Long-term follow-up of hematologic relapse-free survival in a phase 2 study of blinatumomab in patients with MRD in B-lineage ALL. Blood. 2012;120:5185-5187. [PMID: 23024237 DOI: 10.1182/blood-2012-07-441030]

CD4+CD25highCD127low/-FoxP3 + Regulatory T-Cell Population in Acute Leukemias: A Review of the Literature

Regulatory T-cells (Tregs) are a very important subtype of lymphocytes when it comes to self-control in the human immunological system. Tregs are decisive not only in the protection against destruction of own tissues by autoimmune immunocompetent cells but also in the immunological answer to developing cancers. On the other hand, Tregs could be responsible for the progression of acute and chronic leukemias. In our study, we review publications available in the PUMED database concerning acute leukemia, with a particular emphasis on child's leukemias. The percentage of regulatory T-lymphocytes in peripheral blood and bone marrow was elevated compared to those in healthy individuals and correlated with progressive disease. Regulatory T-cells taken from children diagnosed with leukemia showed a higher suppressive capability, which was confirmed by detecting elevated levels of secreted IL-10 and TGF-beta. The possibility of pharmacological intervention in the self-control of the immunological system is now under extensive investigation in many human cancers. Presumably, Treg cells could be a vital part of targeted therapies. Routine Treg determination could be used to assess the severity of disease and prognosis in children with acute lymphoblastic leukemia. This proposition results from the fact that in some studies, higher percentage of Treg cells in peripheral blood was demonstrated. However, observations confirming these facts are scarce; thus, extrapolating them to the population of children with hematological malignancies needs to be verified in additional studies.

Clinical trials of dual-target CAR T cells, donor-derived CAR T cells, and universal CAR T cells for acute lymphoid leukemia

The current treatment for pediatric acute lymphoblastic leukemia (ALL) is highly successful with high cure rate. However, the treatment of adult ALL remains a challenge, particularly for refractory and/or relapsed (R/R) ALL. The advent of new targeted agents, blinatumomab, inotuzumab ozogamycin, and chimeric antigen receptor (CAR) T cells, are changing the treatment paradigm for ALL. Tisagenlecleucel (kymriah, Novartis) is an autologous CD19-targeted CAR T cell product approved for treatment of R/R B cell ALL and lymphoma. In an attempt to reduce the relapse rate and treat those relapsed patients with antigen loss, donor-derived CAR T cells and CD19/CD22 dual-target CAR T cells are in clinical trials. Gene-edited “off-the-shelf” universal CAR T cells are also undergoing active clinical development. This review summarized new clinical trials and latest updates at the 2018 ASH Annual Meeting on CAR T therapy for ALL with a focus on dual-target CAR T and universal CAR T cell trials.

Clinical trial update on bispecific antibodies, antibody-drug conjugates, and antibody-containing regimens for acute lymphoblastic leukemia

The relapse rate remains high after chemotherapy for adult patients with acute lymphoblastic leukemia (ALL). With better molecular diagnosis and classification as well as better assessment for minimal residual disease, major progress in the treatment for refractory and/or relapsed ALL is being made. In addition to the tyrosine kinase inhibitors (TKIs) for Philadelphia chromosome-positive ALL, immunotherapeutic agents, blinatumomab, inotuzumab ozogamicin (INO), and chimeric antigen receptor (CAR) T cells, are changing the treatment paradigm for ALL. Blinatumomab and INO are being incorporated into induction chemotherapy regimens and combined with TKIs for ALL therapy. A novel low-intensity regimen, miniHCVD-INO-blinatumomab, appears to be less toxic and more effective than conventional intensive chemotherapy regimens. This review summarized new therapeutic researches of ALL and updated latest progress in clinical trials on bispecific antibodies, antibody-drug conjugates, and new regimens incorporating these novel antibodies.

B-cell depleting immunotherapies: therapeutic opportunities and toxicities

INTRODUCTION

The last few years have witnessed what can certainly be defined as a 'period of renaissance' for immunotherapy in the field of hematological malignancies. In particular, antibody-mediated and cell-mediated immunotherapy have significantly changed the treatment approach of patients with B-cell lymphoproliferative disorders. These therapies, initially employed in patients with refractory/relapsed disease, are now integrated in the treatment of newly diagnosed patients. Together with the therapeutic success, we have also learnt that these innovative therapies can induce relevant, sometimes life-threatening or even fatal, side effects. Areas covered: In this review article, we analyzed the applicative therapeutic scenario and the peculiar toxicities associated with approaches of immunotherapy, paying particular attention to the new emerging side effects, substantially unknown before the introduction of these therapies. Expert commentary: Both monoclonal antibodies and cell therapy with lymphocytes genetically modified to be redirected against leukemia targets through the transduction with chimeric antigen receptors (CARs) have obtained unprecedented success in rescuing patients with resistant B-cell malignancies. Complications, such as neurotoxicity, cytokine release syndrome or persistent B-cell lymphopenia, must always be taken into consideration and diagnosed in a timely manner in patients with B-cell neoplasms to guarantee optimal management, thus avoiding they blunting the efficacy of immunotherapy.

Bispecific Antibodies in Hematologic Malignancies: When, to Whom, and How Should Be Best Used?

PURPOSE OF REVIEW

The purpose of this review is to discuss the current recommendations for the use of bispecific antibodies (bsAb) in hematologic malignancies and explore the future in this field.

RECENT FINDINGS

Bispecific antibodies are molecules able to target two different antigen-binding sites: one towards a tumor antigen and another to activate a cytotoxic cell. Phase II/III trials on blinatumomab for acute lymphoblastic leukemia (ALL) have demonstrated its efficacy for treating minimal residual disease (MRD+) and relapsed refractory (r/r) Philadelphia positive (Ph+) and negative (Ph-) ALL in adults and children. Currently, the only bispecific antibody (bsAb) approved for its use in hematologic malignancies is blinatumomab. However, multiple trials are under development not only to explore blinatumomab's clinical activity in other neoplasia, such as lymphoma or multiple myeloma, but also to develop new molecules against different antigens.

