Sorafenib promotes graft-versus-leukemia activity in mice and humans through IL-15 production in FLT3-ITD-mutant leukemia cells

Gilteritinib: An FMS-like tyrosine kinase 3/AXL tyrosine kinase inhibitor for the treatment of relapsed or refractory acute myeloid leukemia patients

Acute myeloid leukemia has recently undergone a significant transition into identifying and successfully inhibiting driver mutations leading to disease. One of the most common mutations in acute myeloid leukemia involves the protein FMS-like tyrosine kinase 3 (FLT3), which leads to ligand-independent activation of intracellular signaling cascades leading to the survival and proliferation of the acute leukemia blast cell. Preclinical studies have demonstrated the presence of two dominant types of mutations of this protein: internal tandem duplication and tyrosine kinase domain mutations. Successful inhibition of this protein has proven to be challenging. While FLT3 has been shown to be successfully inhibited and shown to improve overall survival in the frontline therapy of acute myeloid leukemia in combination with cytarabine and anthracycline, relapsed and refractory (R/R) patients have not been shown to be a successful population until recently. A phase III trial (ADMIRAL trial) demonstrated significant overall survival benefit in patients receiving gilteritinib compared to patients receiving salvage chemotherapy. This review will provide an overview of the preclinical, clinical, and practical use of gilteritinib in the treatment of patients with relapsed and refractory acute myeloid leukemia with FLT3 mutation.

Successful Treatment of Early Relapsed High-Risk AML After Allogeneic Hematopoietic Stem Cell Transplantation With Biomodulatory Therapy

Early relapse of acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an often unsuccessful therapeutic challenge. Since treatment options are few and efficacy is low, new approaches such as de novo allo-HSCT, targeted therapies and biomodulatory drugs have been developed, albeit prognosis is very poor. In this manuscript we present an unusual case of a patient with high-risk AML with an unbalanced jumping translocation and FLT3-TKD (low) mutation who presented with early relapse (FLT3 negative) after allo-HSCT, refractory to one cycle of azacytidine and discontinuation of immunosuppression (IS). As salvage therapy, the patient received a biomodulatory therapy consisting of low-dose azacytidine 75 mg/day (given s.c. d1-7 of 28), pioglitazone 45 mg/day orally, and all-trans-retinoic acid (ATRA) 45 mg/m2/day orally achieving a complete remission after two cycles of therapy. Even after cessation of treatment after 5 cycles, the patient remained in complete remission with full chimerism in peripheral blood and bone marrow for another 7 months. In conclusion, we report about an unusual case of long-lasting complete remission of early relapsed high-risk AML after allo-HSCT treated with azacytidine, pioglitazone and ATRA after standard of care treatment with HMA and discontinuation of IS failed.

Dissecting the biology of allogeneic HSCT to enhance the GvT effect whilst minimizing GvHD

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) was the first successful therapy for patients with haematological malignancies, predominantly owing to graft-versus-tumour (GvT) effects. Dramatic methodological changes, designed to expand eligibility for allo-HSCT to older patients and/or those with comorbidities, have led to the use of reduced-intensity conditioning regimens, in parallel with more aggressive immunosuppression to better control graft-versus-host disease (GvHD). Consequently, disease relapse has become the major cause of death following allo-HSCT. Hence, the prevention and treatment of relapse has come to the forefront and remains an unmet medical need. Despite >60 years of preclinical and clinical studies, the immunological requirements necessary to achieve GvT effects without promoting GvHD have not been fully established. Herein, we review learnings from preclinical modelling and clinical studies relating to the GvT effect, focusing on mechanisms of relapse and on immunomodulatory strategies that are being developed to overcome disease recurrence after both allo-HSCT and autologous HSCT. Emphasis is placed on discussing current knowledge and approaches predicated on the use of cell therapies, cytokines to augment immune responses and dual-purpose antibody therapies or other pharmacological agents that can control GvHD whilst simultaneously targeting cancer cells.

Oncogenic KrasG12D causes myeloproliferation via NLRP3 inflammasome activation

Oncogenic Ras mutations occur in various leukemias. It was unclear if, besides the direct transforming effect via constant RAS/MEK/ERK signaling, an inflammation-related effect of KRAS contributes to the disease. Here, we identify a functional link between oncogenic KrasG12D and NLRP3 inflammasome activation in murine and human cells. Mice expressing active KrasG12D in the hematopoietic system developed myeloproliferation and cytopenia, which is reversed in KrasG12D mice lacking NLRP3 in the hematopoietic system. Therapeutic IL-1-receptor blockade or NLRP3-inhibition reduces myeloproliferation and improves hematopoiesis. Mechanistically, KrasG12D-RAC1 activation induces reactive oxygen species (ROS) production causing NLRP3 inflammasome-activation. In agreement with our observations in mice, patient-derived myeloid leukemia cells exhibit KRAS/RAC1/ROS/NLRP3/IL-1β axis activity. Our findings indicate that oncogenic KRAS not only act via its canonical oncogenic driver function, but also enhances the activation of the pro-inflammatory RAC1/ROS/NLRP3/IL-1β axis. This paves the way for a therapeutic approach based on immune modulation via NLRP3 blockade in KRAS-mutant myeloid malignancies.

Immune escape and immunotherapy of acute myeloid leukemia

In spite of the recent approval of new promising targeted therapies, the clinical outcome of patients with acute myeloid leukemia (AML) remains suboptimal, prompting the search for additional and synergistic therapeutic rationales. It is increasingly evident that the bone marrow immune environment of AML patients is profoundly altered, contributing to the severity of the disease but also providing several windows of opportunity to prompt or rewire a proficient antitumor immune surveillance. In this Review, we present current evidence on immune defects in AML, discuss the challenges with selective targeting of AML cells, and summarize the clinical results and immunologic insights from studies that are testing the latest immunotherapy approaches to specifically target AML cells (antibodies, cellular therapies) or more broadly reactivate antileukemia immunity (vaccines, checkpoint blockade). Given the complex interactions between AML cells and the many components of their environment, it is reasonable to surmise that the future of immunotherapy in AML lies in the rational combination of complementary immunotherapeutic strategies with chemotherapeutics or other oncogenic pathway inhibitors. Identifying reliable biomarkers of response to improve patient selection and avoid toxicities will be critical in this process.

