Diabetes is a chronic debilitating disease that results from insufficient production of insulin from pancreatic β-cells. Islet cell replacement can effectively treat diabetes but is currently severely limited by the reliance upon cadaveric donor tissue. We have developed a protocol to efficiently differentiate commercially available human embryonic stem cells (hESCs) in vitro into a highly enriched PDX1+ pancreatic progenitor cell population that further develops in vivo to mature pancreatic endocrine cells. Immature pancreatic precursor cells were transplanted into immunodeficient mice with streptozotocin-induced diabetes, and glycemia was initially controlled with exogenous insulin. As graft-derived insulin levels increased over time, diabetic mice were weaned from exogenous insulin and human C-peptide secretion was eventually regulated by meal and glucose challenges. Similar differentiation of pancreatic precursor cells was observed after transplant in immunodeficient rats. Throughout the in vivo maturation period hESC-derived endocrine cells exhibited gene and protein expression profiles that were remarkably similar to the developing human fetal pancreas. Our findings support the feasibility of using differentiated hESCs as an alternative to cadaveric islets for treating patients with diabetes.

A pool of stem cells that arise from the mesoderm during embryogenesis initiates hematopoiesis. However, factors that regulate the expansion of blood stem cells are poorly understood. We show here that cytokine-induced proliferation of primitive human hematopoietic cells could be inhibited with antibodies to hedgehog (Hh). Conversely, Sonic hedgehog (Shh) treatment induced the expansion of pluripotent human hematopoietic repopulating cells detected in immunodeficient mice. Noggin, a specific inhibitor of bone morphogenetic protein 4 (BMP-4), was capable of inhibiting Shh-induced proliferation in a similar manner to anti-Hh; however, anti-Hh had no effect on BMP-4-induced proliferation. Our study shows that Shh functions as a regulator of primitive hematopoietic cells via mechanisms that are dependent on downstream BMP signals.

OBJECTIVEDifferentiation of human embryonic stem (hES) cells to fully developed cell types holds great therapeutic promise. Despite significant progress, the conversion of hES cells to stable, fully differentiated endocrine cells that exhibit physiologically regulated hormone secretion has not yet been achieved. Here we describe an efficient differentiation protocol for the in vitro conversion of hES cells to functional glucagon-producing α- cells.RESEARCH DESIGN AND METHODSUsing a combination of small molecule screening and empirical testing, we developed a six-stage differentiation protocol for creating functional α-cells. An extensive in vitro and in vivo characterization of the differentiated cells was performed.RESULTSA high rate of synaptophysin expression (>75%) and robust expression of glucagon and the α-cell transcription factor ARX was achieved. After a transient polyhormonal state in which cells coexpress glucagon and insulin, maturation in vitro or in vivo resulted in depletion of insulin and other β-cell markers with concomitant enrichment of α-cell markers. After transplantation, these cells secreted fully processed, biologically active glucagon in response to physiologic stimuli including prolonged fasting and amino acid challenge. Moreover, glucagon release from transplanted cells was sufficient to reduce demand for pancreatic glucagon, resulting in a significant decrease in pancreatic α-cell mass.CONCLUSIONSThese results indicate that fully differentiated pancreatic endocrine cells can be created via stepwise differentiation of hES cells. These cells may serve as a useful screening tool for the identification of compounds that modulate glucagon secretion as well as those that promote the transdifferentiation of α-cells to β-cells.

Delta-mediated Notch signaling controls cell fate decisions during invertebrate and murine development. However, in the human, functional roles for Delta have yet to be described. This study reports the characterization of Delta-1 and Delta-4 in the human. Human Delta-4 was found to be expressed in a wide range of adult and fetal tissues, including sites of hematopoiesis. Subsets of immature hematopoietic cells, along with stromal and endothelial cells that support hematopoiesis, were shown to express Notch and both Delta-1 and Delta-4. Soluble forms of human Delta-1 (h Delta-1) and h Delta-4 proteins were able to augment the proliferation of primitive human hematopoietic progenitors in vitro. Intravenous transplantation of treated cultures into immune-deficient mice revealed that h Delta-1 is capable of expanding pluripotent human hematopoietic repopulating cells detected in vivo. This study provides the first evidence for a role of Delta ligands as a mitogenic regulator of primitive hematopoietic cells in the human. (Blood. 2001;97:1960-1967)

Recent evidence indicates that human hematopoietic stem cell properties can be found among cells lacking CD34 and lineage commitment markers (CD34−Lin−). A major barrier in the further characterization of human CD34− stem cells is the inability to detect this population using in vitro assays because these cells only demonstrate hematopoietic activity in vivo. Using cell surface markers AC133 and CD7, subfractions were isolated within CD34−CD38−Lin− and CD34+CD38−Lin− cells derived from human cord blood. Although the majority of CD34−CD38−Lin− cells lack AC133 and express CD7, an extremely rare population of AC133+CD7− cells was identified at a frequency of 0.2%. Surprisingly, these AC133+CD7− cells were highly enriched for progenitor activity at a frequency equivalent to purified fractions of CD34+ stem cells, and they were the only subset among the CD34−CD38−Lin− population capable of giving rise to CD34+ cells in defined liquid cultures. Human cells were detected in the bone marrow of non-obese/severe combined immunodeficiency (NOD/SCID) mice 8 weeks after transplantation of ex vivo–cultured AC133+CD7− cells isolated from the CD34−CD38−Lin− population, whereas 400-fold greater numbers of the AC133−CD7− subset had no engraftment ability. These studies provide novel insights into the hierarchical relationship of the human stem cell compartment by identifying a rare population of primitive human CD34− cells that are detectable after transplantation in vivo, enriched for in vitro clonogenic capacity, and capable of differentiation into CD34+ cells.

Numerous studies have shown that the bone marrow (BM) niche plays a key role in mouse hematopoietic stem cell (HSC) function and involves contributions from a broad array of cell types. However, the composition and role of the human BM HSC niche have not been investigated. Here, using human bone biopsy specimens, we provide evidence of HSC propensity to localize to endosteal regions of the trabecular bone area (TBA). Through functional xenograft transplantation, we found that human HSCs localizing to the TBA have superior regenerative and self-renewal capacity and are molecularly distinct from those localizing to the long bone area (LBA). In addition, osteoblasts in the TBA possess unique characteristics and express a key network of factors that regulate TBA- versus LBA-localized human HSCs in vivo. Our study reveals that BM localization and architecture play a critical role in defining the functional and molecular properties of human HSCs.

The molecular basis governing functional behavior of human hematopoietic stem cells (HSCs) is largely unknown. Here, using in vitro and in vivo assays, we isolate and define progenitors versus repopulating HSCs from multiple stages of human development for global gene expression profiling. Accounting for both the hierarchical relationship between repopulating cells and their progenitors, and the enhanced HSC function unique to early stages of ontogeny, the human homologs of Hairy Enhancer of Split-1 (HES-1) and Hepatocyte Leukemia Factor (HLF) were identified as candidate regulators of HSCs. Transgenic human hematopoietic cells expressing HES-1 or HLF demonstrated enhanced in vivo reconstitution ability that correlated to increased cycling frequency and inhibition of apoptosis, respectively. Our report identifies regulatory factors involved in HSC function that elicit their effect through independent systems, suggesting that a unique orchestration of pathways fundamental to all human cells is capable of controlling stem cell behavior.

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