers suitable anti-CD123 CAR design optimization for the treatment of AML.

Immunotherapy in hematologic malignancies: past, present, and future

The field of immunotherapy in cancer treatments has been accelerating over recent years and has entered the forefront as a leading area of ongoing research and promising therapies that have changed the treatment landscape for a variety of solid malignancies. Prior to its designation as the Science Breakthrough of the Year in 2013, cancer immunotherapy was active in the treatment of hematologic malignancies. This review provides a broad overview of the past, present, and potential future of immunotherapy in hematologic malignancies.

Harnessing the Immunotherapy Revolution for the Treatment of Childhood Cancers

Cancer immunotherapies can be classified into agents that amplify natural immune responses (e.g., checkpoint inhibitors) versus synthetic immunotherapies designed to initiate new responses (e.g., monoclonal antibodies [mAbs], chimeric antigen receptors [CARs]). Checkpoint inhibitors mediate unprecedented benefit in some adult cancers, but have not demonstrated significant activity in pediatric cancers, likely due their paucity of neoantigens. In contrast, synthetic immunotherapies such as mAbs and CAR T cells demonstrate impressive effects against childhood cancers. Intense efforts are underway to enhance the effectiveness of pediatric cancer immunotherapies through improved engineering of synthetic immunotherapies and by combining these with agents designed to amplify immune responses.

CAR-T therapy for leukemia: progress and challenges

Despite the rapid development of therapeutic strategies, leukemia remains a type of difficult-to-treat hematopoietic malignancy that necessitates introduction of more effective treatment options to improve life expectancy and quality of patients. Genetic engineering in adoptively transferred T cells to express antigen-specific chimeric antigen receptors (CARs) has proved highly powerful and efficacious in inducing sustained responses in patients with refractory malignancies, as exemplified by the success of CD19-targeting CAR-T treatment in patients with relapsed acute lymphoblastic leukemia. Recent strategies, including manipulating intracellular activating domains and transducing viral vectors, have resulted in better designed and optimized CAR-T cells. This is further facilitated by the rapid identification of an accumulating number of potential leukemic antigens that may serve as therapeutic targets for CAR-T cells. This review will provide a comprehensive background and scrutinize recent important breakthrough studies on anti-leukemia CAR-T cells, with focus on recently identified antigens for CAR-T therapy design and approaches to overcome critical challenges.

Cancer Immunotherapy: Whence and Whither

The current concepts and practice of cancer immunotherapy evolved from classical experiments that distinguished "self" from "non-self" and the finding that humoral immunity is complemented by cellular immunity. Elucidation of the biology underlying immune checkpoints and interactions between ligands and ligand receptors that govern the immune system's ability to recognize tumor cells as foreign has led to the emergence of new strategies that mobilize the immune system to reverse this apparent tolerance. Some of these approaches have led to new therapies such as the use of mAbs to interfere with the immune checkpoint. Others have exploited molecular technologies to reengineer a subset of T cells to directly engage and kill tumor cells, particularly those of B-cell malignancies. However, before immunotherapy can become a more effective method of cancer care, there are many challenges that remain to be addressed and hurdles to overcome. Included are manipulation of tumor microenvironment (TME) to enhance T effector cell infiltration and access to the tumor, augmentation of tumor MHC expression for adequate presentation of tumor associated antigens, regulation of cytokines and their potential adverse effects, and reduced risk of secondary malignancies as a consequence of mutations generated by the various forms of genetic engineering of immune cells. Despite these challenges, the future of immunotherapy as a standard anticancer therapy is encouraging. Mol Cancer Res; 15(6); 635-50. ©2017 AACR.