Durable remission of post-transplant relapsed FLT3-ITD AML in response to gilteritinib administration after a second transplant from the same donor

Patients with FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) acute myeloid leukemia (AML) respond to conventional induction chemotherapy, with remission rates similar to those seen in other subtypes; however, they are much more likely to relapse and relapse is rapid. For this reason, eligible patients receive consolidation therapy with early allogenic transplantation, but the recurrence rate remains high, even after transplantation. Moreover, the optimal therapy for patients with FLT3-ITD AML who relapse after allogeneic hematopoietic stem cell transplantation remains unclear. Here, we report a case in which graft-versus-leukemia (GVL) effects were induced by gilteritinib administration after a second transplant from the same donor, resulting in sustained remission of early FLT3-ITD AML relapse after allogeneic transplantation. Several studies suggest that the benefits of FLT3 tyrosine kinase inhibitors (FLT3-TKI) after allogeneic transplantation are attributable to GVL induction, as well as direct effects on FLT3 mutation-positive leukemia cells. With this in mind, we induced lymphodepletion using L-PAM to further enhance GVL induction by donor lymphocytes and FLT3-TKI. We believe that enhancement of GVL induction by lymphodepletion should be considered before FLT3-TKI use, if the prognosis is very poor, such as in patients with recurrence following allogeneic transplantation.

Mechanisms of Leukemia Immune Evasion and Their Role in Relapse After Haploidentical Hematopoietic Cell Transplantation

Over the last decade, the development of multiple strategies to allow the safe transfer from the donor to the patient of high numbers of partially HLA-incompatible T cells has dramatically reduced the toxicities of haploidentical hematopoietic cell transplantation (haplo-HCT), but this was not accompanied by a similar positive impact on the incidence of post-transplantation relapse. In the present review, we will elaborate on how the unique interplay between HLA-mismatched immune system and malignancy that characterizes haplo-HCT may impact relapse biology, shaping the selection of disease variants that are resistant to the “graft-vs.-leukemia” effect. In particular, we will present current knowledge on genomic loss of HLA, a relapse modality first described in haplo-HCT and accounting for a significant proportion of relapses in this setting, and discuss other more recently identified mechanisms of post-transplantation immune evasion and relapse, including the transcriptional downregulation of HLA class II molecules and the enforcement of inhibitory checkpoints between T cells and leukemia. Ultimately, we will review the available treatment options for patients who relapse after haplo-HCT and discuss on how a deeper insight into relapse immunobiology might inform the rational and personalized selection of therapies to improve the largely unsatisfactory clinical outcome of relapsing patients.

Overcoming Resistance to FLT3 Inhibitors in the Treatment of FLT3-Mutated AML

Acute myeloid leukaemia (AML) carrying internal tandem duplication (ITD) of Fms-Like Tyrosine kinase 3 (FLT3) gene is associated with high risk of relapse and poor clinical outcome upon treatment with conventional chemotherapy. FLT3 inhibitors have been approved for the treatment of this AML subtype but leukaemia relapse remains to be a major cause of treatment failure. Mechanisms of drug resistance have been proposed, including evolution of resistant leukaemic clones; adaptive cellular mechanisms and a protective leukaemic microenvironment. These models have provided important leads that may inform design of clinical trials. Clinically, FLT3 inhibitors in combination with conventional chemotherapy as induction treatment for fit patients; with low-intensity treatment as salvage treatment or induction for unfit patients as well as maintenance treatment with FLT3 inhibitors post HSCT hold promise to improve survival in this AML subtype.

Current and Future Molecular Targets for Acute Myeloid Leukemia Therapy

OPINION STATEMENT

Acute myeloid leukemia (AML) disease prognosis is poor and there is a high risk of chemo-resistant relapse for both young and old patients. Thus, there is a demand for alternative and target-specific drugs to improve the 5-year survival rate. Current treatment mainstays include chemotherapy, or mutation-specific targeting molecules including FLT3 inhibitors, IDH inhibitors, and monoclonal antibodies. Efforts to devise new, targeted therapy have included recent advances in methods for high-throughput genomic screening and the availability of computer-assisted techniques for the design of novel agents predicted to specifically inhibit mutant molecules involved in leukemogenesis. Crosstalk between the leukemia cells and the bone marrow microenvironment through cell surface molecules, such as the integrins αvβ3 and αvβ5, might influence drug response and AML progression. This review article focuses on current AML treatment options, new AML targeted therapies, the role of integrins in AML progression, and a potential therapeutic agent-integrin αvβ3 antagonist.

How I treat acute myeloid leukemia in the era of new drugs

The acute myeloid leukemia (AML) treatment landscape has changed substantially since 2017. New targeted drugs have emerged, including venetoclax to target B-cell lymphoma 2, midostaurin and gilteritinib to target FLT3, and ivosidenib and enasidenib to target mutant isocitrate dehydrogenase 1 and 2, respectively. Other additions include reapproval of gemtuzumab ozogomycin to target CD33, glasdegib to target the hedgehog pathway, and a liposomal formulation of daunorubicin and cytarabine (CPX-351). Genomically heterogeneous AML has a tendency to evolve, particularly under selective treatment pressure. For decades, treatment decisions have largely centered around chemotherapy drug intensity. Physicians now have access to an increasing number of drugs with novel mechanisms of action and distinctive side-effect profiles. Key issues faced by hematologists in this era of new drugs include (1) the timely identification of actionable mutations at diagnosis and at relapse; (2) deciding which drug to use among several therapeutic options; and (3) increasing awareness of how to anticipate, mitigate, and manage common complications associated with these new agents. This article will use 3 case presentations to discuss some of the new treatment challenges encountered in AML management, with the goal of providing practical guidance to aid the practicing physician.

