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]

Tumor-antigen-binding bispecific antibodies for cancer treatment

Bi- and multispecific antibody derivatives (bsAbs) can be considered as the next generation of targeted biologics for cancer therapy. The general concept of bsAbs is a physical connection of recombinant antibody-derived entities with at least two binding specificities. This generates bsAbs that bind at least two antigens or epitopes, thus altering their binding functionalities and specificities in comparison to "normal" antibodies. Most bsAbs are produced as recombinant proteins, either as large IgG-like proteins that contain Fc regions, or as smaller entities with multiple antigen-binding regions but without Fc. Application of bsAbs in experimental cancer therapy currently includes molecules that bind different cell surface proteins to achieve more complete blockage of proliferative or angiogenesis-associated pathways. This approach of blocking more than one pathway component, or to simultaneously hit complementing pathways, also may limit potential escape mechanisms of cancer cells. BsAbs also are applied in the clinic as vehicles to deliver immune effector cells and/or cytokines to tumors.

Low expression of T-cell transcription factor BCL11b predicts inferior survival in adult standard risk T-cell acute lymphoblastic leukemia patients

Background

Risk stratification, detection of minimal residual disease (MRD), and implementation of novel therapeutic agents have improved outcome in acute lymphoblastic leukemia (ALL), but survival of adult patients with T-cell acute lymphoblastic leukemia (T-ALL) remains unsatisfactory. Thus, novel molecular insights and therapeutic approaches are urgently needed.

Methods

We studied the impact of B-cell CLL/lymphoma 11b (BCL11b), a key regulator in normal T-cell development, in T-ALL patients enrolled into the German Multicenter Acute Lymphoblastic Leukemia Study Group trials (GMALL; n = 169). The mutational status (exon 4) of BCL11b was analyzed by Sanger sequencing and mRNA expression levels were determined by quantitative real-time PCR. In addition gene expression profiles generated on the Human Genome U133 Plus 2.0 Array (affymetrix) were used to investigate BCL11b low and high expressing T-ALL patients.

Results

We demonstrate that BCL11b is aberrantly expressed in T-ALL and gene expression profiles reveal an association of low BCL11b expression with up-regulation of immature markers. T-ALL patients characterized by low BCL11b expression exhibit an adverse prognosis [5-year overall survival (OS): low 35% (n = 40) vs. high 53% (n = 129), P = 0.02]. Within the standard risk group of thymic T-ALL (n = 102), low BCL11b expression identified patients with an unexpected poor outcome compared to those with high expression (5-year OS: 20%, n = 18 versus 62%, n = 84, P < 0.01). In addition, sequencing of exon 4 revealed a high mutation rate (14%) of BCL11b.

Conclusions

In summary, our data of a large adult T-ALL patient cohort show that low BCL11b expression was associated with poor prognosis; particularly in the standard risk group of thymic T-ALL. These findings can be utilized for improved risk prediction in a significant proportion of adult T-ALL patients, which carry a high risk of standard therapy failure despite a favorable immunophenotype.

Targeted therapy with monoclonal antibodies in acute lymphoblastic leukemia

PURPOSE OF REVIEW

To describe the current new targeted therapy with monoclonal and bispecific antibodies in adult acute lymphoblastic leukemia (ALL), to improve response rates and outcome.

RECENT FINDINGS

Blast cells in ALL express a variety of specific antigens, such as CD19, CD20, CD22, CD33 and CD52, and recently monoclonal antibodies (MoAbs) became available to target these antigens. The anti-CD20 MoAb rituximab has substantially improved the outcome in Burkitt lymphoma/leukemia, and is currently applied in de-novo B-precursor ALL. The MoAbs directed against CD22, linked to cytotoxic agents, either to calicheamicin (inotuzomab ozogamicin) or to plant or bacterial toxins (epratuzumab) are explored in refractory/relapsed childhood and adult ALL. Targeting CD19 is of great interest, as it is expressed in all B-lineage cells, including early precursors. The new bispecific antibody blinatumomab combines single chain antibodies to CD19 and CD3, and thereby T cells lyse the CD19 bearing B cells and is effective in patients with positive minimal residual disease (MRD) or refractory/relapsed ALL.

SUMMARY

Antibody therapy in ALL is very promising, with high rate of complete remission and MRD-negativity in advanced ALL. It is currently explored in de-novo ALL to establish the best setting in combination with chemotherapy or even as a monotherapy.

Treatment of High-Risk Philadelphia Chromosome–Negative Acute Lymphoblastic Leukemia in Adolescents and Adults According to Early Cytologic Response and Minimal Residual Disease After Consolidation Assessed by Flow Cytometry: Final Results of the PETHEMA ALL-AR-03 Trial

Purpose

Minimal residual disease (MRD) is an important prognostic factor in adults with acute lymphoblastic leukemia (ALL) and may be used for treatment decisions. The Programa Español de Tratamientos en Hematología (PETHEMA) ALL-AR-03 trial (Treatment of High Risk Adult Acute Lymphoblastic Leukemia [LAL-AR/2003]) assigned adolescent and adult patients (age 15 to 60 years) with high-risk ALL (HR-ALL) without the Philadelphia (Ph) chromosome to chemotherapy or to allogeneic hematopoietic stem-cell transplantation (allo-HSCT) according to early cytologic response (day 14) and flow-MRD level after consolidation.

Patients and Methods

Patients with good early cytologic response (< 10% blasts in bone marrow at day 14 of induction) and a flow-MRD level less than 5 × 10−4 at the end of consolidation were assigned to delayed consolidation and maintenance therapy, and allo-HSCT was scheduled in patients with poor early cytologic response or flow-MRD level ≥ 5 × 10−4.

