Clinical significance of CD33 nonsynonymous single-nucleotide polymorphisms in pediatric patients with acute myeloid leukemia treated with gemtuzumab-ozogamicin-containing chemotherapy

Developing a membrane-proximal CD33-targeting CAR T cell

BACKGROUND

CD33 is a tractable target in acute myeloid leukemia (AML) for chimeric antigen receptor (CAR) T cell therapy, but clinical success is lacking.

METHODS

We developed 3P14HLh28Z, a novel CD33-directed CD28/CD3Z-based CAR T cell derived from a high-affinity binder obtained through membrane-proximal fragment immunization in humanized mice.

RESULTS

We found that immunization exclusively with the membrane-proximal domain of CD33 is necessary for identification of membrane-proximal binders in humanized mice. Compared with clinically validated lintuzumab-based CAR T cells targeting distal CD33 epitopes, 3P14HLh28Z showed enhanced in vitro functionality as well as superior tumor control and increased overall survival in both low antigen density and clinically relevant patient-derived xenograft models. Increased activation and enhanced polyfunctionality led to enhanced efficacy.

CONCLUSIONS

Showing for the first time that a membrane-proximal CAR is superior to a membrane-distal one in the setting of CD33 targeting, our results demonstrate the rationale for targeting membrane-proximal epitopes with high-affinity binders. We also demonstrate the importance of optimizing CAR T cells for functionality in settings of both low antigen density and clinically relevant patient-derived models.

Drug-regulated CD33-targeted CAR T cells control AML using clinically optimized rapamycin dosing

Chimeric antigen receptor (CAR) designs that incorporate pharmacologic control are desirable; however, designs suitable for clinical translation are needed. We designed a fully human, rapamycin-regulated drug product for targeting CD33+ tumors called dimerizaing agent-regulated immunoreceptor complex (DARIC33). T cell products demonstrated target-specific and rapamycin-dependent cytokine release, transcriptional responses, cytotoxicity, and in vivo antileukemic activity in the presence of as little as 1 nM rapamycin. Rapamycin withdrawal paused DARIC33-stimulated T cell effector functions, which were restored following reexposure to rapamycin, demonstrating reversible effector function control. While rapamycin-regulated DARIC33 T cells were highly sensitive to target antigen, CD34+ stem cell colony-forming capacity was not impacted. We benchmarked DARIC33 potency relative to CD19 CAR T cells to estimate a T cell dose for clinical testing. In addition, we integrated in vitro and preclinical in vivo drug concentration thresholds for off-on state transitions, as well as murine and human rapamycin pharmacokinetics, to estimate a clinically applicable rapamycin dosing schedule. A phase I DARIC33 trial has been initiated (PLAT-08, NCT05105152), with initial evidence of rapamycin-regulated T cell activation and antitumor impact. Our findings provide evidence that the DARIC platform exhibits sensitive regulation and potency needed for clinical application to other important immunotherapy targets.

Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16a/NKG2D Immune-Modulating TriNKET® CC-96191

Increasing efforts are focusing on natural killer (NK) cell immunotherapies for AML. Here, we characterized CC-96191, a novel CD33/CD16a/NKG2D immune-modulating TriNKET®. CC-96191 simultaneously binds CD33, NKG2D, and CD16a, with NKG2D and CD16a co-engagement increasing the avidity for, and activation of, NK cells. CC-96191 was broadly active against human leukemia cells in a strictly CD33-dependent manner, with maximal efficacy requiring the co-engagement of CD16a and NKG2D. A frequent CD33 single nucleotide polymorphism, R69G, reduced CC-96191 potency but not maximal activity, likely because of reduced CD33 binding. Similarly, the potency, but not the maximal activity, of CC-96191 was reduced by high concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact activity. In the presence of CD33+ AML cells, CC-96191 activated NK cells but not T cells; while maximum anti-AML efficacy was similar, soluble cytokine levels were 10- to >100-fold lower than with a CD33/CD3 bispecific antibody. While CC-96191-mediated cytolysis was not affected by ABC transporter proteins, it was reduced by anti-apoptotic BCL-2 family proteins. Finally, in patient marrow specimens, CC-96191 eliminated AML cells but not normal monocytes, suggesting selectivity of TriNKET-induced cytotoxicity toward neoplastic cells. Together, these findings support the clinical exploration of CC-96191 as in NCT04789655.

Discovery, classification, evolution and diversity of Siglecs

Immunoglobulin (Ig) superfamily proteins play diverse roles in vertebrates, including regulation of cellular responses by sensing endogenous or exogenous ligands. Siglecs are a family of glycan-recognizing proteins belonging to the Ig superfamily (i.e., I-type lectins). Siglecs are expressed on various leukocyte types and are involved in diverse aspects of immunity, including the regulation of inflammatory responses, leukocyte proliferation, host-microbe interaction, and cancer immunity. Sialoadhesin/Siglec-1, CD22/Siglec-2, and myelin-associated glycoprotein/Siglec-4 were among the first to be characterized as members of the Siglec family, and along with Siglec-15, they are relatively well-conserved among tetrapods. Conversely, CD33/Siglec-3-related Siglecs (CD33rSiglecs, so named as they show high sequence similarity with CD33/Siglec-3) are encoded in a gene cluster with many interspecies variations and even intraspecies variations within some lineages such as humans. The rapid evolution of CD33rSiglecs expressed on leukocytes involved in innate immunity likely reflects the selective pressure by pathogens that interact and possibly exploit these Siglecs. Human Siglecs have several additional unique and/or polymorphic properties as compared with closely related great apes, changes possibly related to the loss of the sialic acid Neu5Gc, another distinctly human event in sialobiology. Multiple changes in human CD33rSiglecs compared to great apes include many examples of human-specific expression in non-immune cells, coinciding with human-specific diseases involving such cell types. Some Siglec gene polymorphisms have dual consequences-beneficial in a situation but detrimental in another. The association of human Siglec gene polymorphisms with several infectious and non-infectious diseases likely reflects the ongoing competition between the host and microbial pathogens.

Multiplex Base Editing to Protect from CD33-Directed Therapy: Implications for Immune and Gene Therapy

On-target toxicity to normal cells is a major safety concern with targeted immune and gene therapies. Here, we developed a base editing (BE) approach exploiting a naturally occurring CD33 single nucleotide polymorphism leading to removal of full-length CD33 surface expression on edited cells. CD33 editing in human and nonhuman primate (NHP) hematopoietic stem and progenitor cells (HSPCs) protects from CD33-targeted therapeutics without affecting normal hematopoiesis in vivo , thus demonstrating potential for novel immunotherapies with reduced off-leukemia toxicity. For broader applications to gene therapies, we demonstrated highly efficient (>70%) multiplexed adenine base editing of the CD33 and gamma globin genes, resulting in long-term persistence of dual gene-edited cells with HbF reactivation in NHPs. In vitro , dual gene-edited cells could be enriched via treatment with the CD33 antibody-drug conjugate, gemtuzumab ozogamicin (GO). Together, our results highlight the potential of adenine base editors for improved immune and gene therapies.