FLT3 inhibitors in acute myeloid leukemia: ten frequently asked questions

The FMS-like tyrosine kinase 3 (FLT3) gene is mutated in approximately one third of patients with acute myeloid leukemia (AML), either by internal tandem duplications (FLT3-ITD), or by a point mutation mainly involving the tyrosine kinase domain (FLT3-TKD). Patients with FLT3-ITD have a high risk of relapse and low cure rates. Several FLT3 tyrosine kinase inhibitors have been developed in the last few years with variable kinase inhibitory properties, pharmacokinetics, and toxicity profiles. FLT3 inhibitors are divided into first generation multi-kinase inhibitors (such as sorafenib, lestaurtinib, midostaurin) and next generation inhibitors (such as quizartinib, crenolanib, gilteritinib) based on their potency and specificity of FLT3 inhibition. These diverse FLT3 inhibitors have been evaluated in myriad clinical trials as monotherapy or in combination with conventional chemotherapy or hypomethylating agents and in various settings, including front-line, relapsed or refractory disease, and maintenance therapy after consolidation chemotherapy or allogeneic stem cell transplantation. In this practical question-and-answer-based review, the main issues faced by the leukemia specialists on the use of FLT3 inhibitors in AML are addressed.

The role of allogeneic stem cell transplantation in the management of acute myeloid leukaemia: a triumph of hope and experience

Acute myeloid leukaemia (AML) is the commonest indication for allogeneic stem cell transplantation (allo-SCT) worldwide. The accumulated experience of allografting in AML over the last four decades has provided critical insights into both the contribution of the conditioning regimen and the graft-versus-leukaemia effect to the curative potential of the most common form of immunotherapy utilised in standard clinical practice. Coupled with advances in donor availability and transplant technologies, this has resulted in allo-SCT becoming an important treatment modality for the majority of adults with high-risk AML. At the same time, advances in genomic classification, coupled with progress in the accurate quantification of measurable residual disease, have increased the precision with which allo-mandatory patients can be identified, whilst simultaneously permitting accurate identification of those patients who can be spared the toxicity of an allograft. Despite this progress, disease recurrence still remains a major cause of transplant failure and AML has served as a paradigm for the development of strategies to reduce the risk of relapse - notably the novel concept of post-transplant maintenance, utilising pharmacological or cellular therapies.

Immune Monitoring After Allogeneic Hematopoietic Cell Transplantation: Toward Practical Guidelines and Standardization

Hematopoietic cell transplantation (HCT) is often a last resort, but potentially curative treatment option for children suffering from hematological malignancies and a variety of non-malignant disorders, such as bone marrow failure, inborn metabolic disease or immune deficiencies. Although efficacy and safety of the HCT procedure has increased significantly over the last decades, the majority of the patients still suffer from severe acute toxicity, viral reactivation, acute or chronic graft-versus-host disease (GvHD) and/or, in case of malignant disease, relapses. Factors influencing HCT outcomes are numerous and versatile. For example, there is variation in the selected graft sources, type of infused cell subsets, cell doses, and the protocols used for conditioning, as well as immune suppression and treatment of adverse events. Moreover, recent pharmacokinetic studies show that medications used in the conditioning regimen (e.g., busulphan, fludarabine, anti-thymocyte globulin) should be dosed patient-specific to achieve optimal exposure in every individual patient. Due to this multitude of variables and site-specific policies/preferences, harmonization between HCT centers is still difficult to achieve. Literature shows that adequate immune recovery post-HCT limits both relapse and non-relapse mortality (death due to viral reactivations and GvHD). Monitoring immune parameters post-HCT may facilitate a timely prediction of outcome. The use of standardized assays to measure immune parameters would facilitate a fast comparison between different strategies tested in different centers or between different clinical trials. We here discuss immune cell markers that may contribute to clinical decision making and may be worth to standardize in multicenter collaborations for future trials.

FLT3 mutations in acute myeloid leukemia: Therapeutic paradigm beyond inhibitor development

FMS-like tyrosine kinase 3 (FLT3) is a type III receptor tyrosine kinase that plays an important role in hematopoietic cell survival, proliferation and differentiation. The most clinically important point is that mutation of the FLT3 gene is the most frequent genetic alteration and a poor prognostic factor in acute myeloid leukemia (AML) patients. There are two major types of FLT3 mutations: internal tandem duplication mutations in the juxtamembrane domain (FLT3-ITD) and point mutations or deletion in the tyrosine kinase domain (FLT3-TKD). Both mutant FLT3 molecules are activated through ligand-independent dimerization and trans-phosphorylation. Mutant FLT3 induces the activation of multiple intracellular signaling pathways, mainly STAT5, MAPK and AKT signals, leading to cell proliferation and anti-apoptosis. Because high-dose chemotherapy and allogeneic hematopoietic stem cell transplantation cannot sufficiently improve the prognosis, clinical development of FLT3 kinase inhibitors expected. Although several FLT3 inhibitors have been developed, it takes more than 20 years from the first identification of FLT3 mutations until FLT3 inhibitors become clinically available for AML patients with FLT3 mutations. To date, three FLT3 inhibitors have been clinically approved as monotherapy or combination therapy with conventional chemotherapeutic agents in Japan and/or Europe and United states. However, several mechanisms of resistance to FLT3 inhibitors have already become apparent during their clinical trials. The resistance mechanisms are complex and emerging resistant clones are heterogenous. Further basic and clinical studies are required to establish the best therapeutic strategy for AML patients with FLT3 mutations.

Immune Escape after Hematopoietic Stem Cell Transplantation (HSCT): From Mechanisms to Novel Therapies

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. Recent advances in understanding its molecular basis have opened the way to new therapeutic strategies, including targeted therapies. However, despite an improvement in prognosis it has been documented in recent years (especially in younger patients) that allogenic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative treatment in AML and the first therapeutic option for high-risk patients. After allo-HSCT, relapse is still a major complication, and is observed in about 50% of patients. Current evidence suggests that relapse is not due to clonal evolution, but instead to the ability of the AML cell population to escape immune control by a variety of mechanisms including the altered expression of HLA-molecules, production of anti-inflammatory cytokines, relevant metabolic changes and expression of immune checkpoint (ICP) inhibitors capable of “switching-off” the immune response against leukemic cells. Here, we review the main mechanisms of immune escape and identify potential strategies to overcome these mechanisms.

