Critical differences in hematopoiesis and lymphoid development between humans and mice

During the last five decades, elegant mouse models of hematopoiesis have yielded most of the seminal insights into this complex biological system of self-renewal and lineage commitment. More recent advances in assays to measure human stem and progenitor cells as well as high resolution RNA profiling have revealed that although the basic roadmap of blood development is generally conserved across mammals, evolutionary pressures have generated many differences between the species that have important biological and translational implications. To enhance the utility of the mouse as a model organism, it is more important than ever that research data are presented with regard to how they might be influenced by the species of origin as well as the developmental source of the hematopoietic tissue.

Single-Cell RNA-Seq Mapping of Human Thymopoiesis Reveals Lineage Specification Trajectories and a Commitment Spectrum in T Cell Development

The challenges in recapitulating in vivo human T cell development in laboratory models have posed a barrier to understanding human thymopoiesis. Here, we used single-cell RNA sequencing (sRNA-seq) to interrogate the rare CD34+ progenitor and the more differentiated CD34- fractions in the human postnatal thymus. CD34+ thymic progenitors were comprised of a spectrum of specification and commitment states characterized by multilineage priming followed by gradual T cell commitment. The earliest progenitors in the differentiation trajectory were CD7- and expressed a stem-cell-like transcriptional profile, but had also initiated T cell priming. Clustering analysis identified a CD34+ subpopulation primed for the plasmacytoid dendritic lineage, suggesting an intrathymic dendritic specification pathway. CD2 expression defined T cell commitment stages where loss of B cell potential preceded that of myeloid potential. These datasets delineate gene expression profiles spanning key differentiation events in human thymopoiesis and provide a resource for the further study of human T cell development.

The T-ALL related gene BCL11B regulates the initial stages of human T-cell differentiation

The initial stages of T-cell differentiation are characterized by a progressive commitment to the T-cell lineage, a process that involves the loss of alternative (myelo-erythroid, NK, B) lineage potentials. Aberrant differentiation during these stages can result in T-cell acute lymphoblastic leukemia (T-ALL). However, the mechanisms regulating the initial stages of human T-cell differentiation are obscure. Through loss of function studies, we showed BCL11B, a transcription factor recurrently mutated T-ALL, is essential for T-lineage commitment, particularly the repression of NK and myeloid potentials, and the induction of T-lineage genes, during the initial stages of human T-cell differentiation. In gain of function studies, BCL11B inhibited growth of and induced a T-lineage transcriptional program in T-ALL cells. We found previously unknown differentiation stage-specific DNA binding of BCL11B at multiple T-lineage genes; target genes showed BCL11B-dependent expression, suggesting a transcriptional activator role for BCL11B at these genes. Transcriptional analyses revealed differences in the regulatory actions of BCL11B between human and murine thymopoiesis. Our studies show BCL11B is a key regulator of the initial stages of human T-cell differentiation and delineate the BCL11B transcriptional program, enabling the dissection of the underpinnings of normal T-cell differentiation and providing a resource for understanding dysregulations in T-ALL.

Engineering the human thymic microenvironment to support thymopoiesis in vivo

A system that allows manipulation of the human thymic microenvironment is needed both to elucidate the extrinsic mechanisms that control human thymopoiesis and to develop potential cell therapies for thymic insufficiency. In this report, we developed an implantable thymic microenvironment composed of two human thymic stroma populations critical for thymopoiesis; thymic epithelial cells (TECs) and thymic mesenchyme (TM). TECs and TM from postnatal human thymi were cultured in specific conditions, allowing cell expansion and manipulation of gene expression, before reaggregation into a functional thymic unit. Human CD34+ hematopoietic stem and progenitor cells (HSPC) differentiated into T cells in the aggregates in vitro and in vivo following inguinal implantation of aggregates in immune deficient mice. Cord blood HSPC previously engrafted into murine bone marrow (BM), migrated to implants, and differentiated into human T cells with a broad T cell receptor repertoire. Furthermore, lentiviral-mediated expression of vascular endothelial growth factor in TM enhanced implant size and function and significantly increased thymocyte production. These results demonstrate an in vivo system for the generation of T cells from human HSPC and represent the first model to allow manipulation of gene expression and cell composition in the microenvironment of the human thymus.