Graphical abstract

Treating CD33-Positive de novo Acute Myeloid Leukemia in Pediatric Patients: Focus on the Clinical Value of Gemtuzumab Ozogamicin

Although survival in pediatric acute myeloid leukemia (AML) has increased considerably over the past decades, refractory disease and relapse rates remain high. Refractory and relapsed disease are difficult to treat, with overall survival rates less than 40-50%. Preventing relapse should, therefore, be one of the highest priorities. Current conventional chemotherapy regimens are hard to intensify due to associated toxic complications, hence more effective therapies that do not increase toxicity are needed. A promising targeted agent is the CD33-directed antibody-drug conjugate gemtuzumab ozogamicin (GO). Because CD33 is highly expressed on leukemic cells in the majority of AML patients, GO can be useful for a broad range of patients. Better relapse-free survival (RFS) after therapy including GO has been reported in several pediatric clinical trials; however, ambiguity about the clinical value of GO in newly diagnosed children remains. Treatment with GO in de novo AML patients aged ≥1 month, in combination with standard chemotherapy is approved in the United States, whereas in Europe, GO is only approved for newly diagnosed patients aged ≥15 years. In this review, we aimed to clarify the clinical value of GO for treatment of newly diagnosed pediatric AML patients. Based on current literature, GO seems to have additional value, in terms of RFS, and acceptable toxicity when used in addition to chemotherapy during initial treatment. Moreover, in KMT2A-rearranged patients, the clinical value of GO was even more evident. Also, we addressed predictors of response, being CD33 expression and SNPs, PgP-1 and Annexin A5. The near finalized intent-to-file clinical trial in the MyeChild consortium investigates whether fractionated dosing has additional value for pediatric AML, which may pave the way for a broader application of GO in pediatric AML.

Clinical, immunophenotypic, and cytogenetic characteristics of high-grade myelodysplastic syndromes with CD41-positive progenitor cells

BACKGROUND

Patients with myelodysplastic syndromes (MDS) with progenitors expressing CD41 (CD41+ MDS) showed a poor prognosis in a previous study but their detailed characteristics remain unclear.

METHODS

One hundred thirty-seven subjects at our institution were diagnosed with excess blasts (EB)-1, EB-2, and acute myeloid leukemia with a low blast count (20%-30%). The immunophenotypes of progenitor cells in their bone marrow (BM) were determined by CD45-gating flow cytometry. A false-positive reaction to CD41 was eliminated by examining the flow cytometry data of lymphocytes and monocytes in addition to progenitors and by examining CD42b in histological sections. The characteristics were compared between CD41+ and CD41- MDS patients.

RESULTS

Forty-three patients (31%) were CD41+. Additionally, 91% of the CD41+ MDS patients were very high-risk defined by the Revised International Prognostic Score System, which was higher than in patients with CD41- MDS (p = 0.015). Approximately 60% of the CD41+ MDS patients had a monosomal karyotype and very poor cytogenetics, which was higher than in CD41- MDS patients (p < 0.001). Normal cytogenetics was less common in CD41+ patients (p = 0.0016). Blasts with bleb formation were more abundant in CD41+ MDS patients (p = 0.026). All CD41+ MDS patients were positive for CD13 and were mostly positive for CD33. The frequency of aberrant expression of other antigens on progenitors was similar between CD41+ and CD41- MDS patients.

CONCLUSIONS

We determined clinical, immunophenotypic, and cytogenetic characteristics of CD41+ MDS patients. Further studies are needed to improve the survival of these patients.

Treatment options for acute myeloid leukemia patients aged <60 years

Treatment of acute myeloid leukemia (AML) has changed over the last few years, after the discovery of new drugs selectively targeting AML blasts. Although 3/7 remains the standard of care for most AML patients, several new targeted agents (such as FLT3 inhibitors, CPX-351, gemtuzumab ozogamicin, BCL-2 inhibitor, and oral azacitidine), either as single agents or combined with standard chemotherapy, are approaching clinical practice, starting a new era in AML management. Moreover, emerging evidence has demonstrated that high-risk AML patients might benefit from both allogeneic stem cell transplant and maintenance therapy, providing new opportunities, as well as new challenges, for treating clinicians. In this review, we summarize available data on first-line therapy in young AML patients focusing on targeted therapies, integrating established practice with new evidence, in the effort to outline the contours of a new therapeutic paradigm, that of a “total therapy”, which goes beyond obtaining complete remission.

No Evidence that CD33 rs12459419 Polymorphism Predicts Gemtuzumab Ozogamicin Response in Consolidation Treatment of Acute Myeloid Leukemia Patients: Experience of the PETHEMA Group

Gemtuzumab ozogamicin (GO) is a conjugate of a monoclonal antibody and calicheamicin, which has been reapproved for the treatment of acute myeloid leukemia (AML). AML patients with the CD33 rs12459419 CC genotype might benefit from the addition of GO to intensive treatment in contrast to patients with CT/TT genotypes. Nevertheless, contradictory results have been reported. We sought to shed light on the prediction of GO response in AML patients with rs12459419 polymorphism who were treated with GO in the consolidation (n = 70) or reinduction (n = 20) phase. The frequency distribution of the rs12459419 polymorphism in the complete cohort of patients was 44.4% (n = 40), 50% (n = 45), and 5.6% (n = 5) for CC, CT, and TT genotypes, respectively. Regarding the patients treated with GO for consolidation, we performed a Kaplan-Meier analysis of overall survival and relapse-free survival according to the rs12459419 polymorphism (CC vs. CT/TT patients) and genetic risk using the European Leukemia Net (ELN) 2010 risk score. We also carried out a Cox regression analysis for the prediction of overall survival, with age and ELN 2010 as covariates. We found no statistical significance in the univariate or multivariate analysis. Additionally, we performed a global Kaplan-Meier analysis for the patients treated with GO for reinduction and did not find significant differences; however, our cohort was too small to draw any conclusion from this analysis. The use of GO in consolidation treatment is included in the approval of the compound; however, evidence regarding its efficacy in this setting is lacking. Rs12459419 polymorphism could help in the selection of patients who might benefit from GO. Regrettably, in our cohort, the rs12459419 polymorphism does not seem to be an adequate tool for the selection of patients who might benefit from the addition of GO in consolidation cycles.