Optimized depletion of chimeric antigen receptor T cells in murine xenograft models of human acute myeloid leukemia

We and others previously reported potent antileukemia efficacy of CD123-redirected chimeric antigen receptor (CAR) T cells in preclinical human acute myeloid leukemia (AML) models at the cost of severe hematologic toxicity. This observation raises concern for potential myeloablation in patients with AML treated with CD123-redirected CAR T cells and mandates novel approaches for toxicity mitigation. We hypothesized that CAR T-cell depletion with optimal timing after AML eradication would preserve leukemia remission and allow subsequent hematopoietic stem cell transplantation. To test this hypothesis, we compared 3 CAR T-cell termination strategies: (1) transiently active anti-CD123 messenger RNA-electroporated CART (RNA-CART123); (2) T-cell ablation with alemtuzumab after treatment with lentivirally transduced anti-CD123-4-1BB-CD3ζ T cells (CART123); and (3) T-cell ablation with rituximab after treatment with CD20-coexpressing CART123 (CART123-CD20). All approaches led to rapid leukemia elimination in murine xenograft models of human AML. Subsequent antibody-mediated depletion of CART123 or CART123-CD20 did not impair leukemia remission. Time-course studies demonstrated that durable leukemia remission required CAR T-cell persistence for 4 weeks prior to ablation. Upon CAR T-cell termination, we further demonstrated successful hematopoietic engraftment with a normal human donor to model allogeneic stem cell rescue. Results from these studies will facilitate development of T-cell depletion strategies to augment the feasibility of CAR T-cell therapy for patients with AML.

Immune-Mediated Therapies for Liver Cancer

In recent years, immunotherapy has gained renewed interest as an alternative therapeutic approach for solid tumors. Its premise is based on harnessing the power of the host immune system to destroy tumor cells. Development of immune-mediated therapies, such as vaccines, adoptive transfer of autologous immune cells, and stimulation of host immunity by targeting tumor-evasive mechanisms have advanced cancer immunotherapy. In addition, studies on innate immunity and mechanisms of immune evasion have enhanced our understanding on the immunology of liver cancer. Preclinical and clinical studies with immune-mediated therapies have shown potential benefits in patients with liver cancer. In this review, we summarize current knowledge and recent developments in tumor immunology by focusing on two main primary liver cancers: hepatocellular carcinoma and cholangiocarcinoma.

Biology and relevance of human acute myeloid leukemia stem cells

Evidence of human acute myeloid leukemia stem cells (AML LSCs) was first reported nearly 2 decades ago through the identification of rare subpopulations of engrafting cells in xenotransplantation assays. These AML LSCs were shown to reside at the apex of a cellular hierarchy that initiates and maintains the disease, exhibiting properties of self-renewal, cell cycle quiescence, and chemoresistance. This cancer stem cell model offers an explanation for chemotherapy resistance and disease relapse and implies that approaches to treatment must eradicate LSCs for cure. More recently, a number of studies have both refined and expanded our understanding of LSCs and intrapatient heterogeneity in AML using improved xenotransplant models, genome-scale analyses, and experimental manipulation of primary patient cells. Here, we review these studies with a focus on the immunophenotype, biological properties, epigenetics, genetics, and clinical associations of human AML LSCs and discuss critical questions that need to be addressed in future research.

Therapeutic targeting of acute myeloid leukemia stem cells

For more than 50 years, investigators have considered a malignant stem cell as the potential origin of and a key therapeutic target for acute myeloid leukemia (AML) and other forms of cancer.^1-4 The nature and existence of tumor-initiating cells for leukemia and other malignancies have long been the subject of intense and rigorous study; indeed, the promise of the potential to eradicate such cells is clear. However, until recently, deficiencies in our understanding of the nature of these cell populations, coupled with a limited ability to therapeutically exploit their weaknesses, have been limiting factors in realizing the goal of targeting leukemic stem cells (LSCs). Exciting new insights into the fundamental underpinnings of LSCs are now being made in an era in which drug development pipelines offer the potential to specifically target pathways of significance. Therefore, the focus in this new era, characterized by the confluence of understanding LSCs and the ability to target them, is shifting from "if it can be done" to "how it will be done." Moving from a theoretical stage to this hopeful era of possibilities, new challenges expectedly arise, and our focus now must shift to determining the best strategy by which to target LSCs, with their well-documented heterogeneity and readily evident intra- and interpatient variability. The purpose of this review is therefore both to summarize the key scientific findings pertinent to AML LSC targeting and to consider methods of clinical evaluation that will be most effective for identifying successful LSC-directed therapies.

