How to train your T cell: genetically engineered chimeric antigen receptor T cells versus bispecific T-cell engagers to target CD19 in B acute lymphoblastic leukemia

Safety and efficacy of a novel anti-CD19 chimeric antigen receptor T cell product targeting a membrane-proximal domain of CD19 with fast on- and off-rates against non-Hodgkin lymphoma: a first-in-human study

BACKGROUND

Commercial anti-CD19 chimeric antigen receptor T-cell therapies (CART19) are efficacious against advanced B-cell non-Hodgkin lymphoma (NHL); however, most patients ultimately relapse. Several mechanisms contribute to this failure, including CD19-negative escape and CAR T dysfunction. All four commercial CART19 products utilize the FMC63 single-chain variable fragment (scFv) specific to a CD19 membrane-distal epitope and characterized by slow association (on) and dissociation (off) rates. We hypothesized that a novel anti-CD19 scFv that engages an alternative CD19 membrane-proximal epitope independent of FMC63 and that is characterized by faster on- and off-rates could mitigate CART19 failure and improve clinical efficacy.

METHODS

We developed an autologous CART19 product with 4-1BB co-stimulation using a novel humanized chicken antibody (h1218). This antibody is specific to a membrane-proximal CD19 epitope and harbors faster on/off rates compared to FMC63. We tested h1218-CART19 in vitro and in vivo using FMC63-CART19-resistant models. We conducted a first-in-human multi-center phase I clinical trial to test AT101 (clinical-grade h1218-CART19) in patients with relapsed or refractory (r/r) NHL.

RESULTS

Preclinically, h1218- but not FMC63-CART19 were able to effectively eradicate lymphomas expressing CD19 point mutations (L174V and R163L) or co-expressing FMC63-CAR19 as found in patients relapsing after FMC63-CART19. Furthermore, h1218-CART19 exhibited enhanced killing of B-cell malignancies in vitro and in vivo compared with FMC63-CART19. Mechanistically, we found that h1218-CART19 had reduced activation-induced cell death (AICD) and enhanced expansion compared to FMC63-CART19 owing to faster on- and off-rates. Based on these preclinical results, we performed a phase I dose-escalation trial, testing three dose levels (DL) of AT101 (the GMP version of h1218) using a 3 + 3 design. In 12 treated patients (7 DLBCL, 3 FL, 1 MCL, and 1 MZL), AT101 showed a promising safety profile with 8.3% grade 3 CRS (n = 1) and 8.3% grade 4 ICANS (n = 1). In the whole cohort, the overall response rate was 91.7%, with a complete response rate of 75.0%, which improved to 100% in DL-2 and -3. AT101 expansion correlates with CR and B-cell aplasia.

CONCLUSIONS

We developed a novel, safe, and potent CART19 product that recognizes a membrane-proximal domain of CD19 with fast on- and off-rates and showed significant efficacy and promising safety in patients with relapsed B-cell NHL.

TRIAL REGISTRATION

NCT05338931; Date: 2022-04-01.

Apoptosis: a Janus bifrons in T-cell immunotherapy

Immunotherapy has revolutionized the treatment of cancer. In particular, immune checkpoint blockade, bispecific antibodies, and adoptive T-cell transfer have yielded unprecedented clinical results in hematological malignancies and solid cancers. While T cell-based immunotherapies have multiple mechanisms of action, their ultimate goal is achieving apoptosis of cancer cells. Unsurprisingly, apoptosis evasion is a key feature of cancer biology. Therefore, enhancing cancer cells' sensitivity to apoptosis represents a key strategy to improve clinical outcomes in cancer immunotherapy. Indeed, cancer cells are characterized by several intrinsic mechanisms to resist apoptosis, in addition to features to promote apoptosis in T cells and evade therapy. However, apoptosis is double-faced: when it occurs in T cells, it represents a critical mechanism of failure for immunotherapies. This review will summarize the recent efforts to enhance T cell-based immunotherapies by increasing apoptosis susceptibility in cancer cells and discuss the role of apoptosis in modulating the survival of cytotoxic T lymphocytes in the tumor microenvironment and potential strategies to overcome this issue.

