Proteogenomic Reprogramming to a Functional Human Totipotent Stem Cell State via a PARP-DUX4 Regulatory Axis.

PARP1 (ARTD1) and Tankyrases (TNKS1/TNKS2; PARP5a/5b) are poly-ADP-ribose polymerases (PARPs) with catalytic and non-catalytic functions that regulate both the genome and proteome during zygotic genome activation (ZGA), totipotent, and pluripotent embryonic stages. Here, we show that primed, conventional human pluripotent stem cells (hPSC) cultured continuously under non-specific TNKS1/TNKS2/PARP1-inhibited chemical naive reversion conditions underwent epigenetic reprogramming to clonal blastomere-like stem cells. TIRN stem cells concurrently expressed hundreds of gene targets of the ZGA-priming pioneer factor DUX4, as well as a panoply of four-cell (4C)-specific (e.g., TPRXL, HOX clusters), eight-cell (8C)-specific (e.g., DUXA, GSC, GATA6), primitive endoderm-specific (e.g., GATA4, SOX17), trophectoderm-specific (e.g., CDX2, TFAP2C), and naive epiblast-specific (e.g., DNMT3L, NANOG, POU5F1(OCT4)) factors; all in a hybrid, combinatorial single-cell manner. Mapping of proteomic and single-cell expressions of TIRN cells against human preimplantation embryo references identified them as relatively homogenous 4C-8C stage populations. Injection of TIRN cells into murine 8C-16C-staged embryos resulted in efficient totipotent-like single cell contributions of human cells to both extra-embryonic (trophectoderm, placenta) and embryonic (neural, fetal liver, hematopoietic) lineages in human-murine blastocyst and fetal chimeras. Pairing of proteome with ubiquitinome analyses of TIRN cells revealed a global shutdown of ADP-ribosylation, and a perturbed TNKS/PARP1 equilibrium which not only impacted the protein levels of hundreds of TNKS/PARP1 substrates via a rewiring of the ubiquitin-proteosome system (UPS), but also de-repressed expression of hundreds of developmental genes associated with PARP1 suppression. ChIP-Seq analysis of core NANOG-SOX2-OCT4 (NSO) pluripotency factors in TIRN cells identified reprogrammed DUX4-accessible distal and cis-regulatory enhancer regions that were co-bound by PARP1 (NSOP). These NSOP enhancer regions possessed co-binding motifs for hundreds of the same ZGA-associated, embryonic, and extraembryonic lineage-specifying pioneer factors (e.g., HOX, FOX, GATA, SOX, TBX, CDX families) that were concurrently co-expressed in TIRN cells; suggesting that PARP1 and DUX4 cooperate with NSO pluripotency core factors to regulate the epigenetic plasticity of a human totipotency program. These findings provide the first demonstration that global, proteome-wide perturbations of post-translational modifications (i.e., ADP-ribosylation, ubiquitination) can regulate epigenetic reprogramming during human embryogenesis. Totipotent TIRN stem cells will provide a valuable cell culture model for studying the proteogenomic regulation of lineage specification from human blastomere stages and may facilitate the efficient generation of human organs in interspecies chimeras.

Antiviral cellular therapy for enhancing T-cell reconstitution before or after hematopoietic stem cell transplantation (ACES): a two-arm, open label phase II interventional trial of pediatric patients with risk factor assessment.

Viral infections remain a major risk in immunocompromised pediatric patients, and virus-specific T cell (VST) therapy has been successful for treatment of refractory viral infections in prior studies. We performed a phase II multicenter study (NCT03475212) for the treatment of pediatric patients with inborn errors of immunity and/or post allogeneic hematopoietic stem cell transplant with refractory viral infections using partially-HLA matched VSTs targeting cytomegalovirus, Epstein-Barr virus, or adenovirus. Primary endpoints were feasibility, safety, and clinical responses (>1 log reduction in viremia at 28 days). Secondary endpoints were reconstitution of antiviral immunity and persistence of the infused VSTs. Suitable VST products were identified for 75 of 77 clinical queries. Clinical responses were achieved in 29 of 47 (62%) of patients post-HSCT including 73% of patients evaluable at 1-month post-infusion, meeting the primary efficacy endpoint (>52%). Secondary graft rejection occurred in one child following VST infusion as described in a companion article. Corticosteroids, graft-versus-host disease, transplant-associated thrombotic microangiopathy, and eculizumab treatment correlated with poor response, while uptrending absolute lymphocyte and CD8 T cell counts correlated with good response. This study highlights key clinical factors that impact response to VSTs and demonstrates the feasibility and efficacy of this therapy in pediatric HSCT.

