Developmental approaches in immunological control of acute myelogenous leukaemia

After many years of hope and disillusionment, the possibility of utilizing immune-mediated approaches to control neoplastic clones has become a reality in various haematological malignancies. This is largely a consequence of the continuous advances in knowledge and the progressive development of more refined technologies that have led to a better understanding of the biology of the malignant cells and of the host immune system, to a more precise definition of disease entities and to the design of innovative therapeutic programmes. In this chapter, we will review different immunological strategies that have reached clinical practice in patients with acute myelogenous leukaemia (AML), the focus of this volume, and discuss pre-clinical developments that may in the near future translate into the design of new immunotherapeutic protocols for the management of AML. Treatment of AML with antibody directed therapy will also be discussed.     

Immune checkpoint inhibitors in acute myeloid leukemia

Understanding the immune biology of AML and designing rational approaches to target or harness the immune environment to improve outcomes is an area of intense research in AML. There are two primary immune checkpoint harnessing modalities under clinical evaluation in AML: T-cell (such as PD1 inhibitors nivolumab and pembrolizumab) and macrophage (such as the anti-CD47 antibody magrolimab) These work synergistically with hypomethylating agents. Patients who do not achieve complete or partial responses based on IWG criteria often achieve durable stable disease or hematologic improvement, which may provide meaningful benefit for patients, even in the absence of traditional response unlike cytotoxic therapies. Patients should ideally be prospectively selected for CPI based therapies based on pre-treatment biomarkers, as there are definite populations that are more likely to respond. Immune toxicities are often mistaken for infection or other adverse event; however, if identified and treated early and aggressively with steroids, immune toxicity outcomes can be improved. Therefore, in the formative stage of development ideally only centers with experience in immune therapies should perform CPI studies in AML.     

Impact of karyotype on treatment outcome in acute myeloid leukemia

Over the course of the last three decades it has become apparent that the majority of cases of acute myeloid leukemia (AML) are characterized by at least one of a variety of recurrent chromosomal abnormalities. Whilst in many instances it remains uncertain as to which abnormalities represent primary events in the pathogenesis of AML, those which provide critical second hits that are required for progression to full blown leukemia or those that are merely markers of the leukemic process, it is nevertheless clear that diagnostic karyotype is a key determinant of outcome in this disease. Indeed there is mounting evidence to support the notion that cytogenetic analysis can serve to identify biologically distinct subsets of AML that demand tailored therapeutic approaches. This underpins the trend towards more widespread adoption of routine cytogenetic and molecular analysis in the characterization of patients with a diagnosis of acute leukemia. A key challenge for the future is to use this information to achieve greater consensus in risk group assignment of AML which will provide a more reliable framework for determining the most appropriate treatment approach for individual patients with this disease.     

Potential targeting of FLT3 acute myeloid leukemia

Aberrant FLT3 receptor signaling is common in acute myeloid leukemia (AML) and has important implications for the biology and clinical management of the disease. Patients with FLT3-mutated AML frequently present with critical illness, are more likely to relapse after treatment, and have worse clinical outcomes than their FLT3 wildtype counterparts. The clinical management of FLT3-mutated AML has been transformed by the development of FLT3 inhibitors, which are now in use in the frontline and relapsed/refractory settings. However, many questions regarding the optimal approach to the treatment of these patients remain. In this paper, we will review the rationale for targeting the FLT3 receptor in AML, the impact of FLT3 mutation on patient prognosis, the current standard of care approaches to FLT3-mutated AML management, and the diverse array of FLT3 inhibitors in use and under investigation. We will also explore new opportunities and strategies for targeting the FLT3 receptor. These include targeting the receptor in patients with non-canonical FLT3 mutations or wild-type FLT3, pairing FLT3 inhibitors with other novel therapies, using minimal residual disease testing to guide the targeting of FLT3, and novel immunotherapeutic approaches.     