Role of Pharmacogenetics in the Treatment of Acute Myeloid Leukemia: Systematic Review and Future Perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by remarkable toxicity and great variability in response to treatment. Plenteous pharmacogenetic studies have already been published for classical therapies, such as cytarabine or anthracyclines, but such studies remain scarce for newer drugs. There is evidence of the relevance of polymorphisms in response to treatment, although most studies have limitations in terms of cohort size or standardization of results. The different responses associated with genetic variability include both increased drug efficacy and toxicity and decreased response or resistance to treatment. A broad pharmacogenetic understanding may be useful in the design of dosing strategies and treatment guidelines. The aim of this study is to perform a review of the available publications and evidence related to the pharmacogenetics of AML, compiling those studies that may be useful in optimizing drug administration.

Pseudogene-Mediated Gene Conversion After CRISPR-Cas9 Editing Demonstrated by Partial CD33 Conversion with SIGLEC22P

Although gene editing workflows typically consider the possibility of off-target editing, pseudogene-directed homology repair has not, to our knowledge, been reported previously. Here, we employed a CRISPR-Cas9 strategy for targeted excision of exon 2 in CD33 in U937 human monocyte cell line. Candidate clonal cell lines were screened by using a clinically relevant antibody known to label the IgV domain encoded by exon 2 (P67.6, gemtuzumab). In addition to the anticipated deletion of exon 2, we also found unexpected P67.6-negative cell lines, which had apparently retained CD33 exon 2. Sequencing revealed that these lines underwent gene conversion from the nearby SIGLEC22P pseudogene during homology repair that resulted in three missense mutations relative to CD33. Ectopic expression studies confirmed that the P67.6 epitope is dependent upon these amino acids. In summation, we report that pseudogene-directed homology repair can lead to aberrant CRISPR gene editing.

Therapeutic Targeting of Acute Myeloid Leukemia by Gemtuzumab Ozogamicin

Acute myeloid leukemia (AML) is a complex hematological malignancy characterized by genetic and clinical heterogeneity and high mortality. Despite the recent introduction of novel pharmaceutical agents in hemato-oncology, few advancements have been made in AML for decades. In the last years, the therapeutic options have rapidly changed, with the approval of innovative compounds that provide new opportunities, together with new challenges for clinicians: among them, on 1 September, 2017 the Food and Drug Administration granted approval for Gemtuzumab Ozogamicin (GO) in combination with daunorubicin and cytarabine for the treatment of adult patients affected by newly diagnosed CD33⁺ AML. Benefits of GO-based regimens were also reported in the pre- and post-transplantation settings. Moreover, several biomarkers of GO response have been suggested, including expression of CD33 and multidrug resistance genes, cytogenetic and molecular profiles, minimal residual disease and stemness signatures. Among them, elevated CD33 expression on blast cells and non-adverse cytogenetic or molecular risk represent largely validated predictors of good response.

CD33 Expression and Gentuzumab Ozogamicin in Acute Myeloid Leukemia: Two Sides of the Same Coin

Simple Summary

Roughly 85–90% of adult and pediatric acute myeloid leukemia (AML) are CD33-positive. Gemtuzumab ozogamicin (GO), a humanized murine IgG4 anti-CD33 antibody, is the first target therapy approved in AML therapeutic scenario. This review focuses on current biological information and clinical data from several studies investigating the use of GO in patients with AML. Over the years, flow cytometry, cytogenetics, molecular techniques, and genotyping studies of CD33 SNPs have provided a comprehensive analysis of promising biomarkers for GO responses and have potentially helped to identify subgroups of patients that may benefit from GO addition to standard chemotherapies. Increased understanding of molecular mutations, altered intracellular pathways, and their potential relationship with CD33 expression may open new therapeutic landscapes based on combinatorial regimens in an AML scenario.

Abstract

Acute myeloid leukemia (AML), the most frequent acute leukemia in adults, has been historically treated with infusional cytarabine (ara-c) + daunorubicin (3 + 7) for at least 40 years. The first “target therapy” to be introduced was the monoclonal anti-CD33 gemtuzumab ozogamicin (GO) in 2004. Unfortunately, in 2010 it was voluntarily withdrawn from the market both for safety reasons related to potential liver toxicity and veno-occlusive disease (VOD) and because clinical studies failed to confirm the clinical benefit during induction and maintenance. Seven years later, GO was re-approved based on new data, including insights into its mechanism of action on its target receptor CD33 expressed on myeloid cells. The present review focuses on current biological information and clinical data from several studies investigating GO. Cytogenetic, molecular, and immunophenotypic data are now able to predict the potential positive advantages of GO, with the exception of high-risk AML patients who do not seem to benefit. GO can be considered a ‘repurposed drug’ that could be beneficial for some patients with AML, mostly in combination with new drugs already approved or currently in testing.

A novel C2 domain binding CD33xCD3 bispecific antibody with potent T-cell redirection activity against acute myeloid leukemia

CD33 is expressed in 90% of patients with acute myeloid leukemia (AML), and its extracellular portion consists of a V domain and a C2 domain. A recent study showed that a single nucleotide polymorphism (SNP), rs12459419 (C > T), results in the reduced expression of V domain-containing CD33 and limited efficacy of V domain-binding anti-CD33 antibodies. We developed JNJ-67571244, a novel human bispecific antibody capable of binding to the C2 domain of CD33 and to CD3, to induce T-cell recruitment and CD33+ tumor cell cytotoxicity independently of their SNP genotype status. JNJ-67571244 specifically binds to CD33-expressing target cells and induces cytotoxicity of CD33+ AML cell lines in vitro along with T-cell activation and cytokine release. JNJ-67571244 also exhibited statistically significant antitumor activity in vivo in established disseminated and subcutaneous mouse models of human AML. Furthermore, this antibody depletes CD33+ blasts in AML patient blood samples with concurrent T-cell activation. JNJ-67571244 also cross-reacts with cynomolgus monkey CD33 and CD3, and dosing of JNJ-67571244 in cynomolgus monkeys resulted in T-cell activation, transient cytokine release, and sustained reduction in CD33+ leukocyte populations. JNJ-67571244 was well tolerated in cynomolgus monkeys up to 30 mg/kg. Lastly, JNJ-67571244 mediated efficient cytotoxicity of cell lines and primary samples regardless of their SNP genotype status, suggesting a potential therapeutic benefit over other V-binding antibodies. JNJ-67571244 is currently in phase 1 clinical trials in patients with relapsed/refractory AML and high-risk myelodysplastic syndrome.