Harnessing bioengineered myeloid progenitors for precision immunotherapies.

Granulocytes and macrophages are the frontline defenders of the innate immune system. These myeloid cells play a crucial role in not only eliminating pathogens and tumor cells, but also regulating adaptive immune responses. In neonatal sepsis and post-chemotherapy agranulocytosis, the absence of these cells leaves the host highly vulnerable to infections. Beyond replacement to prevent or control neutropenic sepsis, engineered myeloid cells may offer distinct opportunities for cell therapies. For example, the mobility and specific homing capacities of neutrophils to sites of inflammation could be exploited to deliver biocidal agents, or anti-inflammatory healing signals during sepsis, autoimmunity, and organ transplantation. Additionally, myeloid cells can be engineered to express chimeric antigen receptors (CAR), carry chemotherapeutics, or enhance lymphoid tumor killing. However, traditional methods of cell isolation are incapable of providing sufficient cell numbers of these short-lived cells; their propensity for premature activation further complicates their cell engineering. Here, we review current and future biotherapeutic innovations that employ engineered multipotent myeloid progenitors derived from either self-renewing human induced pluripotent stem cells (hiPSC) or primary CD34+ hematopoietic stem-progenitors. We provide a roadmap for solving the challenges of sourcing, cost, and production of engineered myeloid cell therapies.

Generation of Pericytic-Vascular Progenitors from Tankyrase/PARP-Inhibitor-Regulated Naïve (TIRN) Human Pluripotent Stem Cells.

Tankyrase/PARP inhibitor-regulated naïve human pluripotent stem cells (TIRN-hPSC) represent a new class of human stem cells for regenerative medicine that can differentiate into multi-lineage progenitors with improved in vivo functionality. Chemical reversion of conventional, primed hPSC to a TIRN-hPSC state alleviates dysfunctional epigenetic donor cell memory, lineage-primed gene expression, and potentially disease-associated aberrations in their differentiated progeny. Here, we provide methods for the reversion of normal or diseased patient-specific primed hPSC to TIRN-hPSC and describe their subsequent differentiation into embryonic-like pericytic-endothelial "naïve" vascular progenitors (N-VP). N-VP possess improved vascular functionality, high epigenetic plasticity, maintain greater genomic stability, and are more efficient in migrating to and re-vascularizing ischemic tissues than those generated from primed isogenic hPSC. We also describe detailed methods for the ocular transplantation and quantitation of vascular engraftment of N-VP into the ischemia-damaged neural retina of a humanized mouse model of ischemic retinopathy. The application of TIRN-hPSC-derived N-VP will advance vascular cell therapies of ischemic retinopathy, myocardial infarction, and cerebral vascular stroke.

Rosai-Dorfman Disease Presenting as Massive Mediastinal Lymphadenopathy in an Elderly Man.

We present a patient case of a 73-year-old man with new-onset substernal chest pain and B symptoms, found on computed tomography imaging to have massive mediastinal lymphadenopathy of more than 6 cm. Positron emission tomography imaging revealed fluorodeoxyglucose-avid nodes further extending to the axillary, abdominal, and inguinal regions. After a broad patient work-up for infectious, malignant, and rheumatic causes, he was ultimately diagnosed with Rosai-Dorfman disease, a rare histiocytic neoplasm, by excisional lymph node biopsy.

Reduced Intensity Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Pediatric Inherited Immune Deficiencies and Bone Marrow Failure Syndromes.