Clonal evolution and immune evasion in posttransplantation relapses

Despite the considerable improvements witnessed over the last few decades in the feasibility and safety of allogeneic hematopoietic cell transplantation (allo-HCT) for hematological malignancies, disease relapse continues to represent a frequent occurrence, with largely unsatisfactory salvage options. Recent studies have shed new light on the biology of posttransplantation relapses, demonstrating that they can frequently be explained using an evolutionary perspective: The changes in disease clonal structure and immunogenicity that are often documented at relapse may in fact represent the end results of a process of selection, allowing the outgrowth of variants that are more capable of resisting the therapeutic control of allo-HCT. This review provides an overview of the mechanisms forming the basis of relapse, including clonal evolution, gain of tropism for privileged sites, genomic and nongenomic changes in the HLA asset, and enforcement of immune checkpoints. Finally, this review discusses how these mechanisms may combine in complex patterns and how understanding and untangling these interactions may provide key knowledge for the selection of personalized therapeutic approaches.

Immunotherapy for acute myeloid leukemia: from allogeneic stem cell transplant to novel therapeutics

Immunotherapy in the form of allogeneic stem cell transplantation (SCT) plays an instrumental role in the treatment of acute myeloid leukemia (AML), with non-transplant modalities of immunotherapy including checkpoint blockade now being actively explored. Here, we provide an overview of the graft versus leukemia (GVL) effect in AML as a window into understanding the prospects of AML immunotherapy. We explore the roles of various cell types in orchestrating anti-leukemic immunity, as well as those contributing to the unique immune suppressive state of myeloid diseases. We discuss specific approaches to engage the immune system, while noting the challenges of the AML antigen landscape and the barriers to immune modulation. We review the potential for immunomodulatory agents in combination with cellular therapies, donor lymphocyte infusion, and following SCT. Finally, to address the challenge of minimal residual disease (MRD) following chemotherapy, we propose combination epigenetic and immunotherapy for the eradication of MRD.

The Graft-Versus-Leukemia Effect in AML

Allogeneic hematopoietic stem cell transplantation (allo-SCT) is the most established and commonly used cellular immunotherapy in cancer care. It is the most potent anti-leukemic therapy in patients with acute myeloid leukemia (AML) and is routinely used with curative intent in patients with intermediate and poor risk disease. Donor T cells, and possibly other immune cells, eliminate residual leukemia cells after prior (radio)chemotherapy. This immune-mediated response is known as graft-versus-leukemia (GvL). Donor alloimmune responses can also be directed against healthy tissues, which is known as graft-versus-host disease (GvHD). GvHD and GvL often co-occur and, therefore, a major barrier to exploiting the full immunotherapeutic benefit of donor immune cells against patient leukemia is the immunosuppression required to treat GvHD. However, curative responses to allo-SCT and GvHD do not always occur together, suggesting that these two immune responses could be de-coupled in some patients. To make further progress in successfully promoting GvL without GvHD, we must transform our limited understanding of the cellular and molecular basis of GvL and GvHD. Specifically, in most patients we do not understand the antigenic basis of immune responses in GvL and GvHD. Identification of antigens important for GvL but not GvHD, and vice versa, could impact on donor selection, allow us to track GvL immune responses and begin to specifically harness and strengthen anti-leukemic immune responses against patient AML cells, whilst minimizing the toxicity of GvHD.

The Interplay Between the Genetic and Immune Landscapes of AML: Mechanisms and Implications for Risk Stratification and Therapy

AML holds a unique place in the history of immunotherapy by virtue of being among the first malignancies in which durable remissions were achieved with "adoptive immunotherapy," now known as allogeneic stem cell transplantation. The successful deployment of unselected adoptive cell therapy established AML as a disease responsive to immunomodulation. Classification systems for AML have been refined and expanded over the years in an effort to capture the variability of this heterogeneous disease and risk-stratify patients. Current systems increasingly incorporate information about cytogenetic alterations and genetic mutations. The advent of next generation sequencing technology has enabled the comprehensive identification of recurrent genetic mutations, many with predictive power. Recurrent genetic mutations found in AML have been intensely studied from a cell intrinsic perspective leading to the genesis of multiple, recently approved targeted therapies including IDH1/2-mutant inhibitors and FLT3-ITD/-TKD inhibitors. However, there is a paucity of data on the effects of these targeted agents on the leukemia microenvironment, including the immune system. Recently, the phenomenal success of checkpoint inhibitors and CAR-T cells has re-ignited interest in understanding the mechanisms leading to immune dysregulation and suppression in leukemia, with the objective of harnessing the power of the immune system via novel immunotherapeutics. A paradigm has emerged that places crosstalk with the immune system at the crux of any effective therapy. Ongoing research will reveal how AML genetics inform the composition of the immune microenvironment paving the way for personalized immunotherapy.

Advances in understanding the pathogenesis of graft-versus-host disease

Acute graft-versus-host disease (GVHD) remains a major complication after allogeneic haematopoietic stem cell transplantation (allo-HSCT). The emergence of different immuno-prophylaxis strategies, such as post-transplant cyclophosphamide or anti-thymocyteglobulin has reduced the incidence of acute GVHD in recent years. The biology of the acute GVHD we observe in the clinic may change due to the use of novel immuno-stimulatory agents, including immune checkpoint inhibitors or anti-neoplastic immune-modifiers, like lenalidomide, given before or after allo-HSCT. Here we discuss the recent advances in our understanding of acute GVHD with a focus on early events of the disease, including tissue damaging factors, innate immune cells, costimulatory pathways, immune cell signalling, immuno-regulatory cell types, biomarkers of GVHD and regenerative approaches. New insight in the pathogenesis of acute GVHD has revealed the role of pro-inflammatory intracellular signalling, defects in intestinal tissue regeneration and anti-bacterial defence, as well as a reduced diversity of the microbiome, which will be the basis for the development of novel therapies.