Novel Targets of Immunosuppression in Transplantation

It is increasingly recognized that calcineurin inhibitors (CNI) such as cyclosporine and tacrolimus are not ideal immunosuppressive agents. Side effects, including increased rates of infection, hypertension, and malignancy, can be severe. Thus, in the past decade, there has been much focus on the development of novel therapeutic agents and strategies designed to replace or minimize CNI exposure in transplant patients. This article reviews potential novel targets in T cells, alloantibody-producing B cells, plasma cells, and complement in transplantation.

The journey to CAR T cell therapy: the pediatric and young adult experience with relapsed or refractory B-ALL

Outcomes of pediatric and young adult patients diagnosed with acute lymphoblastic leukemia (ALL) have improved significantly in the past few decades. Treatment advances have provided 5-year survival rates ranging from 78 to 91% depending on the age at diagnosis. However, approximately 2-3% of patients will present with refractory disease that is unresponsive to chemotherapy, and 10-15% of patients will relapse. Outcomes post-relapse show significantly reduced 5-year survival rates that continue to decrease with each subsequent relapse. Despite our increased understanding of risk factors and disease predictors, treatment strategies for patients with relapsed or refractory (r/r) disease, including variations of chemotherapy and stem cell transplant, remain ineffective for many patients. To improve outcomes of patients with r/r disease, immunotherapies targeting specific B cell antigens are being developed. Tisagenlecleucel is an autologous anti-CD19 chimeric antigen receptor (CAR) T cell therapy recently approved by the US Food and Drug Administration for patients with refractory leukemia or those with second or later relapse. In this treatment strategy, a patient's own T cells are transduced to express an anti-CD19 CAR that, when reintroduced into the patient, directs specific binding and killing of CD19+ B cells. In a phase 2, single-arm, multicenter, global study, tisagenlecleucel resulted in a remission rate of 81% in pediatric and adolescent patients with r/r B cell ALL. This review article summarizes four typical cases of pediatric and adolescent r/r B-cell ALL, focusing on the patient's journey from initial diagnosis to treatment with CAR T cell therapy.

Novel Therapies in Acute Lymphoblastic Leukemia

PURPOSE OF REVIEW

Treatment options for patients with acute lymphoblastic leukemia (ALL) beyond standard chemotherapy have grown significantly in recent years. In this review, we highlight new targeted therapies in ALL, with an emphasis on immunotherapy.

RECENT FINDINGS

Major advances include antibody-based therapies, such as naked monoclonal antibodies, antibody-drug conjugates and bispecific T cell engaging (BiTE) antibodies, as well as adoptive cellular therapies such as chimeric antigen receptor (CAR) T cells. Apart from the above immunotherapeutic approaches, other targeted therapies are being employed in Philadelphia chromosome-positive (Ph+) ALL, Philadelphia-like (Ph-like) ALL, and T cell ALL. These new treatment strategies are changing the treatment landscape of ALL and challenging the current standard of care. Clinical trials will hopefully help determine how to best incorporate these novel therapies into existing treatment algorithms.

Chemotherapy-free and reduced intensity approaches in elderly patients with B-lineage acute lymphoblastic leukemia

Management of older patients - defined by convention above the age of 60 years, but varying widely within study groups - with acute lymphoblastic leukemia (ALL) is still a challenge. The complete remission (CR) rate in these patients is lower than in other age groups and the percentage of deaths in induction or in CR remains high, ranging from 7 to 40%. Overall survival rates do not exceed 30%, depending on the age group included in the different trials group and on the follow-up duration. These unsatisfactory results are sustained by the fact that pre-existing comorbidities often hamper treatment delivery and if treatment intensification improves the CR rates it also increases toxicity and the percentage of deaths. Overall, the median life expectancy is rising world-wide, being in the western world around/over 80 years (and increasing); in addition, the proportion of elderly individuals is growing progressively. This means that the management of these frail patients represents a true clinical unmet need. While in Ph+ ALL the introduction of tyrosine kinase inhibitors (TKI) has markedly impacted on the outcome of patients of all ages, in Ph- ALL prognosis in the elderly still remains largely unsatisfactory. Novel strategies - mostly based on the use of monoclonal antibodies or of targeted strategies if druggable mutations can be identified - are largely needed. In the present review, we will discuss the past and current scenario, and provide an overview on the developing approaches for both Ph- and Ph+ elderly ALL, represented in particular by immunotherapy.

Antibody-based therapies in patients with acute lymphoblastic leukemia

The use of multiagent combination chemotherapy regimens results in cure rates of >90% for children and ∼40% for adults with acute lymphoblastic leukemia (ALL) but is associated with extensive toxicity and disappointingly low efficacy in relapsed patients. ALL blast cells express several surface antigens, including CD20, CD22, and CD19, which represent valuable targets for immunotherapy. Monoclonal antibodies, antibody-drug conjugates, and bispecific T-cell-engaging antibodies targeting these antigens offer novel mechanisms of action. Within the last several years, the anti-CD20 antibody rituximab has been added to chemotherapy for newly diagnosed patients <60 years with CD20+ pre-B ALL and significantly improved the 2-year event-free survival from 52% to 65%. In adults with relapsed or refractory CD22+ ALL, the antibody-drug conjugate inotuzumab ozogamicin resulted in a complete response rate of 81% and median overall survival of 7.7 months with reduced toxicity compared with standard chemotherapy. Similarly, the bispecific T-cell-engaging antibody blinatumomab yielded a complete response rate of 44% and a median overall survival of 7.7 months in an extensively treated ALL population. Moreover, ∼80% of ALL patients in complete remission with evidence of minimal residual disease (MRD) achieved a complete MRD response following treatment with blinatumomab. These results highlight the tremendous promise of antibody-based treatment approaches for ALL. Ongoing and future research is critical to further define the role of the various immunotherapies in the frontline treatment of ALL. Additional challenges include the optimal sequencing of the available antibodies in the relapsed setting as well as their integration with stem cell transplant and chimeric antigen receptor T-cell therapy.