Design and Production An Effective Bispecific Tandem Chimeric Antigen Receptor on T Cells against CD123 and Folate Receptor ß towards B-Acute Myeloid Leukaemia Blasts

Objective

The clinical studies of acute myeloid leukaemia (AML) revealed that antigen escaping variants cause cancer recurrence even after treatment with chimeric antigen receptor (CAR)-T cells that target a single tumour antigen. Due to the heterogeneous expression of antigens on leukaemia blasts, we hypothesized that a novel bispecific CAR, directed to the folate receptor beta (FRβ)-binding single-chain variable fragment (scFv) and an IL3α-binding receptor (CD123) that has more expression in AML blasts, can decrease CAR-T cell exhaustion and increase the efficacy of CAR-T cells to prevent antigen escaping and consequent recurrence of AML.

Materials and Methods

In this experimental study, the survival, proliferation, and cytolysis of CAR-T cells remains suboptimal even with a costimulatory endodomain. Hence, we designed and constructed a tandem CAR that joins an FRβ and CD123 in the second generation retroviral vector to generate a bispecific tandem CAR (TanCAR-T cell).

Results

TanCAR FRβ-CD123 T cells showed distinct binding to FRβ or CD123 expressing cells. They could lyse the leukaemia cell lines (66.1 ± 11%) comparable to the single CAR-T cells against these determinants. TanCAR FRβ- CD123 T cells simultaneously engaged FRβ and CD123, which promoted T cell activation in targeting and lysis of the examined leukaemia cell lines. TanCAR-T cell significantly induced interferon gamma (IFNγ) and interleukin 2 (IL-2) production more than single CAR-T cells, which produced a synergistic enhancement of TanCAR FRβ-CD123 T cell function when dual antigens faced simultaneously.

Conclusion

Dual-specific TanCAR FRβ-CD123 T cells showed therapeutic potential to improve AML control by co- engaging FRβ and CD123 molecules in a robust, divalent immune system. This strategy may be a useful therapeutic approach in patients with relapsed B-cell malignancies.

Preclinical characterization and comparison between CD3/CD19 bispecific and novel CD3/CD19/CD20 trispecific antibodies against B-cell acute lymphoblastic leukemia: targeted immunotherapy for acute lymphoblastic leukemia

The CD19-targeting bispecific T-cell engager blinatumomab has shown remarkable efficacy in patients with relapsed/refractory B-cell precursor acute lymphoblastic leukemia. However, several studies showed that blinatumomab has a short plasma half-life due to its low molecular weight, and thus its clinical use is limited. Furthermore, multiple trials have shown that approximately 30% of blinatumomab-relapsed cases are characterized by CD19 negative leukemic cells. Here, we design and characterize two novel antibodies, A-319 and A-2019. Blinatumomab and A-319 are CD3/CD19 bispecific antibodies with different molecular sizes and structures, and A-2019 is a novel CD3/CD19/CD20 trispecific antibody with an additional anti-CD20 function. Our in vitro, ex vivo, and in vivo experiments demonstrated that A-319 and A-2019 are potent antitumor agents and capable of recruiting CD3 positive T cells, enhancing T-cell function, mediating B-cell depletion, and eventually inhibiting tumor growth in Raji xenograft models. The two molecules are complementary in terms of efficacy and specificity profile. The activity of A-319 demonstrated superior to that of A-2019, whereas A-2019 has an additional capability to target CD20 in cells missing CD19, suggesting its potential function against CD19 weak or negative CD20 positive leukemic cells.

Management of cytokine release syndrome and neurotoxicity in chimeric antigen receptor (CAR) T cell therapy

INTRODUCTION

Chimeric antigen receptor (CAR) T cell immunotherapy has demonstrated remarkable anti-tumor activity in B-cell malignancies and is under investigation in other hematologic malignancies and solid tumors. While highly efficacious, post-infusion T cell activity often results in massive cytokine release precipitating cytokine release syndrome (CRS), the signature toxicity of CAR T cells. This toxicity is characterized by systemic immune activation resulting in fever, hypotension, respiratory insufficiency and capillary leak. Either in conjunction with or in the absence of CRS, a subset of patients may also develop mild to severe neurotoxicity. Although the precise pathogenesis of CRS and neurotoxicity aren't fully elucidated, risk factors and mitigation strategies have been reported. Areas covered: This manuscript provides an in-depth overview of the pathogenesis, clinical characteristics, current toxicity management strategies, and future perspectives pertaining to CRS and neurotoxicity. Expert Opinion: As CAR T cell based therapies gain popularity in the management of various malignancies, the complimentary toxicities of CRS and neurotoxicity pose a clinical challenge in practice. Risk adaptive modeling incorporating disease profile, patient demographics, lymphodepletion, cell dosing, CAR T construct, and potentially cytokine gene polymorphisms may be instructive to assess individualized risk and optimal CRS/neurotoxicity management.