PURPOSE: Allogeneic bone marrow transplantation (alloBMT) is the only cure for many primary immune deficiency disorders (PIDD), primary immune regulatory disorders (PIRD), and inherited bone marrow failure syndromes (IBMFS). METHODS: We report the results of 25 patients who underwent alloBMT using reduced intensity conditioning (RIC), alternative donors, and post-transplantation cyclophosphamide (PTCy). In an attempt to reduce regimen-related toxicities, we removed low-dose TBI from the prep and added mycophenolate mofetil and tacrolimus for graft-versus-host disease (GVHD) prophylaxis for all donor types in the latter 14 patients. Donors were haploidentical related (n = 14), matched unrelated (n = 9), or mismatched unrelated (n = 2). The median age was 9 years (range 5 months-21 years). RESULTS: With a median follow-up of 26 months (range 7 months-9 years), the 2-year overall survival is 92%. There were two deaths, one from infection, and one from complications after a second myeloablative BMT. Three patients developed secondary graft failure, one at 2 years and two at >3 years, successfully treated with CD34 cell boost in one or second BMT in two. The remaining 20 patients have full or stable mixed donor chimerism and are disease-free. The incidence of mixed chimerism is increased since removing TBI from the prep. The 6-month cumulative incidence of grade II acute GVHD is 17%, with no grade III-IV. The 1-year cumulative incidence of chronic GVHD is 14%, with severe of 5%. CONCLUSION: This alloBMT platform using alternative donors, RIC, and PTCy is associated with excellent rates of engraftment and low rates of GVHD and non-relapse mortality, and offers a curative option for patients with PIDD, PIRD, and IBMFS. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04232085.

Myeloablative haploidentical BMT with posttransplant cyclophosphamide for hematologic malignancies in children and adults.

Promising results have been reported for patients with high-risk hematologic malignancies undergoing HLA-haploidentical bone marrow transplantation (haploBMT) with posttransplantation cyclophosphamide (PTCy), but there are few data on outcomes with myeloablative conditioning in this context. We report the results of a single-institution, prospective phase 2 trial of myeloablative haploBMT using busulfan-based or total body irradiation-based conditioning in 96 children or adults (median age, 42 years; range, 1-65 years) with high-risk hematologic malignancies. Recovery of neutrophils and platelets occurred at a median of 24 and 29 days. Engraftment of donor cells with chimerism >95% was achieved in 91%. The cumulative incidence of acute graft-versus-host disease (GVHD) grades II to IV and grades III to IV at day 100 was 11% and 4%, and of chronic GVHD at 6 and 12 months was 4% and 15%, with 6% moderate to severe. The cumulative incidence of nonrelapse mortality was 6% at 100 days and 11% at 1 year (19% in those aged >55 years). The cumulative incidence of relapse at 1 year was 35%; at 3 years, it was 43%. In multivariable analysis, relapse was associated with increased age (P = .02 for age 20-55 years and P = .02 for age >55 years) and with minimal residual disease before transplantation (P = .05). The overall survival at 1 and 3 years is 73% and 54%, and event-free survival at 1 and 3 years is 57% and 49%. We show that haploBMT with PTCy after myeloablative conditioning is safe and efficacious for adult and pediatric patients with hematologic malignancies. Careful consideration must be given to using myeloablative conditioning in patients age >55 years. This trial was registered at www.clinicaltrials.gov as #NCT00796562.

Vascular progenitors generated from tankyrase inhibitor-regulated naïve diabetic human iPSC potentiate efficient revascularization of ischemic retina.

Here, we report that the functionality of vascular progenitors (VP) generated from normal and disease-primed conventional human induced pluripotent stem cells (hiPSC) can be significantly improved by reversion to a tankyrase inhibitor-regulated human naïve epiblast-like pluripotent state. Naïve diabetic vascular progenitors (N-DVP) differentiated from patient-specific naïve diabetic hiPSC (N-DhiPSC) possessed higher vascular functionality, maintained greater genomic stability, harbored decreased lineage-primed gene expression, and were more efficient in migrating to and re-vascularizing the deep neural layers of the ischemic retina than isogenic diabetic vascular progenitors (DVP). These findings suggest that reprogramming to a stable naïve human pluripotent stem cell state may effectively erase dysfunctional epigenetic donor cell memory or disease-associated aberrations in patient-specific hiPSC. More broadly, tankyrase inhibitor-regulated naïve hiPSC (N-hiPSC) represent a class of human stem cells with high epigenetic plasticity, improved multi-lineage functionality, and potentially high impact for regenerative medicine.

Chemical Reversion of Conventional Human Pluripotent Stem Cells to a Naïve-like State with Improved Multilineage Differentiation Potency.