Results

Complete remission was attained in 282 (87%) of 326 patients, and 179 (76%) of 236 patients who completed early consolidation were assigned by intention-to treat to receive allo-HSCT (71) or chemotherapy (108). Five-year disease-free survival (DFS) and overall survival (OS) probabilities were 37% and 35% for the whole series, 32% and 37% for patients assigned to allo-HSCT, and 55% and 59% for those assigned to chemotherapy. Multivariable analysis showed poor MRD clearance (≥ 1 × 10−3 after induction and ≥ 5 × 10−4 after early consolidation) as the only prognostic factor for DFS and OS.

Conclusion

Prognosis for Ph-negative HR-ALL in adolescents and adults with good early response to induction and low flow-MRD levels after consolidation is quite favorable when allo-HSCT is avoided. In this study, the pattern of MRD clearance was the only prognostic factor for DFS and OS.

Tumor immunology and cancer immunotherapy: summary of the 2013 SITC primer

Knowledge of the basic mechanisms of the immune system as it relates to cancer has been increasing rapidly. These developments have accelerated the translation of these advancements into medical breakthroughs for many cancer patients. The immune system is designed to discriminate between self and non-self, and through genetic recombination there is virtually no limit to the number of antigens it can recognize. Thus, mutational events, translocations, and other genetic abnormalities within cancer cells may be distinguished as “altered-self” and these differences may play an important role in preventing the development or progression of cancer. However, tumors may utilize a variety of mechanisms to evade the immune system as well. Cancer biologists are aiming to both better understand the relationship between tumors and the normal immune system, and to look for ways to alter the playing field for cancer immunotherapy. Summarized in this review are discussions from the 2013 SITC Primer, which focused on reviewing current knowledge and future directions of research related to tumor immunology and cancer immunotherapy, including sessions on innate immunity, adaptive immunity, therapeutic approaches (dendritic cells, adoptive T cell therapy, anti-tumor antibodies, cancer vaccines, and immune checkpoint blockade), challenges to driving an anti-tumor immune response, monitoring immune responses, and the future of immunotherapy clinical trial design.

New frontiers in pediatric Allo-SCT

The inaugural meeting of 'New Frontiers in Pediatric Allogeneic Stem Cell Transplantation' organized by the Pediatric Blood and Transplant Consortium (PBMTC) was held at the American Society of Pediatric Hematology and Oncology Annual Meeting. This meeting provided an international platform for physicians and investigators active in the research and utilization of pediatric Allo-SCT in children and adolescents with malignant and non-malignant disease (NMD), to share information and develop future collaborative strategies. The primary objectives of the conference included: (1) to present advances in Allo-SCT in pediatric ALL and novel pre and post-transplant immunotherapy; (2) to highlight new strategies in alternative allogeneic stem cell donor sources for children and adolescents with non-malignant hematological disorders; (3) to discuss timing of immune reconstitution after Allo-SCT and methods of facilitating more rapid recovery of immunity; (4) to identify strategies of utilizing Allo-SCT in pediatric myeloproliferative disorders; (5) to develop diagnostic and therapeutic approaches to hematological complications post pediatric Allo-SCT; (6) to enhance the understanding of new novel cellular therapeutic approaches to pediatric malignant and non-malignant hematological disorders; and (7) to discuss optimizing drug therapy in pediatric recipients of Allo-SCT. This paper will provide a brief overview of the conference.

Immunoglobulin and T cell receptor gene high-throughput sequencing quantifies minimal residual disease in acute lymphoblastic leukemia and predicts post-transplantation relapse and survival

Minimal residual disease (MRD) quantification is an important predictor of outcome after treatment for acute lymphoblastic leukemia (ALL). Bone marrow ALL burden ≥ 10(-4) after induction predicts subsequent relapse. Likewise, MRD ≥ 10(-4) in bone marrow before initiation of conditioning for allogeneic (allo) hematopoietic cell transplantation (HCT) predicts transplantation failure. Current methods for MRD quantification in ALL are not sufficiently sensitive for use with peripheral blood specimens and have not been broadly implemented in the management of adults with ALL. Consensus-primed immunoglobulin (Ig), T cell receptor (TCR) amplification and high-throughput sequencing (HTS) permit use of a standardized algorithm for all patients and can detect leukemia at 10(-6) or lower. We applied the LymphoSIGHT HTS platform (Sequenta Inc., South San Francisco, CA) to quantification of MRD in 237 samples from 29 adult B cell ALL patients before and after allo-HCT. Using primers for the IGH-VDJ, IGH-DJ, IGK, TCRB, TCRD, and TCRG loci, MRD could be quantified in 93% of patients. Leukemia-associated clonotypes at these loci were identified in 52%, 28%, 10%, 35%, 28%, and 41% of patients, respectively. MRD ≥ 10(-4) before HCT conditioning predicted post-HCT relapse (hazard ratio [HR], 7.7; 95% confidence interval [CI], 2.0 to 30; P = .003). In post-HCT blood samples, MRD ≥10(-6) had 100% positive predictive value for relapse with median lead time of 89 days (HR, 14; 95% CI, 4.7 to 44, P < .0001). The use of HTS-based MRD quantification in adults with ALL offers a standardized approach with sufficient sensitivity to quantify leukemia MRD in peripheral blood. Use of this approach may identify a window for clinical intervention before overt relapse.