Blinatumomab, a bispecific B-cell and T-cell engaging antibody, in the treatment of B-cell malignancies

Blinatumomab (Blincyto, Amgen), a bi-specific antibody, is a first-in-class, targeted immunotherapy agent for treatment of B-cell malignancies with a novel mechanism of action which involves in-vivo engagement of the patient's T cells with CD19-expressing tumour cells. Clinical trials have demonstrated its efficacy in relapsed B-cell Acute Lymphoblastic Leukaemia (B-ALL) and B-cell Non-Hodgkin's Lymphoma including in patients who are refractory to chemotherapy. This review summarises the development and design of Blinatumomab, the outcome of clinical studies demonstrating its efficacy and how to manage the administration, practically, including relevant toxicities. We compare and contrast it to other emerging agents for treatment of B-cell malignancies.

Current and future role of bispecific T-cell engagers in pediatric acute lymphoblastic leukemia

INTRODUCTION

The clinical application of immunotherapy has resulted into a significant improvement in the outcome of children with relapsed/refractory B-cell precursor acute lymphoblastic leukemia (r/r BCP-ALL). In this setting, the use of bispecific T-cell-engager antibodies (BiTEs), such as blinatumomab, which harness the cytotoxic activity of T cells against CD19-positive lymphoblasts, has emerged as a most promising and impactful strategy. Areas covered: This review discusses the main structural and functional features of BiTEs, as well as the current status of their clinical application in childhood ALL. Moreover, future prospects to increase the efficacy of BiTEs are addressed. Expert commentary: The promising results obtained in patients with advanced BCP-ALL pave the way for further improvement in the context of less resistant/advanced disease. Future research is rapidly progressing on several aspects, including the use of blinatumomab in first-line protocols, identification of factors predicting response, use of combinatorial approaches and bioengineering of new molecules with dual specificity or increased potency, stability and half-life. The results of these studies, expected to be available in the next future, will provide further advancement in the development of effective, impactful, targeted immunotherapy for treatment of childhood BCP-ALL, with the concrete potential to revolutionize the clinical practice.

CD3-Bispecific Antibody Therapy Turns Solid Tumors into Inflammatory Sites but Does Not Install Protective Memory

Immunotherapy of cancer with CD3-targeting bispecific antibodies (CD3 bsAb) is a fast developing field, and multiple tumor-associated antigens (TAA) are evaluated for hematologic and solid malignancies. The efficacy of these CD3 bsAb is usually examined in xenograft mouse tumor models with human T cells or in genetically engineered mouse models, where human TAA are introduced. These models often fail to fully recapitulate the natural tumor environment, especially for solid cancers, because of interspecies differences. Here, we investigated the systemic and intratumoral effects of a mouse CD3 bsAb in a fully immune-competent mouse melanoma model. Systemic administration of 0.5 mg/kg antibody induced a brief overall T-cell activation that was selectively sustained in the tumor microenvironment for several days. A fast subsequent influx of inflammatory macrophages into the tumor microenvironment was observed, followed by an increase in the number of CD4⁺ and CD8⁺ T cells. Although the capacity to directly kill melanoma cells in vitro was very modest, optimal tumor elimination was observed in vivo, even in the absence of CD8⁺ T cells, implying a redundancy in T-cell subsets for therapeutic efficacy. Finally, we took advantage of the full immune competence of our mouse model and tested immune memory induction. Despite a strong initial immunity against melanoma, treatment with the CD3 bsAb did not install protective memory responses. The observed mechanisms of action revealed in this immune-competent mouse model might form a rational basis for combinatorial approaches.

Efficacy and safety of blinatumomab treatment in adult Korean patients with relapsed/refractory acute lymphoblastic leukemia on behalf of the Korean Society of Hematology ALL Working Party

Blinatumomab, a bispecific T cell-engaging antibody, has demonstrated efficacy for relapsed or refractory acute lymphoblastic leukemia (ALL). In this study, we evaluated the efficacy and toxicity of blinatumomab in adult Korean patients with relapsed or refractory Philadelphia-negative B cell precursor ALL. A total of 50 patients received blinatumomab treatment between June 2016 and August 2017 in Korea. The median number of prior therapy was one (range, 1-4). Among the 49 evaluable patients, 22 (44.9%) achieved complete response (CR) or CR with incomplete blood count recovery, and 16 of whom subsequently underwent allogenic stem cell transplantation. Although no statistically significant differences were observed, patients with extramedullary disease and poor performance status had lower responses to blinatumomab treatment. In addition, the use of high-dose dexamethasone prior to blinatumomab treatment did not affect the response to blinatumomab. The median event-free survival and overall survival of the responders were 7.5 and 8.1 months, respectively. For non-hematologic toxicities, the most common toxicity was infection. The incidences of severe cytokine release syndrome and neurologic toxicity each was 4%. In conclusion, blinatumomab was an effective and tolerable therapy in adult Korean patients with relapsed or refractory Philadelphia-negative B cell precursor ALL.

Should immunologic strategies be incorporated into frontline ALL therapy?

Survival rates in adult patients with acute lymphoblastic leukemia (ALL) have markedly improved during the past decade. The one-size-fits-all-ages approach has been replaced with adaptation of pediatric-inspired treatment protocols for younger adults. Yet different treatment strategies for older patients are needed due to chemotherapy-related toxicities. A new era of immunotherapy has arrived, offering opportunities for targeted treatments for ALL subtypes. While CD20 targeting with rituximab has been demonstrated to improve survival when combined with chemotherapy, it has little activity as a single agent in ALL. In contrast, antibody targeting of CD19 and CD22 with blinatumomab and inotuzumab ozogamicin, respectively, has had remarkable single-agent activity in the relapsed setting. Studies are now underway to test these agents in combination with chemotherapy in the frontline setting. The goal of these studies is to improve event-free survival and overall survival by using these approaches in the frontline to eradicate minimal residual disease and, particularly in older adults with ALL, to reduce treatment-related toxicity by limiting the exposure to traditional multi-agent chemotherapy with its attendant toxicities. This review focuses on new immunotherapeutic treatment options and strategies for frontline treatment, including a brief discussion of the use of true immunotherapy, chimeric antigen receptor T-cells, for relapsed B-cell ALL, the potential for targeting CD38 in T-cell ALL, and how these approaches are facilitating the next steps to improve survival for adult patients with ALL.

