Association of Combined Focal 22q11.22 Deletion and IKZF1 Alterations With Outcomes in Childhood Acute Lymphoblastic Leukemia.

IMPORTANCE: Alterations in the IKZF1 gene drive B-cell acute lymphoblastic leukemia (B-ALL) but are not routinely used to stratify patients by risk because of inconsistent associations with outcomes. We describe a novel deletion in 22q11.22 that was consistently associated with very poor outcomes in patients with B-ALL with IKZF1 alterations. OBJECTIVE: To determine whether focal deletions within the λ variable chain region in chromosome 22q11.22 were associated with patients with B-ALL with IKZF1 alterations with the highest risk of relapse and/or death. DESIGN, SETTING, AND PARTICIPANTS: This cohort study included 1310 primarily high-risk pediatric patients with B-ALL who were taken from 6 independent clinical cohorts, consisting of 3 multicenter cohorts (AALL0232 [2004-2011], P9906 [2000-2003], and patients with Down syndrome who were pooled from national and international studies) and 3 single-institution cohorts (University of Utah [Salt Lake City], Children's Hospital of Philadelphia [Philadelphia, Pennsylvania], and St. Jude Children's Hospital [Memphis, Tennessee]). Data analysis began in 2011 using patients from the older studies first, and data analysis concluded in 2021. EXPOSURES: Focal 22q11.22 deletions. MAIN OUTCOMES AND MEASURES: Event-free and overall survival was investigated. The hypothesis that 22q11.22 deletions stratified the prognostic effect of IKZF1 alterations was formulated while investigating nearby deletions in VPREB1 in 2 initial cohorts (n = 270). Four additional cohorts were then obtained to further study this association (n = 1040). RESULTS: This study of 1310 patients with B-ALL (717 male [56.1%] and 562 female patients [43.9%]) found that focal 22q11.22 deletions are frequent (518 of 1310 [39.5%]) in B-ALL and inconsistent with physiologic V(D)J recombination. A total of 299 of 1310 patients with B-ALL had IKZF1 alterations. Among patients with IKZF1 alterations, more than half shared concomitant focal 22q11.22 deletions (159 of 299 [53.0%]). Patients with combined IKZF1 alterations and 22q11.22 deletions had worse outcomes compared with patients with IKZF1 alterations and wild-type 22q11.22 alleles in every cohort examined (combined cohorts: 5-year event-free survival rates, 43.3% vs 68.5%; hazard ratio [HR], 2.18; 95% CI, 1.54-3.07; P < .001; 5-year overall survival rates, 66.9% vs 83.9%; HR, 2.05; 95% CI, 1.32-3.21; P = .001). While 22q11.22 deletions were not prognostic in patients with wild-type IKZF1 , concomitant 22q11.22 deletions in patients with IKZF1 alterations stratified outcomes across additional risk groups, including patients who met the IKZF1plus criteria, and maintained independent significance in multivariate analysis for event-free survival (HR, 2.05; 95% CI, 1.27-3.29; P = .003) and overall survival (HR, 1.83; 95% CI, 1.01-3.34; P = .05). CONCLUSIONS AND RELEVANCE: This cohort study suggests that 22q11.22 deletions identify patients with B-ALL and IKZF1 alterations who have very poor outcomes and may offer a new genetic biomarker to further refine B-ALL risk stratification and treatment strategies.

The chaperonin CCT8 controls proteostasis essential for T cell maturation, selection, and function.

T cells rely for their development and function on the correct folding and turnover of proteins generated in response to a broad range of molecular cues. In the absence of the eukaryotic type II chaperonin complex, CCT, T cell activation induced changes in the proteome are compromised including the formation of nuclear actin filaments and the formation of a normal cell stress response. Consequently, thymocyte maturation and selection, and T cell homeostatic maintenance and receptor-mediated activation are severely impaired. In the absence of CCT-controlled protein folding, Th2 polarization diverges from normal differentiation with paradoxical continued IFN-γ expression. As a result, CCT-deficient T cells fail to generate an efficient immune protection against helminths as they are unable to sustain a coordinated recruitment of the innate and adaptive immune systems. These findings thus demonstrate that normal T cell biology is critically dependent on CCT-controlled proteostasis and that its absence is incompatible with protective immunity.