Naïve human pluripotent stem cells (N-hPSC) with improved functionality may have a wide impact in regenerative medicine. The goal of this protocol is to efficiently revert lineage-primed, conventional human pluripotent stem cells (hPSC) maintained on either feeder-free or feeder-dependent conditions to a naïve-like pluripotency with improved functionality. This chemical naïve reversion method employs the classical leukemia inhibitory factor (LIF), GSK3ß, and MEK/ERK inhibition cocktail (LIF-2i), supplemented with only a tankyrase inhibitor XAV939 (LIF-3i). LIF-3i reverts conventional hPSC to a stable pluripotent state adopting biochemical, transcriptional, and epigenetic features of the human pre-implantation epiblast. This LIF-3i method requires minimal cell culture manipulation and is highly reproducible in a broad repertoire of human embryonic stem cell (hESC) and transgene-free human induced pluripotent stem cell (hiPSC) lines. The LIF-3i method does not require a re-priming step prior to the differentiation; N-hPSC can be differentiated directly with extremely high efficiencies and maintain karyotypic and epigenomic stabilities (including at imprinted loci). To increase the universality of the method, conventional hPSC are first cultured in the LIF-3i cocktail supplemented with two additional small molecules that potentiate protein kinase A (forskolin) and sonic hedgehog (sHH) (purmorphamine) signaling (LIF-5i). This brief LIF-5i adaptation step significantly enhances the initial clonal expansion of conventional hPSC and permits them to be subsequently naïve-reverted with LIF-3i alone in bulk quantities, thus obviating the need for picking/subcloning rare N-hPSC colonies later. LIF-5i-stabilized hPSCs are subsequently maintained in LIF-3i alone without the need of anti-apoptotic molecules. Most importantly, LIF-3i reversion markedly improves the functional pluripotency of a broad repertoire of conventional hPSC by decreasing their lineage-primed gene expression and erasing the interline variability of directed differentiation commonly observed amongst independent hPSC lines. Representative characterizations of LIF-3i-reverted N-hPSC are provided, and experimental strategies for functional comparisons of isogenic hPSC in lineage-primed vs. naïve-like states are outlined.

Reduced-Intensity Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Solid Tumors in Pediatric and Young Adult Patients.

High-risk, recurrent, or refractory solid tumors in pediatric, adolescent, and young adult (AYA) patients have an extremely poor prognosis despite current intensive treatment regimens. We piloted an allogeneic bone marrow transplant platform using reduced-intensity conditioning (RIC) and partially HLA-mismatched (haploidentical) related donors for this population of pediatric and AYA solid tumor patients. Sixteen patients received fludarabine, cyclophosphamide, melphalan, and low-dose total body irradiation RIC haploidentical BMT (haploBMT) followed by post-transplantation cyclophosphamide (PTCy), mycophenolate mofetil, and sirolimus. All assessable patients were full donor chimeras on day 30 with a median neutrophil recovery of 19 days and platelet recovery of 21 days. One patient (7%) exhibited secondary graft failure associated with concomitant infection. The median follow-up time was 15 months. Overall survival was 88%, 56%, and 21% at 6, 12, and 24 months, respectively. Median survival from transplant date was 14 months with a median progression-free survival 7 months. We observed limited graft-versus-host disease in 3 patients and nonrelapse mortality in 1 patient. We demonstrated that RIC haploBMT with PTCy is feasible and has acceptable toxicities in patients with incurable pediatric and AYA solid tumors; thus, this approach serves as a platform for post-transplant strategies to prevent relapse and optimize progression-free survival.

Tankyrase inhibition promotes a stable human naïve pluripotent state with improved functionality.

The derivation and maintenance of human pluripotent stem cells (hPSCs) in stable naïve pluripotent states has a wide impact in human developmental biology. However, hPSCs are unstable in classical naïve mouse embryonic stem cell (ESC) WNT and MEK/ERK signal inhibition (2i) culture. We show that a broad repertoire of conventional hESC and transgene-independent human induced pluripotent stem cell (hiPSC) lines could be reverted to stable human preimplantation inner cell mass (ICM)-like naïve states with only WNT, MEK/ERK, and tankyrase inhibition (LIF-3i). LIF-3i-reverted hPSCs retained normal karyotypes and genomic imprints, and attained defining mouse ESC-like functional features, including high clonal self-renewal, independence from MEK/ERK signaling, dependence on JAK/STAT3 and BMP4 signaling, and naïve-specific transcriptional and epigenetic configurations. Tankyrase inhibition promoted a stable acquisition of a human preimplantation ICM-like ground state via modulation of WNT signaling, and was most efficacious in efficiently reprogrammed conventional hiPSCs. Importantly, naïve reversion of a broad repertoire of conventional hiPSCs reduced lineage-primed gene expression and significantly improved their multilineage differentiation capacities. Stable naïve hPSCs with reduced genetic variability and improved functional pluripotency will have great utility in regenerative medicine and human disease modeling.