New Approaches to the Management of Adult Acute Lymphoblastic Leukemia

Traditional treatment regimens for adult acute lymphoblastic leukemia, including allogeneic hematopoietic cell transplantation, result in an overall survival of approximately 40%, a figure hardly comparable with the extraordinary 80% to 90% cure rate currently reported in children. When translated to the adult setting, modern pediatric-type regimens improve the survival to approximately 60% in young adults. The addition of tyrosine kinase inhibitors for patients with Philadelphia chromosome-positive disease and the measurement of minimal residual disease to guide risk stratification and postremission approaches has led to additional improvements in outcomes. Relapsed disease and treatment toxicity-sparing no patient but representing a major concern especially in the elderly-are the most critical current issues awaiting further therapeutic advancement. Recently, there has been considerable progress in understanding the disease biology, specifically the Philadelphia-like signature, as well as other high-risk subgroups. In addition, there are several new agents that will undoubtedly contribute to additional improvement in the current outcomes. The most promising agents are monoclonal antibodies, immunomodulators, and chimeric antigen receptor T cells, and, to a lesser extent, several new drugs targeting key molecular pathways involved in leukemic cell growth and proliferation. This review examines the evidence supporting the increasing role of the new therapeutic tools and treatment options in different disease subgroups, including frontline and relapsed or refractory disease. It is now possible to define the best individual approach on the basis of the emerging concepts of precision medicine.

Tumor Antigen Escape from CAR T-cell Therapy

Emerging data from chimeric antigen receptor (CAR) T-cell trials in B-cell malignancies demonstrate that a common mechanism of resistance to this novel class of therapeutics is the emergence of tumors with loss or downregulation of the target antigen. Antigen loss or antigen-low escape is likely to emerge as an even greater barrier to success in solid tumors, which manifest greater heterogeneity in target antigen expression. Potential approaches to overcome this challenge include engineering CAR T cells to achieve multispecificity and to respond to lower levels of target antigen and more efficient induction of natural antitumor immune responses as a result of CAR-induced inflammation. In this article, we review the evidence to date for antigen escape and downregulation and discuss approaches currently under study to overcome these obstacles.Significance: Antigen escape and downregulation have emerged as major issues impacting the durability of CAR T-cell therapy. Here, we explore their incidence and ways to overcome these obstacles in order to improve clinical outcomes. Cancer Discov; 8(10); 1219-26. ©2018 AACR.

Bispecific antibody based therapeutics: Strengths and challenges

Monoclonal antibody-based targeted therapy has greatly improved treatment options for patients. However, long-term efficacy of such antibodies is limited by resistance mechanisms. New insights into the mechanisms by which tumors evade immune control have driven innovative therapeutic strategies to eliminate cancer by re-directing immune cells to tumors. Advances in protein engineering technology have generated multiple bispecific antibody (BsAb) formats capable of targeting multiple antigens as a single agent. Approval of two BsAb and three check point blocking mAbs represent a paradigm shift in the use of antibody constructs. Since BsAbs can directly target immune cells to tumors, drug resistance and severe adverse effects are much reduced. The wave of next generation "bispecific or multispecific antibodies" has advanced multiple candidates into ongoing clinical trials. In this review, we focus on preclinical and clinical studies in hematological malignancies as well as discuss reasons for the limited success of BsAbs against solid tumors.

Immunotherapy for pancreatic cancer: A long and hopeful journey

Multiple therapeutic strategies have been developed to treat pancreatic cancer. However, the outcomes of these approaches are disappointing. Due to deeper understandings of the pivotal roles of the immune system in pancreatic cancer tumorigenesis and progression, novel therapeutic strategies based on immune cells and the tumor microenvironment are being investigated. Some of these approaches, such as checkpoint inhibitors, chimeric antigen receptor T-cell therapy, and BiTE antibodies, have achieved exciting outcomes in preclinical and clinical trials. The current review describes the roles of immune cells and the immunosuppressive microenvironment in the development of pancreatic cancer, as well as the preclinical and clinical outcomes and benefits of recent immunotherapeutic approaches, which may help us further disclose the mechanisms of pancreatic cancer progression and the dialectical views of feasibility and effectiveness of immunotherapy in treatment of pancreatic cancer.

Antiviral Activity of HIV gp120-Targeting Bispecific T Cell Engager Antibody Constructs

Today's gold standard in HIV therapy is combined antiretroviral therapy (cART). It requires strict adherence by patients and lifelong medication, which can lower the viral load below detection limits and prevent HIV-associated immunodeficiency but cannot cure patients. The bispecific T cell-engaging (BiTE) antibody technology has demonstrated long-term relapse-free outcomes in patients with relapsed and refractory acute lymphocytic leukemia. Here, we generated BiTE antibody constructs that target the HIV-1 envelope protein gp120 (HIV gp120) using either the scFv B12 or VRC01, the first two extracellular domains (1 + 2) of human CD4 alone or joined to the single chain variable fragment (scFv) of the antibody 17b fused to an anti-human CD3ε scFv. These engineered human BiTE antibody constructs showed engagement of T cells for redirected lysis of HIV gp120-transfected CHO cells. Furthermore, they substantially inhibited HIV-1 replication in peripheral blood mononuclear cells (PBMCs) as well as in macrophages cocultured with autologous CD8⁺ T cells, the most potent being the human CD4(1 + 2) BiTE [termed CD(1 + 2) h BiTE] antibody construct and the CD4(1 + 2)L17b BiTE antibody construct. The CD4(1 + 2) h BiTE antibody construct promoted HIV infection of human CD4^-/CD8⁺ T cells. In contrast, the neutralizing B12 and the VRC01 BiTE antibody constructs, as well as the CD4(1 + 2)L17b BiTE antibody construct, did not. Thus, BiTE antibody constructs targeting HIV gp120 are very promising for constraining HIV and warrant further development as novel antiviral therapy with curative potential.IMPORTANCE HIV is a chronic infection well controlled with the current cART. However, we lack a cure for HIV, and the HIV pandemic goes on. Here, we showed in vitro and ex vivo that a BiTE antibody construct targeting HIV gp120 resulted in substantially reduced HIV replication. In addition, these BiTE antibody constructs display efficient killing of gp120-expressing cells and inhibited replication in ex vivo HIV-infected PBMCs or macrophages. We believe that BiTE antibody constructs recognizing HIV gp120 could be a very valuable strategy for a cure of HIV in combination with cART and compounds which reverse latency.

