Using Tissue-Specific Mesenchymal Stem Cells to Make Insulin-Producing Beta Cells from Embryonic Stem Cells


Embryonic stem cell lines are made from four-five-day-old human embryos. At this stage of development, the embryo is a sphere of cells with two distinct cell populations; an outside layer of flat trophoblast cells and an inner clump of round inner cell mass (ICM) cells. The embryo consists of ~100 cells four days after fertilization, and ~150 cells five days after fertilization.

Trophoblast

Embryonic stem cell (ESC) derivation involves the removal of the trophoblast cells (which are collectively called the trophectoderm) and the isolation of the ICM cells. There are several ways to remove the trophectoderm, but the most commonly-used technique is “immunosurgery,” which uses antibodies that bind to proteins on the surfaces of the trophectoderm, and serum to initiate destruction of the trophoblast cells. The isolated ICM cells are then cultured, and if they grow, they may produce an embryonic stem cell line.

Immunosurgery was first perfected by Davor Solter and Barbara B. Knowles on mouse embryos. They used an antiserum that was raised in rabbits when the rabbits were immunized against mouse spleen tissue. When mouse embryos were incubated with this antiserum plus serum from mice, all the cells of the mouse embryo died. However, if they used the rabbit antiserum and serum from guinea pig, then only the trophoblast cells were destroyed. For human embryonic stem cell derivation, the rabbits are immunized again human red blood cells, and this rabbit antiserum is used with guinea pig serum. The serum contains proteins called “complement,” which bind to cells that have antibodies attached to them and bore holes in those cells, thus destroying them.

When ICM cells are cultured, they are placed on a layer of mouse cells that have been treated with a chemical called mitomycin C to prevent them from dividing. These non-dividing cells act as “feeder cells” that keep the ICM cells from differentiating. Because ICM cells are grown on animal cells, they cannot be used for clinical purposes, since they will possess animal proteins can carbohydrates on their surfaces, which would be attacked by the patient’s immune system. However, several ESC lines have been derived without animal products, and it is possible to make ESC lines that would be safe or human use.

ESC derivation

ESC derivation results in the destruction of human embryos. There is not two ways about it. Even though there are potential ways around this problem, the majority of ESC lines were made literally over the dead bodies of very young human beings. All the rationalization in the world (the embryo is too young, too small, too inchoate, too unwanted, going to die anyway, in the wrong place at the wrong time) do not undo the fact that the embryo is a very young human being, and making an ESC line from it ends his/her life.

Getting the ESC line to differentiate in what you want it to be is another problem. If any undifferentiated cells remain after differentiation, they can cause tumors. Therefore, there is a need to ensure that differentiation is efficient and complete. To this end, Doug Melton’s lab at Harvard University has published a remarkable paper in the journal Nature that uses mesenchymal stem cells from particular organs to direct the differentiation of ESC lines.

Melton’s lab, in particular Julie M. Sneddon and Malgorzata Borowiak (say that fast five times), established 16 lines of tissue-specific mesenchymal stem cells (MSCs) from embryonic, neonatal and adult mouse intestine, liver, spleen, and pancreas and human pancreas too. Then they cultured mouse ESCs on these MSC lines to determine if they could drive the ESCs to differentiate into pancreas cells. In the embryo, pancreatic precursors express several genes in a nested, hierarchical fashion. First, they express Sox17, which is a common endodermal marker, and then pancreatic progenitors all express Pdx1. Of these pancreatic progenitors, some express Ngn3 and these will become endocrine rather than exocrine cells, and othe the Ngn3-expressing cells, a few will become beta cells that make insulin.

Melton and his co-workers tried to determine if any of these genes was up-regulated in their ESC lines if that were co-cultured with their established MSC lines. They discovered that four lines – MSC1, 2, 3, & 4, all affected gene expression when co-cultured with ESCs. MSC 1 and 2 induced and increase in Sox17 expression and MSC 3 and 4 increased the expression of Ngn3 in ESCs.

These changes in gene expression were due to increased cell proliferation of cells actually expressing these genes and not due to differential survival. Also, no combination of growth factors could achieve the same results as the accompanying MSC lines. Thus there is more going on here than the MSCs just secreting the right growth factors. The MSCs must be making contact with the ESCs and inducing them to differentiate into a particular cell type.