Antibody therapy for pediatric leukemia

Despite increasing cure rates for pediatric leukemia, relapsed disease still carries a poor prognosis with significant morbidity and mortality. Novel targeted therapies are currently being investigated in an attempt to reduce adverse events and improve survival outcomes. Antibody therapies represent a form of targeted therapy that offers a new treatment paradigm. Monoclonal antibodies are active in pediatric acute lymphoblastic leukemia (ALL) and are currently in Phase III trials. Antibody-drug conjugates (ADCs) are the next generation of antibodies where a highly potent cytotoxic agent is bound to an antibody by a linker, resulting in selective targeting of leukemia cells. ADCs are currently being tested in clinical trials for pediatric acute myeloid leukemia and ALL. Bispecific T cell engager (BiTE) antibodies are a construct whereby each antibody contains two binding sites, with one designed to engage the patient's own immune system and the other to target malignant cells. BiTE antibodies show great promise as a novel and effective therapy for childhood leukemia. This review will outline recent developments in targeted agents for pediatric leukemia including monoclonal antibodies, ADCs, and BiTE antibodies.

Pediatric posttransplant relapsed/refractory B-precursor acute lymphoblastic leukemia shows durable remission by therapy with the T-cell engaging bispecific antibody blinatumomab

We report on posttransplant relapsed pediatric patients with B-precursor acute lymphoblastic leukemia with no further standard of care therapy who were treated with the T-cell engaging CD19/CD3-bispecific single-chain antibody construct blinatumomab on a compassionate use basis. Blast load was assessed prior to, during and after blinatumomab cycle using flow cytometry to detect minimal residual disease, quantitative polymerase chain reaction for rearrangements of the immunoglobulin or T-cell receptor genes, and bcr/abl mutation detection in one patient with Philadelphia chromosome-positive acute lymphoblastic leukemia. Blinatumomab was administered as a 4-week continuous intravenous infusion at a dosage of 5 or 15 μg/m(2)/day. Nine patients received a total of 18 cycles. Four patients achieved complete remission after the first cycle of treatment; 2 patients showed a complete remission from the second cycle after previous reduction of blast load by chemotherapy. Three patients did not respond, of whom one patient proceeded to a second cycle without additional chemotherapy and again did not respond. Four patients were successfully retransplanted in molecular remission from haploidentical donors. After a median follow up of 398 days, the probability of hematologic event-free survival is 30%. Major toxicities were grade 3 seizures in one patient and grade 3 cytokine release syndrome in 2 patients. Blinatumomab can induce molecular remission in pediatric patients with posttransplant relapsed B-precursor acute lymphoblastic leukemia and facilitate subsequent allogeneic hematopoietic stem cell transplantation from haploidentical donor with subsequent long-term leukemia-free survival.

Blinatumomab, a Bi-Specific Anti-CD19/CD3 BiTE(®) Antibody for the Treatment of Acute Lymphoblastic Leukemia: Perspectives and Current Pediatric Applications

Leukemia is the most common childhood malignancy and acute lymphoblastic leukemia (ALL) represents the largest sub-type. Despite remarkable improvements over the last 40 years, standard therapy fails in 10–20% of newly diagnosed patients. Survival for children with relapsed ALL is poor, and the development and implementation of novel therapeutic strategies in pediatric ALL are critical to further advancements. Immunotherapeutic approaches have been central to more novel ALL therapies. However, more recent innovation in antibody engineering has improved potency and efficacy, and antibody–drug conjugates (ADCs) are an especially attractive option in severely immunocompromised patients. An even more sophisticated antibody design is that of bi-specific T-cell engaging or BiTE^® antibodies, which directly recruit effector T cells to augment the anti-neoplastic effect. This review focuses on blinatumomab, a bi-specific anti-CD19/CD3 antibody that has shown efficacy in adult patients with precursor B-ALL and is currently being evaluated in the pediatric setting.

Preclinical characterization of AMG 330, a CD3/CD33-bispecific T-cell-engaging antibody with potential for treatment of acute myelogenous leukemia

There is high demand for novel therapeutic options for patients with acute myelogenous leukemia (AML). One possible approach is the bispecific T-cell-engaging (BiTE, a registered trademark of Amgen) antibody AMG 330 with dual specificity for CD3 and the sialic acid-binding lectin CD33 (SIGLEC-3), which is frequently expressed on the surface of AML blasts and leukemic stem cells. AMG 330 binds with low nanomolar affinity to CD33 and CD3ε of both human and cynomolgus monkey origin. Eleven human AML cell lines expressing between 14,400 and 56,700 CD33 molecules per cell were all potently lysed with EC(50) values ranging between 0.4 pmol/L and 3 pmol/L (18-149 pg/mL) by previously resting, AMG 330-redirected T cells. Complete lysis was achieved after 40 hours of incubation. In the presence of AML cells, AMG 330 specifically induced expression of CD69 and CD25 as well as release of IFN-γ, TNF, interleukin (IL)-2, IL-10, and IL-6. Ex vivo, AMG 330 mediated autologous depletion of CD33-positive cells from cynomolgous monkey bone marrow aspirates. Soluble CD33 at concentrations found in bone marrow of patients with AML did not significantly affect activities of AMG 330. Neoexpression of CD33 on newly activated T cells was negligible as it was limited to 6% of T cells in only three out of ten human donors tested. Daily intravenous administration with as low as 0.002 mg/kg AMG 330 significantly prolonged survival of immunodeficient mice adoptively transferred with human MOLM-13 AML cells and human T cells. AMG 330 warrants further development as a potential therapy for AML.