Acute myeloid leukemia targets for bispecific antibodies

Despite substantial gains in our understanding of the genomics of acute myelogenous leukemia (AML), patient survival remains unsatisfactory especially among the older age group. T cell-based therapy of lymphoblastic leukemia is rapidly advancing; however, its application in AML is still lagging behind. Bispecific antibodies can redirect polyclonal effector cells to engage chosen targets on leukemia blasts. When the effector cells are natural-killer cells, both antibody-dependent and antibody-independent mechanisms could be exploited. When the effectors are T cells, direct tumor cytotoxicity can be engaged followed by a potential vaccination effect. In this review, we summarize the AML-associated tumor targets and the bispecific antibodies that have been studied. The potentials and limitations of each of these systems will be discussed.

Future directions in chimeric antigen receptor T cell therapy

PURPOSE OF REVIEW

The impact of immunotherapy has grown exponentially in the past 5 years. Principle illustrations are encouraging results with engineered T cells expressing a chimeric antigen receptor (CAR). This experimental therapy is developing simultaneously in pediatric and adult clinical trials, making this field particularly relevant and exciting for pediatric oncologists.

RECENT FINDINGS

CAR-modified T cells targeting CD19 have produced dramatic antitumor responses in patients with relapsed/refractory B cell acute lymphoblastic leukemia. Clinical trials from several institutions, in both children and adults, using distinct CAR T cell products have demonstrated similar high complete remission rates of 61-93%, with durable remissions observed. Although the development of CARs for other malignancies has lagged behind, research into novel approaches to overcome inherent challenges is promising.

SUMMARY

Clinical trials of CAR-modified T cells have produced unprecedented results and are anticipated to have a broader impact as this approach expands into other indications, including other cancers and frontline therapy. The potential for long-term disease control, if fully realized, will have a transformative impact on the field.

Chimeric Antigen Receptor T Cells and Hematopoietic Cell Transplantation: How Not to Put the CART Before the Horse

Hematopoietic cell transplantation (HCT) remains an important and potentially curative option for most hematologic malignancies. As a form of immunotherapy, allogeneic HCT (allo-HCT) offers the potential for durable remissions but is limited by transplantation- related morbidity and mortality owing to organ toxicity, infection, and graft-versus-host disease. The recent positive outcomes of chimeric antigen receptor T (CART) cell therapy in B cell malignancies may herald a paradigm shift in the management of these disorders and perhaps other hematologic malignancies as well. Clinical trials are now needed to address the relative roles of CART cells and HCT in the context of transplantation-eligible patients. In this review, we summarize the state of the art of the development of CART cell therapy for leukemia, lymphoma, and myeloma and discuss our perspective of how CART cell therapy can be applied in the context of HCT.

Chimaeric antigen receptor T-cell therapy for tumour immunotherapy

Chimaeric antigen receptor (CAR) T-cell therapies, as one of the cancer immunotherapies, have heralded a new era of treating cancer. The accumulating data, especially about CAR-modified T cells against CD19 support that CAR T-cell therapy is a highly effective immune therapy for B-cell malignancies. Apart from CD19, there have been many trials of CAR T cells directed other tumour specific or associated antigens (TSAs/TAAs) in haematologic malignancies and solid tumours. This review will briefly summarize basic CAR structure, parts of reported TSAs/TAAs, results of the clinical trials of CAR T-cell therapies as well as two life-threatening side effects. Experiments in vivo or in vitro, ongoing clinical trials and the outlook for CAR T-cell therapies also be included. Our future efforts will focus on identification of more viable cancer targets and more strategies to make CAR T-cell therapy safer.

Acute Myeloid Leukemia: Advancements in Diagnosis and Treatment

OBJECTIVE

Leukemia is the most common pediatric malignancy and a major cause of morbidity and mortality in children. Among all subtypes, a lack of consensus exists regarding the diagnosis and treatment of acute myeloid leukemia (AML). Patient survival rates have remained modest for the past three decades in AML. Recently, targeted therapy has emerged as a promising treatment.