Evaluating measurable residual disease in acute myeloid leukemia

Mounting evidence indicates that the presence of measurable ("minimal") residual disease (MRD), defined as posttherapy persistence of leukemic cells at levels below morphologic detection, is a strong, independent prognostic marker of increased risk of relapse and shorter survival in patients with acute myeloid leukemia (AML) and can be used to refine risk-stratification and treatment response assessment. Because of the association between MRD and relapse risk, it has been postulated that testing for MRD posttreatment may help guide postremission treatment strategies by identifying high-risk patients who might benefit from preemptive treatment. This strategy, which remains to be formally tested, may be particularly attractive with availability of agents that could be used to specifically eradicate MRD. This review examines current methods of MRD detection, challenges to adopting MRD testing in routine clinical practice, and recent recommendations for MRD testing in AML issued by the European LeukemiaNet MRD Working Party. Inclusion of MRD as an end point in future randomized clinical trials will provide the data needed to move toward standardizing MRD assays and may provide a more accurate assessment of therapeutic efficacy than current morphologic measures.

Perspectives of Fc engineered antibodies in CD19 targeting immunotherapies in pediatric B-cell precursor acute lymphoblastic leukemia

CD19 immunotherapies based on T cells opened new avenues in the treatment of pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). However, Fc engineered CD19 antibodies may also bear great potential. In light of recent preclinical and clinical data, perspectives of such antibodies designed for improved effectiveness in BCP-ALL are presented.

Bispecific antibodies in haematological malignancies

Bispecific antibodies (bsAbs) combine the binding sites of two monoclonal antibodies in one molecule. The close proximity of a tumor specific antigen and an effector cell antigen results in a targeted activation of effector cells. The mechanism is similar to the chimeric antigen receptor (CAR) T-cells, recently approved in two haematologic cancers. CAR T-cells and bsAb represent the most powerful tools for major-histocompatibility complex (MHC) independent T-cell immune response against cancer. In contrast to CAR T-cells, bsAbs are "off the shelf" drugs. As a drawback, the efficacy is dependent on a prolonged application. More than 40 years of intensive research generate a plethora of bispecific constructs with a remarkable difference in manufacturability, stability, half-life time and receptor affinity. Blinatumomab was the first approved bsAb in relapsed and refractory acute lymphoblastic leukemia. By the mature experience of blinatumomab in more than 10 clinical trials over more than one decade, we learned some lessons on how to use this new principle. The efficacy is higher in patients with less tumor burden, suggesting the use as consolidation more than for initial debulking. Main resistance mechanisms are extramedullary relapses and the expression of the inhibitory PD-L1 molecule, suggesting the value of combination with checkpoint inhibitors. CD19 loss is infrequent after blinatumomab, preserving the option for alternative CD19-direct treatments. New bsAbs in lymphoma, myeloma and acute myeloid leukemia enter phase-I trials, together with many new constructs in solid cancer.

Outcome of patients with relapsed/refractory acute lymphoblastic leukemia after blinatumomab failure: No change in the level of CD19 expression

Blinatumomab, a bi-specific T-cell engaging CD3-CD19 antibody construct, has shown significant activity in patients with relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia (ALL). Despite this improvement, most patients relapse. Here, we describe the outcome of 68 patients with R/R ALL after failure of blinatumomab therapy: 38 (56%) blinatumomab refractory; 30 (44%) relapsing after initial response. After a median follow-up of 49 months, 9 (13%) patients remained alive. The median overall survival after blinatumomab failure was 5.2 months. At the time of failure, among 61 patients evaluated for immunophenotype, 56 (92%) had CD19-positive blasts; only five (8%) had ALL recurrence with CD19-negative disease. Two patients progressed with lower CD19 expression. In summary, the outcome of patients with R/R ALL after blinatumomab failure is poor and treatment of these patients remains an unmet medical need. Our findings indicate that blinatumomab therapy would not exclude a significant number of patients from the potential benefit of subsequent CD19-directed therapies such as chimeric antigen receptor T-cell therapy.

Bruton tyrosine kinase inhibitor ONO/GS-4059: from bench to bedside

The Bruton tyrosine kinase (BTK) inhibitor, ibrutinib, has been approved for the treatment of chronic lymphocytic leukemia, mantle cell lymphoma, and Waldenstroms macroglobulinemia. Acquired resistance to ibrutinib due to BTK C481S mutation has been reported. Mutations in PLC?2 can also mediate resistance to ibrutinib. Untoward effects due to off-target effects are also disadvantages of ibrutinib. More selective and potent BTK inhibitors (ACP-196, ONO/GS-4059, BGB-3111, CC-292) are being investigated. This review summarized the preclinical research and clinical data of ONO/GS-4059.

5-Azacytidine prevents relapse and produces long-term complete remissions in leukemia xenografts treated with Moxetumomab pasudotox

Moxetumomab pasudotox (Moxe) is a chimeric protein composed of an anti-CD22 Fv fused to a portion of Pseudomonas exotoxin A and kills CD22-expressing leukemia cells. It is very active in hairy-cell leukemia, but many children with relapsed/refractory acute lymphoblastic leukemia (ALL) either respond transiently or are initially resistant. Resistance to Moxe in cultured cells is due to low expression of diphthamide genes (DPH), but only two of six ALL blast samples from resistant patients had low DPH expression. To develop a more clinically relevant model of resistance, we treated NSG mice bearing KOPN-8 or Reh cells with Moxe. More than 99.9% of the cancer cells were killed by Moxe, but relapse occurred from discrete bone marrow sites. The resistant cells would no longer grow in cell culture and showed major chromosomal changes and changes in phenotype with greatly decreased CD22. RNA deep sequencing of resistant KOPN-8 blasts revealed global changes in gene expression, indicating dedifferentiation toward less-mature B cell precursors, and showed an up-regulation of myeloid genes. When Moxe was combined with 5-azacytidine, resistance was prevented and survival increased to over 5 months in the KOPN-8 model and greatly improved in the Reh model. We conclude that Moxe resistance in mice is due to a new mechanism that could not be observed using cultured cells and is prevented by treatment with 5-azacytidine.