Next Melton and his colleagues determined if this interaction with MSCs caused the ESCs to lose their ability to self-renew. The answer was a clear “no.” Even though these ESC lines were expressing genes characteristic of endodermal or pancreatic tissue, they did not lose their ability to differentiate into pancreatic tissue when appropriately induced to do so, and they also id not lose their ability to self-renew and grow competently in culture.

In a more stringent test, these ESCs that had been grown on tissue-specific MSCs were implanted into mice. As Melton points out in the paper, the “most efficient published protocols for in vitro differentiation of pluripotent cells to beta-cells yield only a small percentage (typically 0-15%) of insulin-positive cells, and these do not secrete insulin in a glucose-responsive manner.” Could the MSC-conditioned ESCs do any better?

Before implantation, the ESCs were differentiated into endodermal progenitors (Sox17-expressing cells), and co-cultured with MSCs for at least 3-7 passages. Then they were differentiated into beta cells and transplanted into mice. There were a few important controls that were used; Just saline, implantations of MSCs alone, and ESCs that had been differentiated into beta cells, but had never been passaged on MSCs. Finally, human pancreatic islets were used as a positive control.

The results were interesting to say the least. The saline and MSC alone implantations showed no insulin production with or without glucose. Likewise the human pancreatic islets made insulin in a glucose-dependent manner (no surprise there). The ESC-derived beta cells that had never been passaged on MSCs made insulin, and even showed some ability to respond to glucose and make more insulin after glucose ingestion. However, the beta cells derived from ESCs that had been passaged on MSCs made insulin in a glucose-dependent manner. The experiment produced a wide range of variability since the number of transplanted cells differed between each trial, but the implanted beta cells derived from ESCs passaged on tissue-specific MSCs definitely performed the best, and even did as well or better than the implanted human beta cells in some cases.

a, Schematic depicting implantation of human ESC-derived progenitors. b, Immunofluorescence staining of human ESC-derived endoderm, passaged seven times on mesenchyme and engrafted for 3 months (top panel) or further differentiated to Pdx1+ stage and then engrafted for 2 months (bottom panel). c, Glucose-tolerance test of animals implanted with PBS or mesenchyme only, human islets or Pdx1+ pancreatic progenitors derived from unpassaged (P0), or passaged (P4 or P7) human endoderm. d, Fasting- and glucose-induced (45 min glucose) plasma human C-peptide levels. Pairs of bars represent two time points per animal; data represent mean of two technical replicates ± s.d.
a, Schematic depicting implantation of human ESC-derived progenitors. b, Immunofluorescence staining of human ESC-derived endoderm, passaged seven times on mesenchyme and engrafted for 3 months (top panel) or further differentiated to Pdx1+ stage and then engrafted for 2 months (bottom panel). c, Glucose-tolerance test of animals implanted with PBS or mesenchyme only, human islets or Pdx1+ pancreatic progenitors derived from unpassaged (P0), or passaged (P4 or P7) human endoderm. d, Fasting- and glucose-induced (45 min glucose) plasma human C-peptide levels. Pairs of bars represent two time points per animal; data represent mean of two technical replicates ± s.d.

Melton notes at the end of his paper that this technique worked rather well for coaxing ESCs to form pancreatic derivatives, but it could very well be applicable to other systems as well. Also, it could probably work with induced pluripotent stem cells, which have many (though not all) of the characteristics of ESCs and can be made without killing human embryos. Thus another technique for increasing ESC differentiation seems to be on the table.

A Co-culture System Makes Better Cartilage for Tissue Replacement


At joints, the bones are covered with cartilage to act as a shock absorber. Articular cartilage, or cartilage at joints, is usually characterized by very low friction, high wear resistance, but very abilities to regenerate. Articular cartilage is responsible for much of the compressive resistance and load bearing qualities of joints, and without it, even activities as simple and walking is too painful. Osteoarthritis is a condition that results from cartilage failure, and limits the range of joint motion, increases the bone damage and also causes a respectable amount of pain. When the cartilage of the articular surface erodes, the bone is exposed and grinding of the bone creates bone spurs, extensive inflammation and pain.

Treating osteoarthritis requires that one make new cartilage that has similar properties as articular cartilage. Unfortunately, mesenchymal stem cells that are differentiated into cartilage making cells (chondrocytes) and implanted into the knee tend to make fibrocartilage, which is different than the hyaline cartilage that composes articular cartilage. Fibrocartilage does not possess the high-wear resistance characteristics of hyaline cartilage and it tends to erode rather rapidly after formation. Therefore, directing mesenchymal stem cells (MSCs) to form proper cartilage is a genuine challenge.

