The main focus of this paper was to investigate the current research, challenges, and the future research needed to allow replacement of B-cells from human pluripotent stem cells (hPSC). This is a important topic because diabetes is a worldwide health problem affecting over 200 million individuals and is associated with several long term health problems. Type 1 diabetes mellitus results from the autoimmune destruction of the B-cells of the islets of Langerhans that produce insulin in the pancreas. Type 1 diabetes can be treated with insulin injections to control blood glucose levels but these injections can not fully compensate for B-cell loss. Thus replacement of B-cells from hPSC may provide a better solution for the treatment of diabetes.
Current Research:
Human embryonic stem cells (hESC) can be differentiated into glucose responsive B-like cells by incorporating signalling molecules required for B-cell development in vivo to the differentiation process.
4 stages for the development of B-cells from hESC
1. Endoderm Formation: The nodal signalling pathway controls endoderm formation in most vertebrate species. The nodal related protein activin can be applied to hESC to promote their differentiation into definitive endoderm.
2. Pancreas Specification: Definitive endoderm can produce a vast array of cell types . hESC derived endoderm can be differentiated into pancreatic progenitors by applying signalling molecules such as fibroblast growth factor (FGF), bone morphogenic protein (BMP), retonic acid, and hedgehog signalling molecules.
3. Endocrine Specification: Pancreatic progenitors can be promoted to adopt a endocrine cell fate by inhibiting notch signalling and preventing exocrine cell formation. Epidermal growth factor (EGF) can then be used to expand the endocrine progenitors.
derived
4. B-cell Maturation: Some pathways thought to be involved in B-cell maturation include the incretin signalling pathway mediated by glucagon-like peptide-1 (GLP1) and nerve growth factor (NGF). However B-cell maturation is not well understood so the promotion of hESCpancreatic endocrine cells into B-like cells has had limited success. Thus a better understanding of B-cell maturation is needed to more successfully guide hPSC into B-cells in vitro.
Challenges and Future Research:
The recombinant proteins needed to direct the differentiation of PSC are expensive to manufacture and thus so far scientists have been unable to produce a sufficient number of B-cells for human transplantation. Thus there is a need to develop a large amount of cost-effective small molecules to direct the PSC differentiation into B-cells. Recent studies screening chemical liberies have found compound such as IDE1 and IDE2 that promote hESC differentiation into definitive endoderm. In addition indolactum was found to promote the differentiation of definitive endoderm to pancreatic progenitors.
Teratomas have been found to be associated with PSC derived cell transplants. These teratomas are thought to be associated with undifferentiated hESC thus better cell-sorting techniques need to be applied to hESC cultures to reduce the chance of teratoma formation. Cell sorting techniques using immunocytochemistry and or immunohistochemstry have shown promise for future research. But all PSC will need to be tested for cancer forming cells in future research.
The transplantation site for PSC derived B-cells should ideally promote the long term survival of the grafted tissue while maximizing the patients safety. In current animal trials PSC derived B-cells are transplanted into the liver from the portal vein due to the fact that the majority of insulin is utilized in the liver. However research has shown that B-cell transplantation to this site has resulted in death of approximately half of the B-cells, thus there is a need to investigate other transplantation sites for B-cells.
Patients that receive hESC derived B-cells transplants will require life long immunosepressive drugs to prevent graft rejection. Thus research is needed to minimize or eliminate the use of immunospressive drugs in these patients. Research areas to combat the immune response to B-cell transplantation include the use CD3 specific antibodies; microencapsulation of grafted tissue; transplantation of cells to immuno privileged sites; and creating large banks of hESC and matching human leukocyte antigen (HLA) to recipient patients. In addition current research has shown that human somatic cells can be reprogrammed into a ESC like state. Induced PSC (iPSC) are ideal because they could be derived from patients thus generating patient specific B-cells for autologus transplant and combating the patients immune response.
Critique:
In a personal critique of this publication, Christopher N. Mayhew and James M. Wells provide a easy to read and understandable review of the use of human pluripotent stem cells to replace B-cells in diabetic patients. Although a more detailed description of the signalling pathways involved would have helped my understanding of the differentiation process of human pluripotent stem cells into B-cells the diagram provided in the paper worked well to illustrate the molecules involved in the process. The authors also did a great job of illustrating the problems associated with the transplantation of hESC derived B-like cells into diabetic patients and highlighting the research that is necessary to combat these problems and make this procedure possible in the future. I particularly find this paper of extreme interest since research involving the differentiation of hPSC can potentially be used to treat a vast array of human health problems, in addition to diabetes.
This paper can be located at http://www.ncbi.nlm.nih.gov/pubmed/19855279