Hemophagocytic lymphohistiocytosis in children with chronic granulomatous disease

Hemophagocytic lymphohistiocytosis (HLH) is characterized by fever, cytopenias, splenomegaly, and hemophagocytosis by macrophages activated by high cytokine levels. Chronic granulomatous disease (CGD) is characterized by recurrent infections, hyperinflammation, and excessive cytokine release. This may predispose patients with CGD to developing HLH during an infection. We conducted a retrospective review of patients with CGD, treated at our institution between 1999 and 2008. Three out of 17 patients developed HLH. Patients with CGD may be at increased risk for developing HLH. Remission of HLH was achieved after treatment with antimicrobials, steroids, and intravenous immunoglobulin This approach to treatment appears to be effective.

Treatment of children with recurrent high grade gliomas with a bevacizumab containing regimen

Children with recurrent high grade gliomas (HGG) have a dismal outcome with a median progression free survival (PFS) of 12 weeks. Adults with recurrent HGG treated with irinotecan and bevacizumab reportedly have a 63% response rate and a median PFS of 23 weeks. There is a paucity of corresponding published pediatric data. We retrospectively reviewed the records of patients less than 21 years of age with recurrent or progressive WHO grade 3-4 gliomas who were treated with bevacizumab containing regimens at our institution between January 2006 and September 2008. We identified eight patients. Six out of eight patients received irinotecan, temozolomide and bevacizumab, one patient received irinotecan and bevacizumab, and one patient received CCNU and bevacizumab. Three patients had stable disease for 30-93 weeks. The remaining five patients developed progressive disease within 17 weeks. The median PFS was 15 weeks and the 6-month PFS was 38%. Contrast enhancing disease responded or remained stable in five out of seven patients whereas non-enhancing disease progressed in three out of four patients. New distant non-enhancing lesions developed in three patients. The most common side effects included diarrhea, vomiting, thrombocytopenia and neutropenia. Bevacizumab was well tolerated when used in combination with conventional chemotherapy (irinotecan in most cases). PFS in our cohort was much shorter and the response rate was inferior in this small cohort of patients when compared with published adult data. However, bevacizumab containing regimens might be effective in a subset of pediatric patients, especially those with predominantly contrast-enhancing disease.

The Metabolic Landscape of Thymic T Cell Development In Vivo and In Vitro

Although metabolic pathways have been shown to control differentiation and activation in peripheral T cells, metabolic studies on thymic T cell development are still lacking, especially in human tissue. In this study, we use transcriptomics and extracellular flux analyses to investigate the metabolic profiles of primary thymic and in vitro-derived mouse and human thymocytes. Core metabolic pathways, specifically glycolysis and oxidative phosphorylation, undergo dramatic changes between the double-negative (DN), double-positive (DP), and mature single-positive (SP) stages in murine and human thymus. Remarkably, despite the absence of the complex multicellular thymic microenvironment, in vitro murine and human T cell development recapitulated the coordinated decrease in glycolytic and oxidative phosphorylation activity between the DN and DP stages seen in primary thymus. Moreover, by inducing in vitro T cell differentiation from Rag1-/- mouse bone marrow, we show that reduced metabolic activity at the DP stage is independent of TCR rearrangement. Thus, our findings suggest that highly conserved metabolic transitions are critical for thymic T cell development.