DATA SOURCES

We searched the PubMed database for recently published research papers on diagnostic development, target therapy, and other novel therapies of AML. Clinical trial information was obtained from ClinicalTrials.gov. For the major purpose of this review that is to outline the latest therapeutic development of AML, we only listed the ongoing clinical trials for reference. However, the published results of complete clinical trials were also mentioned.

STUDY SELECTION

This article reviewed the latest developments related to the diagnosis and treatment of AML. In the first portion, we provided some novel insights on the molecular basis of AML, as well as provided an update on the classification of AML. In the second portion, we summarized the results of research on potential molecular therapeutic agents including monoclonal antibodies, tyrosine kinase/Fms-like tyrosine kinase 3 (FLT3) inhibitors, epigenetic/demethylating agents, and cellular therapeutic agents. We will also highlight ongoing research and clinical trials in pediatric AML.

RESULTS

We described clonal evolution and how it changes our view on leukemogenesis, treatment responses, and disease relapse. Pediatric-specific genomic mapping was discussed with a novel diagnostic method highlighted. In the later portion of this review, we summarized the researches on potential molecular therapeutic agents including monoclonal antibodies, tyrosine kinase/FLT3 inhibitors, epigenetic/demethylating agents, and cellular therapeutic agents.

CONCLUSION

Gene sequencing techniques should set the basis for next-generation diagnostic methods of AML, and target therapy should be the focus of future clinical research in the exploration of therapeutic possibilities.

Antileukemia Efficacy and Mechanisms of Action of SL-101, a Novel Anti-CD123 Antibody Conjugate, in Acute Myeloid Leukemia

Purpose: The persistence of leukemia stem cells (LSC)-containing cells after induction therapy may contribute to minimal residual disease (MRD) and relapse in acute myeloid leukemia (AML). We investigated the clinical relevance of CD34⁺CD123⁺ LSC-containing cells and antileukemia potency of a novel antibody conjugate SL-101 in targeting CD123⁺ LSCs.Experimental Methods and Results: In a retrospective study on 86 newly diagnosed AML patients, we demonstrated that a higher proportion of CD34⁺CD123⁺ LSC-containing cells in remission was associated with persistent MRD and predicted shorter relapse-free survival in patients with poor-risk cytogenetics. Using flow cytometry, we explored the potential benefit of therapeutic targeting of CD34⁺CD38^-CD123⁺ cells by SL-101, a novel antibody conjugate comprising an anti-CD123 single-chain Fv fused to Pseudomonas exotoxin A The antileukemia potency of SL-101 was determined by the expression levels of CD123 antigen in a panel of AML cell lines. Colony-forming assay established that SL-101 strongly and selectively suppressed the function of leukemic progenitors while sparing normal counterparts. The internalization, protein synthesis inhibition, and flow cytometry assays revealed the mechanisms underlying the cytotoxic activities of SL-101 involved rapid and efficient internalization of antibody, sustained inhibition of protein synthesis, induction of apoptosis, and blockade of IL3-induced p-STAT5 and p-AKT signaling pathways. In a patient-derived xenograft model using NSG mice, the repopulating capacity of LSCs pretreated with SL-101 in vitro was significantly impaired.Conclusions: Our data define the mechanisms by which SL-101 targets AML and warrant further investigation of the clinical application of SL-101 and other CD123-targeting strategies in AML. Clin Cancer Res; 23(13); 3385-95. ©2017 AACR.

Generating and Expanding Autologous Chimeric Antigen Receptor T Cells from Patients with Acute Myeloid Leukemia

Adoptive transfer of genetically engineered T cells can lead to profound and durable responses in patients with hematologic malignancies, generating enormous enthusiasm among scientists, clinicians, patients, and biotechnology companies. The success of adoptive cellular immunotherapy depends upon the ability to manufacture good quality T cells. We discuss here the methodologies and reagents that are used to generate T cells for the preclinical study of chimeric antigen receptor T cell therapy for acute myeloid leukemia (AML).