Recognition of adult and pediatric acute lymphoblastic leukemia blasts by natural killer cells

In this study, we aimed to investigate the pathways of recognition of acute lymphoblastic leukemia blasts by natural killer cells and to verify whether differences in natural killer cell activating receptor ligand expression among groups defined by age of patients, or presence of cytogenetic/molecular aberrations correlate with the susceptibility to recognition and killing. We analyzed 103 newly diagnosed acute lymphoblastic leukemia patients: 46 adults and 57 children. Pediatric blasts showed a significantly higher expression of Nec-2 (P=0.03), ULBP-1 (P=0.01) and ULBP-3 (P=0.04) compared to adult cells. The differential expression of these ligands between adults and children was confined to B-lineage acute lymphoblastic leukemia with no known molecular alterations. Within molecularly defined subgroups of patients, a high surface expression of NKG2D and DNAM1 ligands was found on BCR-ABL(+) blasts, regardless of patient age. Accordingly, BCR-ABL(+) blasts proved to be significantly more susceptible to natural killer-dependent lysis than B-lineage blasts without molecular aberrations (P=0.03). Cytotoxic tests performed in the presence of neutralizing antibodies indicated a pathway of acute lymphoblastic leukemia cell recognition in the setting of the Nec-2/DNAM-1 interaction. These data provide a biological explanation of the different roles played by alloreactive natural killer cells in pediatric versus adult acute lymphoblastic leukemia and suggest that new natural killer-based strategies targeting specific subgroups of patients, particularly those BCR-ABL(+), are worth pursuing further.

CD16xCD33 bispecific killer cell engager (BiKE) activates NK cells against primary MDS and MDSC CD33+ targets

Myelodysplastic syndromes (MDS) are stem cell disorders that can progress to acute myeloid leukemia. Although hematopoietic cell transplantation can be curative, additional therapies are needed for a disease that disproportionally afflicts the elderly. We tested the ability of a CD16xCD33 BiKE to induce natural killer (NK) cell function in 67 MDS patients. Compared with age-matched normal controls, CD7(+) lymphocytes, NK cells, and CD16 expression were markedly decreased in MDS patients. Despite this, reverse antibody-dependent cell-mediated cytotoxicity assays showed potent degranulation and cytokine production when resting MDS-NK cells were triggered with an agonistic CD16 monoclonal antibody. Blood and marrow MDS-NK cells treated with bispecific killer cell engager (BiKE) significantly enhanced degranulation and tumor necrosis factor-α and interferon-γ production against HL-60 and endogenous CD33(+) MDS targets. MDS patients had a significantly increased proportion of immunosuppressive CD33(+) myeloid-derived suppressor cells (MDSCs) that negatively correlated with MDS lymphocyte populations and CD16 loss on NK cells. Treatment with the CD16xCD33 BiKE successfully reversed MDSC immunosuppression of NK cells and induced MDSC target cell lysis. Lastly, the BiKE induced optimal MDS-NK cell function irrespective of disease stage. Our data suggest that the CD16xCD33 BiKE functions against both CD33(+) MDS and MDSC targets and may be therapeutically beneficial for MDS patients.

Molecular therapeutic approaches for pediatric acute myeloid leukemia

Approximately two-thirds of children with acute myeloid leukemia (AML) are cured with intensive multi-agent chemotherapy. However, refractory and relapsed AML remains a significant source of childhood cancer mortality, highlighting the need for new therapies. Further therapy intensification with traditional cytotoxic chemotherapy in pediatric AML is not feasible given the risks of both short-term and long-term organ dysfunction. Substantial emphasis has been placed upon the development of molecularly targeted therapeutic approaches for adults and children with high-risk subtypes of AML with the goal of improving remission induction and minimizing relapse. Several promising agents are currently in clinical testing or late preclinical development for AML, including monoclonal antibodies against leukemia cell surface proteins, kinase inhibitors, proteasome inhibitors, epigenetic agents, and chimeric antigen receptor engineered T cell immunotherapies. Many of these therapies have been specifically tested in children with relapsed/refractory AML in Phase 1 and 2 trials with a smaller number of new agents under Phase 3 evaluation for children with de novo AML. Although successful identification and implementation of new drugs for children with AML remain a formidable challenge, enthusiasm for novel molecular therapeutic approaches is great given the potential for significant clinical benefit for children who do not have other curative options.

Biting back: BiTE antibodies as a promising therapy for acute myeloid leukemia

The experience with gemtuzumab ozogamicin has highlighted both the potential value and limitations of antibodies in acute myeloid leukemia (AML). Recently, bispecific T-cell engager (BiTE) antibodies have emerged as a means to harness polyclonal cytotoxic T-cells and cause highly efficient lysis of targeted tumor cells. Promising early results have been obtained with the CD19-directed BiTE antibody, blinatumomab, in patients with acute lymphoblastic leukemia. A first candidate for AML is the CD33/CD3 molecule, AMG 330, for which several recent preclinical studies demonstrated high potency and efficacy in destroying CD33(+) human AML cells. Many questions remain to be addressed, but BiTE antibodies may offer an exciting new tool in a disease for which the outcomes in many patients remain unsatisfactory.

Current and future management of Ph/BCR-ABL positive ALL

Following the introduction of targeted therapy with tyrosine kinase inhibitors (TKI) at the beginning of the past decade, the outcome of patients with Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph+ ALL) has dramatically improved. Presently, the use of refined programs with first/second generation TKI's and chemotherapy together with allogeneic stem cell transplantation allow up to 50% of all patients to be cured. Further progress is expected with the new TKI ponatinib, overcoming resistance caused by T315I point mutation, other targeted therapies, autologous transplantation in molecularly negative patients, therapeutic monoclonal antibodies like inotuzumab ozogamicin and blinatumomab, and chimeric antigen receptor-modified T cells. Ph+ ALL could become curable in the near future even without allogeneic stem cell transplantation, minimizing the risk of therapy-related death and improving greatly the quality of patients' life.