Tailoring CD19xCD3-DART exposure enhances T-cells to eradication of B-cell neoplasms

Many patients with B-cell malignancies can be successfully treated, although tumor eradication is rarely achieved. T-cell-directed killing of tumor cells using engineered T-cells or bispecific antibodies is a promising approach for the treatment of hematologic malignancies. We investigated the efficacy of CD19xCD3 DART bispecific antibody in a broad panel of human primary B-cell malignancies. The CD19xCD3 DART identified 2 distinct subsets of patients, in which the neoplastic lymphocytes were eliminated with rapid or slow kinetics. Delayed responses were always overcome by a prolonged or repeated DART exposure. Both CD4 and CD8 effector cytotoxic cells were generated, and DART-mediated killing of CD4⁺ cells into cytotoxic effectors required the presence of CD8⁺ cells. Serial exposures to DART led to the exponential expansion of CD4 ⁺ and CD8 ⁺ cells and to the sequential ablation of neoplastic cells in absence of a PD-L1-mediated exhaustion. Lastly, patient-derived neoplastic B-cells (B-Acute Lymphoblast Leukemia and Diffuse Large B Cell Lymphoma) could be proficiently eradicated in a xenograft mouse model by DART-armed cytokine induced killer (CIK) cells. Collectively, patient tailored DART exposures can result in the effective elimination of CD19 positive leukemia and B-cell lymphoma and the association of bispecific antibodies with unmatched CIK cells represents an effective modality for the treatment of CD19 positive leukemia/lymphoma.

Blinatumomab activity in a patient with Down syndrome B-precursor acute lymphoblastic leukemia

Persistent minimal residual disease (MRD) after consolidation may indicate chemotherapy insensitivity in B-precursor acute lymphoblastic leukemia (BP-ALL). Given the strong association of MRD and outcome in non-Down syndrome (non-DS) BP-ALL, it is likely that MRD levels are also of prognostic significance in DS BP-ALL. We report here the successful use of blinatumomab, a bispecific T-cell engager antibody construct, in a patient with DS BP-ALL and persistent MRD at the end of consolidation. Blinatumomab has been shown to have excellent results in patients with relapsed/refractory BP-ALL. This patient had no significant toxicity and achieved MRD negativity after only one cycle of blinatumomab.

Blinatumomab for minimal residual disease in adults with B-cell precursor acute lymphoblastic leukemia

Approximately 30% to 50% of adults with acute lymphoblastic leukemia (ALL) in hematologic complete remission after multiagent therapy exhibit minimal residual disease (MRD) by reverse transcriptase-polymerase chain reaction or flow cytometry. MRD is the strongest predictor of relapse in ALL. In this open-label, single-arm study, adults with B-cell precursor ALL in hematologic complete remission with MRD (≥10^-3) received blinatumomab 15 µg/m² per day by continuous IV infusion for up to 4 cycles. Patients could undergo allogeneic hematopoietic stem-cell transplantation any time after cycle 1. The primary end point was complete MRD response status after 1 cycle of blinatumomab. One hundred sixteen patients received blinatumomab. Eighty-eight (78%) of 113 evaluable patients achieved a complete MRD response. In the subgroup of 110 patients with Ph-negative ALL in hematologic remission, the Kaplan-Meier estimate of relapse-free survival (RFS) at 18 months was 54%. Median overall survival (OS) was 36.5 months. In landmark analyses, complete MRD responders had longer RFS (23.6 vs 5.7 months; P = .002) and OS (38.9 vs 12.5 months; P = .002) compared with MRD nonresponders. Adverse events were consistent with previous studies of blinatumomab. Twelve (10%) and 3 patients (3%) had grade 3 or 4 neurologic events, respectively. Four patients (3%) had cytokine release syndrome grade 1, n = 2; grade 3, n = 2), all during cycle 1. After treatment with blinatumomab in a population of patients with MRD-positive B-cell precursor ALL, a majority achieved a complete MRD response, which was associated with significantly longer RFS and OS compared with MRD nonresponders. This study is registered at www.clinicaltrials.gov as #NCT01207388.

Bispecific antibodies: design, therapy, perspectives

Antibodies (Abs) containing two different antigen-binding sites in one molecule are called bispecific. Bispecific Abs (BsAbs) were first described in the 1960s, the first monoclonal BsAbs were generated in the 1980s by hybridoma technology, and the first article describing the therapeutic use of BsAbs was published in 1992, but the number of papers devoted to BsAbs has increased significantly in the last 10 years. Particular interest in BsAbs is due to their therapeutic use. In the last decade, two BsAbs - catumaxomab in 2009 and blinatumomab in 2014, were approved for therapeutic use. Papers published in recent years have been devoted to various methods of BsAb generation by genetic engineering and chemical conjugation, and describe preclinical and clinical trials of these drugs in a variety of diseases. This review considers diverse BsAb-production methods, describes features of therapeutic BsAbs approved for medical use, and summarizes the prospects of practical application of promising new BsAbs.