CD47/SIRPα blocking enhances CD19/CD3-bispecific T cell engager antibody-mediated lysis of B cell malignancies

T cell immunotherapies are promising options in leukemia, among which the CD19/CD3-bispecific T cell engager antibody blinatumomab (MT103) has shown high response rates at very low doses in patients with lymphoma. However, the high CD47 expression in human lymphoma cells has limited the curative effects of blinatumomab other antibodies. Here we report the combined use of blinatumomab with a CD47-blocking antibody. CD47 antibodies preferentially enabled phagocytosis of non-Hodgkin lymphoma cells by both human and murine macrophages. Treatment of human non-Hodgkin lymphoma cell-engrafted mice with CD47 antibody and blinatumomab separately inhibited lymphoma partially, while combination treatment led to persistent control of lymphoma. These antibodies enhanced the therapeutic efficacy through mechanisms combining both innate and adaptive immune responses by induction of phagocytosis and T cell cytotoxicity. The combination strategy in this study might be applicable to many other cancers.

Pre-clinical validation of B cell maturation antigen (BCMA) as a target for T cell immunotherapy of multiple myeloma

Multiple myeloma has a continued need for more effective and durable therapies. B cell maturation antigen (BCMA), a plasma cell surface antigen and member of the tumor necrosis factor (TNF) receptor superfamily, is an attractive target for immunotherapy of multiple myeloma due to its high prevalence on malignant plasma cells. The current work details the pre-clinical evaluation of BCMA expression and development of a chimeric antigen receptor (CAR) targeting this antigen using a fully human single chain variable fragment (scFv). We demonstrate that BCMA is prevalently, but variably expressed by all MM with expression on 25–100% of malignant plasma cells. Extensive Immunohistochemical analysis of normal tissue expression using commercially available polyclonal antibodies demonstrated expression within B-lineage cells across a number of tissues as expected. Based upon the highly restricted expression of BCMA within normal tissues, we generated a set of novel, fully human scFv binding domains to BCMA by screening a naïve B-cell derived phage display library. Using a series of in vitro and pre-clinical in vivo studies, we identified a scFv with high specificity for BCMA and robust anti-myeloma activity when used as the binding domain of a second-generation CAR bearing a CD137 costimulatory domain. This BCMA-specific CAR is currently being evaluated in a Phase 1b clinical study in relapsed and refractory MM patients (NCT02546167).

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.

Current progress in innovative engineered antibodies

As of May 1, 2017, 74 antibody-based molecules have been approved by a regulatory authority in a major market. Additionally, there are 70 and 575 antibody-based molecules in phase III and phase I/II clinical trials, respectively. These total 719 antibody-based clinical stage molecules include 493 naked IgGs, 87 antibody-drug conjugates, 61 bispecific antibodies, 37 total Fc fusion proteins, 17 radioimmunoglobulins, 13 antibody fragments, and 11 immunocytokines. New uses for these antibodies are being discovered each year. For oncology, many of the exciting new approaches involve antibody modulation of T-cells. There are over 80 antibodies in clinical trials targeting T cell checkpoints, 26 T-cell-redirected bispecific antibodies, and 145 chimeric antigen receptor (CAR) cell-based candidates (all currently in phase I or II clinical trials), totaling more than 250 T cell interacting clinical stage antibody-based candidates. Finally, significant progress has been made recently on routes of delivery, including delivery of proteins across the blood-brain barrier, oral delivery to the gut, delivery to the cellular cytosol, and gene- and viral-based delivery of antibodies. Thus, there are currently at least 864 antibody-based clinical stage molecules or cells, with incredible diversity in how they are constructed and what activities they impart. These are followed by a next wave of novel molecules, approaches, and new methods and routes of delivery, demonstrating that the field of antibody-based biologics is very innovative and diverse in its approaches to fulfill their promise to treat unmet medical needs.