Managing cytokine release syndrome associated with novel T cell-engaging therapies

Chimeric antigen receptor (CAR)-modified T cells and bispecific T cell-engaging antibodies have demonstrated dramatic clinical responses in recent clinical trials. The hallmark of these novel highly active immunotherapies is nonphysiologic T cell activation, which has correlated not only with greatly increased efficacy but also with notable toxicity in some cases. We and others have observed a cytokine release syndrome (CRS), which correlates with both toxicity and efficacy in patients receiving T cell-engaging therapies. In addition to elevations in effector cytokines, such as interferon-γ, cytokines associated with hemophagocytic lymphohistiocytosis or macrophage activation syndrome, such as interleukin (IL)-10 and IL-6, may also be markedly elevated. Whereas corticosteroids may control some of these toxicities, their potential to block T cell activation and abrogate clinical benefit is a concern. Detailed studies of T cell proliferation and the resultant immune activation produced by these novel therapies have led to more targeted approaches that have the potential to provide superior toxicity control without compromising efficacy. One approach we have developed targets IL-6, a prominent cytokine in CRS, using the IL-6R antagonist tocilizumab. We will review the pathophysiology and management options for CRS associated with T cell-engaging therapies.

Monoclonal antibodies as therapeutics in human malignancies

ABSTRACT: 

Monoclonal antibodies (mAbs) are a proven effective therapeutic modality in human malignancy. Several mAbs are approved to targets critical in aberrant oncogenic signaling within tumors and their microenvironment. These targets include secreted ligands (e.g., VEGF and HGH), their receptors (e.g., HER2 and VEGFR2), cell surface counter receptors and their receptor-bound ligands (e.g., PD1 and PD1L, respectively). The ability to genetically engineer the structure and/or functions of mAbs has significantly improved their effectiveness. Furthermore, advances in gene expression profiling, proteomics, deep sequencing and deciphering of complex signaling networks have revealed novel therapeutic targets. We review target selection, approved indications and the rationale for mAb utilization in solid and hematologic malignancies. We also discuss novel mAbs in early- and late-phase clinical trials that are likely to change the natural history of disease and improve survival. The future challenge is to design mAb-based novel trial designs for diagnostics and therapeutics for human malignancies.

Emerging drugs for acute lymphocytic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is typically treated with complex multi-agent chemotherapy regimens over a prolonged time period. Long-term outcomes depend on the age of the patient and the biological characteristics of the leukemic cells. While pediatric patients achieve cure more often than adults, therapy can continue to be improved for all patients with this disease.

AREAS COVERED

The current management strategy for ALL is reviewed. Recently, targeted therapies have been shown to improve survival in subsets of patients, most notably in those with Philadelphia chromosome-positive ALL or with leukemic cells that express the surface antigen CD20. Several innovative compounds are under investigation, and the most promising ones to date will be discussed.

EXPERT OPINION

The incorporation of monoclonal antibody therapy represents a targeted and powerful approach to the management of ALL. Bispecific T-cell engaging agents, such as blinatumomab, are able to facilitate immune-mediated killing of leukemia cells. Immunoconjugates (i.e., monoclonal antibodies linked to various cytotoxins) allow small doses of very potent chemotherapy to be delivered directly to a leukemia cell with hope of sparing normal tissue. As the genetic and molecular characterization of ALL is more completely understood, patients will receive treatment plans that are more individualized than previously possible.

Toxicity management for patients receiving novel T-cell engaging therapies

PURPOSE OF REVIEW

Recent clinical trials using T-cell engaging immunotherapies such as bispecific antibodies which target T cells and tumor cells, as well as engineered T cells that express targeting and activation molecules known as chimeric antigen receptors, have demonstrated powerful proof of concept. These therapies result in a significant degree of immune activation in the patient, which has correlated with greatly increased efficacy but also with notable toxicity. These therapies produce nonphysiologic T-cell activation, which is the hallmark of these new, highly active treatments.

RECENT FINDINGS

We and others have noted cytokine activation profiles that correlate with both toxicity and efficacy in patients receiving T-cell engaging therapies. Effector cytokines such as interferon-γ are elevated, but so are cytokines that are associated with macrophage activation syndrome/hemophagocytic lymphohistiocytosis, such as interleukin (IL)-10 and IL-6. Although corticosteroids can control some of these toxicities, a targeted approach may produce superior toxicity control without interfering with efficacy. One approach we have developed targets IL-6, a key cytokine in the toxicity response, using the IL-6 receptor antagonist tocilizumab.

SUMMARY

Detailed studies of the T-cell activation produced by these novel therapies has led to more targeted approaches that have the potential to control toxicity while maintaining efficacy.

Treatment of Philadelphia-positive acute lymphoid leukemia

SUMMARY Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) represents approximately 15–30% of ALL in adults and is characterized by the expression of the fusion protein BCR–ABL with oncogenic activity. Remission and survival rates were lower whereas relapse risk was increased in Ph+ compared with Philadelphia-negative ALL, until remarkable improvements in the management of Ph+ ALL were achieved through the introduction of tyrosine kinase inhibitors that reduce the activity of the BCR–ABL protein. However, in patients achieving complete remission, allogeneic hematopoietic stem cell transplantation is in most cases a mandatory therapeutic step because rate of relapses are still high. This review will illustrate the current therapeutic options for the management of Ph+ ALL and indicate how better curative options may stem from appropriate implementation of tyrosine kinase inhibitors and novel antitumoral agents.