The PI3Kδ Inhibitor Idelalisib Inhibits Homing in an in Vitro and in Vivo Model of B ALL

The quest continues for targeted therapies to reduce the morbidity of chemotherapy and to improve the response of resistant leukemia. Adhesion of acute lymphoblastic leukemia (ALL) cells to bone marrow stromal cells triggers intracellular signals that promote cell-adhesion-mediated drug resistance (CAM-DR). Idelalisib, an U.S. Food and Drug Administration (FDA)-approved PI3Kδ-specific inhibitor has been shown to be effective in CLL in down-regulating p-Akt and prolonging survival in combination with Rituximab; herein we explore the possibility of its use in B ALL and probe the mechanism of action. Primary B ALL in contact with OP9 stromal cells showed increased p-Akt^ser473. Idelalisib decreased p-Akt in patient samples of ALL with diverse genetic lesions. Addition of idelalisib to vincristine inhibited proliferation when compared to vincristine monotherapy in a subset of samples tested. Idelalisib inhibited ALL migration to SDF-1α in vitro and blocked homing of ALL cells to the bone marrow in vivo. This report tests PI3Kδ inhibitors in a more diverse group of ALL than has been previously reported and is the first published report of idelalisib inhibiting homing of ALL cells to bone marrow. Our data support further pre-clinical evaluation of idelalisib for the therapy of B ALL.

Erythropoiesis from human embryonic stem cells through erythropoietin-independent AKT signaling

Unlimited self renewal capacity and differentiation potential make human pluripotent stem cells (PSC) a promising source for the ex vivo manufacture of red blood cells (RBCs) for safe transfusion. Current methods to induce erythropoiesis from PSC suffer from low yields of RBCs, most of which are immature and contain embryonic and fetal rather than adult hemoglobins. We have previously shown that homodimerization of the intracellular component of MPL (ic-MPL) induces erythropoiesis from human cord blood progenitors. The goal of this study was to investigate the potential of ic-MPL dimerization to induce erythropoiesis from human embryonic stem cells (hESCs) and to identify the signaling pathways activated by this strategy. We present here the evidence that ic-MPL dimerization induces erythropoietin (EPO)-independent erythroid differentiation from hESC by inducing the generation of erythroid progenitors and by promoting more efficient erythroid maturation with increased RBC enucleation as well as increased gamma:epsilon globin ratio and production of beta-globin protein. ic-MPL dimerization is significantly more potent than EPO in inducing erythropoiesis, and its effect is additive to EPO. Signaling studies show that dimerization of ic-MPL, unlike stimulation of the wild type MPL receptor, activates AKT in the absence of JAK2/STAT5 signaling. AKT activation upregulates GATA-1 and FOXO3 transcriptional pathways with resulting inhibition of apoptosis, modulation of cell cycle, and enhanced maturation of erythroid cells. These findings open up potential new targets for the generation of therapeutically relevant RBC products from hPSC.

End of induction minimal residual disease alone is not a useful determinant for risk stratified therapy in pediatric T-cell acute lymphoblastic leukemia

The role of end of induction minimal residual disease (MRD) as determined by flow cytometry for treatment assignment in pediatric T-cell acute lymphoblastic leukemia (T-ALL) is not well defined. We studied 33 children with newly diagnosed T-ALL. Thirty-two of 33 patients remain in continuous complete remission at a median of 4 years. Nineteen patients were MRD positive at the end of induction and all remain in remission with augmented Berlin Frankfurt Münster-based therapy. One patient underwent hematopoietic stem cell transplant for rising MRD. Persistent end of induction MRD alone is not an indication to alter therapy in pediatric T-ALL.

Study of infant feeding practices: factors associated with faulty feeding

KEM Hospital, Mumbai was recognized as a 'baby-friendly' hospital on the basis of adherence to the 'Ten steps to successful breastfeeding', a decade ago. This study was undertaken to determine the sustainability of the programme in terms of feeding practices undertaken by the mothers on the basis of advice given to them. A total of 92.11 per cent of the infants up to 6 months of age received exclusive breastfeeding. Timely complementary feeding rate was 95 per cent. Thus interventions used in the programme seem sustainable.