Novel CD33 antibodies unravel localization, biology and therapeutic implications of CD33 isoforms

The aim of this study was to establish the therapeutic relevance of the CD33D2 isoform by developing novel antibodies targeting the IgC domain of CD33. Two novel IgC-targeting antibodies, HL2541 and 5C11-2, were developed, and CD33 isoforms were assessed using multiple assays in cells overexpressing either CD33FL or CD33D2 isoforms, unmodified acute myeloid leukemia (AML) cell lines and primary AML specimens representing different genotypes for the CD33 splicing single nucleotide polymorphism. CD33D2 was recognized on cells overexpressing CD33D2 and unmodified AML cell lines; however, minimal/no cell surface detection of CD33D2 was observed in primary AML specimens. Both isoforms were detected intracellularly using novel antibodies. Minimal cell surface expression of CD33D2 on primary AML/progenitor cells warrants further studies on anti-CD33D2 immunotherapeutics.

Biomarkers of Gemtuzumab Ozogamicin Response for Acute Myeloid Leukemia Treatment

Gemtuzumab ozogamicin (GO, Mylotarg®) consists of a humanized CD33-targeted antibody-drug conjugated to a calicheamicin derivative. Growing evidence of GO efficacy in acute myeloid leukemia (AML), demonstrated by improved outcomes in CD33-positive AML patients across phase I to III clinical trials, led to the Food and Drug Administration (FDA) approval on 1 September 2017 in CD33-positive AML patients aged 2 years and older. Discrepancies in GO recipients outcome have raised significant efforts to characterize biomarkers predictive of GO response and have refined the subset of patients that may strongly benefit from GO. Among them, CD33 expression levels, favorable cytogenetics (t(8;21), inv(16)/t(16;16), t(15;17)) and molecular alterations, such as NPM1, FLT3-internal tandem duplications and other signaling mutations, represent well-known candidates. Additionally, in depth analyses including minimal residual disease monitoring, stemness expression (LSC17 score), mutations or single nucleotide polymorphisms in GO pathway genes (CD33, ABCB1) and molecular-derived scores, such as the recently set up CD33_PGx6_Score, represent promising markers to enhance GO response prediction and improve patient management.

Apoptosis and genes involved in oral cancer - a comprehensive review

Oral cancers needs relentless research due to high mortality and morbidity associated with it. Despite of the comparable ease in accessibility to these sites, more than 2/3^rd cases are diagnosed in advanced stages. Molecular/genetic studies augment clinical assessment, classification and prediction of malignant potential of oral lesions, thereby reducing its incidence and increasing the scope for early diagnosis and treatment of oral cancers. Herein we aim to review the role of apoptosis and genes associated with it in oral cancer development in order to aid in early diagnosis, prediction of malignant potential and evaluation of possible treatment targets in oral cancer. An internet-based search was done with key words apoptosis, genes, mutations, targets and analysis to extract 72 articles after considering inclusion and exclusion criteria. The knowledge of genetics and genomics of oral cancer is of utmost need in order to stop the rising prevalence of oral cancer. Translational approach and interventions at the early stage of oral cancer, targeted destruction of cancerous cells by silencing or promoting involved genes should be the ideal intervention.

CD markers polymorphisms as prognostic biomarkers in hematological malignancies

The clusters of differentiation (CD) are surface molecules used for immunophenotyping of cells. The expression of CD markers is widely used to classify hematological malignancies, including leukemia and lymphoma. Single nucleotide polymorphisms (SNPs) are crucial genetic changes that can be associated with abnormal expression and function of CD markers. In this paper, we assess the prognostic effect of CD markers’ SNPs in hematological malignancies. Materials and methods and relevant literature was identified by a PubMed search (2001-2019) of English language papers using the following terms: ‘polymorphism’, ‘CD marker’, ‘leukemia’, ‘lymphoma’, ‘prognosis’, ‘CD marker’, and ‘polymorphism’. Many studies have demonstrated the effects of CD markers’ polymorphisms on risk of hematological malignancies. Also, SNPs of CD markers can be related with clinicopathological features, invasiveness, and response to therapy of these disorders. Considering the importance of SNPs in the expressions of CD markers, these genetic changes could be used as potential prognostic biomarkers in hematological malignancies. It is hoped that the evaluation of SNPs in CD markers will enable early diagnosis, prognosis, and detection of response to treatment. However, better understanding of SNPs in CD markers that are involved in hematological malignancies requires further studies on different populations of the worldwide.

Biological Hallmarks of Cancer in Alzheimer's Disease

Although Alzheimer's disease (AD) is an international health research priority for our aging population, little therapeutic progress has been made. This lack of progress may be partially attributable to disease heterogeneity. Previous studies have identified an inverse association of cancer and AD, suggesting that cancer history may be one source of AD heterogeneity. These findings are particularly interesting in light of the number of common risk factors and two-hit models hypothesized to commonly drive both diseases. We reviewed the ten hallmark biological alterations of cancer cells to investigate overlap with the AD literature and identified overlap of all ten hallmarks in AD, including (1) potentially common underlying risk factors, such as increased inflammation, deregulated cellular energetics, and genome instability; (2) inversely regulated mechanisms, including cell death and evading growth suppressors; and (3) functions with more complex, pleiotropic mechanisms, some of which may be stage-dependent in AD, such as cell adhesion/contact inhibition and angiogenesis. Additionally, we discuss the recent observation of a biological link between cancer and AD neuropathology. Finally, we address the therapeutic implications of this topic. The significant overlap of functional pathways and molecules between these diseases, some similarly and some oppositely regulated or functioning in each disease, supports the need for more research to elucidate cancer-related AD genetic and functional heterogeneity, with the aims of better understanding AD risk mediators, as well as further exploring the potential for some types of drug repurposing towards AD therapeutic development.

Evaluation of CD33 as a genetic risk factor for Alzheimer's disease

In 2011, genome-wide association studies implicated a polymorphism near CD33 as a genetic risk factor for Alzheimer's disease. This finding sparked interest in this member of the sialic acid-binding immunoglobulin-type lectin family which is linked to innate immunity. Subsequent studies found that CD33 is expressed in microglia in the brain and then investigated the molecular mechanism underlying the CD33 genetic association with Alzheimer's disease. The allele that protects from Alzheimer's disease acts predominately to increase a CD33 isoform lacking exon 2 at the expense of the prototypic, full-length CD33 that contains exon 2. Since this exon encodes the sialic acid ligand-binding domain, the finding that the loss of exon 2 was associated with decreased Alzheimer's disease risk was interpreted as meaning that a decrease in functional CD33 and its associated immune suppression was protective from Alzheimer's disease. However, this interpretation may need to be reconsidered given current findings that a genetic deletion which abrogates CD33 is not associated with Alzheimer's disease risk. Therefore, integrating currently available findings leads us to propose a model wherein the CD33 isoform lacking the ligand-binding domain represents a gain of function variant that reduces Alzheimer's disease risk.