Neuropathology of a Case With Fatal CAR T-Cell-Associated Cerebral Edema.

Chimeric antigen receptor (CAR) T cells are a new and powerful class of cancer immunotherapeutics that have shown potential for the treatment of hematopoietic malignancies. The tremendous promise of this approach is tempered by safety concerns, including potentially fatal neurotoxicity, sometimes but not universally associated with cytokine release syndrome. We describe the postmortem examination of a brain from a 21-year-old patient with relapsed pre-B cell acute lymphoblastic leukemia (ALL) who died from fulminant cerebral edema following CAR T-cell infusion. We found a range of changes that included activation of microglia, expansion of perivascular spaces by proteinaceous exudate, and clasmatodendrosis-a beading of glial fibrillary acidic protein consistent with astrocyte injury. Notably, within the brain parenchyma, we identified only infrequent T cells and did not identify ALL cells or CAR T cells. The overall findings are nonspecific but raise the possibility of astrocyte and blood-brain barrier dysfunction as a potential etiology of fatal CAR T-cell neurotoxicity in this patient.

Trim33 is essential for macrophage and neutrophil mobilization to developmental or inflammatory cues.

Macrophages infiltrate and establish in developing organs from an early stage, often before these have become vascularized. Similarly, leukocytes, in general, can quickly migrate through tissues to any site of wounding. This unique capacity is rooted in their characteristic amoeboid motility, the genetic basis of which is poorly understood. Trim33 (also known as Tif1-γ), a nuclear protein that associates with specific DNA-binding transcription factors to modulate gene expression, has been found to be mainly involved in hematopoiesis and gene regulation mediated by TGF-ß. Here, we have discovered that in Trim33-deficient zebrafish embryos, primitive macrophages are unable to colonize the central nervous system to become microglia. Moreover, both macrophages and neutrophils of Trim33-deficient embryos display a reduced basal mobility within interstitial tissues, and a profound lack of a response to inflammatory recruitment signals, including local bacterial infections. Correlatively, Trim33-deficient mouse bone marrow-derived macrophages display a strongly reduced three-dimensional amoeboid mobility in fibrous collagen gels. The transcriptional regulator Trim33 is thus revealed as being essential for the navigation of macrophages and neutrophils towards developmental or inflammatory cues within vertebrate tissues.

NACA deficiency reveals the crucial role of somite-derived stromal cells in haematopoietic niche formation.

The ontogeny of haematopoietic niches in vertebrates is essentially unknown. Here we show that the stromal cells of the caudal haematopoietic tissue (CHT), the first niche where definitive haematopoietic stem/progenitor cells (HSPCs) home in zebrafish development, derive from the caudal somites through an epithelial-mesenchymal transition (EMT). The resulting stromal cell progenitors accompany the formation of the caudal vein sinusoids, the other main component of the CHT niche, and mature into reticular cells lining and interconnecting sinusoids. We characterize a zebrafish mutant defective in definitive haematopoiesis due to a deficiency in the nascent polypeptide-associated complex alpha subunit (NACA). We demonstrate that the defect resides not in HSPCs but in the CHT niche. NACA-deficient stromal cell progenitors initially develop normally together with the sinusoids, and HSPCs home to the resulting niche, but stromal cell maturation is compromised, leading to a niche that is unable to support HSPC maintenance, expansion and differentiation.

Targeting insulin-like growth factor 1 leads to amelioration of inflammatory demyelinating disease.