How I treat ALL in Down's syndrome: pathobiology and management

Children with Down syndrome are at high risk for developing B-cell precursor acute lymphoblastic leukemia (DS-ALL) associated with poor outcome due to both a high relapse rate and increased treatment-related mortality (TRM) from infections. Biologically, these heterogeneous leukemias are characterized by under-representation of the common cytogenetic subgroups of childhood ALL and overrepresentation of CRLF2-IL7R-JAK-STAT activating genetic aberrations. Although relapse is the major determinant of poor outcomes in this population, de-escalation of chemotherapy intensity might be feasible in the 10% to 15% DS-ALL patients with ETV6-RUNX1 or high hyperdipoidy in whom TRM is the major limiting event. As infection-associated TRM occurs during all treatment phases, including the maintenance period, increased surveillance and supportive care is required throughout therapy. Improvement in outcome will require better understanding of the causes of treatment failure and TRM, incorporation of new therapies targeting the unique biological properties of DS-ALL, and enhanced supportive care measures to reduce the risk of infection-related TRM. To facilitate these goals, an international collaboration plans to establish a prospective DS-ALL registry and develop specific supportive care recommendations for this at-risk population.

Antigen-based immunotherapy for the treatment of acute lymphoblastic leukemia: the emerging role of blinatumomab

Acute lymphoblastic leukemia (ALL) arises from immature B and T lymphoblasts. An increasing array of cytogenetic and molecular markers have been identified in ALL, which allows for increasingly sophisticated prognostication, as well as identification of potential new targets for therapy. The treatment of ALL in children has shown astounding success in the last 50 years, with more than 90% of children now able to be cured of their ALL. In adults, these success rates have not been duplicated. However, the use of pediatric-intensive regimens in young adults has shown increasing success. The use of monoclonal antibodies conjugated to drugs, immunotoxins, and cells also has shown early success and promises to enhance the outcome of newly diagnosed patients. Blinatumomab, a bispecific T-cell engager antibody, brings a malignant B cell in proximity to a T cell with redirected lysis. This antibody construct has shown promising results in patients with relapsed and refractory disease and is entering randomized clinical trials in newly diagnosed patients. The addition of monoclonal antibody therapy to chemotherapy in adults promises to enhance outcomes while hopefully not increasing toxicity. After many years of stagnation, it appears that the therapy of adults with ALL is showing significant improvement.

Human mesenchymal stromal cells deliver systemic oncolytic measles virus to treat acute lymphoblastic leukemia in the presence of humoral immunity

Clinical trials of oncolytic attenuated measles virus (MV) are ongoing, but successful systemic delivery in immune individuals remains a major challenge. We demonstrated high-titer anti-MV antibody in 16 adults with acute lymphoblastic leukemia (ALL) following treatments including numerous immunosuppressive drugs. To resolve this challenge, human bone marrow-derived mesenchymal stromal cells (BM-MSCs) were used to efficiently deliver MV in a systemic xenograft model of precursor B-lineage-ALL. BM-MSCs were successfully loaded with MV ex vivo, and MV was amplified intracellularly, without toxicity. Live cell confocal imaging demonstrated a viral hand-off between BM-MSCs and ALL targets in the presence of antibody. In a murine model of disseminated ALL, successful MV treatment (judged by bioluminescence quantification and survival) was completely abrogated by passive immunization with high-titer human anti-MV antibody. Importantly, no such abrogation was seen in immunized mice receiving MV delivered by BM-MSCs. These data support the use of BM-MSCs as cellular carriers for MV in patients with ALL.

Chimeric antigen receptors for the adoptive T cell therapy of hematologic malignancies

The genetic modification of autologous T cells with chimeric antigen receptors (CARs) represents a breakthrough for gene engineering as a cancer therapy for hematologic malignancies. By targeting the CD19 antigen, we have demonstrated robust and rapid anti-leukemia activity in patients with heavily pre-treated and chemotherapy-refractory B cell acute lymphoblastic leukemia (B-ALL). We demonstrated rapid induction of deep molecular remissions in adults, which has been recently confirmed in a case report involving a child with B-ALL. In contrast to the results when treating B-ALL, outcomes have been more modest in patients with chronic lymphocytic leukemia (CLL) or other non-hodgkin's lymphoma (NHL). We review the clinical trial experience targeting B-ALL and CLL and speculate on the possible reasons for the different outcomes and propose potential optimization to CAR T cell therapy when targeting CLL or other indolent NHL. Lastly, we discuss the pre-clinical development and potential for clinical translation for using CAR T cells against multiple myeloma and acute myeloid leukemia. We highlight the potential risks and benefits by targeting these poor outcome hematologic malignancies.

New approaches to manipulate minimal residual disease after allogeneic stem cell transplantation

Minimal residual disease (MRD) is a complex topic that has been studied extensively in hematologic malignancies given its clinical implications related to prognosis. However, methods to monitor and treat MRD, especially after stem cell transplantation, are not well defined and vary in different disease processes. Alternative transplant strategies, such as reduced-intensity conditioning, have altered the way we assess and address MRD after transplantation. Development of new diagnostic tools have allowed for higher sensitivity and specificity of testing. Both targeted chemotherapeutic agents and immunotherapies have been developed to treat MRD in hopes of improving patient outcomes. This article aims to address ways to define and manipulate MRD specifically after stem cell transplantation.

Cellular determinants for preclinical activity of a novel CD33/CD3 bispecific T-cell engager (BiTE) antibody, AMG 330, against human AML

CD33 is a valid target for acute myeloid leukemia (AML) but has proven challenging for antibody-drug conjugates. Herein, we investigated the cellular determinants for the activity of the novel CD33/CD3-directed bispecific T-cell engager antibody, AMG 330. In the presence of T cells, AMG 330 was highly active against human AML cell lines and primary AML cells in a dose- and effector to target cell ratio-dependent manner. Using cell lines engineered to express wild-type CD33 at increased levels, we found a quantitative relationship between AMG 330 cytotoxicity and CD33 expression; in contrast, AMG 330 cytotoxicity was neither affected by common CD33 single nucleotide polymorphisms nor expression of the adenosine triphosphate-binding cassette (ABC) transporter proteins, P-glycoprotein or breast cancer resistance protein. Unlike bivalent CD33 antibodies, AMG 330 did not reduce surface CD33 expression. The epigenetic modifier drugs, panobinostat and azacitidine, increased CD33 expression in some cell lines and augmented AMG 330-induced cytotoxicity. These findings demonstrate that AMG 330 has potent CD33-dependent cytolytic activity in vitro, which can be further enhanced with other clinically available therapeutics. As it neither modulates CD33 expression nor is affected by ABC transporter activity, AMG 330 is highly promising for clinical exploration as it may overcome some limitations of previous CD33-targeted agents.