A paper that appear in Stem Cell Translational Medicine from Gilda A. Barabino, who is a faculty member at the Wallace H. Coulter Department of Biomedical Engineering at Georgia Institute of Technology and Emory University, examines a technique to coax MSCs to make articular cartilage.

As Barbino points out, traditional protocols that direct MSCs to differentiate into chondrocytes uses culture systems of MSCs that have been treated with various growth factors, such as transforming growth factor-β. Unfortunately, these culture systems tend to fall short in meeting the needs of clinical applications, largely because they yield terminally differentiated cells that enlarge and then form bone.

In this study Barbino and her co-workers co-cultured bone marrow-derived MSCs with juvenile articular chondrocytes. The rationale is that the MSCs would receive just the right growth factors in just the right concentrations and at the right time to drive MSC cartilage formation. Physical contact between cells can also do a better job of driving them to differentiate into various cells types rather than simply treating them with growth factors.

Barbino and others discovered that an initial chondrocyte/MSC ratio of 63:1 worked the best and the MSCs form chondrocytes that had the right cells shape, behavior, and characteristics of articular chondrocytes.

Next, Barbino and her team grew the MSCs in a three-dimensional agarose system. Three-dimensional systems are generally thought to more realistically recapitulate the cartilage-making system present at joints. In this 3-D culture system, when co-cultured with juvenile articular chondrocytes, bone marrow MSCs develop into robust neocartilage that was structurally and mechanically stronger than the same cultures that only contained chondrocytes.

There was another advantage to this culture system; cultured MSCs that are induced to form cartilage tend to cease all expression of a surface protein called CD44, which is an important regulator in cartilage biology. However, when cultured in the 3-D culture, the MSCs retained the expression of CD44, which suggests that these co-cultured MSCs, which cultured in a 3-D culture system form chondrocytes that make superior articular cartilage, but retain CD44, which allows cartilage maintenance.

This shows that making articular cartilage from MSCs is probably possible and only requires the right culture system. Also, co-culturing MSCs with articular chondrocytes in a 3-D culture system might be one of the better culture systems for developing clinically relevant cartilage for tissue replacements.

Making Artificial Tissues With Bioprinters


Brian Derby from the University of Manchester is using inkjet technology to distribute cells onto scaffolds that are shaped as a particular organ. Inkjet and laserjet technologies can build three-dimensional scaffolds that are coated with cells that will grow into the scaffold, assume its shape and degrade the scaffold, leaving only the tissue in its place.

This type of technology, which involves the simultaneous placement of biodegradable scaffold and cells in a three-dimensional structure that resembles that of an organ is called additive manufacture and it might very well be the future of replacement organ production.  Additive manufacture recreates the biological structure in a three-dimensional, digital image, from which two-dimensional, digital slices are taken and fashioned one layer at a time.  The summation of all the digital slices eventually produces a three-dimensional structure.

Inkjet technology dispenses the material that makes the scaffold in very small droplets that quickly solidify.  The materials is loaded into an actual inkjet printer cartridge that is sprayed onto the surface.  More droplets are placed on top of previous droplets in a very specific pattern and this repetitive distribution of droplets develop into a pattern that is very complex and forms a scaffold that nicely mimics the conditions inside the body.  The scaffold also provides a surface the for cells to adhere, grow and thrive.  The scaffold and its internal structure control the behavior and maintain the health of the cells embedded in the scaffold.  This method of distributing cells onto a surface through a printer is called “bioprinting.”

In his article, published in the journal Science, Derby examines experiments in which porous structures are made by means of bioprinting.  Bioprinting uses inkjet and laserjet technologies to distribute cells or molecules onto a surface in a desired pattern.  In the case of porous structures, cells interweave throughout the scaffold and such cell-encrusted scaffolds can be placed in the body to encourage cell growth.  Depending on the composition of the scaffold and the cells embedded in it, the scaffold can become a part of the body or the cells will dissolve it.   Such a treatment can help heal patients with particular injuries such as cavity wounds.

Bioprinted cells can also be deposited onto scaffolds with various other chemicals, such as hormones, growth factors, or small molecules that influence the behavior of the cells.  The inclusion of such molecules with the scaffold can coax cells to differentiate into distinct cell types, such as, for example, bone- or cartilage-producing cells.