In patients with multiple sclerosis (MS) and in mice with experimental autoimmune encephalomyelitis (EAE), proliferating autoreactive T cells play an important role in the pathogenesis of the disease. Due to the importance of these myelin-specific T cells, these cells have been therapeutic targets in a variety of treatments. Previously we found that Lenaldekar (LDK), a novel small molecule, could inhibit exacerbations in a preclinical model of MS when given at the start of an EAE exacerbation. In those studies, we found that LDK could inhibit human T cell recall responses and murine myelin responses in vitro. In these new studies, we found that LDK could inhibit myelin specific T cell responses through the insulin-like growth factor-1 receptor (IGF-1R) pathway. Alteration of this pathway led to marked reduction in T cell proliferation and expansion. Blocking this pathway could account for the observed decreases in clinical signs and inflammatory demyelinating disease, which was accompanied by axonal preservation. Our data indicate that IGF-1R could be a potential target for new therapies for the treatment of autoimmune diseases where autoreactive T cell expansion is a requisite for disease.

Ribosomal protein SA haploinsufficiency in humans with isolated congenital asplenia.

Isolated congenital asplenia (ICA) is characterized by the absence of a spleen at birth in individuals with no other developmental defects. The patients are prone to life-threatening bacterial infections. The unbiased analysis of exomes revealed heterozygous mutations in RPSA in 18 patients from eight kindreds, corresponding to more than half the patients and over one-third of the kindreds studied. The clinical penetrance in these kindreds is complete. Expression studies indicated that the mutations carried by the patients-a nonsense mutation, a frameshift duplication, and five different missense mutations-cause autosomal dominant ICA by haploinsufficiency. RPSA encodes ribosomal protein SA, a component of the small subunit of the ribosome. This discovery establishes an essential role for RPSA in human spleen development.

DiGeorge syndrome gene tbx1 functions through wnt11r to regulate heart looping and differentiation.

DiGeorge syndrome (DGS) is the most common microdeletion syndrome, and is characterized by congenital cardiac, craniofacial and immune system abnormalities. The cardiac defects in DGS patients include conotruncal and ventricular septal defects. Although the etiology of DGS is critically regulated by TBX1 gene, the molecular pathways underpinning TBX1's role in heart development are not fully understood. In this study, we characterized heart defects and downstream signaling in the zebrafish tbx1(-/-) mutant, which has craniofacial and immune defects similar to DGS patients. We show that tbx1(-/-) mutants have defective heart looping, morphology and function. Defective heart looping is accompanied by failure of cardiomyocytes to differentiate normally and failure to change shape from isotropic to anisotropic morphology in the outer curvatures of the heart. This is the first demonstration of tbx1's role in regulating heart looping, cardiomyocyte shape and differentiation, and may explain how Tbx1 regulates conotruncal development in humans. Next we elucidated tbx1's molecular signaling pathway guided by the cardiac phenotype of tbx1(-/-) mutants. We show for the first time that wnt11r (wnt11 related), a member of the non-canonical Wnt pathway, and its downstream effector gene alcama (activated leukocyte cell adhesion molecule a) regulate heart looping and differentiation similarly to tbx1. Expression of both wnt11r and alcama are downregulated in tbx1(-/-) mutants. In addition, both wnt11r (-/-) mutants and alcama morphants have heart looping and differentiation defects similar to tbx1(-/-) mutants. Strikingly, heart looping and differentiation in tbx1(-/-) mutants can be partially rescued by ectopic expression of wnt11r or alcama, supporting a model whereby heart looping and differentiation are regulated by tbx1 in a linear pathway through wnt11r and alcama. This is the first study linking tbx1 and non-canonical Wnt signaling and extends our understanding of DGS and heart development.

Discovery of biologically active oncologic and immunologic small molecule therapies using zebrafish: overview and example of modulation of T cell activation.