Expression of tumor-associated antigens in acute myeloid leukemia: Implications for specific immunotherapeutic approaches

The expression of tumor-associated antigens (TAAs) might play a critical role in the control of minimal residual disease (MRD) in acute myeloid leukemia (AML), and therefore might be associated with clinical outcome in AML. In a DNA microarray analysis of 116 AML samples, we found a significant correlation between high mRNA levels of G250/CA9 and longer overall survival (P = .022), a similar trend with high mRNA levels of PRAME (P = .103), and a hint for RHAMM/HMMR. In contrast, for other TAAs like WT1, TERT, PRTN3, BCL2, and LAMR1, we found no correlation with clinical outcome. High expression of at least 1 of the 3 TAAs, RHAMM/HMMR, PRAME, or G250/CA9, provided the strongest favorable prognostic effect (P = .005). Specific T-cell responses were detected in 8 (47%) of 17 patients with AML in complete remission for RHAMM/HMMR-R3 peptide, in 7 (70%) of 10 for PRAME-P3 peptide, and in 6 (60%) of 10 for newly characterized G250/CA9-G2 peptide, a significant increased immune response compared with patients with AML patients who had refractory disease (P < .001). Furthermore, we could demonstrate specific lysis of T2 cells presenting these epitope peptides. In conclusion, expression of the TAAs RHAMM/HMMR, PRAME, and G250/CA9 can induce strong antileukemic immune responses, possibly enabling MRD control. Thus, these TAAs represent interesting targets for polyvalent immunotherapeutic approaches in AML.     

Multi-dimensional analysis identifies an immune signature predicting response to decitabine treatment in elderly patients with AML

Decitabine is a DNA-hypomethylating agent that has been widely applied for the treatment of acute myeloid leukaemia (AML) patients who are elderly or unfit for intensive therapy. Although effective, the complete response rate to decitabine is only around 30% and the overall survival remains poor. Emerging data support that regulation of DNA methylation is critical to control immune cell development, differentiation and activation. We hypothesize that defining how decitabine influences the immune responses in AML will facilitate the development of novel immune-based leukaemia therapeutics. Here, we performed phenotypic and functional immune analysis on clinical samples from AML patients receiving decitabine treatment and demonstrated a significant impact of decitabine on the immune system. T-cell expression of inhibitory molecules was upregulated and the ability of CD8 T cells to produce cytokines was decreased upon decitabine treatment. Importantly, in an unbiased comprehensive analysis, we identified a unique immune signature containing a cluster of key immune markers that clearly separate patients who achieved complete remission after decitabine from those who failed to do so. Therefore, this immune signature has a strong predictive value for clinical response. Collectively, our study suggests that immune-based analyses may predict clinical response to decitabine and provide a therapeutic strategy to improve the treatment of AML.     

Immunopathogenic mechanisms and modulatory approaches to graft-versus-host disease prevention in acute myeloid leukaemia

Allogeneic haematopoietic stem cell transplantation (HSCT) remains the only potential cure for intermediate to high-risk acute myeloid leukaemia (AML). The therapeutic effect of HSCT is largely dependent on the powerful donor-derived immune response against recipient leukaemia cells, known as graft-versus-leukaemia effect (GvL). However, the donor-derived immune system can also cause acute or chronic damage to normal recipient organs and tissues, in a process known as graft-versus-host disease (GvHD). GvHD is a leading cause of non-relapse mortality in HSCT recipients. There are many similarities and cross talk between the immune pathways of GvL and GvHD. Studies have demonstrated that both processes require the presence of mismatched alloantigens between the donor and recipient, and activation of immune responses centered around donor T-cells, which can be further modulated by various recipient or donor factors. Dissecting GvL from GvHD to achieve more effective GvHD prevention and enhanced GvL has been the holy grail of HSCT research. In this review, we focused on the key factors that contribute to the immune responses of GvL and GvHD, the effect on GvL with different GvHD prophylactic strategies, and the potential impact of various AML relapse prevention therapy or treatments on GvHD.     