CD33_PGx6_Score Predicts Gemtuzumab Ozogamicin Response in Childhood Acute Myeloid Leukemia: A Report From the Children's Oncology Group

PURPOSE

The US Food and Drug Administration recently announced reapproval of gemtuzumab ozogamicin (GO) for treatment of CD33-positive acute myeloid leukemia (AML), thus opening up opportunities to develop strategies for effective use of GO. In light of our recent report showing prognostic significance of CD33 splicing single nucleotide polymorphisms (SNPs), the objective of this study was to comprehensively evaluate CD33 SNPs for accurate prediction of patients with AML who are more or less likely to respond to GO.

PATIENTS AND METHODS

We investigated the five new CD33 SNPs (rs2455069, rs35112940, rs61736475, rs1803254, and rs201074739) for association with CD33 leukemic cell surface expression and clinical response in pediatric patients with AML enrolled in the Children's Oncology Group AAML0531 trial. We further developed a composite CD33 pharmacogenetics (PGx) score using six CD33 SNPs (CD33_PGx6_score) for association with clinical outcome.

RESULTS

Four CD33 SNPs were associated with cell surface CD33 levels and clinical response in the GO versus no-GO arms. Therefore, the CD33_PGx6_score was built using directional genotype scores for the previously reported splicing SNP and five new SNPs. Patients with a CD33_PGx6_score of 0 or higher had higher CD33 expression levels compared with patients with a score of less than 0 (P < .001). In addition, patients with a score of 0 or higher demonstrated an improved disease-free survival in the GO versus no-GO arms (62.5% ± 7.8% v 46.8% ± 8.3%, respectively; P = .008) and a reduced risk of relapse (28.3% ± 7.2% v 49.9% ± 8.4%, respectively; P < .001). No improvement from GO was observed in patients with a CD33-PGx6_score of less than 0. Consistent results were observed across the risk groups.

CONCLUSION

In this study, we report a composite CD33_PGx6_score using directional genotype scores of CD33 SNPs. Once validated, our findings hold promise for use of the CD33_PGx6_score to guide efficient use of GO in patients with AML. In addition, because the CD33_PGx6_score considers SNPs with varying abundance in different ethnic groups, it has potential for global application.

Possible Influences of Endogenous and Exogenous Ligands on the Evolution of Human Siglecs

Sialic acids, a group of acidic sugars abundantly expressed in the tissues of deuterostome animals but rarely found in microbes, serve as a "signature of self" for these animals. Cognate sensors for sialic acids include Siglecs, a family of transmembrane lectins of vertebrate immune systems that recognize glycans containing sialic acids. A type of sialic acid called N-glycolylneuraminic acid (Neu5Gc) is abundant in many mammalian lineages including great apes, the closest extant relatives of modern human, but was lost in the lineage leading to modern human via the pseudogenization of the CMAH gene encoding the enzyme that converts N-acetylneuraminic acid (Neu5Ac) to Neu5Gc. Loss of Neu5Gc appears to have influenced the evolution of human Siglecs, such as the adjustment of sialic acid binding preferences and the inactivation of at least one Siglec. In addition, various mechanistic studies using model systems and genetic association studies have revealed that some human Siglecs interact with pathogens and influence the outcome of infections, and these pathogens in turn likely influence the evolution of these Siglecs. By understanding the evolutionary forces affecting Siglecs, we shall achieve a better appreciation of Siglec functions, and by understanding Siglec functions, we can obtain deeper insight into the evolutionary processes driving Siglec evolution.

Gemtuzumab ozogamicin for treatment of newly diagnosed CD33-positive acute myeloid leukemia

In September 2017, the US FDA announced re-approval of gemtuzumab ozogamicin (GO), a CD33-targeting immunoconjugate, for treatment of newly diagnosed and relapsed/refractory acute myeloid leukemia (AML). This is a very significant step toward defining new treatment regimens in AML, as the treatment has essentially stayed unchanged with the '7 + 3 induction regimen' (7 days cytarabine and 3 days of anthracycline) since 1973. GO is the first antibody-drug conjugate to receive FDA approval for treating cancer. This review article discusses the challenges faced and lessons learned during the journey of GO for AML treatment. Selected trials that have made significant contribution in our understanding of the most efficacious and safe use of GO for treating AML patients as well as factors influencing GO response are highlighted in this article.

The return of gemtuzumab ozogamicin: a humanized anti-CD33 monoclonal antibody-drug conjugate for the treatment of newly diagnosed acute myeloid leukemia

Through the years gemtuzumab ozogamicin (GO) has moved from a panacea in the treatment of acute myeloid leukemia (AML) to a pariah and back again. Early promise of targeted therapy with accelerated approval in the United States in 2000 gave way to fear over increased toxicity in the absence of efficacy, which subsequently resulted in the drug manufacturer voluntarily withdrawing GO from the market in 2010. We outline the history of GO in terms of initial drug development and early clinical trials that ultimately led the way to GO frontline use in AML based on a series of Phase III studies. Among these studies, we discuss the similarities and differences in terms of dosing, frequency, response rates, and toxicities that ultimately led to the re-approval of GO in 2017 based on efficacy, particularly in patients with core-binding factor (CBF) leukemia. Herein, we also review the clinical efficacy of GO in the frontline treatment of acute promyelocytic leukemia, which is based on either initial patient high-risk disease or potential co-morbidities that preclude the use of arsenic trioxide (ATO). Finally, we assess the current evidence for biomarkers aside from initial cytogenetics that may predict a favorable response to GO.