Zebrafish models continue to gain popularity as in vivo models for drug discovery. Described in this overview are advantages and challenges of zebrafish drug screening, as well as a novel in vivo screen for immunomodulatory compounds using transgenic, T cell reporting zebrafish larvae designed for discovery of compounds targeting T cell leukemia. This assay system allows rapid screening of large numbers of compounds while avoiding the pitfalls of assays based on cell cultures, which lack biologic context and are afflicted by genomic instability. The rationale for this approach is based on similarities of immature normal T cells and developmentally arrested, malignant lymphoblasts in mammalian species. The screening algorithm has been used to identify a nontoxic compound with activity in both acute leukemia models and models of multiple sclerosis, demonstrating the utility of this screening procedure.

Tbl3 regulates cell cycle length during zebrafish development.

The regulation of cell cycle rate is essential for the correct timing of proliferation and differentiation during development. Changes to cell cycle rate can have profound effects on the size, shape and cell types of a developing organ. We previously identified a zebrafish mutant ceylon (cey) that has a severe reduction in T cells and hematopoietic stem/progenitor cells (HSPCs). Here we find that the cey phenotype is due to absence of the gene transducin (beta)-like 3 (tbl3). The tbl3 homolog in yeast regulates the cell cycle by maintaining rRNA levels and preventing p53-induced cell death. Zebrafish tbl3 is maternally expressed, but later in development its expression is restricted to specific tissues. Tissues expressing tbl3 are severely reduced in cey mutants, including HSPCs, the retina, exocrine pancreas, intestine, and jaw cartilage. Specification of these tissues is normal, suggesting the reduced size is due to a reduced number of differentiated cells. Tbl3 MO injection into either wild-type or p53-/- mutant embryos phenocopies cey, indicating that loss of tbl3 causes specific defects in cey. Progression of both hematopoietic and retinal development is delayed beginning at 3 day post fertilization due to a slowing of the cell cycle. In contrast to yeast, reduction of Tbl3 causes a slowing of the cell cycle without a corresponding increase in p53 induced cell death. These data suggest that tbl3 plays a tissue-specific role regulating cell cycle rate during development.

Genomic amplification of an endogenous retrovirus in zebrafish T-cell malignancies.

Genomic instability plays a crucial role in oncogenesis. Somatically acquired mutations can disable some genes and inappropriately activate others. In addition, chromosomal rearrangements can amplify, delete, or even fuse genes, altering their functions and contributing to malignant phenotypes. Using array comparative genomic hybridization (aCGH), a technique to detect numeric variations between different DNA samples, we examined genomes from zebrafish (Danio rerio) T-cell leukemias of three cancer-prone lines. In all malignancies tested, we identified recurring amplifications of a zebrafish endogenous retrovirus. This retrovirus, ZFERV, was first identified due to high expression of proviral transcripts in thymic tissue from larval and adult fish. We confirmed ZFERV amplifications by quantitative PCR analyses of DNA from wild-type fish tissue and normal and malignant D. rerio T cells. We also quantified ZFERV RNA expression and found that normal and neoplastic T cells both produce retrovirally encoded transcripts, but most cancers show dramatically increased transcription. In aggregate, these data imply that ZFERV amplification and transcription may be related to T-cell leukemogenesis. Based on these data and ZFERV's phylogenetic relation to viruses of the murine-leukemia-related virus class of gammaretroviridae, we posit that ZFERV may be oncogenic via an insertional mutagenesis mechanism.

Zebrafish screen identifies novel compound with selective toxicity against leukemia.