A Prospective Study of Peritransplant Sorafenib for Patients with FLT3-ITD Acute Myeloid Leukemia Undergoing Allogeneic Transplantation

FLT3-ITD-mutated acute myeloid leukemia (AML) remains a therapeutic challenge. FLT3 inhibition in the setting of minimal residual disease and a new immune system via allogeneic transplantation offers a promise of improved survival for these patients. We performed a prospective study of patients with FLT3-ITD AML undergoing allogeneic transplant that was conducted to evaluate the safety, tolerability, and outcome of sorafenib administered peritransplant. Sorafenib dosing was individualized, starting at 200 mg twice a day (BID), and titrated based on tolerability or toxicities until a tolerable dose was identified. Forty-four patients, with a median age of 52 years, undergoing allogeneic transplant were started on sorafenib in the peritransplant period (21 pretransplant). The median duration of post-transplant follow-up was 27.6 months (range, 5.2 to 60.4). Overall survival was 76% at both 24 and 36 months. Event-free survival at 24 and 36 months was 74% and 64%, respectively. Ten patients died in the post-transplant period, with 6 deaths due to relapsed leukemia and 4 from transplant-associated toxicity. Tolerable doses ranged from 200 mg every other day to 400 mg BID with similar exposure. Correlative studies evaluating FLT3 inhibition via a plasma inhibitory activity assay showed consistent inhibition of FLT3 at all tolerability-determined dosing levels. Sorafenib is well tolerated in the peritransplant setting irrespective of the conditioning intensity or the donor source. Our findings indicate that sorafenib dosing can be individualized in the post-transplantation setting according to patient tolerability. This approach results in effective in vivo FLT3 inhibition and yields encouraging survival results.

Current Advances in Immunotherapy for Acute Leukemia: An Overview of Antibody, Chimeric Antigen Receptor, Immune Checkpoint, and Natural Killer

Recently, due to the application of hematopoietic stem cell transplantation and small molecule inhibitor, the survival of acute leukemia is prolonged. However, the 5 year survival rate remains low due to a high incidence of relapse. Immunotherapy is expected to improve the prognosis of patients with relapsed or refractory hematological malignancies because it does not rely on the cytotoxic mechanisms of conventional therapy. In this paper, the advances of immunotherapy in acute leukemia are reviewed from the aspects of Antibody including Unconjugated antibodies, Antibody-drug conjugate and Bispecific antibody, Chimeric Antigen Receptor (CARs), Immune checkpoint, Natural killer cells. The immunological features, mechanisms and limitation in clinic will be described.

Graft-Versus-Host Disease-Free Antitumoral Signature After Allogeneic Donor Lymphocyte Injection Identified by Proteomics and Systems Biology

PURPOSE

As a tumor immunotherapy, allogeneic hematopoietic cell transplantation with subsequent donor lymphocyte injection (DLI) aims to induce the graft-versus-tumor (GVT) effect but often also leads to acute graft-versus-host disease (GVHD). Plasma tests that can predict the likelihood of GVT without GVHD are still needed.

PATIENTS AND METHODS

We first used an intact-protein analysis system to profile the plasma proteome post-DLI of patients who experienced GVT and acute GVHD for comparison with the proteome of patients who experienced GVT without GVHD in a training set. Our novel six-step systems biology analysis involved removing common proteins and GVHD-specific proteins, creating a protein-protein interaction network, calculating relevance and penalty scores, and visualizing candidate biomarkers in gene networks. We then performed a second proteomics experiment in a validation set of patients who experienced GVT without acute GVHD after DLI for comparison with the proteome of patients before DLI. We next combined the two experiments to define a biologically relevant signature of GVT without GVHD. An independent experiment with single-cell profiling in tumor antigen–activated T cells from a patient with post–hematopoietic cell transplantation relapse was performed.

RESULTS

The approach provided a list of 46 proteins in the training set, and 30 proteins in the validation set were associated with GVT without GVHD. The combination of the two experiments defined a unique 61-protein signature of GVT without GVHD. Finally, the single-cell profiling in activated T cells found 43 of the 61 genes. Novel markers, such as RPL23, ILF2, CD58, and CRTAM, were identified and could be extended to other antitumoral responses.

CONCLUSION

Our multiomic analysis provides, to our knowledge, the first human plasma signature for GVT without GVHD. Risk stratification on the basis of this signature would allow for customized treatment plans.

Augmentation of IFN-γ+ CD8+ T cell responses correlates with survival of HCC patients on sorafenib therapy

BACKGROUNDSorafenib has been shown to reduce the extent of immunosuppression in patients with hepatocellular carcinoma (HCC). The rationale of this investigation was to identify biomarkers that can predict treatment efficacy of sorafenib in HCC patients and to unravel the mechanism by which sorafenib impedes immune suppression mediated by distinct immunosuppressive cell subsets.METHODSWith informed consent, blood samples were collected from 30 patients with advanced HCC, at baseline and 2 time points after initiation of sorafenib treatment. The frequency of PD-1+ T cells, ERK2 phosphorylation on flt-3+ Tregs and MDSCs, and T effector cell function were quantified by using flow cytometry.RESULTSElevated levels of CD8+Ki67+ T cells producing IFN-γ were associated with improved progression-free survival and overall survival (OS). High frequencies of these T cells were correlated with significantly reduced risk of death over time. Patients with an increased pretreatment T effector/Treg ratio showed significant improvement in OS. ERK+flt-3+ Tregs and MDSCs were significantly decreased after sorafenib therapy. Increased numbers of baseline flt-3+p-ERK+ MDSCs were associated with survival benefit of patients.CONCLUSIONA high baseline CD4+ T effector/Treg ratio is a potential biomarker of prognostic significance in HCC. CD8+Ki67+ T cells producing IFN-γ are a key biomarker of response to sorafenib therapy resulting in survival benefit. The immune modulation resulted from sorafenib-mediated blockade of signaling through the VEGF/VEGFR/flt-3 pathway, affecting ERK phosphorylation. These insights may help identify patients who likely would benefit from VEGFR antagonism and inform efforts to improve the efficacy of sorafenib in combination with immunotherapy.TRIAL REGISTRATIONNCT02072486.FUNDINGNational Comprehensive Cancer Network Oncology Research Program from general research support provided by Bayer US LLC (NCCNSORA0002), National Cancer Institute grant P30CA016056, and pilot funds from Roswell Park Alliance Foundation.