Enrichment of Scleroderma Vascular Disease-Associated Autoantigens in Endothelial Lineage Cells.

OBJECTIVE: Scleroderma patients with autoantibodies to CENPs and/or interferon-inducible protein 16 (IFI-16) are at increased risk of severe vascular complications. This study was undertaken to determine whether these autoantigens are enriched in cells of the vasculature. METHODS: Successive stages of embryoid bodies (EBs) as well as vascular progenitors were used to evaluate the expression of scleroderma autoantigens IFI-16 and CENP by immunoblotting. CD31 was included to mark early blood vessels. IFI-16 and CD31 expression were defined in paraffin-embedded skin sections from scleroderma patients and from healthy controls. IFI-16 expression was determined by flow cytometric analysis in circulating endothelial cells (CECs) and circulating hematopoietic progenitor cells. RESULTS: Expression of CENP-A, IFI-16, and CD31 was enriched in EBs on days 10 and 12 of differentiation, and particularly in cultures enriched in vascular progenitors (IFI-16, CD31, and CENPs A and B). This pattern was distinct from that of comparator autoantigens. Immunohistochemical staining of paraffin-embedded skin sections showed enrichment of IFI-16 in CD31-positive vascular endothelial cells in biopsy specimens from scleroderma patients and normal controls. Flow cytometric analysis revealed IFI-16 expression in circulating hematopoietic progenitor cells but minimal expression in CECs. CONCLUSION: Our findings indicate that expression of the scleroderma autoantigens IFI-16 and CENPs, which are associated with severe vascular disease, is increased in vascular progenitors and mature endothelial cells. High level, lineage-enriched expression of autoantigens may explain the striking association between clinical phenotypes and the immune targeting of specific autoantigens.

Direct Reprogramming of Human Primordial Germ Cells into Induced Pluripotent Stem Cells: Efficient Generation of Genetically Engineered Germ Cells.

Primordial germ cells (PGCs) share many properties with embryonic stem cells (ESCs) and innately express several key pluripotency-controlling factors, including OCT4, NANOG, and LIN28. Therefore, PGCs may provide a simple and efficient model for studying somatic cell reprogramming to induced pluripotent stem cells (iPSCs), especially in determining the regulatory mechanisms that fundamentally define pluripotency. Here, we report a novel model of PGC reprogramming to generate iPSCs via transfection with SOX2 and OCT4 using integrative lentiviral. We also show the feasibility of using nonintegrative approaches for generating iPSC from PGCs using only these two factors. We show that human PGCs express endogenous levels of KLF4 and C-MYC protein at levels similar to embryonic germ cells (EGCs) but lower levels of SOX2 and OCT4. Transfection with both SOX2 and OCT4 together was required to induce PGCs to a pluripotent state at an efficiency of 1.71%, and the further addition of C-MYC increased the efficiency to 2.33%. Immunohistochemical analyses of the SO-derived PGC-iPSCs revealed that these cells were more similar to ESCs than EGCs regarding both colony morphology and molecular characterization. Although leukemia inhibitory factor (LIF) was not required for the generation of PGC-iPSCs like EGCs, the presence of LIF combined with ectopic exposure to C-MYC yielded higher efficiencies. Additionally, the SO-derived PGC-iPSCs exhibited differentiation into representative cell types from all three germ layers in vitro and successfully formed teratomas in vivo. Several lines were generated that were karyotypically stable for up to 24 subcultures. Their derivation efficiency and survival in culture significantly supersedes that of EGCs, demonstrating their utility as a powerful model for studying factors regulating pluripotency in future studies.

Gaucher Disease-Induced Pluripotent Stem Cells Display Decreased Erythroid Potential and Aberrant Myelopoiesis.