To detect targeted antileukemia agents we have designed a novel, high-content in vivo screen using genetically engineered, T-cell reporting zebrafish. We exploited the developmental similarities between normal and malignant T lymphoblasts to screen a small molecule library for activity against immature T cells with a simple visual readout in zebrafish larvae. After screening 26 400 molecules, we identified Lenaldekar (LDK), a compound that eliminates immature T cells in developing zebrafish without affecting the cell cycle in other cell types. LDK is well tolerated in vertebrates and induces long-term remission in adult zebrafish with cMYC-induced T-cell acute lymphoblastic leukemia (T-ALL). LDK causes dephosphorylation of members of the PI3 kinase/AKT/mTOR pathway and delays sensitive cells in late mitosis. Among human cancers, LDK selectively affects survival of hematopoietic malignancy lines and primary leukemias, including therapy-refractory B-ALL and chronic myelogenous leukemia samples, and inhibits growth of human T-ALL xenografts. This work demonstrates the utility of our method using zebrafish for antineoplastic candidate drug identification and suggests a new approach for targeted leukemia therapy. Although our efforts focused on leukemia therapy, this screening approach has broad implications as it can be translated to other cancer types involving malignant degeneration of developmentally arrested cells.

Human T cell expansion and experimental autoimmune encephalomyelitis inhibited by Lenaldekar, a small molecule discovered in a zebrafish screen.

Immune-mediated diseases [multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE)] are driven by proliferating, highly activated autoreactive T-cells that are unresponsive to in vivo immunoregulatory mechanisms. The compound Lenaldekar (LDK) was identified in a zebrafish screen by inhibiting T-cell expansion. By monitoring mitogen- and antigen-driven proliferation, we found that LDK inhibited human and murine T-cell expansion in a non-cytolytic manner. This suppressive activity directly correlated with the degree of activation/proliferation of the T-cells. In testing LDK in an EAE model of MS, exacerbations were suppressed in treated animals. Therefore, LDK represents a novel therapeutic approach to T-cell-mediated autoimmune diseases.

A model 450 million years in the making: zebrafish and vertebrate immunity.

Since its first splash 30 years ago, the use of the zebrafish model has been extended from a tool for genetic dissection of early vertebrate development to the functional interrogation of organogenesis and disease processes such as infection and cancer. In particular, there is recent and growing attention in the scientific community directed at the immune systems of zebrafish. This development is based on the ability to image cell movements and organogenesis in an entire vertebrate organism, complemented by increasing recognition that zebrafish and vertebrate immunity have many aspects in common. Here, we review zebrafish immunity with a particular focus on recent studies that exploit the unique genetic and in vivo imaging advantages available for this organism. These unique advantages are driving forward our study of vertebrate immunity in general, with important consequences for the understanding of mammalian immune function and its role in disease pathogenesis.

Alcama mediates Edn1 signaling during zebrafish cartilage morphogenesis.

The zebrafish pharyngeal cartilage is derived from the pharyngeal apparatus, a vertebrate-specific structure derived from all three germ layers. Developmental aberrations of the pharyngeal apparatus lead to birth defects such as Treacher-Collins and DiGeorge syndromes. While interactions between endoderm and neural crest (NC) are known to be important for cartilage formation, the full complement of molecular players involved and their roles remain to be elucidated. Activated leukocyte cell adhesion molecule a (alcama), a member of the immunoglobulin (Ig) superfamily, is among the prominent markers of pharyngeal pouch endoderm, but to date no role has been assigned to this adhesion molecule in the development of the pharyngeal apparatus. Here we show that alcama plays a crucial, non-autonomous role in pharyngeal endoderm during zebrafish cartilage morphogenesis. alcama knockdown leads to defects in NC differentiation, without affecting NC specification or migration. These defects are reminiscent of the phenotypes observed when Endothelin 1 (Edn1) signaling, a key regulator of cartilage development is disrupted. Using gene expression analysis and rescue experiments we show that Alcama functions downstream of Edn1 signaling to regulate NC differentiation and cartilage morphogenesis. In addition, we also identify a role for neural adhesion molecule 1.1 (nadl1.1), a known interacting partner of Alcama expressed in neural crest, in NC differentiation. Our data shows that nadl1.1 is required for alcama rescue of NC differentiation in edn1(-/-) mutants and that Alcama interacts with Nadl1.1 during chondrogenesis. Collectively our results support a model by which Alcama on the endoderm interacts with Nadl1.1 on NC to mediate Edn1 signaling and NC differentiation during chondrogenesis.