Targeting Leukemia Stem Cell-Niche Dynamics: A New Challenge in AML Treatment

One of the most urgent needs in AML is to improve the disease cure rate as relapse still occurs in 60–80% of patients. Recent evidence suggests that dismal clinical outcomes may be improved by a better definition of the tight interaction between the AML cell population and the bone marrow (BM) microenvironment (“the niche”); the latter has been progressively highlighted to have an active role in the disease process. It has now been well established that the leukemic population may misinterpret niche-derived signals and remodel the niche, providing a shelter to AML cells and protecting them from the cytotoxic effects of chemoradiotherapy. Novel imaging technological advances and preclinical disease models have revealed that, due to the finite number of BM niches, leukemic stem cells (LSCs) and normal hematopoietic stem cells (HSCs) compete for the same functional areas. Thus, the removal of LSCs from the BM niche and the promotion of normal HSC engraftment should be the primary goals in antileukemic research. In addition, it is now becoming increasingly clear that AML-niche dynamics are disease stage specific. In AML, the niche has been linked to disease pathogenesis in the preleukemic stage, the niche becomes permissive once leukemic cells are established, and the niche is transformed into a self-reinforcing structure at a later disease stage. These concepts have been fostered by the demonstration that, in unrelated AML types, endosteal vessel loss occurs as a primary AML-induced niche alteration, and additional AML-induced alterations of the niche and normal hematopoiesis evolve focally and in parallel. Obviously, this endosteal vessel loss plays a fundamental role in AML pathogenesis by causing excessive vascular permeability, hypoxia, altered perfusion, and reduced drug delivery. Each of these alterations may be effectively targeted by various therapeutic procedures, but preservation of endosteal vessel integrity might be the best option for any future antileukemic treatment.

Targeting Tyrosine Kinases in Acute Myeloid Leukemia: Why, Who and How?

Acute myeloid leukemia (AML) is a myeloid malignancy carrying a heterogeneous molecular panel of mutations participating in the blockade of differentiation and the increased proliferation of myeloid hematopoietic stem and progenitor cells. The historical "3 + 7" treatment (cytarabine and daunorubicin) is currently challenged by new therapeutic strategies, including drugs depending on the molecular landscape of AML. This panel of mutations makes it possible to combine some of these new treatments with conventional chemotherapy. For example, the FLT3 receptor is overexpressed or mutated in 80% or 30% of AML, respectively. Such anomalies have led to the development of targeted therapies using tyrosine kinase inhibitors (TKIs). In this review, we document the history of TKI targeting, FLT3 and several other tyrosine kinases involved in dysregulated signaling pathways.

Novel treatments for relapsed/refractory acute myeloid leukemia with FLT3 mutations

Introduction: Mutations in the gene encoding for the FMS-like tyrosine kinase 3 (FLT3) are present in about 30% of adults with AML and are associated with shorter disease-free and overall survival after initial therapy. Prognosis of relapsed/refractory AML with FLT3 mutations is even more dismal with median overall survival of a few months only. Areas covered: This review will cover current and emerging treatments for relapsed/refractory AML with FLT3 mutations, preclinical rationale and clinical trials with new encouraging data for this particularly challenging population. The authors discuss mechanisms of resistance to FLT3 inhibitors and how these insights serve to identify current and future treatments. As allogeneic stem cell transplant in the first remission is the preferred therapy for newly diagnosed AML patients with FLT3 mutations, the authors discuss the role of maintenance after SCT for the prevention of relapse. Expert opinion: Relapsed/refractory AML with FLT3 mutations remains a therapeutic challenge with currently available treatments. However, the evolution of targeted therapies with next-generation FLT3 inhibitors and their combinations with chemotherapy is showing much promise. Moreover, growing understanding of the pathways of resistance to treatment has led to the identification of various targeted therapies currently being explored, which in time will improve outcomes.

Clinical considerations for the use of FLT3 inhibitors in acute myeloid leukemia

Internal tandem duplications and tyrosine kinase mutations in the fms-like tyrosine kinase 3 (FLT3) receptor can occur in acute myeloid leukemia (AML) and portend a poor prognosis. Midostaurin, a multikinase inhibitor that targets FLT3, demonstrated a survival benefit in FLT3-mutated AML in combination with front-line chemotherapy. Despite this advancement, the use of FLT3 inhibitors in clinical practice is complicated by significant drug-drug interactions and uncertainty about optimal timing, duration, and sequencing of therapy. As monotherapy, the utility of FLT3 inhibitors was initially limited by incomplete and transient clinical responses and the development of acquired resistance. This led to the development of more potent and selective FLT3 inhibitors designed to overcome common resistance mechanisms. One of these second generation FLT3 inhibitors, gilteritinib, is now FDA-approved for the treatment of relapsed or refractory AML. Now that multiple FLT3 inhibitors are commercially available, it is important to further delineate the role of these agents in the AML population. This review aims to provide a comprehensive overview of the role of FLT3 inhibitors in AML and apply the current literature to clinical practice.

FLT3 overexpression in acute leukaemias: New insights into the search for molecular mechanisms

FLT3 overexpression is a recurrent event in various acute leukaemia subtypes. This transcriptional deregulation is important to define the prognostic risk for many patients. Of note, the molecular mechanisms leading to this gene upregulation are unknown for a substantial number of cases. In this Mini-Review, we highlight the role of FLT3 overexpression in acute leukaemia and discuss emerging mechanisms accounting for this upregulation. The benefits of using targeted therapy are also addressed in the overexpression context, posing other therapeutic possibilities based on state-of-the-art knowledge that could be considered for future research.

Melatonin enhances sorafenib-induced cytotoxicity in FLT3-ITD acute myeloid leukemia cells by redox modification

Acute myeloid leukemia (AML) with an internal tandem duplication in Fms-related tyrosine kinase 3 (FLT3-ITD) is identified as a subgroup with poor outcome and intrinsic resistance to chemotherapy and therefore urgent need for development of novel therapeutic strategies.

Methods: The antitumor effects of melatonin alone or combined with sorafenib were evaluated via flow cytometry and immunoblotting assays in FLT-ITD AML cells. Also, the ex vivo and in vivo models were used to test the synergistic effects of melatonin and sorafenib against leukemia with FLT3/ITD mutation.

Results: Our study shows for the first time that melatonin inhibits proliferation and induces apoptosis in FLT3/ITD-positive leukemia cells. Mechanistically, melatonin preferentially causes overproduction of reactive oxygen species (ROS) and ultimately massive cell death in FLT3-ITD AML cells. Moreover, melatonin significantly enhances the cytotoxicity induced by the FLT3 tyrosine kinase inhibitor sorafenib in AML cells with FLT3/ITD through redox modification. Importantly, combination of melatonin and sorafenib exhibited highly synergistic therapeutic activity in MV4-11 xenografts and a murine model bearing FLT3/ITD leukemia.