Gaucher disease (GD) is the most common lysosomal storage disease resulting from mutations in the lysosomal enzyme glucocerebrosidase (GCase). The hematopoietic abnormalities in GD include the presence of characteristic Gaucher macrophages that infiltrate patient tissues and cytopenias. At present, it is not clear whether these cytopenias are secondary to the pathological activity of Gaucher cells or a direct effect of GCase deficiency on hematopoietic development. To address this question, we differentiated induced pluripotent stem cells (iPSCs) derived from patients with types 1, 2, and 3 GD to CD34(+)/CD45(+)/CD43(+)/CD143(+) hematopoietic progenitor cells (HPCs) and examined their developmental potential. The formation of GD-HPCs was unaffected. However, these progenitors demonstrated a skewed lineage commitment, with increased myeloid differentiation and decreased erythroid differentiation and maturation. Interestingly, myeloid colony-formation assays revealed that GD-HPCs, but not control-HPCs, gave rise to adherent, macrophage-like cells, another indication of abnormal myelopoiesis. The extent of these hematologic abnormalities correlated with the severity of the GCase mutations. All the phenotypic abnormalities of GD-HPCs observed were reversed by incubation with recombinant GCase, indicating that these developmental defects were caused by the mutated GCase. Our results show that GCase deficiency directly impairs hematopoietic development. Additionally, our results suggest that aberrant myelopoiesis might contribute to the pathological properties of Gaucher macrophages, which are central to GD manifestations. The hematopoietic developmental defects we observed reflect hematologic abnormalities in patients with GD, demonstrating the utility of GD-iPSCs for modeling this disease.

Cancer-like epigenetic derangements of human pluripotent stem cells and their impact on applications in regeneration and repair.

A growing body of work has raised concern that many human pluripotent stem cell (hPSC) lines possess tumorigenic potential following differentiation to clinically relevant lineages. In this review, we highlight recent work characterizing the spectrum of cancer-like epigenetic derangements in human embryonic stem cells (hESC) and human induced pluripotent stem cells (hiPSC) that are associated with reprogramming errors or prolonged culture that may contribute to such tumorigenicity. These aberrations include cancer-like promoter DNA hypermethylation and histone marks associated with pluripotency, as well as aberrant X-chromosome regulation. We also feature recent work that suggests optimized high-fidelity reprogramming derivation methods can minimize cancer-associated epigenetic aberrations in hPSC, and thus ultimately improve the ultimate clinical utility of hiPSC in regenerative medicine.

Gaucher iPSC-derived macrophages produce elevated levels of inflammatory mediators and serve as a new platform for therapeutic development.

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the acid ß-glucocerebrosidase (GCase; GBA) gene. The hallmark of GD is the presence of lipid-laden Gaucher macrophages, which infiltrate bone marrow and other organs. These pathological macrophages are believed to be the sources of elevated levels of inflammatory mediators present in the serum of GD patients. The alteration in the immune environment caused by GD is believed to play a role in the increased risk of developing multiple myeloma and other malignancies in GD patients. To determine directly whether Gaucher macrophages are abnormally activated and whether their functional defects can be reversed by pharmacological intervention, we generated GD macrophages by directed differentiation of human induced pluripotent stem cells (hiPSC) derived from patients with types 1, 2, and 3 GD. GD hiPSC-derived macrophages expressed higher levels of tumor necrosis factor α, IL-6, and IL-1ß than control cells, and this phenotype was exacerbated by treatment with lipopolysaccharide. In addition, GD hiPSC macrophages exhibited a striking delay in clearance of phagocytosed red blood cells, recapitulating the presence of red blood cell remnants in Gaucher macrophages from bone marrow aspirates. Incubation of GD hiPSC macrophages with recombinant GCase, or with the chaperones isofagomine and ambroxol, corrected the abnormal phenotypes of GD macrophages to an extent that reflected their known clinical efficacies. We conclude that Gaucher macrophages are the likely source of the elevated levels of inflammatory mediators in the serum of GD patients and that GD hiPSC are valuable new tools for studying disease mechanisms and drug discovery.

Dynamic Interactions Between Cancer Stem Cells And Their Stromal Partners.

The cancer stem cell (CSC) paradigm presumes the existence of self-renewing cancer cells capable of regenerating all tumor compartments and exhibiting stem cell-associated phenotypes. Recent interpretations of the CSC hypothesis envision stemness as a dynamic trait of tumor-initiating cells rather than a defined and unique cell type. Bidirectional crosstalk between the tumor microenvironment and the cancer bulk is well described in the literature and the tumor-associated stroma, vasculature and immune infiltrate have all been implicated as direct contributors to tumor development. These non-neoplastic cell types have also been shown to organize specific niches within the tumor bulk where they can control the intra-tumor CSC content and alter the fate of CSCs and tumor progenitors during tumorigenesis to acquire phenotypic features for invasion, metastasis and dormancy. Despite the complexity of the tumor-stroma interactome, novel therapeutic approaches envision combining tumor-ablative treatment with manipulation of the tumor microenvironment. We will review the currently available literature that provides clues about the complex cellular network that regulate the CSC phenotype and its niches during tumor progression.