Redirecting T cells to hematological malignancies with bispecific antibodies

There is a need to improve outcomes for patients with recurrent and/or refractory hematological malignancies. Immunotherapy holds the promise to meet this need, because it does not rely on the cytotoxic mechanism of conventional therapies. Among different forms of immunotherapy, redirecting T cells to hematological malignancies with bispecific antibodies (BsAbs) is an attractive strategy. BsAbs are an "off-the-shelf" product that is easily scalable in contrast to adoptive T-cell therapies. Among these, the bispecific T-cell engager blinatumomab has emerged as the most successful BsAb to date. It consists of 2 single-chain variable fragments specific for CD19 present on B-cell malignancies and CD3 expressed on almost all T cells. Blinatumomab has shown potent antitumor activity as a single agent, particularly for acute lymphoblastic leukemia, resulting in its US Food and Drug Administration approval. However, although successful in inducing remissions, these are normally short-lived, with median response durations of <1 year. Nevertheless, the success of blinatumomab has reinvigorated the BsAb field, which is bustling with preclinical and clinical studies for not only B-cell-derived lymphoblastic leukemia and lymphoma but also acute myeloid leukemia and multiple myeloma. Here, we will review the successes and challenges of T-cell-targeted BsAbs for the immunotherapy of hematological malignancies with special focus on conducted clinical studies and strategies to improve their efficacy.

Characteristics and Therapeutic Targeting of Minimal Residual Disease in Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. Early response to therapy, especially the measurement of minimal residual disease (MRD), remains the most reliable and strongest independent prognostic parameter. Intriguingly, little is known on the mechanisms sustaining MRD in that disease. Here, we summarize existing evidence on the influences of molecular genetics and clonal architecture of childhood ALL on disease persistence. Also, the impact of the leukemic niche on residual leukemia cells in the bone marrow and extramedullary compartments is reviewed. We further discuss existing in vivo models of minimal residual disease based on different cellular labelling strategies and engraftment of ALL cells in immunodeficient mouse strains. We finally draw some conclusions on potential strategies targeting residual ALL cells, with a focus on cellular and antibody-based immunotherapy.

Progress in adult ALL: incorporation of new agents to frontline treatment

Treatment of acute lymphoblastic leukemia (ALL) in adults remains a challenge, as the delivery of intensive chemotherapeutic regimens in this population is less feasible than it is in the pediatric population. This has led to higher rates of treatment-related toxicity as well as lower overall survival in the adult population. Over the past several years, a host of novel therapies (eg, immunotherapy and targeted therapies) with better tolerability than traditional chemotherapy are now being introduced into the relapsed/refractory population with very encouraging results. Additionally, insights into how to choose effective therapies for patients while minimizing drug toxicity through pharmacogenomics and the use of minimal residual disease (MRD) monitoring to escalate/de-escalate therapy have enhanced our ability to reduce treatment-related toxicity. This has led to the design of a number of clinical trials which incorporate both novel therapeutics as well as MRD-directed treatment pathways into the frontline setting. The use of increasingly personalized treatment strategies for specific disease subsets combined with standardized and rapid molecular diagnostic testing in the initial diagnosis and frontline treatment of ALL will hopefully lead to further improvements in survival for our adult patients.

Efficacy and safety of bispecific T-cell engager blinatumomab and the potential to improve leukemia-free survival in B-cell acute lymphoblastic leukemia

INTRODUCTION

Immunotherapy is a promising modality of treatment of neoplastic diseases, including acute lymphoblastic leukemia (ALL). The CD19/CD3-bispecific T cell-engaging (BiTE®) monoclonal antibody blinatumomab can transiently bind cytotoxic T cells to CD19⁺ target B cells of ALL inducing their serial lysis. Areas covered: This review focuses on the efficacy and safety of blinatumomab used for the treatment of relapsed/refractory (R/R) ALL and minimal residual disease (MRD)-positive B-cell precursor (BCP) ALL in adults and children, as well as the future prospects of this drug in the treatment of ALL. Expert commentary: Blinatumomab has demonstrated encouraging response rates in MRD-positive and R/R in adults with Philadelphia chromosome-positive and -negative ALL, as well as in children with R/R ALL. Blinatumomab has a favorable safety profile, although reversible CNS events and cytokine release syndrome can occur. Ongoing trials in ALL incorporate blinatumomab in the first line therapy of BCP ALL in combination with chemotherapy, targeted therapies or other immunotherapies with the aim of increasing the depth of the remission and decreasing the probability of relapse.

Lineage switch under blinatumomab treatment of relapsed common acute lymphoblastic leukemia without MLL rearrangement

Blinatumomab is a bispecific T-cell engaging αCD19 antibody used in refractory or relapsed B-cell precursor acute lymphoblastic leukemia (ALL). Recently, lineage switch to a myeloid phenotype has been described following CD19 targeting treatment in three pediatric patients with mixed lineage leukemia (MLL) rearranged ALL. We report the case of a female who received blinatumomab for a first relapse of ALL without MLL alterations. She suffered from a second relapse early after hematopoietic stem cell transplantation and was treated with blinatumomab again. During this treatment, the leukemia lost CD19 expression as well as nearly all other B-cell markers, while still harboring the initial minimal residual disease marker, and switched to a myeloid phenotype.

Phase 1 study of the anti-CD22 immunotoxin moxetumomab pasudotox for childhood acute lymphoblastic leukemia

Novel therapies are needed to overcome chemotherapy resistance for children with relapsed/refractory acute lymphoblastic leukemia (ALL). Moxetumomab pasudotox is a recombinant anti-CD22 immunotoxin. A multicenter phase 1 study was conducted to determine the maximum-tolerated cumulative dose (MTCD) and evaluate safety, activity, pharmacokinetics, and immunogenicity of moxetumomab pasudotox in children, adolescents, and young adults with ALL (N = 55). Moxetumomab pasudotox was administered as a 30-minute IV infusion at doses of 5 to 50 µg/kg every other day for 6 (cohorts A and B) or 10 (cohort C) doses in 21-day cycles. Cohorts B and C received dexamethasone prophylaxis against capillary leak syndrome (CLS). The most common treatment-related adverse events were reversible weight gain, hepatic transaminase elevation, and hypoalbuminemia. Dose-limiting CLS occurred in 2 of 4 patients receiving 30 µg/kg of moxetumomab pasudotox every other day for 6 doses. Incorporation of dexamethasone prevented further dose-limiting CLS. Six of 14 patients receiving 50 µg/kg of moxetumomab pasudotox for 10 doses developed hemolytic uremic syndrome (HUS), thrombotic microangiopathy (TMA), or HUS-like events, exceeding the MTCD. Treatment expansion at 40 µg/kg for 10 doses (n = 11) exceeded the MTCD because of 2 HUS/TMA/HUS-like events. Dose level 6B (ie, 50 µg/kg × 6 doses) was the MTCD, selected as the recommended phase 2 dose. Among 47 evaluable patients, an objective response rate of 32% was observed, including 11 (23%) composite complete responses, 5 of which were minimal residual disease negative by flow cytometry. Moxetumomab pasudotox showed a manageable safety profile and evidence of activity in relapsed or refractory childhood ALL. This trial was registered at www.clinicaltrials.gov as #NCT00659425.