A Unique Human Immunoglobulin Heavy Chain Variable Domain-Only CD33 CAR for the Treatment of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains a challenging pediatric and adult disease. Given the elevated expression of the CD33 antigen on leukemic blasts, therapeutic approaches to AML now feature the approved antibody drug conjugate (Mylotarg, GO) and investigational CART cell approaches incorporating CD33-binding domains derived from humanized scFvs. We designed a functional chimeric antigen receptor utilizing a human targeting sequence, derived from a heavy chain variable domain, termed CAR33VH. Lentiviral-based expression vectors which encoded CAR constructs incorporating the novel binding domain (CAR33VH), or the My96 scFv control binder (My96CAR) in frame with a CD8 hinge and transmembrane domain, a 4-1BB costimulatory domain and a CD3 zeta activation domain, were transduced into primary human CD4⁺ and CD8⁺ T cells, and CAR expression was confirmed by flow cytometry. CAR33VH, similar to My96CAR, demonstrated robust and specific cytotoxicity in short-term and long-term co-incubation killing assays against CD33⁺ AML lines. In overnight cytokine release assays in which CAR T cells were challenged with the CD33⁺ tumor cells HL-60, MOLM-14 and KG-1a, CAR33VH elicited IFN-gamma, TNF-alpha and IL-2. This was seen with CD33⁺ cell lines, but not when CAR T were cultured alone. Studies with a CD33⁻ cell line engineered to stably express the full length CD33 variant 1, or the naturally occurring CD33 splice variant 2, revealed that both CAR33VH and My96CAR, target the V domain of CD33, suggesting a similar therapeutic profile. Colony-formation assays utilizing peripheral blood CD34⁺ hematopoietic stem cells treated with CAR33VH, My96CAR, or with an untransduced T cell control, yielded similar numbers of BFU-E erythroid and CFU-GM myeloid colonies, suggesting a lack of CAR-related overt toxicity. In an in vivo AML model, NSG mice engrafted with MOLM-14 cells stably expressing firefly luciferase, both CAR33VH and CARMy96 efficiently eliminated tumors. In conclusion, we demonstrate for the first time the feasibility and efficacy of employing human variable domain-only binder derived from a phage display library in an anti-AML CAR design. CAR33VH, comprised of a human heavy-chain variable fragment-only antigen binding domain, was efficient in tumor killing in vitro and in vivo, and showed comparable functionality to the scFv-based My96CAR.

CD33 Splicing Polymorphism Determines Gemtuzumab Ozogamicin Response in De Novo Acute Myeloid Leukemia: Report From Randomized Phase III Children's Oncology Group Trial AAML0531

Purpose Gemtuzumab ozogamicin (GO), a CD33-targeted immunoconjugate, is a re-emerging therapy for acute myeloid leukemia (AML). CD33 single nucleotide polymorphism rs12459419 C>T in the splice enhancer region regulates the expression of an alternatively spliced CD33 isoform lacking exon2 (D2-CD33), thus eliminating the CD33 IgV domain, which is the antibody-binding site for GO, as well as diagnostic immunophenotypic panels. We aimed to determine the impact of the genotype of this splicing polymorphism in patients with AML treated with GO-containing chemotherapy. Patients and Methods CD33 splicing single nucleotide polymorphism was evaluated in newly diagnosed patients with AML randomly assigned to receive standard five-course chemotherapy alone (No-GO arm, n = 408) or chemotherapy with the addition of two doses of GO once during induction and once during intensification (GO arm, n = 408) as per the Children's Oncology Group AAML0531 trial. Results The rs12459419 genotype was CC in 415 patients (51%), CT in 316 patients (39%), and TT in 85 patients (10%), with a minor allele frequency of 30%. The T allele was significantly associated with higher levels of D2-CD33 transcript ( P < 1.0E^-6) and with lower diagnostic leukemic cell surface CD33 intensity ( P < 1.0E^-6). Patients with the CC genotype had significantly lower relapse risk in the GO arm than in the No-GO arm (26% v 49%; P < .001). However, in patients with the CT or TT genotype, exposure to GO did not influence relapse risk (39% v 40%; P = .85). Disease-free survival was higher in patients with the CC genotype in the GO arm than in the No-GO arm (65% v 46%, respectively; P = .004), but this benefit of GO addition was not seen in patients with the CT or TT genotype. Conclusion Our results suggest that patients with the CC genotype for rs12459419 have a substantial response to GO, making this a potential biomarker for the selection of patients with a likelihood of significant response to GO.

Gemtuzumab ozogamicin in acute myeloid leukemia

CD33 is variably expressed on leukemia blasts in almost all patients with acute myeloid leukemia (AML) and possibly leukemia stem cells in some. Efforts to target CD33 therapeutically have focused on gemtuzumab ozogamicin (GO; Mylotarg), an antibody-drug conjugate delivering a DNA-damaging calicheamicin derivative. GO is most effective in acute promyelocytic leukemia but induces remissions in other AML types and received accelerated approval in the US in 2000. However, because a large follow-up study showed no survival improvement and increased early deaths the drug manufacturer voluntarily withdrew the US New Drug Application in 2010. More recently, a meta-analysis of data from several trials reported better survival in adults with favorable- and intermediate-risk cytogenetics but not adverse-risk AML randomized to receive GO along with intensive induction chemotherapy. As a result, GO is being re-evaluated by regulatory agencies. Responses to GO are diverse and predictive biological response markers are needed. Besides cytogenetic risk, ATP-binding cassette transporter activity and possibly CD33 display on AML blasts may predict response, but established clinical assays and prospective validation are lacking. Single-nucleotide polymorphisms in CD33 may also be predictive, most notably rs12459419 where the minor T-allele leads to decreased display of full-length CD33 and preferential translation of a splice variant not recognized by GO. Data from retrospective analyses suggest only patients with the rs12459419 CC genotype may benefit from GO therapy but confirmation is needed. Most important may be markers for AML cell sensitivity to calicheamicin, which varies over 100 000-fold, but useful assays are unavailable. Novel CD33-targeted drugs may overcome some of GO's limitations but it is currently unknown whether such drugs will be more effective in patients benefitting from GO and/or improve outcomes in patients not benefitting from GO, and what the supportive care requirements will be to enable their safe use.

Evaluation of DNMT3A genetic polymorphisms as outcome predictors in AML patients

DNMT3A mutation is known as a recurrent event in acute myelogenous leukemia (AML) patients. However, association between DNMT3A genetic polymorphisms and AML patients' outcomes is unknown. DNMT3A 11 SNPs (rs11695471, rs2289195, rs734693, rs2276598, rs1465825, rs7590760, rs13401241, rs7581217, rs749131, rs41284843 and rs7560488) were genotyped in 344 diagnostic non-FAB-M3 AML patients from southern China. Patients underwent combined chemotherapy with cytarabine and anthracyclines. DNMT3A mRNA expression was analyzed in PBMCs from randomly selected AML patients. Multivariate analysis and combined genotype analysis showed that rs2276598 was associated with increased while rs11695471 and rs734693 were associated with decreased chemosensitivity (P<0.05), while rs11695471 (worse for OS), rs2289195 (favorable for OS and DFS) and rs2276598 (favorable for DFS) were significantly associated with disease prognosis (P<0.05). In conclusion, DNMT3A polymorphisms may be potential predictive markers for AML patients' outcomes, which might improve prognostic stratification of AML.