CD33 target validation and sustained depletion of AML blasts in long-term cultures by the bispecific T-cell-engaging antibody AMG 330

Antibody-based immunotherapy represents a promising strategy to target and eliminate chemoresistant leukemic cells. Here, we evaluated the CD33/CD3-bispecific T cell engaging (BiTE) antibody (AMG 330) for its suitability as a therapeutic agent in acute myeloid leukemia (AML). We first assessed CD33 expression levels by flow cytometry and found expression in >99% of patient samples (n = 621). CD33 was highest expressed in AMLs with NPM1 mutations (P < .001) and lower in AMLs with complex karyotypes and t(8;21) translocations (P < .001). Furthermore, leukemic stem cells within the CD34(+)/CD38(-) compartment displayed CD33 at higher levels than healthy donor stem cells (P = .047). In MS-5 feeder cell-based long-term cultures that supported the growth of primary AML blasts for up to 36 days, AMG 330 efficiently recruited and expanded residual CD3(+)/CD45RA(-)/CCR7(+) memory T cells within the patient sample. Even at low effector to target ratios, the recruited T cells lysed autologous blasts completely in the majority of samples and substantially in the remaining samples in a time-dependent manner. This study provides the first correlation of CD33 expression levels with AML genotype in a comprehensive analysis of adult patients. Targeting CD33 ex vivo using AMG 330 in primary AML samples led to T cell recruitment and expansion and remarkable antibody-mediated cytotoxicity, suggesting efficient therapeutic potential in vivo.

Acute lymphoblastic leukemia in adults: encouraging developments on the way to higher cure rates

Conventional cytotoxic chemotherapy for adult acute lymphoblastic leukemia (ALL) is not adequate to cure most patients of the disease. Complete remission is achieved in the majority of patients, but responses are often not durable. Allogeneic stem cell transplant is used for patients with high risk features, including those who are positive for minimal residual disease after induction and consolidation therapy. Nevertheless, transplant is a toxic intervention, and does not guarantee long-term disease-free survival. Monoclonal antibodies target surface antigens present on leukemic blasts, with the aim of minimizing off-target toxicity. Rituximab, an antibody directed against CD20, prolongs the survival of younger adults with ALL when added to chemotherapy in the frontline setting. Novel agents, such as the cytotoxin-antibody conjugate inotuzumab, and the bispecific T-cell engaging compound blinatumomab, have exhibited marked antileukemic activity in the relapsed setting. As these agents continue in clinical development, it will be important to eventually incorporate them in the frontline treatment approach. We review current strategies for treating adult ALL, with a focus on novel and targeted therapies that are under development.

CAR-modified anti-CD19 T cells for the treatment of B-cell malignancies: rules of the road

INTRODUCTION

Malignancies of the B lymphocyte or its precursor include B-cell non-Hodgkin lymphoma as well as chronic and acute lymphoid leukemias. These are among the most common hematologic malignancies and many patients with B-cell malignancies are incurable. Although most patients initially respond to first-line treatment, relapse is frequent and is associated with a poor prognosis. T cells that are genetically engineered to express chimeric antigen receptors (CARs) recognizing the B-cell-associated molecule CD19 have emerged as a potentially potent and exciting therapeutic modality in recent years.

AREAS COVERED

This review explores the current peer-reviewed publications in the field and a discussion of expert opinion.

EXPERT OPINION

Genetic engineering of T cells has become clinically feasible and appears to be safe. Here we provide an insight into the process of patient selection, engineered T-cell production, infusion procedure, expected toxicities and efficacy of this exciting approach as it is practiced in the treatment of B-cell malignancies. Anti-CD19-redirected T cells likely represent the vanguard of an exciting new approach to treating cancer.

Bispecific small molecule-antibody conjugate targeting prostate cancer

Bispecific antibodies, which simultaneously target CD3 on T cells and tumor-associated antigens to recruit cytotoxic T cells to cancer cells, are a promising new approach to the treatment of hormone-refractory prostate cancer. Here we report a site-specific, semisynthetic method for the production of bispecific antibody-like therapeutics in which a derivative of the prostate-specific membrane antigen-binding small molecule DUPA was selectively conjugated to a mutant αCD3 Fab containing the unnatural amino acid, p-acetylphenylalanine, at a defined site. Homogeneous conjugates were generated in excellent yields and had good solubility. The efficacy of the conjugate was optimized by modifying the linker structure, relative binding orientation, and stoichiometry of the ligand. The optimized conjugate showed potent and selective in vitro activity (EC50 ~ 100 pM), good serum half-life, and potent in vivo activity in prophylactic and treatment xenograft mouse models. This semisynthetic approach is likely to be applicable to the generation of additional bispecific agents using drug-like ligands selective for other cell-surface receptors.

Acute myeloid leukemia and novel biological treatments: monoclonal antibodies and cell-based gene-modified immune effectors

In the context of acute myeloid leukemia (AML) treatment, the interface between chemotherapy and immunotherapy is at present getting closer as never before. Scientific research is oriented in overcoming the main limits of actual chemotherapeutic regimens against AML, which still accounts for a considerable number of relapsed or resistant forms. A lot of investments have been done in the use of monoclonal antibodies (mAbs) and recently gene-modified immune cells have been considered as an alternative approach whenever chemotherapy fails to eradicate the disease. In this sense, AML is a potential suitable target for immunotherapeutic approaches, due to overexpression of several tumor antigens. Here we describe the state of the art of mAbs and cellular therapies employing engineered immune effectors, developed against specific AML antigens, in a window embracing preclinical research and translational studies to the clinical setting.