Making Better Chimeric Antigen Receptors for Adoptive T-cell Therapy

Chimeric antigen receptors (CAR) are engineered fusion proteins constructed from antigen recognition, signaling, and costimulatory domains that can be expressed in cytotoxic T cells with the purpose of reprograming the T cells to specifically target tumor cells. CAR T-cell therapy uses gene transfer technology to reprogram a patient's own T cells to stably express CARs, thereby combining the specificity of an antibody with the potent cytotoxic and memory functions of a T cell. In early-phase clinical trials, CAR T cells targeting CD19 have resulted in sustained complete responses within a population of otherwise refractory patients with B-cell malignancies and, more specifically, have shown complete response rates of approximately 90% in patients with relapsed or refractory acute lymphoblastic leukemia. Given this clinical efficacy, preclinical development of CAR T-cell therapy for a number of cancer indications has been actively investigated, and the future of the CAR T-cell field is extensive and dynamic. Several approaches to increase the feasibility and safety of CAR T cells are currently being explored, including investigation into the mechanisms regulating the persistence of CAR T cells. In addition, numerous early-phase clinical trials are now investigating CAR T-cell therapy beyond targeting CD19, especially in solid tumors. Trials investigating combinations of CAR T cells with immune checkpoint blockade therapies are now beginning and results are eagerly awaited. This review evaluates several of the ongoing and future directions of CAR T-cell therapy.

The promise of chimeric antigen receptor T cells (CARTs) in leukaemia

The success of genetically engineered T cells that express chimeric antigen receptors (CARTs) has been a momentous step forward in harnessing the potent cancer fighting abilities of the immune system. The efficacy seen in relapsed/refractory (r/r) acute lymphoblastic leukaemia (ALL), not only by inducing remission, but also in maintaining long-term disease control, has been unprecedented. While the foundation for this approach has been firmly set in place, continued development will improve the efficacy, toxicity and applicability to other malignancies of this new class of 'living drugs'. In this review, we provide a comprehensive overview of the most current clinical trial data in both acute and chronic leukaemias, and discuss some of the potential ways to enhance the activity and safety of CART therapy going forward.

Acute Myeloid Leukemia Targeting by Chimeric Antigen Receptor T Cells: Bridging the Gap from Preclinical Modeling to Human Studies

Acute myeloid leukemia (AML) still represents an unmet clinical need for adult and pediatric high-risk patients, thus demanding advanced and personalized therapies. In this regard, different targeted immunotherapeutic approaches are available, ranging from naked monoclonal antibodies (mAb) to conjugated and multifunctional mAbs (i.e., BiTEs and DARTs). Recently, researchers have focused their attention on novel techniques of genetic manipulation specifically to redirect cytotoxic T cells endowed with chimeric antigen receptors (CARs) toward selected tumor associated antigens. So far, CAR T cells targeting the CD19 antigen expressed by B-cell origin hematological cancers have gained impressive clinical results, leading to the possibility of translating the CAR platform to treat other hematological malignancies such as AML. However, one of the main concerns in the field of AML CAR immunotherapy is the identification of an ideal target cell surface antigen, being highly expressed on tumor cells but minimally present on healthy tissues, together with the design of an anti-AML CAR appropriately balancing efficacy and safety profiles. The current review focuses mainly on AML target antigens and the related immunotherapeutic approaches developed so far, deeply dissecting methods of CAR T cell safety improvements, when designing novel CARs approaching human studies.