Acute myeloid leukemia in older adults

Acute myeloid leukemia (AML) is predominantly a disease of older adults, with a median age at diagnosis of over 65?years. AML in older adults differs biologically and clinically from that in younger ones, and is characterized by stronger intrinsic resistance and lower tolerance to chemotherapy. The effects of age on both patient- and disease-related factors result in a higher incidence of early death during chemotherapy, a lower rate of complete remission, and a reduced chance of long-term survival. Treatment options for older adults with AML include intensive chemotherapy, less-intensive chemotherapy, best supportive care, or enrolment in clinical trials. Given the heterogeneous nature of AML in older adults, therapeutic decisions need to be individualized after systematic assessment of disease biology and patient characteristics. Regardless of treatment, however, outcomes for older AML patients remain in general unsatisfactory. In contrast with the progress made for younger adults, the treatment of AML in older adults has not improved significantly in recent decades. Development of less toxic and more targeted agents may well provide treatment alternatives for a majority of these patients. The overall dismal outcome with currently available treatment approaches has encouraged older AML patients to participate in prospective clinical trials.     

Is it important to decipher the heterogeneity of “normal karyotype AML”?

Almost half of adult acute myelogenous leukemia (AML) is normal cytogenetically, and this subgroup shows a remarkable heterogeneity of genetic mutations at the molecular level and an intermediate response to therapy. The finding of recurrent cytogenetic abnormalities has influenced, in a primary way, the understanding and treatment of leukemias. Yet "normal karyotype AML" lacks such obvious abnormalities, but has a variety of prognostically important genetic abnormalities. Thus, the presence of a FLT3-ITD (internal tandem duplication), MLL-PTD (partial tandem duplication), or the increased expression of ERG or EVI1 mRNAs confer a poor prognosis, and an increased risk of relapse. In contrast, the presence of cytoplasmic nucleophosmin or C/EBPA mutations is associated with lower relapse rates and improved survival. Although resistance to treatment is associated with specific mutations, the degree to which the leukemia resembles a stem cell in its functional properties may provide greater protection from the effects of treatment. Although usually all of the circulating leukemia cells are cleared following treatment, a small residual population of leukemic cells in the bone marrow persists, making this disease hard to eradicate. Increased understanding of the biological consequences of at least some of these mutations in "normal karyotype AML" is leading to more targeted approaches to develop more effective treatments for this disease.     

Acute myeloid leukemia in the elderly: conventional and novel treatment approaches

Acute Myeloid Leukemia (AML) is a disorder affecting primarily elderly individuals and poses significant treatment challenges. Much has been learned about the underlying immunologic, cytogenetic and molecular features of AML in recent years, and many features have been identified that portend a poor prognosis for elderly patients with newly diagnosed AML. Despite this, treatment outcomes for elderly patients remain poor for both newly diagnosed and relapsed disease. While conventional treatment approaches may be appropriate for some elderly patients, the vast majority do not tolerate intensive chemotherapy well, thus alternative strategies have been investigated. Here we review both conventional and novel treatment approaches for elderly patients with AML, including agents in early clinical trials. Treatment options have been divided into several discussions, including conventional treatments, agents complementary to conventional treatments, alternatives to conventional induction therapies, post-induction treatment, and relapsed disease. Current and developing research focuses upon identifying subgroups of patients that benefit more from specific chemotherapeutic agents. Treating elderly patients with AML requires an organized, multidisciplinary approach, taking into account individual patient characteristics, preferences, and comorbidities when formulating treatment plans.     