Conclusion: This study indicates that melatonin, alone or in combination with sorafenib, has potential to improve the therapeutic outcome of AML patients with FLT3-ITD mutation that merits further investigation.

Successful treatment of acute myeloid leukemia co-expressing NUP98/NSD1 and FLT3/ITD with preemptive donor lymphocyte infusions

Patients with acute myeloid leukemia (AML) co-expressing NUP98/NSD1 and FLT3/ITD have a dismal prognosis despite undergoing hematopoietic stem cell transplantation (HSCT). There are a few studies on successful treatment of relapsed AML co-expressing NUP98/NSD1 and FLT3/ITD. We report a refractory case of molecular relapse of AML co-expressing NUP98/NSD1 and FLT3/ITD post-matched sibling HSCT. Donor lymphocyte infusion (DLI) at an early stage of post-transplantation resulted in complete molecular remission for 29 months with durable chronic graft-versus-host disease. Our case suggests the clinical efficacy of preemptive DLI following minimal residual disease analysis for the treatment of refractory AML.

Midostaurin abrogates CD33-directed UniCAR and CD33-CD3 bispecific antibody therapy in acute myeloid leukaemia

Combinatory therapeutic approaches of different targeted therapies in acute myeloid leukaemia are currently under preclinical/early clinical investigation. To enhance anti-tumour effects, we combined the tyrosine kinase inhibitor (TKI) midostaurin and T-cell mediated immunotherapy directed against CD33. Clinically relevant concentrations of midostaurin abrogated T-cell mediated cytotoxicity both after activation with bispecific antibodies and chimeric antigen receptor T cells. This information is of relevance for clinicians exploring T-cell mediated immunotherapy in early clinical trials. Given the profound inhibition of T-cell functionality and anti-tumour activity, we recommend specific FLT3 TKIs for further clinical testing of combinatory approaches with T-cell based immunotherapy.

Sorafenib Therapy Is Associated with Improved Outcomes for FMS-like Tyrosine Kinase 3 Internal Tandem Duplication Acute Myeloid Leukemia Relapsing after Allogeneic Hematopoietic Stem Cell Transplantation

The optimal therapy for patients with acute myeloid leukemia (AML) with FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) who relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains unclear. In this study we retrospectively evaluated the efficacy of sorafenib combined with other therapeutic strategies as salvage therapy for these patients. Eighty-three AML patients with FLT3-ITD relapsing after allo-HSCT were enrolled in this study. Fifty-three patients received salvage therapy containing sorafenib and 30 patients did not. Salvage therapy containing sorafenib was superior to that without sorafenib with respect to complete remission rates, overall survival (OS), and progression-free survival (PFS) (66.0% versus 30.0%, 46.8% versus 20.0%, and 44.9% versus 16.7%, respectively; P = .002, P = .003, and P = .001). Further subgroup analysis revealed that the OS and PFS of patients who received sorafenib combined with chemotherapy followed by donor lymphocyte infusion (DLI) were superior to those receiving other therapeutic regimens, including sorafenib combined with chemotherapy, chemotherapy followed by DLI, and monochemotherapy (P = .003, P < .001). Multivariate analysis revealed that salvage therapy including sorafenib was the only protective factor for longer OS (P = .035; hazard ratio [HR], .526); salvage therapy including sorafenib and DLI were the protective factors for longer PFS (P = .011, HR, .423; P = .019, HR, .508). Our data suggest that sorafenib therapy is associated with improved outcomes for FLT3-ITD AML relapsing after allo-HSCT, and whether sorafenib combined with chemotherapy followed by DLI reveals an optimal efficacy merits further study.

New drugs creating new challenges in acute myeloid leukemia

The therapeutic landscape is rapidly changing, with eight new drugs approved by the Food and Drug Administration within the last 2 years, including midostaurin and gilteritinib for FLT3 mutant newly diagnosed and relapsed/refractory (R/R) acute myeloid leukemia (AML), respectively; CPX-351 (liposomal cytarabine and daunorubicin) for therapy-related AML and AML with myelodysplasia-related changes; gemtuzumab ozogamicin (anti-CD33 monoclonal antibody conjugated with calicheamicin) for newly diagnosed and R/R CD33-positive AML; enasidenib and ivosidenib for IDH2 and IDH1 mutant R/R AML, respectively. Novel therapies have also emerged for newly diagnosed AML in adults who are age 75 years or older, or who have comorbidities that preclude the use of intensive induction chemotherapy. These include venetoclax (BCL-2 inhibitor) in combination with hypomethylating agents (azacitidine or decitabine) or low-dose cytarabine (LDAC), and glasdegib (sonic hedgehog pathway inhibitor) in combination with LDAC. This flurry of new drug approvals has markedly altered the treatment landscape in AML and provided new opportunities, as well as new challenges for treating clinicians. This review will focus on how these drugs might shape clinical practice and the hurdles likely to be faced by new therapies seeking entry into this dynamic and rapidly changing therapeutic landscape.

Immune signature drives leukemia escape and relapse after hematopoietic cell transplantation

Transplantation of hematopoietic cells from a healthy individual (allogeneic hematopoietic cell transplantation (allo-HCT)) demonstrates that adoptive immunotherapy can cure blood cancers: still, post-transplantation relapses remain frequent. To explain their drivers, we analyzed the genomic and gene expression profiles of acute myeloid leukemia (AML) blasts purified from patients at serial time-points during their disease history. We identified a transcriptional signature specific for post-transplantation relapses and highly enriched in immune-related processes, including T cell costimulation and antigen presentation. In two independent patient cohorts we confirmed the deregulation of multiple costimulatory ligands on AML blasts at post-transplantation relapse (PD-L1, B7-H3, CD80, PVRL2), mirrored by concomitant changes in circulating donor T cells. Likewise, we documented the frequent loss of surface expression of HLA-DR, -DQ and -DP on leukemia cells, due to downregulation of the HLA class II regulator CIITA. We show that loss of HLA class II expression and upregulation of inhibitory checkpoint molecules represent alternative modalities to abolish AML recognition from donor-derived T cells, and can be counteracted by interferon-γ or checkpoint blockade, respectively. Our results demonstrate that the deregulation of pathways involved in T cell-mediated allorecognition is a distinctive feature and driver of AML relapses after allo-HCT, which can be rapidly translated into personalized therapies.