Novel pathways to erythropoiesis induced by dimerization of intracellular C-Mpl in human hematopoietic progenitors

The cytokine thrombopoietin (Tpo) plays a critical role in hematopoiesis by binding to the extracellular domain and inducing homodimerization of the intracellular signaling domain of its receptor, c-Mpl. Mpl homodimerization can also be accomplished by binding of a synthetic ligand to a constitutively expressed fusion protein F36VMpl consisting of a ligand binding domain (F36V) and the intracellular signaling domain of Mpl. Unexpectedly, in contrast to Tpo stimulation, robust erythropoiesis is induced after dimerization of F36VMpl in human CD34+ progenitor cells. The goal of this study was to define the hematopoietic progenitor stages at which dimerization of intracellular Mpl induces erythropoiesis and the downstream molecular events that mediate this unanticipated effect. Dimerization (in the absence of erythropoietin and other cytokines) in human common myeloid progenitors and megakaryocytic erythroid progenitors caused a significant increase in CD34+ cells (p < .01) and induced all stages of erythropoiesis including production of enucleated red blood cells. In contrast, erythropoiesis was not seen with Tpo stimulation. CD34+ cell expansion was the result of increased cell cycling and survival (p < .05). Microarray profiling of CD34+ cells demonstrated that a unique transcriptional pattern is activated in progenitors by F36VMpl dimerization. Ligand-inducible dimerization of intracellular Mpl in human myeloerythroid progenitors induces progenitor expansion and erythropoiesis through molecular mechanisms that are not shared by Tpo stimulation of endogenous Mpl.

Association of clinical trial enrollment and survival using contemporary therapy for pediatric acute lymphoblastic leukemia

While early studies reported superior survival for cancer patients enrolled on clinical trials, recent findings are inconclusive. We investigated the association between enrollment on contemporary trials and event-free survival (EFS) in pediatric B-cell acute lymphoblastic leukemia (B-ALL). In a retrospective cohort of 274 children (1-21 years) treated for B-ALL from 2008 to 2015, 55.5% enrolled with no disparity in enrollment by age, sex, or ethnicity. Three-year EFS was similar for enrolled and not enrolled patients (90.1% [95% CI, 82.5-94.5] versus 86.5% [95% CI, 77.7-92.0]). Clinical trial enrollment did not affect pediatric B-ALL survival, albeit in a limited-size cohort treated at a single academic institution.

COVID-19 outcomes in children, adolescents and young adults with cancer

Pediatric oncology patients are at risk for poor outcomes with respiratory viral infections. Outcome data for COVID-19 in children and young adults with cancer are needed; data are sparse for obese/overweight and adolescent and young adult subgroups. We conducted a single center cohort study of COVID-19 outcomes in patients younger than 25 years with cancer. Candidate hospitalization risk factors were analyzed via univariable and multivariable analyses. Eighty-seven patients with cancer and COVID-19 were identified. Most were Hispanic/Latinx (n = 63, 72%). Forty-two (48%) were overweight/obese. Anticancer therapy included chemotherapy only (n = 64, 74%), chimeric antigen receptor T-cells (CAR-T, n = 7), hematopoietic stem cell transplantation (HSCT, n = 12), or CAR-T and HSCT (n = 4). There was no COVID-19 related mortality. Twenty-six patients (30%) required COVID-19 related hospitalization; 4 required multiple hospitalizations. Nine (10%) had severe/critical infection; 6 needed intensive care. COVID-19 resulted in anticancer therapy delays in 22 (34%) of 64 patients on active therapy (median delay = 14 days). Factors associated with hospitalization included steroids within 2 weeks prior to infection, lymphopenia, previous significant non-COVID infection, and low COVID-19 PCR cycle threshold value. CAR-T recipients with B-cell aplasia tended to have severe/critical infection (3 of 7 patients). A COVID-19 antibody response was detected in 14 of 32 patients (44%). A substantial proportion of COVID-19 infected children and young adults with cancer require inpatient management; morbidity may be high in B-cell immunodeficiency. However, a majority of patients can be taken through chemotherapy without prolonged therapy delays. Viral load is a potential outcome predictor in COVID-19 in pediatric cancer.