Molecular and chromosomal alterations: new therapies for relapsed acute myeloid leukemia

Acute myeloid leukemia (AML) remains the most common form of leukemia and the most common cause of leukemia death. Although conventional chemotherapy can cure between 25 and 45% of AML patients, the majority of patients die after relapse or of complications associated with treatment. Thus, more specific and less toxic treatments for AML patients are needed, especially for elderly patients. An indispensable prerequisite to investigate tailored approaches for AML is the recent progress in the understanding the molecular features that distinguish leukemia progenitors from normal hematopoietic counterparts and the identification of a variety of dysregulated molecular pathways. This in turn would allow the identification of tumor-specific characteristics that provide a rational basis for the development of more tailored, and hence potentially more effective and less toxic, therapeutic approaches. In this review, we describe some of the signaling pathways that are aberrantly regulated in AML, with a specific focus on their pathogenetic and therapeutic significance, and we examine some recent therapies directed against these targets, used in clinical trial for relapsed patients or unfit for conventional chemotherapy.     

Childhood acute myeloid leukaemia

Although acute myeloid leukaemia (AML) has long been recognized for its morphological and cytogenetic heterogeneity, recent high-resolution genomic profiling has demonstrated a complexity even greater than previously imagined. This complexity can be seen in the number and diversity of genetic alterations, epigenetic modifications, and characteristics of the leukaemic stem cells. The broad range of abnormalities across different AML subtypes suggests that improvements in clinical outcome will require the development of targeted therapies for each subtype of disease and the design of novel clinical trials to test these strategies. It is highly unlikely that further gains in long-term survival rates will be possible by mere intensification of conventional chemotherapy. In this review, we summarize recent studies that provide new insight into the genetics and biology of AML, discuss risk stratification and therapy for this disease, and profile some of the therapeutic agents currently under investigation.     

Autologous hematopoietic cell transplantation for AML in first remission – An abandoned practice or promising approach?

Patients with acute myeloid leukemia (AML) who achieve complete remission after induction therapy require post remission therapy (PRT) in order to remain disease free. The role of autologous hematopoietic cell transplantation (autoHCT) in the PRT setting is controversial and is largely based on older trials that were hampered by low transplant realization rates and relatively high nonrelapse mortality rates as compared to chemotherapy-based approaches. In this review we summarize current data regarding autoHCT in the PRT setting.Most current studies demonstrate that autoHCT is better than chemotherapy-based PRT in terms of leukemia free survival. In most recent studies, autoHCT results in comparable outcomes to allogeneic hematopoietic cell transplantation (alloHCT) from matched sibling or matched unrelated donors in patients with intermediate-risk AML in first complete remission and can be considered as a valid alternative. Adverse-risk AML patients do not benefit from autoHCT and should be referred to alloHCT.Minimal residual disease (MRD) is a powerful prognostic factor and may identify patients that could benefit from an autoHCT PRT. As with other PRT approaches, MRD negativity at the time of autoHCT is associated with the best outcomes. Prospective risk-adapted approaches that assign patients to autoHCT based on disease-risk and MRD status are ongoing and may pave the way for revisiting autoHCT in specific subpopulations of AML patients in first remission.     

How to address second and therapy-related acute myelogenous leukaemia

Secondary acute myelogenous leukaemia (AML), as compared to de novo AML, occurs in the more elderly population, is independently more resistant to cytotoxic chemotherapy, has a higher relapse rate, and a worse prognosis. Secondary AML (sAML) is a heterogeneous disease, both biologically and clinically, even within the World Health Organization subgroups of sAML. Outcomes are the poorest in subgroups with sAML arising from an antecedent haematologic disorder which has been previously treated (ts-AML), and sAML in patients <55 years of age. This review describes the suboptimal outcomes of contemporary therapy, to support the notion of an unmet need for innovative treatment strategies in sAML. Despite the recent approval of CPX-351, long-term outcomes for this high-risk disease remain dismal. Resistance mechanisms to intensive chemotherapy contribute to relapse. Targeted immune therapy may avoid multidrug resistance mechanisms, but are unlikely to provide long-term remission due to a complex and rapidly evolving clonal disease profile. Advances for sAML will likely be accomplished by CAR T cell therapy or bispecific antibodies providing a bridge to allogeneic stem cell transplantation. Therefore, focus should be placed on novel strategies that can augment the untargeted effector function of allogeneic grafts.     