MicroRNA-mRNA Pairs Associated with Outcome in AML: From In Vitro Cell-Based Studies to AML Patients

Cytarabine is the primary chemotherapeutic agent used for treatment of acute myeloid leukemia (AML). Disease relapse after initial remission remains one of the most pressing therapeutic challenges in the treatment of AML. Relapsed disease is often resistant to cytarabine and subsequent salvage therapy is ineffective. Recent studies have shown that some microRNAs (miRNAs) are associated with prognosis, but have not yet explored the role of miRNAs in cellular response to cytarabine. We identified 20 miRNAs that associate with the in vitro cytarabine chemo-sensitivity or apoptotic response of eight AML cell lines. Out of the 20 miRNAs, data on 18 miRNAs was available in AML patients from The Cancer Genome Atlas database. Our stepwise-integrated analyses (step 1 - miRNA-target mRNA that were significantly correlated in AML patients; step 2 - mRNAs from step 1 with significant association with overall survival (OS)) identified 23 unique miRNA-mRNA pairs predictive of OS in AML patients. As expected HOX genes (HOXA9, HOXB7, and HOXA10) were identified to be regulated by miRs as well as predictive of worse OS. Additionally, miR107-Myb, miR-378-granzyme B involved in granzyme signaling and miR10a-MAP4K4 were identified to be predictive of outcome through integrated analysis. Although additional functional validations to establish clinical/pharmacologic importance of miRNA-mRNA pairs are needed, our results from RNA electrophoretic mobility shift assay confirmed binding of miR-10a, miR-378, and miR-107 with their target genes GALNT1, GZMB, and MYB, respectively. Integration of pathogenic and pharmacologically significant miRNAs and miRNA-mRNA relationships identified in our study opens up opportunities for development of targeted/miRNA-directed therapies.

Therapeutic Targeting of Siglecs using Antibody- and Glycan-Based Approaches

The sialic acid-binding immunoglobulin-like lectins (Siglecs) are a family of immunomodulatory receptors whose functions are regulated by their glycan ligands. Siglecs are attractive therapeutic targets because of their cell type-specific expression pattern, endocytic properties, high expression on certain lymphomas/leukemias, and ability to modulate receptor signaling. Siglec-targeting approaches with therapeutic potential encompass antibody- and glycan-based strategies. Several antibody-based therapies are in clinical trials and continue to be developed for the treatment of lymphoma/leukemia and autoimmune disease, while the therapeutic potential of glycan-based strategies for cargo delivery and immunomodulation is a promising new approach. Here we review these strategies with special emphasis on emerging approaches and disease areas that may benefit from targeting the Siglec family.

Genetics of CD33 in Alzheimer's disease and acute myeloid leukemia

The CD33 single-nucleotide polymorphism (SNP) rs3865444 has been associated with the risk of Alzheimer's disease (AD). Rs3865444 is in linkage disequilibrium with rs12459419 which has been associated with efficacy of an acute myeloid leukemia (AML) chemotherapeutic agent based on a CD33 antibody. We seek to evaluate the extent to which CD33 genetics in AD and AML can inform one another and advance human disease therapy. We have previously shown that these SNPs are associated with skipping of CD33 exon 2 in brain mRNA. Here, we report that these CD33 SNPs are associated with exon 2 skipping in leukocytes from AML patients and with a novel CD33 splice variant that retains CD33 intron 1. Each copy of the minor rs12459419T allele decreases prototypic full-length CD33 expression by ∼ 25% and decreases the AD odds ratio by ∼ 0.10. These results suggest that CD33 antagonists may be useful in reducing AD risk. CD33 inhibitors may include humanized CD33 antibodies such as lintuzumab which was safe but ineffective in AML clinical trials. Here, we report that lintuzumab downregulates cell-surface CD33 by 80% in phorbol-ester differentiated U937 cells, at concentrations as low as 10 ng/ml. Overall, we propose a model wherein a modest effect on RNA splicing is sufficient to mediate the CD33 association with AD risk and suggest the potential for an anti-CD33 antibody as an AD-relevant pharmacologic agent.

Intermediate-risk acute myeloid leukemia therapy: current and future

In recent years, research in molecular genetics has been instrumental in deciphering the molecular heterogeneity of acute myeloid leukemia (AML), in particular the subset of patients with "intermediate-risk" cytogenetics. However, at present, only the markers NPM1, CEBPA, and FLT3 have entered clinical practice. Treatment of intermediate-risk AML patients eligible for intensive therapy has not changed substantially. The "3 + 7" induction therapy still represents the standard of care. The addition of the immunoconjugate gemtuzumab ozogamicin to therapy has been shown to improve outcome; however, the drug is not approved for this use. A common standard for postremission therapy is the administration of repeated cycles of intermediate- to high-dose cytarabine. Allogeneic stem cell transplantation may offer a survival benefit for many patients with intermediate-risk AML. Patients are best selected based on the genetic profile of the leukemia cells and the risk associated with the transplantation itself. A myriad of novel agents targeting mutant leukemia drivers or deregulated pathways are in clinical development. In the past, many novel compounds have not met expectations; nonetheless, with the rapid developments in comprehensive molecular profiling and new drug design, there is the prospect of personalizing therapy and improving patient outcome.

Intermediate-risk acute myeloid leukemia therapy: current and future

In recent years, research in molecular genetics has been instrumental in deciphering the molecular heterogeneity of acute myeloid leukemia (AML), in particular the subset of patients with “intermediate-risk” cytogenetics. However, at present, only the markers NPM1, CEBPA, and FLT3 have entered clinical practice. Treatment of intermediate-risk AML patients eligible for intensive therapy has not changed substantially. The “3 + 7” induction therapy still represents the standard of care. The addition of the immunoconjugate gemtuzumab ozogamicin to therapy has been shown to improve outcome; however, the drug is not approved for this use. A common standard for postremission therapy is the administration of repeated cycles of intermediate- to high-dose cytarabine. Allogeneic stem cell transplantation may offer a survival benefit for many patients with intermediate-risk AML. Patients are best selected based on the genetic profile of the leukemia cells and the risk associated with the transplantation itself. A myriad of novel agents targeting mutant leukemia drivers or deregulated pathways are in clinical development. In the past, many novel compounds have not met expectations; nonetheless, with the rapid developments in comprehensive molecular profiling and new drug design, there is the prospect of personalizing therapy and improving patient outcome.