An anti-CD3/anti-CLL-1 bispecific antibody for the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a major unmet medical need. Most patients have poor long-term survival, and treatment has not significantly changed in 40 years. Recently, bispecific antibodies that redirect the cytotoxic activity of effector T cells by binding to CD3, the signaling component of the T-cell receptor, and a tumor target have shown clinical activity. Notably, blinatumomab is approved to treat relapsed/refractory acute lymphoid leukemia. Here we describe the design, discovery, pharmacologic activity, pharmacokinetics, and safety of a CD3 T cell-dependent bispecific (TDB) full-length human IgG1 therapeutic antibody targeting CLL-1 that could potentially be used in humans to treat AML. CLL-1 is prevalent in AML and, unlike other targets such as CD33 and CD123, is not expressed on hematopoietic stem cells providing potential hematopoietic recovery. We selected a high-affinity monkey cross-reactive anti-CLL-1 arm and tested several anti-CD3 arms that varied in affinity, and determined that the high-affinity CD3 arms were up to 100-fold more potent in vitro. However, in mouse models, the efficacy differences were less pronounced, probably because of prolonged exposure to TDB found with lower-affinity CD3 TDBs. In monkeys, assessment of safety and target cell depletion by the high- and low-affinity TDBs revealed that only the low-affinity CD3/CLL1 TDB was well tolerated and able to deplete target cells. Our data suggest that an appropriately engineered CLL-1 TDB could be effective in the treatment of AML.

In Vitro Pre-Clinical Validation of Suicide Gene Modified Anti-CD33 Redirected Chimeric Antigen Receptor T-Cells for Acute Myeloid Leukemia

Background

Approximately fifty percent of patients with acute myeloid leukemia can be cured with current therapeutic strategies which include, standard dose chemotherapy for patients at standard risk of relapse as assessed by cytogenetic and molecular analysis, or high-dose chemotherapy with allogeneic hematopoietic stem cell transplant for high-risk patients. Despite allogeneic hematopoietic stem cell transplant about 25% of patients still succumb to disease relapse, therefore, novel strategies are needed to improve the outcome of patients with acute myeloid leukemia.

Methods and findings

We developed an immunotherapeutic strategy targeting the CD33 myeloid antigen, expressed in ~ 85–90% of patients with acute myeloid leukemia, using chimeric antigen receptor redirected T-cells. Considering that administration of CAR T-cells has been associated with cytokine release syndrome and other potential off-tumor effects in patients, safety measures were here investigated and reported. We genetically modified human activated T-cells from healthy donors or patients with acute myeloid leukemia with retroviral supernatant encoding the inducible Caspase9 suicide gene, a ΔCD19 selectable marker, and a humanized third generation chimeric antigen receptor recognizing human CD33. ΔCD19 selected inducible Caspase9-CAR.CD33 T-cells had a 75±3.8% (average ± standard error of the mean) chimeric antigen receptor expression, were able to specifically lyse CD33⁺ targets in vitro, including freshly isolated leukemic blasts from patients, produce significant amount of tumor-necrosis-factor-alpha and interferon-gamma, express the CD107a degranulation marker, and proliferate upon antigen specific stimulation. Challenging ΔCD19 selected inducible Caspase9-CAR.CD33 T-cells with programmed-death-ligand-1 enriched leukemia blasts resulted in significant killing like observed for the programmed-death-ligand-1 negative leukemic blasts fraction. Since the administration of 10 nanomolar of a non-therapeutic dimerizer to activate the suicide gene resulted in the elimination of only 76.4±2.0% gene modified cells in vitro, we found that co-administration of the dimerizer with either the BCL-2 inhibitor ABT-199, the pan-BCL inhibitor ABT-737, or mafosfamide, resulted in an additive effect up to complete cell elimination.

Conclusions

This strategy could be investigated for the safety of CAR T-cell applications, and targeting CD33 could be used as a ‘bridge” therapy for patients coming to allogeneic hematopoietic stem cell transplant, as anti-leukemia activity from infusing CAR.CD33 T-cells has been demonstrated in an ongoing clinical trial. Albeit never performed in the clinical setting, our future plan is to investigate the utility of iC9-CAR.CD33 T-cells as part of the conditioning therapy for an allogeneic hematopoietic stem cell transplant for acute myeloid leukemia, together with other myelosuppressive agents, whilst the activation of the inducible Caspase9 suicide gene would grant elimination of the infused gene modified T-cells prior to stem cell infusion to reduce the risk of engraftment failure as the CD33 is also expressed on a proportion of the donor stem cell graft.