Chimeric Antigen Receptor T cells for B Cell Neoplasms: Choose the Right CAR for You

Genetic redirection of T lymphocytes allows us to unleash these potent cellular immune effectors against cancer. Chimeric antigen receptor (CAR) T cells are the best-in-class example that genetic engineering of T cells can lead to deep and durable responses, as has been shown in several clinical trials for CD19+ B cell malignancies. As a consequence, in the last few years, several academic institutions and commercial partners have started developing anti-CD19 CAR T cell products. Although most of these T cell products are highly effective in vivo, basic differences among them can generate different performance characteristics and thereby impact their long-term clinical outcome. Several strategies are being implemented in order to solve the current open issues of CART19 therapy: (i) increasing efficacy against indolent B cell leukemias and lymphomas, (ii) avoiding or preventing antigen-loss relapses, (iii) reducing and managing toxicity, and (iv) bringing this CART therapy to routine clinical practice. The field of CART therapies is thriving, and exciting new avenues are opening for both scientists and patients.

Targeting the 5T4 oncofetal glycoprotein with an antibody drug conjugate (A1mcMMAF) improves survival in patient-derived xenograft models of acute lymphoblastic leukemia

Outcome in childhood acute lymphoblastic leukemia is prognosticated from levels of minimal residual disease after remission induction therapy. Higher levels of minimal residual disease are associated with inferior results even with intensification of therapy, thus suggesting that identification and targeting of minimal residual disease cells could be a therapeutic strategy. Here we identify high expression of 5T4 in subclonal populations of patient-derived xenografts from patients with high, post-induction levels of minimal residual disease. 5T4-positive cells showed preferential ability to overcome the NOD-scidIL2Rγ^null mouse xenograft barrier, migrated in vitro on a CXCL12 gradient, preferentially localized to bone marrow in vivo and displayed the ability to reconstitute the original clonal composition on limited dilution engraftment. Treatment with A1mcMMAF (a 5T4-antibody drug conjugate) significantly improved survival without overt toxicity in mice engrafted with a 5T4-positive acute lymphoblastic leukemia cell line. Mice engrafted with 5T4-positive patient-derived xenograft cells were treated with combination chemotherapy or dexamethasone alone and then given A1mcMMAF in the minimal residual disease setting. Combination chemotherapy was toxic to NOD-scidIL2Rγ^null mice. While dexamethasone or A1mcMMAF alone improved outcomes, the sequential administration of dexamethasone and A1mcMMAF significantly improved survival (P=0.0006) over either monotherapy. These data show that specifically targeting minimal residual disease cells improved outcomes and support further investigation of A1mcMMAF in patients with high-risk B-cell precursor acute lymphoblastic leukemia identified by 5T4 expression at diagnosis.

Catch me if you can: Leukemia Escape after CD19-Directed T Cell Immunotherapies

Immunotherapy is the revolution in cancer treatment of this last decade. Among multiple approaches able to harness the power of the immune system against cancer, T cell based immunotherapies represent one of the most successful examples. In particular, biotechnological engineering of protein structures, like the T cell receptor or the immunoglobulins, allowed the generation of synthetic peptides like chimeric antigen receptors and bispecific antibodies that are able to redirect non-tumor specific T cells to recognize and kill leukemic cells. The anti-CD19/CD3 bispecific antibody blinatumomab and anti-CD19 chimeric antigen receptor T cells (CART19) have produced deep responses in patients with relapsed and refractory B-cell acute leukemias. However, although the majority of these patients responds to anti-CD19 immunotherapy, a subset of them still relapses. Interestingly, a novel family of leukemia escape mechanisms has been described, all characterized by the apparent loss of CD19 on the surface of leukemic blasts. This extraordinary finding demonstrates the potent selective pressure of CART19/blinatumomab that drives extreme and specific escape strategies by leukemic blasts. Patients with CD19-negative relapsed leukemia have very poor prognosis and novel approaches to treat and ideally prevent antigen-loss are direly needed. In this review we discuss the incidence, mechanisms and therapeutic approaches for CD19-negative leukemia relapses occuring after CD19-directed T cell immunotherapies and present our future perspective.