c-Myc plays part in drug resistance mediated by bone marrow stromal cells in acute myeloid leukemia

Acute myeloid leukemia (AML) is a malignant and aggressive disease not sensitive to chemotherapy. The dynamic interaction between AML cells and bone marrow (BM) microenvironment plays a critical role in response of this disease to chemotherapy. It is reported that mesenchymal stromal cells (MSC) are essential component of bone marrow microenvironment which affects the survival of AML cells. The aim of our research is to elucidate the mechanism of drug resistance of AML cells associated with MSC. We found that adhesion of AML cell lines U937, KG1a and primary AML cells to MSC inhibited cytotoxic drug-induced apoptosis. Western blot showed that c-Myc of AML cells cocultured with stroma was up-regulated. Treatment with 10058-F4, a small molecule inhibitor of MYC-MAX heterodimerization, or c-Myc siRNA significantly induced apoptosis. Western blot analysis further showed that inhibition of c-Myc induced expression of caspases-3, cleavage of PARP and reduced expression of Bcl-2, Bcl-xL and vascular endothelial growth factor (VEGF). Thus, we conclude that MSCs protected leukemia cells from apoptosis, at least in part, through c-Myc dependent mechanisms, and that c-Myc contributed to microenvironment-mediated drug resistance in AML. In summary, we declared that c-Myc is a potential therapeutic target for overcoming drug resistance in AML.

Inching toward cure of acute myeloid leukemia: a summary of the progress made in the last 50 years

Despite some claims to the contrary, I believe substantial progress has been made in the last half century toward cure of acute myeloid leukemia in children and adults. The tried and true mechanism for this progress has been clinical trial and error. This method has been supplemented with an ever-increasing amount of work at the clinical laboratory interface that is beginning to allow us to develop specific therapy for afflicted individuals. This review details where we stand today and how we got here.

Associations of genetic polymorphisms of Siglecs with human diseases

Genetic polymorphism studies in humans provide unique opportunities to understand human biology and the mechanisms of diseases. Correlations between polymorphisms in the genes encoding human Siglecs and various diseases have been reported. Leading examples, such as the CD33 polymorphism associated with late-onset Alzheimer's disease, are well supported by genetic replication and mechanistic studies, while some others (such as SIGLEC8 polymorphism associated with bronchial asthma and SIGLEC14 polymorphism associated with exacerbation of chronic obstructive pulmonary disease) may benefit reinforcement by independent genetic replication or mechanistic studies. In a few cases, such as MAG polymorphism associated with psychological disorder and CD22 polymorphism associated with autoimmune disease, the phenotype associated with a genetic polymorphism of a Siglec gene and that of an enzyme gene involved in the biosynthesis of Siglec ligand show some overlap, providing indirect support for the observed genotype-phenotype association. Although studies using engineered mutant mice have provided invaluable insights into the biological functions and mechanisms of diseases, it is not always possible to develop appropriate mouse model to replicate human situations because of significant species-to-species differences, which can be a major obstacle in understanding the biology of some of human CD33/Siglec-3-related Siglecs. Further studies in genetic polymorphisms of human Siglecs, combined with appropriate functional studies, may reveal unexpected biological roles of human Siglecs, and identify possible targets for prevention and/or treatment of certain diseases.

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.

Gemtuzumab ozogamicin can reduce minimal residual disease in patients with childhood acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is an active agent for the treatment of CD33-postive acute myeloid leukemia (AML) and may improve the outcome of specific patient subgroups when combined with conventional chemotherapy. However, to the best of the authors' knowledge, the effects of GO on levels of minimal residual disease (MRD) are unknown.

METHODS

Pediatric patients with AML who received GO, either alone or in combination with chemotherapy on the AML02 multicenter trial, were analyzed to determine the effects of GO on MRD and outcome.

RESULTS

Among 17 patients who received GO alone because of persistent leukemia, 14 had a reduction in their MRD level and 13 became MRD negative. Of the 29 who received chemotherapy in combination with GO after responding poorly to chemotherapy, 28 demonstrated reduced MRD and 13 became MRD negative. Treatment with GO effectively reduced MRD before hematopoietic stem cell transplantation and was not found to be associated with increased treatment-related mortality after transplantation.

CONCLUSIONS

GO is effective in reducing MRD levels in pediatric patients with AML and may improve the outcome of those patients at high risk of disease recurrence.

Antibody-based therapy of acute myeloid leukemia with gemtuzumab ozogamicin

Antibodies have created high expectations for effective yet tolerated therapeutics in acute myeloid leukemia (AML). Hitherto the most exploited target is CD33, a myeloid differentiation antigen found on AML blasts in most patients and, perhaps, leukemic stem cells in some. Treatment efforts have focused on conjugated antibodies, particularly gemtuzumab ozogamicin (GO), an anti-CD33 antibody carrying a toxic calicheamicin-g 1 derivative that, after intracellular hydrolytic release, induces DNA strand breaks, apoptosis, and cell death. Serving as paradigm for this strategy, GO was the first anti-cancer immunoconjugate to obtain regulatory approval in the U.S. While efficacious as monotherapy in acute promyelocytic leukemia (APL), GO alone induces remissions in less than 25-35% of non-APL AML patients. However, emerging data from well controlled trials now indicate that GO improves survival for many non-APL AML patients, supporting the conclusion that CD33 is a clinically relevant target for some disease subsets. It is thus unfortunate that GO has become unavailable in many parts of the world, and the drug's usefulness should be reconsidered and selected patients granted access to this immunoconjugate.

Acute myeloid leukemia stem cells and CD33-targeted immunotherapy

Although the identification of cancer stem cells as therapeutic targets is now actively being pursued in many human malignancies, the leukemic stem cells in acute myeloid leukemia (AML) are a paradigm of such a strategy. Heterogeneity of these cells was suggested by clonal analyses indicating the existence of both leukemias resulting from transformed multipotent CD33(-) stem cells as well others arising from, or predominantly involving, committed CD33(+) myeloid precursors. The latter leukemias, which may be associated with an intrinsically better prognosis, offer a particularly attractive target for stem cell-directed therapies. Targeting the CD33 differentiation antigen with gemtuzumab ozogamicin was the first attempt of such an approach. Emerging clinical data indicate that gemtuzumab ozogamicin is efficacious not only for acute promyelocytic leukemia but, in combination with conventional chemotherapy, also for other favorable- and intermediate-risk AMLs, providing the first proof-of-principle evidence for the validity of this strategy. Herein, we review studies on the nature of stem cells in AML, discuss clinical data on the effectiveness of CD33-directed therapy, and consider the mechanistic basis for success and failure in various AML subsets.