News & Views in ... Regenerative Medicine

Embryonic stem cells may be an inexhaustible source of red blood cells for transfusion

Scientists at Advanced Cell Technology (CA, USA) hope to enable donorless blood transfusions. The company, in collaboration with researchers from University of Illinois (IL, USA) and the Mayo Clinic, USA, has developed a system for producing red blood cells on a clinical scale using human embryonic stem cells. This is the first time that functional red blood cells have been produced in the laboratory.

“Limitations in the supply of blood can have potentially life-threatening consequences for patients with massive blood loss,” commented study author Robert Lanza, Chief Scientific Officer at Advanced Cell Technology. “Embryonic stem cells represent a new source of cells that can be propagated and expanded indefinitely, providing a potentially inexhaustible source of red blood cells for human therapy. We can currently generate 10–100 billion red blood cells from a single six-well plate of stem cells.

Red blood cell precursors, hemiangioblasts, have been created successfully in previous experiments, but this study was the first to create mature red blood cells. The key step is the enucleation of the cells, which the group achieved by culturing the hemioangioblasts on stromal cells from the bone marrow, where red blood cells mature in the body.

“We show that up to 65% of the blood cells underwent multiple maturation events that resulted in the extrusion of the nucleus,” reported study author Shi-Jiang Lu, Advanced Cell Technology. “They formed enucleated erythrocytes with a diameter of 6–8 µm, which is similar to normal red blood cells. We also showed that the cells could express adult β-globin and respond normally to biochemical changes.”

The most useful blood type for transfusion is O-negative, which can be transfused to any patient, but this type is rare in the general population. This study was not able to produce O-negative cells since none of the embryonic stem cell lines approved for use in the USA carry this genotype. However, the team hopes that such a cell line will be identified in the near future. Alternatively, induced pluripotent stem cell technology might allow researchers to create human embryonic stem cell-like progenitors from adult skin cells of O-negative volunteers.

Further experiments will test the safety and function of the hESC-derived cells in animals.

Source: Lu SJ, Feng Q, Park JS et al.: Biological properties and enucleation of red blood cells from human embryonic stem cells. Blood PMID: 18713948 (2008) (Epub ahead of print).

iPS cells are brought a step closer to clinical use with the creation of iPS cells from mice using harmless adenoviruses

Researchers have created induced pluripotent stem (iPS) cells from mice using harmless adenoviruses rather than potentially cancer-causing retroviruses, bringing iPS cells a step closer to clinical use.

The researchers used an adenovirus, which infects the cell and produces the transcription factors required for the cell to revert to a pluripotent state, but does not integrate into the host DNA and disappears from the cells after a few passages. The study, published in Science, is the first to demonstrate creation of iPS cells without viral integration. Several groups are pursuing the same goal by replacing the transcription factors with chemicals.

While the ability to reprogram adult cells into pluripotent cells using iPS technology has caused great excitement in the stem cell community, the use of retroviral vectors has made it impossible to consider developing iPS cell-based therapies towards the clinic, for fear of inducing cancer. Assuming the adenovirus-based technique is successful in human cells, this risk would be removed, paving the way for potential clinical use in the future.

“The next step is to reproduce this work using human cells, and there’s no reason why it can’t work,” commented study author Konrad Hochedlinger. “This basically provides us with a system with which to test the question of whether iPS cells are the equivalent of human embryonic stem cells. That’s a question that, in my opinion, hasn’t been answered yet.”

Source: Stadtfeld M, Nagaya M, Utikal J, Weir G, Hochedlinger K: Induced pluripotent stem cells generated without viral integration. Science PMID: 18818365 (Epub ahead of print) (2008).

Embryonic stem cells can repair cardiac muscle and improve function in a mouse model of a common congenital heart disease. Mice treated with injections of embryonic stem cells had improved heart function and better survival rates.

The mice used in the study had a phenotype similar to heritable dilated cardiomyopathy, including enlarged heart, impaired heart muscle contraction and poor survival.

Approximately 200,000 embryonic stem cells were injected into the left ventricular region of the heart. Just 1 month after treatment, the mice showed improvement in heart function, and a decrease in symptoms such as fluid build-up and poor stamina. The stem cells were shown to have formed new heart tissue and were also thought to have reduced the level of fibrosis caused by existing damage to the heart.

There has been much interest in stem cell therapy for heart attacks and ischemic disease, and this new study suggests that there may be a place for cell therapy in congenital heart disease as well.

“We’ve shown in this transgenic animal model that embryonic stem cells may offer an option in repairing genetic heart problems,” enthused study author Satsuki Yamada.

Source: Yamada S, Nelson TJ, Crespo R et al.: Embryonic Stem Cell Therapy of Heart Failure in Genetic Cardiomyopathy. Stem Cells PMID: 18669912 (2008) (Epub ahead of print).

Researchers have successfully induced reprograming directly from one adult cell type to another, significantly reducing the number of steps required for reprogramming.

Previously, adult cells have been reprogrammed by returning them to a stem-cell-like state and then inducing them to differentiate into a different adult cell type. For example, skin cells from adult patients with amyotrophic lateral sclerosis have recently been reprogrammed to induced pluripotent stem (iPS) cells and then differentiated to form motor neurons, in order to allow study of these cells in vitro. However, the researchers behind the new study, based at the Harvard Stem Cell Institute, MA, USA, and Howard Hughes Medical Institute, MD, USA, felt that there might be a simpler solution.

“The presently accepted regenerative medicine idea is that you make a stem cell from a patient, bring it back to the beginning as it were, then you are left with the problem of how to instruct that cell to become a β-cell or a motor neuron,” elaborated study author Douglas Melton. “We asked the simple question, why should you have to go all the way back to the beginning? Could you go from one cell type to another?”

Dr Melton and his colleagues focus their research on exploring regenerative medicine applications to potentially treat diabetes. In this study they reprogrammed exocrine pancreatic cells to insulin-producing β-cells.

Surprisingly, this ‘lineage switching’ required transfection of just three retroviral genes into the exocrine pancreatic cells. This was enough to transform 20% of the exocrine cells into β-cells.

The investigators initially injected retroviruses containing nine genes into the pancreatic tissue of adult mice, but found that only three of the genes were required.

The resulting reprogramming of pancreatic cells was sufficient to improve hyperglycemia in diabetic mice, but the cells were not glucose responsive. Within 2 months the transcription factors expressed by the three genes were no longer being produced, but the cells remained β-cells.

There are still many hurdles to be overcome before this work could start to enter the clinic. iPS cells are currently not suitable for clinical use because they are created using retroviruses, and hence may cause cancer. In addition, there are problems specific to the pancreas. The pancreas is easily damaged, so it is considered too risky to inject cells directly into the human pancreas; hence, the researchers intend to look at what other cell types could be transformed into β-cells.

Until these problems can be resolved, Melton feels that it is too early to call whether the new iPS techniques or ongoing research with embryonic stem cells will be more successful in treating diabetes.

“Maybe when the history of the whole subject is written, it will be possible to say which was the best idea,” Melton commented. “I can’t emphasize enough at this point that we’re too ignorant to know what is the best way to treat patients and, until we know that, it is essential that we use embryonic stem cells and iPS cells to teach us about the mechanisms of disease. Until we know how to succeed, we have to aggressively pursue all avenues.”

Source: Zhou Q, Brown J, Kanarek A, Rajagopal J, Melton DA: In vivo reprogramming of adult pancreatic exocrine cells to β-cells. Nature 455(7213), 627–632 (2008).