Controversies in the recent (2016) World Health Organization classification of acute myeloid leukemia

The current World Health Organization (WHO) Classification of acute myeloid leukemia (AML), developed in 2016 and published in 2017, codifies the defining features of AML and recognizes several subtypes based on clinical, morphologic, and genetic features. This classification is widely used for the purposes of assigning patients to specific therapeutic approaches and entry into clinical trials. Although the WHO Classification ultimately has its origins in the original 1976 French-American-British Classification, it has been periodically updated by the incorporation of a large body of evidence and input from both diagnosticians and clinicians who study and treat AML. Nevertheless, the recent accumulation of genetic data on the molecular underpinnings of myeloid neoplasms as well as numerous recently approved novel therapies have highlighted areas of controversy in how we currently define and classify AML; the 2016 WHO Classification will continually be revised and updated in future versions based on these advances. The purpose of this review is to explore areas of potential refinement in the current WHO Classification of AML, both in terms of its criteria defining the disease as well as the specific disease subtypes.     

Maintenance therapy in acute myeloid leukemia: What is the future?

Relapse remains the primary obstacle to long-term survival in patients with acute myeloid leukemia (AML) who achieve a remission following standard induction and consolidation therapy. Although allogeneic hematopoietic stem cell transplantation decreases the risk of relapse for many patients, relapse is common even among these patients. A number of approaches to maintenance therapy for AML have been studied with the goal of finding an agent with a tolerable side effect profile that may be given to patients in remission, typically for a prolonged period of time, in order to decrease the risk of relapse. Numerous trials that evaluated cytotoxic agents as maintenance therapy did not find any improvement in survival, but more recent studies of alternative approaches to maintenance including immunomodulation, epigenetic reprogramming, and targeted agents have been much more promising. In this article, we review the current evidence for various maintenance strategies for AML including immunotherapy, hypomethylating agents, and targeted therapies, particularly FLT3 inhibitors. We also discuss promising emerging approaches to maintenance for AML, including the incorporation of measurable residual disease assessment.     

Irradiated B7-1 transduced primary acute myelogenous leukemia (AML) cells can be used as therapeutic vaccines in murine AML

Recent studies have shown that tumor cells genetically modified by transduction of B7-1, a natural ligand for the T-cell costimulatory molecules CD28 and CTLA-4, are rejected in syngeneic hosts. In these reports, transformed cell lines and drug-selected cells have been used for vaccinations. To determine the effectiveness of B7-1-transduced primary acute myelogenous leukemia (AML) cells on the induction of antitumor immunity, we have studied a murine AML model in which primary AML cells were retrovirally transduced with the murine B7-1 cDNA. A defective retroviral producer clone expressing B7-1 and secreting a high titer of virus was used for infection of AML cells. Unselected transduced AML cells, expressing a high level of B7-1, were used for in vivo vaccinations. Our results show that one intravenous (IV) injection of irradiated B7-1-positive (B7-1+) AML cells can provide long-lasting (5 to 6 months) systemic immunity against subsequent challenge with wild-type AML cells. Furthermore, one exposure to irradiated B7-1+ AML cells results in rejection of leukemia by leukemic mice when the vaccination occurs in the early stages of the disease. The antileukemia immunity is CD8+ T-cell-dependent and B7/CD28-mediated, since in vivo treatment of mice with anti-CD8 monoclonal antibody or CTLA-4 Ig leads to abrogation of the specific antileukemia immune response. These results emphasize that B7-1 vaccines may have therapeutic usefulness for patients with AML.     

Mechanisms for resistance in AML insights into molecular pathways mediating resistance to venetoclax

Resistance to therapy continues to pose hurdles in the therapeutic management of acute myeloid leukemia (AML). Although the approval and development of therapies such as venetoclax, was expected to overcome this issue, resistance remains a common occurrence in AML treatment. This review has summarized evidence that will provide insights into acquired mutations that influence response to venetoclax therapy and the utility of novel combination approaches in improving outcomes.