Trans-centromere effects on meiotic recombination in the zebrafish.

We report that lack of crossover along one chromosome arm is associated with high-frequency occurrence of recombination close to the opposing arm's centromere during zebrafish meiotic recombination. Our data indicate that recombination behavior on the two arms of a chromosome is linked. These results inform mapping strategies for telomeric mutants.

The zebrafish as a model for cancer.

For the last three decades significant parts of national science budgets, and international and private funding worldwide, have been dedicated to cancer research. This has resulted in a number of important scientific findings. Studies in tissue culture have multiplied our knowledge of cancer cell pathophysiology, mechanisms of transformation and strategies of survival of cancer cells, revealing therapeutically exploitable differences to normal cells. Rodent animal models have provided important insights on the developmental biology of cancer cells and on host responses to the transformed cells. However, the rate of death from some malignancies is still high, and the incidence of cancer is increasing in the western hemisphere. Alternative animal models are needed, where cancer cell biology, developmental biology and treatment can be studied in an integrated way. The zebrafish offers a number of features, such as its rapid development, tractable genetics, suitability for in vivo imaging and chemical screening, that make it an attractive model to cancer researchers. This Primer will provide a synopsis of the different cancer models generated by the zebrafish community to date. It will discuss the use of these models to further our understanding of the mechanisms of cancer development, and to promote drug discovery. The article was inspired by a workshop on the topic held in July 2009 in Spoleto, Italy, where a number of new zebrafish cancer models were presented. The overarching goal of the article is aimed at raising the awareness of basic researchers, as well as clinicians, to the versatility of this emerging alternative animal model of cancer.

Characterization of the zebrafish T cell receptor beta locus.

Zebrafish (Danio rerio) has become an increasingly important model for immunological study. Its immune system is remarkably similar to that of mammals and includes both the adaptive and innate branches. Zebrafish T cells express functional T cell receptors (TCR), and all four TCR loci are present within the genome. Using 5'-rapid amplification of cDNA ends, we cloned and sequenced zebrafish TCRbeta transcripts. TCRbeta VDJ coding joints demonstrate conservation of mechanisms used by other vertebrate species to increase junctional diversity. Using the sequences obtained, along with previously published data, we comprehensively annotated the zebrafish TCRbeta locus. Overall, organization of the locus resembles that seen in mammals. There are 51 V segments, a single D segment, 27 Jbeta1 segments, a single Jbeta2 segment, and two constant regions. This description of the zebrafish TCRbeta locus has the potential to enhance immunological research in zebrafish and further our understanding of mammalian TCR repertoire generation.

The role and regulation of friend of GATA-1 (FOG-1) during blood development in the zebrafish.

The nuclear protein FOG-1 binds transcription factor GATA-1 to facilitate erythroid and megakaryocytic maturation. However, little is known about the function of FOG-1 during myeloid and lymphoid development or how FOG-1 expression is regulated in any tissue. We used in situ hybridization, gain- and loss-of-function studies in zebrafish to address these problems. Zebrafish FOG-1 is expressed in early hematopoietic cells, as well as heart, viscera, and paraspinal neurons, suggesting that it has multifaceted functions in organogenesis. We found that FOG-1 is dispensable for endoderm specification but is required for endoderm patterning affecting the expression of late-stage T-cell markers, independent of GATA-1. The suppression of FOG-1, in the presence of normal GATA-1 levels, induces severe anemia and thrombocytopenia and expands myeloid-progenitor cells, indicating that FOG-1 is required during erythroid/myeloid commitment. To functionally interrogate whether GATA-1 regulates FOG-1 in vivo, we used bioinformatics combined with transgenic assays. Thus, we identified 2 cis-regulatory elements that control the tissue-specific gene expression of FOG-1. One of these enhancers contains functional GATA-binding sites, indicating the potential for a regulatory loop in which GATA factors control the expression of their partner protein FOG-1.