Allogeneic Stem Cell Transplantation for FLT3-Mutated Acute Myeloid Leukemia: In vivo T-Cell Depletion and Posttransplant Sorafenib Maintenance Improve Survival. A Retrospective Acute Leukemia Working Party-European Society for Blood and Marrow Transplant Study

Acute myeloid leukemia (AML) with FLT3-mutation carries a poor prognosis, and allogeneic stem cell transplantation (allo-SCT) is recommended at first complete remission (CR1). We assessed 462 adults (median age 50 years) with FLT3-mutated AML allografted between 2010 and 2015 from a matched related (40%), unrelated (49%), or haploidentical donor (11%). The median follow-up of alive patients was 39 months. Day-100 acute graft versus host disease (GVHD) grades II–IV and III–IV were encountered in 26% and 9%, whereas the 2-year incidence of chronic and extensive chronic GVHD were 34% and 16%, respectively. The 2-year incidences of relapse and nonrelapse mortality were 34% and 15%, respectively. The 2-year leukemia-free survival, overall survival (OS), and GVHD relapse-free survival (GRFS) were 51%, 59%, and 38%, respectively. In multivariate analysis, NPM1-mutation, transplantation in CR1, in vivo T-cell depletion, and posttransplant sorafenib improved OS, whereas more than one induction (late CR1) negatively affected OS. Similarly, NPM1-mutation, a haploidentical donor, T-cell depletion, and sorafenib maintenance improved GRFS, whereas late CR1 or persistent disease negatively affected it. In conclusion, FLT3-mutated AML remains a challenge even following allo-SCT. In vivo T-cell depletion and posttransplant sorafenib significantly improve OS and GRFS, and may be considered as standard of care.

Clinical implications of tumor-intrinsic mechanisms regulating PD-L1

Treatment with immune checkpoint inhibitors targeting programmed death receptor-1 (PD-1) or programmed death ligand-1 (PD-L1) is effective in many cancer types. Tumors harboring specific mutations modulate antitumor immune responses through the PD-1/PD-L1 axis, and this should be taken into account when designing rational combinatory treatments.

Relapse of Acute Myeloid Leukemia after Allogeneic Stem Cell Transplantation: Prevention, Detection, and Treatment

Acute myeloid leukemia (AML) is a phenotypically and prognostically heterogeneous hematopoietic stem cell disease that may be cured in eligible patients with intensive chemotherapy and/or allogeneic stem cell transplantation (allo-SCT). Tremendous advances in sequencing technologies have revealed a large amount of molecular information which has markedly improved our understanding of the underlying pathophysiology and enables a better classification and risk estimation. Furthermore, with the approval of the FMS-like tyrosine kinase 3 (FLT3) inhibitor Midostaurin a first targeted therapy has been introduced into the first-line therapy of younger patients with FLT3-mutated AML and several other small molecules targeting molecular alterations such as isocitrate dehydrogenase (IDH) mutations or the anti-apoptotic b-cell lymphoma 2 (BCL-2) protein are currently under investigation. Despite these advances, many patients will have to undergo allo-SCT during the course of disease and depending on disease and risk status up to half of them will finally relapse after transplant. Here we review the current knowledge about the molecular landscape of AML and how this can be employed to prevent, detect and treat relapse of AML after allo-SCT.

Strategies for Enhancing and Preserving Anti-leukemia Effects Without Aggravating Graft-Versus-Host Disease

Allogeneic stem cell transplantation (allo-SCT) is a curable method for the treatment of hematological malignancies. In the past two decades, the establishment of haploidentical transplant modalities make “everyone has a donor” become a reality. However, graft-versus-host disease (GVHD) and relapse remain the major two causes of death either in the human leukocyte antigen (HLA)-matched transplant or haploidentical transplant settings, both of which restrict the improvement of transplant outcomes. Preclinical mice model showed that both donor-derived T cells and natural killer (NK) cells play important role in the pathogenesis of GVHD and the effects of graft-versus-leukemia (GVL). Hence, understanding the immune mechanisms of GVHD and GVL would provide potential strategies for the control of leukemia relapse without aggravating GVHD. The purpose of the current review is to summarize the biology of GVHD and GVL responses in preclinical models and to discuss potential novel therapeutic strategies to reduce the relapse rate after allo-SCT. We will also review the approaches, including optimal donor selection and, conditioning regimens, donor lymphocyte infusion, BCR/ABL-specific CTL, and chimeric antigen receptor-modified T cells, which have been successfully used in the clinic to enhance and preserve anti-leukemia activity, especially GVL effects, without aggravating GVHD or alleviate GVHD.

Mechanisms of immune escape after allogeneic hematopoietic cell transplantation

Relapse of the original disease is a major cause of death after allogeneic hematopoietic cell transplantation for acute leukemias. There is growing evidence that relapses may be explained not only by resistance to chemotherapy but also by the escape of tumor cells from the control of the allogeneic immune response. Mechanisms of immune evasion can involve abrogation of leukemia cell recognition due to loss of HLA genes, immunosuppression by immune-checkpoint ligand expression, production of anti-inflammatory factors, release of metabolically active enzymes, loss of proinflammatory cytokine production, and acquisition of novel driver mutations that promote leukemia outgrowth. These mechanisms, and therapeutic targeting of immune escape, will be discussed. We divide the evidence in support of immune-escape mechanisms into animal studies, human laboratory studies, and human clinical experience. A better understanding of the molecular pathways connected to immune escape and relapse may help to improve our therapeutic armamentarium against acute myeloid leukemia relapse.

FLT3 inhibitors in acute myeloid leukemia

FLT3 mutations are one of the most common findings in acute myeloid leukemia (AML). FLT3 inhibitors have been in active clinical development. Midostaurin as the first-in-class FLT3 inhibitor has been approved for treatment of patients with FLT3-mutated AML. In this review, we summarized the preclinical and clinical studies on new FLT3 inhibitors, including sorafenib, lestaurtinib, sunitinib, tandutinib, quizartinib, midostaurin, gilteritinib, crenolanib, cabozantinib, Sel24-B489, G-749, AMG 925, TTT-3002, and FF-10101. New generation FLT3 inhibitors and combination therapies may overcome resistance to first-generation agents.