Recent advances in T-cell immunotherapy for haematological malignancies

In vitro discoveries have paved the way for bench-to-bedside translation in adoptive T cell immunotherapy, resulting in remarkable clinical responses in a variety of haematological malignancies. Adoptively transferred T cells genetically modified to express CD19 CARs have shown great promise, although many unanswered questions regarding how to optimize T-cell therapies for both safety and efficacy remain. Similarly, T cells that recognize viral or tumour antigens though their native receptors have produced encouraging clinical responses. Honing manufacturing processes will increase the availability of T-cell products, while combining T-cell therapies has the ability to increase complete response rates. Lastly, innovative mechanisms to control these therapies may improve safety profiles while genome editing offers the prospect of modulating T-cell function. This review will focus on recent advances in T-cell immunotherapy, highlighting both clinical and pre-clinical advances, as well as exploring what the future holds.

Co-infusion of haplo-identical CD19-chimeric antigen receptor T cells and stem cells achieved full donor engraftment in refractory acute lymphoblastic leukemia

BACKGROUND

Elderly patients with relapsed and refractory acute lymphoblastic leukemia (ALL) have poor prognosis. Autologous CD19 chimeric antigen receptor-modified T (CAR-T) cells have potentials to cure patients with B cell ALL; however, safety and efficacy of allogeneic CD19 CAR-T cells are still undetermined.

CASE PRESENTATION

We treated a 71-year-old female with relapsed and refractory ALL who received co-infusion of haplo-identical donor-derived CD19-directed CAR-T cells and mobilized peripheral blood stem cells (PBSC) following induction chemotherapy. Undetectable minimal residual disease by flow cytometry was achieved, and full donor cell engraftment was established. The transient release of cytokines and mild fever were detected. Significantly elevated serum lactate dehydrogenase, alanine transaminase, bilirubin and glutamic-oxalacetic transaminase were observed from days 14 to 18, all of which were reversible after immunosuppressive therapy.

CONCLUSIONS

Our preliminary results suggest that co-infusion of haplo-identical donor-derived CAR-T cells and mobilized PBSCs may induce full donor engraftment in relapsed and refractory ALL including elderly patients, but complications related to donor cell infusions should still be cautioned.

TRIAL REGISTRATION

Allogeneic CART-19 for Elderly Relapsed/Refractory CD19+ ALL. NCT02799550.

Recent Developments in Cellular Immunotherapy for HSCT-Associated Complications

Allogeneic hematopoietic stem cell transplantation is associated with serious complications, and improvement of the overall clinical outcome of patients with hematological malignancies is necessary. During the last decades, posttransplant donor-derived adoptive cellular immunotherapeutic strategies have been progressively developed for the treatment of graft-versus-host disease (GvHD), infectious complications, and tumor relapses. To date, the common challenge of all these cell-based approaches is their implementation for clinical application. Establishing an appropriate manufacturing process, to guarantee safe and effective therapeutics with simultaneous consideration of economic requirements is one of the most critical hurdles. In this review, we will discuss the recent scientific findings, clinical experiences, and technological advances for cell processing toward the application of mesenchymal stromal cells as a therapy for treatment of severe GvHD, virus-specific T cells for targeting life-threating infections, and of chimeric antigen receptors-engineered T cells to treat relapsed leukemia.

The Promise of Chimeric Antigen Receptor Engineered T Cells in the Treatment of Hematologic Malignancies

Relapsed and refractory hematologic malignancies have a very poor prognosis. Chimeric antigen receptor T cells are emerging as a powerful therapy in this setting. Early clinical trials of genetically modified T cells for the treatment of non-Hodgkin lymphoma, chronic lymphocytic leukemia, and acute lymphoblastic leukemia have shown high complete response rates in patients with few therapeutic options. Exploration is ongoing for other hematologic malignancies including multiple myeloma, acute myeloid leukemia, and Hodgkin lymphoma (HL). At the same time, the design and production of chimeric antigen receptor T cells are being advanced so that this therapy can be more widely utilized. Cytokine release syndrome and neurotoxicity are common, but they are treatable and fully reversible. This review will review available data as well as future developments and challenges in the field.