The Approach to Acute Lymphoblastic Leukemia in Older Patients: Conventional Treatments and Emerging Therapies

Acute lymphoblastic leukemia (ALL) among older adult patients presents significant clinical challenges. As opposed to pediatric populations, in whom long-term outcomes are markedly superior, those for adults remain grim. Nevertheless, younger adults with ALL have experienced a steady improvement in long-term survival in the last few decades. This is significantly different for older ALL patients, for whom long-term outcomes remain poor. Conventional chemotherapies are associated with sub-optimal outcomes and increased toxicity in this population. However, several emerging therapies, including antibody-drug conjugates, bi-specific engagers, and chimeric antigen receptor (CAR) T cells, have demonstrated much promise and are either incorporated into the existing therapeutic paradigms or being actively investigated to improve outcomes.

Novel Immunotherapy Agents for Acute Lymphoblastic Leukaemia

Acute lymphoblastic leukaemia (ALL) in adults has a survival rate of 40–50% at 5 years, with a high relapse rate after first-line chemotherapy. After relapse, results with salvage therapy are currently unsatisfactory. Therefore, both the optimisation of front-line therapy to reduce relapse incidence and the search for effective salvage therapies for relapsed/refractory (r/r) ALL have been of great interest to the medical community in recent years. The well-characterised expression of well-defined cell-surface antigens in B cell ALL (B)-ALL and T cell (T)-ALL, such as CD19, CD20, CD22, and CD52, has led to the development of several immunotherapy strategies, comprising ‘nude’ monoclonal antibodies (moAbs), conjugated moAbs, bispeciphic, or highly sophisticated chimeric antigen receptor (CAR)-T cell therapy. Recently, both the bispecific moAb blinatumomab (anti-CD19 coupled with a CD3 recognition subunit) and the conjugated anti-CD22 moAb inotuzumab-ozogamicin have resulted in higher remission rates (44% versus 25%, and 80.7% versus 29.4%, respectively) and survival advantages (median overall survival [OS]: 7.7 months versus 4 months, and 7.7 months versus 6.7 months, respectively) in patients with r/r B-ALL when compared to standard salvage chemotherapy-based regimens. On the other hand, preliminary reports show feasibility and unprecedented response rates of ≤90% in highly refractory children and adults treated with CAR-modified T cells targeting the B cell specific CD19 antigen, which seem to be durable in a significant proportion of patients. Furthermore, the addition of anti-CD20 moAb rituximab to front-line standard chemotherapy in patients with CD20+ B-ALL has resulted in a clinical benefit, with prolongation of response duration and survival (3-year leukaemia-free survival and OS: 70% versus 38%; p<0.001, and 75% versus 47%; p=0.003). In conclusion, immunotherapy is currently providing additional options for high-risk ALL patients both in front-line or advanced phase. Nonetheless, the optimal positioning of these novel agents, specially in relation to allogeneic haematopoietic stem-cell transplantion, needs to be clarified. This article aims to review several of these new therapeutic immunotherapy options available for patients with adult ALL, as well as their specific toxicity profile.

Clinical applications and safety evaluation of the new CD19 specific T-cell engager antibody construct blinatumomab

INTRODUCTION

Blinatumomab is a T-cell engager antibody construct with dual specificity for CD19 and CD3, inducing serial lysis of CD19 positive B cells by redirecting cytotoxic T cells. It has been approved for the indication of Ph chromosome negative relapsed or refractory B-acute lymphoblastic leukemia (ALL), but has also been tested in ALL with minimal residual disease, relapsed Ph/BCR-ABL positive ALL, relapsed ALL in pediatric patients and relapsed or refractory non-Hodgkin's lymphoma (NHL). Adverse events have been mainly related to infection and hematological toxicities, as well as cytokine release syndrome and neurotoxicity. Areas covered: The review will discuss mechanisms of action, published literature on efficacy in ALL and NHL, specific aspects of administration, frequent adverse events and practical management. Expert opinion: Blinatumomab represents an effective new treatment for highly resistant relapsed/refractory B-precursor ALL. Practical handling bears challenges due to application as four week continous infusion and specific adverse effects which can be well handled by experienced centers. Most promising outcomes are reported for patients with resistant disease but lower tumor load such as MRD positive ALL patients. Future studies will focus on the use of blinatumomab during first-line therapy and the role of stem cell transplantation after blinatumomab treatment.

How should we treat a patient with relapsed Ph-negative B-ALL and what novel approaches are being investigated?

Despite significant improvements in outcome of newly diagnosed B-precursor ALL, the results in relapsed or refractory adult ALL are overall poor. Large retrospective studies revealed significant differences in terms of outcome, with particularly poor response rates in early or refractory relapses, whereas late relapses usually respond very well to repeated standard induction. Particularly new immunotherapy compounds like the CD19 bispecific antibody Blinatumomab and the conjugated CD22 antibody Inotuzumab yielded promising response rates compared to standard therapies in randomised trials. Long-term survival is however still poor. The optimal use of these compounds remains to be defined. Chimeric antigen receptor T-cells are another promising treatment approach and multicenter clinical trials in adult ALL are awaited. For selected patients molecular directed therapies may have a role in relapsed ALL; standard diagnostic algorithms need to be defined. One of the major challenges is to define the role of stem cell transplantation after relapse. Whereas this procedure appears to be the only chance for cure, the mortality and relapse rate are still high and optimisation is urgently needed. Future strategies include optimised use of new compounds as part of combination regimens and the earlier treatment of upcoming relapse in the situation of persistent or recurrent minimal residual disease.