The current status and future impact of targeted therapies in non-Hodgkin lymphoma

A number of new, biologic targeted therapies have been developed for the treatment of lymphoid malignancies. These include anti-CD20 monoclonal antibodies designed with greater binding affinities and different mechanisms of action profiles compared with rituximab. Other extracellular antigens on B cells and T cells are also being targeted. Monoclonal antibodies have been conjugated to radioisotopes and cellular toxins. In addition, several exciting new small-molecule kinase inhibitors are in development that target intracellular pathways that contribute to the pathogenesis of these diseases. Drugs that affect the tumor microenvironment are also under investigation. The advantage of these targeted agents compared with standard chemotherapy is greater tumor specificity, a more favorable toxicity profile, and, when combined with scientific rationale, and in the appropriate setting, perhaps a better long-term outcome.

Novel targeted therapies in acute lymphoblastic leukemia

Chemotherapy alone cures only 25-45% of adult patients with acute lymphoblastic leukemia (ALL), making novel treatment agents and strategies desperately needed. The addition of monoclonal antibodies (rituximab, alemtuzumab, epratzumab) to chemotherapy has demonstrated encouraging results in patients with newly diagnosed and relapsed ALL. The anti-CD22 immunoconjugate, inotuzumab ozogamicin, and the anti-CD19 BiTE(®) antibody, blinatumomab, have demonstrated impressive single agent activity in patients with relapsed or refractory B-ALL. Early reports of chimeric antigen receptor therapies have been promising in patients with relapsed ALL. Other agents targeting NOTCH1, FLT3, the proteasome and DNA methylation are early in development. These new agents hope to improve the outcome of ALL therapy with less toxicity. The challenge going forward will be to find safe and effective combinations and determine where in the treatment schema these agents will be most effective in ALL therapy.

CDR-restricted engineering of native human scFvs creates highly stable and soluble bifunctional antibodies for subcutaneous delivery

While myriad molecular formats for bispecific antibodies have been examined to date, the simplest structures are often based on the scFv. Issues with stability and manufacturability in scFv-based bispecific molecules, however, have been a significant hindrance to their development, particularly for high-concentration, stable formulations that allow subcutaneous delivery. Our aim was to generate a tetravalent bispecific molecule targeting two inflammatory mediators for synergistic immune modulation. We focused on an scFv-Fc-scFv format, with a flexible (A4T)3 linker coupling an additional scFv to the C-terminus of an scFv-Fc. While one of the lead scFvs isolated directly from a naïve library was well-behaved and sufficiently potent, the parental anti-CXCL13 scFv 3B4 required optimization for affinity, stability, and cynomolgus ortholog cross-reactivity. To achieve this, we eschewed framework-based stabilizing mutations in favor of complementarity-determining region (CDR) mutagenesis and re-selection for simultaneous improvements in both affinity and thermal stability. Phage-displayed 3B4 CDR-mutant libraries were used in an aggressive "hammer-hug" selection strategy that incorporated thermal challenge, functional, and biophysical screening. This approach identified leads with improved stability and>18-fold, and 4,100-fold higher affinity for both human and cynomolgus CXCL13, respectively. Improvements were exclusively mediated through only 4 mutations in VL-CDR3. Lead scFvs were reformatted into scFv-Fc-scFvs and their biophysical properties ranked. Our final candidate could be formulated in a standard biopharmaceutical platform buffer at 100 mg/ml with<2% high molecular weight species present after 7 weeks at 4 °C and viscosity<15 cP. This workflow has facilitated the identification of a truly manufacturable scFv-based bispecific therapeutic suitable for subcutaneous administration.

Primer on tumor immunology and cancer immunotherapy

Individualized cancer therapy is a central goal of cancer biologists. Immunotherapy is a rational means to this end—because the immune system can recognize a virtually limitless number of antigens secondary to the biology of genetic recombination in B and T lymphocytes. The immune system is exquisitely structured to distinguish self from non-self, as demonstrated by anti-microbial immune responses. Moreover the immune system has the potential to recognize self from “altered-self”, which is the case for cancer. However, the immune system has mechanisms in place to inhibit self-reactive responses, many of which are usurped by evolving tumors. Understanding the interaction of cancer with the immune system provides insights into mechanisms that can be exploited to disinhibit anti-tumor immune responses. Here, we summarize the 2012 SITC Primer, reviewing past, present, and emerging immunotherapeutic approaches for the treatment of cancer—including targeting innate versus adaptive immune components; targeting and/or utilizing dendritic cells and T cells; the role of the tumor microenvironment; and immune checkpoint blockade.

CD19 expression in acute leukemia is not restricted to the cytogenetically aberrant populations

Aberrant expression of the B lymphoid marker, CD19, in acute myeloid leukemia (AML) has frequently been associated with t(8;21)(q22;q22). However, AML cases lacking t(8;21) may occasionally express CD19. We asked whether CD19 expression is restricted to the karyotypically abnormal leukemic cells in primary leukemia samples. We compared, by fluorescence in situ hybridization, CD19-positive and CD19-negative cells from nine patients with acute leukemia: three non-t(8;21) AML, three t(8;21) AML and three cases of acute lymphoblastic leukemia. There were no significant differences in karyotypic pattern between the CD19-positive and CD19-negative leukemic cells, raising the concern that therapeutically targeting CD19 for acute leukemia may not eradicate all malignant clones.