Dual CD19 and CD123 targeting prevents antigen-loss relapses after CD19-directed immunotherapies

Potent CD19-directed immunotherapies, such as chimeric antigen receptor T cells (CART) and blinatumomab, have drastically changed the outcome of patients with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL). However, CD19-negative relapses have emerged as a major problem that is observed in approximately 30% of treated patients. Developing approaches to preventing and treating antigen-loss escapes would therefore represent a vertical advance in the field. Here, we found that in primary patient samples, the IL-3 receptor α chain CD123 was highly expressed on leukemia-initiating cells and CD19-negative blasts in bulk B-ALL at baseline and at relapse after CART19 administration. Using intravital imaging in an antigen-loss CD19-negative relapse xenograft model, we determined that CART123, but not CART19, recognized leukemic blasts, established protracted synapses, and eradicated CD19-negative leukemia, leading to prolonged survival. Furthermore, combining CART19 and CART123 prevented antigen-loss relapses in xenograft models. Finally, we devised a dual CAR-expressing construct that combined CD19- and CD123-mediated T cell activation and demonstrated that it provides superior in vivo activity against B-ALL compared with single-expressing CART or pooled combination CART. In conclusion, these findings indicate that targeting CD19 and CD123 on leukemic blasts represents an effective strategy for treating and preventing antigen-loss relapses occurring after CD19-directed therapies.

Checkpoint Antibodies but not T Cell-Recruiting Diabodies Effectively Synergize with TIL-Inducing γ-Irradiation

T cell-recruiting bispecific antibodies (bsAb) show promise in hematologic malignancies and are also being evaluated in solid tumors. In this study, we investigated whether T cell-recruiting bsAbs synergize with hypofractionated tumor radiotherapy (hRT) and/or blockade of the programmed death-1 (PD-1) immune checkpoint, both of which can increase tumor-infiltrating lymphocyte (TIL) numbers. Unexpectedly, large melanomas treated with hRT plus bsAb (AC133×CD3) relapsed faster than those treated with hRT alone, accompanied by massive TIL apoptosis. This fast relapse was delayed by the further addition of anti-PD-1. Mechanistic investigations revealed restimulation-induced cell death mediated by BIM and FAS as an additional cause of bsAb-mediated TIL depletion. In contrast, the double combination of hRT and anti-PD-1 strongly increased TIL numbers, and even very large tumors were completely eradicated. Our study reveals the risk that CD3-engaging bsAbs can induce apoptotic TIL depletion followed by rapid tumor regrowth, reminiscent of tolerance induction by CD3 mAb-mediated T-cell depletion, warranting caution in their use for the treatment of solid tumors. Our findings also argue that combining radiotherapy and anti-PD-1 can be quite potent, including against very large tumors. Cancer Res; 76(16); 4673-83. ©2016 AACR.

Emerging therapies provide new opportunities to reshape the multifaceted interactions between the immune system and lymphoma cells

The acquisition of a complete neoplastic phenotype requires cancer cells to develop escape mechanisms from the host immune system. This phenomenon, commonly referred to as 'immune evasion,' represents a hallmark of cancers and results from a Darwinian selection of the fittest tumor clones. First reported in solid tumors, cancer immunoescape characterizes several hematological malignancies. The biological bases of cancer immunoescape have recently been disclosed and include: (i) impaired human leukocyte antigen-mediated cancer cell recognition (B2M, CD58, CTIIA, CD80/CD86, CD28 and CTLA-4 mutations); (ii) deranged apoptotic mechanisms (reduced pro-apoptotic signals and/or increased expression of anti-apoptotic molecules); and (iii) changes in the tumor microenvironment involving regulatory T cells and tumor-associated macrophages. These immune-escape mechanisms characterize both Hodgkin and non-Hodgkin (B and T cell) lymphomas and represent a promising target for new anti-tumor therapies. In the present review, the principles of cancer immunoescape and their role in human lymphomagenesis are illustrated. Current therapies targeting these pathways and possible applications for lymphoma treatment are also addressed.

The Addition of the BTK Inhibitor Ibrutinib to Anti-CD19 Chimeric Antigen Receptor T Cells (CART19) Improves Responses against Mantle Cell Lymphoma

PURPOSE

Responses to therapy with chimeric antigen receptor T cells recognizing CD19 (CART19, CTL019) may vary by histology. Mantle cell lymphoma (MCL) represents a B-cell malignancy that remains incurable despite novel therapies such as the BTK inhibitor ibrutinib, and where data from CTL019 therapy are scant. Using MCL as a model, we sought to build upon the outcomes from CTL019 and from ibrutinib therapy by combining these in a rational manner.