Vascular progenitors from cord blood-derived induced pluripotent stem cells possess augmented capacity for regenerating ischemic retinal vasculature.

BACKGROUND: The generation of vascular progenitors (VPs) from human induced pluripotent stem cells (hiPSCs) has great potential for treating vascular disorders such as ischemic retinopathies. However, long-term in vivo engraftment of hiPSC-derived VPs into the retina has not yet been reported. This goal may be limited by the low differentiation yield, greater senescence, and poor proliferation of hiPSC-derived vascular cells. To evaluate the potential of hiPSCs for treating ischemic retinopathies, we generated VPs from a repertoire of viral-integrated and nonintegrated fibroblast and cord blood (CB)-derived hiPSC lines and tested their capacity for homing and engrafting into murine retina in an ischemia-reperfusion model. METHODS AND RESULTS: VPs from human embryonic stem cells and hiPSCs were generated with an optimized vascular differentiation system. Fluorescence-activated cell sorting purification of human embryoid body cells differentially expressing endothelial/pericytic markers identified a CD31(+)CD146(+) VP population with high vascular potency. Episomal CB-induced pluripotent stem cells (iPSCs) generated these VPs with higher efficiencies than fibroblast-iPSC. Moreover, in contrast to fibroblast-iPSC-VPs, CB-iPSC-VPs maintained expression signatures more comparable to human embryonic stem cell VPs, expressed higher levels of immature vascular markers, demonstrated less culture senescence and sensitivity to DNA damage, and possessed fewer transmitted reprogramming errors. Luciferase transgene-marked VPs from human embryonic stem cells, CB-iPSCs, and fibroblast-iPSCs were injected systemically or directly into the vitreous of retinal ischemia-reperfusion-injured adult nonobese diabetic-severe combined immunodeficient mice. Only human embryonic stem cell- and CB-iPSC-derived VPs reliably homed and engrafted into injured retinal capillaries, with incorporation into damaged vessels for up to 45 days. CONCLUSIONS: VPs generated from CB-iPSCs possessed augmented capacity to home, integrate into, and repair damaged retinal vasculature.

Mesenchymal stem cell secretome and regenerative therapy after cancer.

Cancer treatment generally relies on tumor ablative techniques that can lead to major functional or disfiguring defects. These post-therapy impairments require the development of safe regenerative therapy strategies during cancer remission. Many current tissue repair approaches exploit paracrine (immunomodulatory, pro-angiogenic, anti-apoptotic and pro-survival effects) or restoring (functional or structural tissue repair) properties of mesenchymal stem/stromal cells (MSC). Yet, a major concern in the application of regenerative therapies during cancer remission remains the possible triggering of cancer recurrence. Tumor relapse implies the persistence of rare subsets of tumor-initiating cancer cells which can escape anti-cancer therapies and lie dormant in specific niches awaiting reactivation via unknown stimuli. Many of the components required for successful regenerative therapy (revascularization, immunosuppression, cellular homing, tissue growth promotion) are also critical for tumor progression and metastasis. While bi-directional crosstalk between tumorigenic cells (especially aggressive cancer cell lines) and MSC (including tumor stroma-resident populations) has been demonstrated in a variety of cancers, the effects of local or systemic MSC delivery for regenerative purposes on persisting cancer cells during remission remain controversial. Both pro- and anti-tumorigenic effects of MSC have been reported in the literature. Our own data using breast cancer clinical isolates have suggested that dormant-like tumor-initiating cells do not respond to MSC signals, unlike actively dividing cancer cells which benefited from the presence of supportive MSC. The secretome of MSC isolated from various tissues may partially diverge, but it includes a core of cytokines (i.e. CCL2, CCL5, IL-6, TGFß, VEGF), which have been implicated in tumor growth and/or metastasis. This article reviews published models for studying interactions between MSC and cancer cells with a focus on the impact of MSC secretome on cancer cell activity, and discusses the implications for regenerative therapy after cancer.