Preclinical Evaluation of a Novel Dual Targeting PI3Kδ/BRD4 Inhibitor, SF2535, in B-Cell Acute Lymphoblastic Leukemia

The PI3K/Akt pathway—and in particular PI3Kδ—is known for its role in drug resistant B-cell acute lymphoblastic leukemia (B-ALL) and it is often upregulated in refractory or relapsed B-ALL. Myc proteins are transcription factors responsible for transcribing pro-proliferative genes and c-Myc is often overexpressed in cancers. The chromatin regulator BRD4 is required for expression of c-Myc in hematologic malignancies including B-ALL. Previously, combination of BRD4 and PI3K inhibition with SF2523 was shown to successfully decrease Myc expression. However, the underlying mechanism and effect of dual inhibition of PI3Kδ/BRD4 in B-ALL remains unknown. To study this, we utilized SF2535, a novel small molecule dual inhibitor which can specifically target the PI3Kδ isoform and BRD4. We treated primary B-ALL cells with various concentrations of SF2535 and studied its effect on specific pharmacological on-target mechanisms such as apoptosis, cell cycle, cell proliferation, and adhesion molecules expression usingin vitro and in vivo models. SF2535 significantly downregulates both c-Myc mRNA and protein expression through inhibition of BRD4 at the c-Myc promoter site and decreases p-AKT expression through inhibition of the PI3Kδ/AKT pathway. SF2535 induced apoptosis in B-ALL by downregulation of BCL-2 and increased cleavage of caspase-3, caspase-7, and PARP. Moreover, SF2535 induced cell cycle arrest and decreased cell counts in B-ALL. Interestingly, SF2535 decreased the mean fluorescence intensity (MFI) of integrin α4, α5, α6, and β1 while increasing MFI of CXCR4, indicating that SF2535 may work through inside-out signaling of integrins. Taken together, our data provide a rationale for the clinical evaluation of targeting PI3Kδ/BRD4 in refractory or relapsed B-ALL using SF2535.

Processing Human Thymic Tissue for Single Cell RNA-Seq

Single cell RNA sequencing of human thymic cells is dependent on isolation of highly pure and viable cell populations. This protocol describes the isolation of CD34⁺ progenitor and more differentiated CD34^– fractions from post-natal thymic tissue to study thymopoiesis. CD34⁺ cells represent <1% of thymic cells, so this protocol uses magnetic- followed by fluorescence-activated cell separation to isolate highly enriched CD34⁺ cells.

For complete details on the use and execution of this protocol, please refer to Le et al. (2020).

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Protocol for processing of human thymus for single cell RNA-seq

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Thymus dissection and density gradient centrifugation isolate mononuclear cells

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Magnetic-activated cell separation isolates CD34⁺/CD34^– cells

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Fluorescence-activated cell separation isolates populations for RNA-seq

Comparison of human pluripotent stem cell differentiation protocols to generate neuroblastoma tumors

Neuroblastoma is the most common pediatric extracranial solid tumor and is derived from trunk neural crest cells (tNCC) and its progenitor sympathoadrenal (SA) cells. While human pluripotent stem cell (PSC) models of neuroblastoma have been described, the PSC were differentiated using protocols that made neural crest cells, but not specifically the trunk subtype. Here, we compared four recent protocols to differentiate pluripotent stem cells (PSC) toward SA cells and examined their efficiency at generating SA cells along with earlier cell states (neuromesodermal progenitors [NMP], tNCC), as well as generating MYCN-driven tumors. Interestingly, the protocols that created cells with the highest level of NMP markers did not produce cells with the highest tNCC or SA cell markers. We identified a protocol that consistently produced cells with the highest level of SA markers using two PSC lines of different genders. This protocol also generated tumors with the highest level of PHOX2B, a marker of neuroblastoma. Transcriptionally, however, each protocol generates tumors that resemble neuroblastoma. Two of the protocols repeatedly produced adrenergic neuroblastoma whereas the other two protocols were ambiguous. Thus, we identified a protocol that reliably generates adrenergic neuroblastoma.