EXPERIMENTAL DESIGN

MCL cell lines and primary MCL samples were combined with autologous or normal donor-derived anti-CD19 CAR T cells along with ibrutinib. The effect of the combination was studied in vitro and in mouse xenograft models.

RESULTS

MCL cells strongly activated multiple CTL019 effector functions, and MCL killing by CTL019 was further enhanced in the presence of ibrutinib. In a xenograft MCL model, we showed superior disease control in the CTL019- as compared with ibrutinib-treated mice (median survival not reached vs. 95 days, P < 0.005) but most mice receiving CTL019 monotherapy eventually relapsed. Therefore, we added ibrutinib to CTL019 and showed that 80% to 100% of mice in the CTL019 + ibrutinib arm and 0% to 20% of mice in the CTL019 arm, respectively, remained in long-term remission (P < 0.05).

CONCLUSIONS

Combining CTL019 with ibrutinib represents a rational way to incorporate two of the most recent therapies in MCL. Our findings pave the way to a two-pronged therapeutic strategy in patients with MCL and other types of B-cell lymphoma. Clin Cancer Res; 22(11); 2684-96. ©2016 AACR.

Blinatumomab for the treatment of acute lymphoblastic leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is a potentially fatal disease that involves clonal expansion of early lymphoid progenitor cells. Much of drug development for ALL treatment involves targeting antigens of the clonal cell surface. Blinatumomab belongs to an emerging class of anti-cancer therapeutics referred to as bispecific T-cell engaging antibodies. The Food and Drug Administration approved its use in relapsed or refractory adult Philadelphia chromosome-negative B-cell precursor ALL in December of 2014.

MECHANISM OF ACTION AND PHARMACODYNAMICS

Blinatumomab contains both an anti-CD3 and anti-CD19 arm, allowing for the juxtaposition of CD3+ T-cells to malignant CD19+ B-cells, thereby resulting in granzyme- and perforin-mediated B-cell apoptosis.

PRECLINICAL PHARMACOLOGY

Preclinical studies suggest that blinatumomab's efficacy is related to the effector-to-target ratio and to the difference between its affinity for CD19 and CD3.

PHARMACOKINETICS AND METABOLISM

Preclinical and early phase clinical studies have allowed for the characterization of the pharmacokinetics of blinatumomab, including the determination of its short half-life. The metabolic pathway has not been fully characterized but is thought to be similar to that of other antibodies.

CLINICAL STUDIES

Phase I and II studies led to the identification of an ideal stepwise dose, involving long-term continuous intravenous infusion (CIVI), to optimize its efficacy and reduce the risk of certain toxicities. A high remission rate and duration were noted among a relapsed/refractory population of patients.

SAFETY

The results of clinical trials have identified cytokine release syndrome and neurotoxicity, among others, as serious drug-related toxicities, leading to the institution of a Risk Evaluation and Mitigation Strategy.

DISCUSSION AND CONCLUSIONS

Blinatumomab represents a significant addition to the treatment options for ALL, but it is not without its limitations, of which are its short-half life, necessitating long-term CIVI, and the eventual emergence of CD19-negative clones. Continual development of the agent involves assessing its role in the frontline setting and in combination with chemotherapy.

Profile of blinatumomab and its potential in the treatment of relapsed/refractory acute lymphoblastic leukemia

The CD19 marker is expressed on the surface of normal and malignant immature or mature B-cells. On the other hand, immunotherapy involving T-cells is a promising modality of treatment for many neoplastic diseases including leukemias and lymphomas. The CD19/CD3-bispecific T-cell-engaging (BiTE^®) monoclonal antibody blinatumomab can transiently engage cytotoxic T-cells to CD19+ target B-cells inducing serial perforin-mediated lysis. In the first clinical trial, blinatumomab showed efficacy in non-Hodgkin’s lymphomas, but the most important trials have been conducted in relapsed/refractory (R/R) acute lymphoblastic leukemia (ALL) and in ALL with minimal residual disease. Encouraging reports on the activity of blinatumomab in R/R Philadelphia chromosome-negative B-cell precursor ALL led to its approval by the US Food and Drug Administration on December 3, 2014 after an accelerated review process. This review focuses on the profile of blinatumomab and its activity in R/R ALL.