Cells do suffer some damage during bioprinting, and the rule of thumb is the more energy is used to deposit the cells onto the scaffold, the lower the viability of the cells after bioprinting.  To deposit and pattern cells in a scaffold there are three techniques that are used:  inkjet printing, microextrusion, which is also known as filament plotting, and laser forward transfer.  Bioprinting has probably the highest viability rates, and that has come after the techniques have been precisely worked out to ensure a minimum of damage.  Microextrusion shows extremely variable rates of cell survival after the cells are deposited.  Laser forward transfer suffers from the need for higher energy lasers to more precisely and efficiently deposit the cells, but this same higher energy kills off the cells.

Even though this technology has come a long way, it has a way to go before it is ready for the clinic.  Scaffolds are being used in clinical trials, but scaffold synthesis suffers from inconsistency, and until a consistent high-quality is delivered, scaffold production will not be ready for commercial production.

Despite these caveats, there have been some successes.  For example, D’Lima and others used an solution of chemicals in water (poly(ethylene glycol) dimethacrylate to be exact) that also contained cartilage-making cells (chondrocytes).  They printed this suspension a bone defect in a cultured bone and then used a chemical not unlike what dentists use to harden tooth plastic called a photoinitiator.  Such chemicals crosslink and bond together in response to particular wavelengths of light, and D’Lima used light to crosslink the chemicals to make a wet gel that contained the cells.  After several days, this printed structure appeared to have integrated into the surrounding tissue.  This experiment demonstrates that this technology is at least feasible.  The hanging issue is the toxicity of the photoinitiator chemicals to cells (X. Cui, et al Tissue Eng. A 18, 1304 (2012).  However, this has been studied, and it turns out the susceptibility to these chemicals is very cell type-specific.  Thus, picking the right photoinitiator could potentially make this technique rather safe (see C. G. Williams, et al Biomaterials 26,1211 2005).

(A) Schematic of bioprinting a cartilage analog structure, combining inkjet printing with a poly(ethylene glycol) dimethacrylate (PEGDMA) solution containing cells in suspension with a simultaneous photopolymerization process. (B) Light microscopy image of cell-containing polyethylene hydrogel printed into a defect formed in an osteochondral plug (scale bar, 2 mm). After culture, the cells within the printed material express ECM similar to those in the adjacent tissue

Scaffolds, however, can also be used to make external tissues, for example, skin patches.  Derby is working with ear, nose, and throat surgeons at the Manchester Royal Infirmary.  His goal is to use bioprinting to make patches that can be implanted into the inside of the nose or throat.

Derby explains: “It is very difficult to transplant even a small patch of tissue to repair the inside of the nose or mouth.  Current practice, to transplant the patient’s skin to these areas, is regarded as unsatisfactory because they transplants do not possess mucous generating cells or salivary glands.  We are working on techniques to print sheets of cells that are suitable for implantation in the mouth and nose.”

Derby hopes that someday bioprinting can be used to grow tumors in realistic cultures that will make superior models for drug testing and drug development.

TIMP3 Secreted by Mesenchymal Stem Cells Protects the Blood Brain Barrier After a Traumatic Brain Injury


Mesenchymal stem cells (MSCs) are found in multiple tissues and locations throughout our bodies, and they have the ability to differentiate into bone, fat, cartilage, and smooth muscle. MSCs also have the ability to suppress unwanted immune responses and inflammation. Therefore, MSCs are prime candidates for regenerative medical treatments.

MSCs have been used to experimentally treat traumatic brain injury (for example, Galindo LT et al., Neurol Res Int 2011;2011:564089). One of the main concerns after traumatic brain injury is damage to the blood brain barrier (BBB). BBB damage allows inflammatory cells to access the brain and further damage it. Therefore, healing the damage to the BBB or protecting the BBB after a traumatic brain injury is vital to the brain after a traumatic brain injury.

After a traumatic brain injury, the vascular system suffers damage and begins to leak. When blood leaks into tissues, it tends to irritate the tissues and damage them. MSCs release a soluble factor known as TIMP3 (tissue metalloproteinase-3) that degrades blood-based proteins known to cause damage to tissues when blood vessels leak. TIMP3 production by MSCs can also protect the BBB from degradation after a traumatic brain injury.

Researchers from the University of Texas Health Sciences Center, UC San Francisco, and two biotechnology companies have examined the protective role of MSCs and one particular protein secreted by MSCs in protecting the BBB after traumatic brain injury.

Shibani Pati, from UC San Francisco, and his collaborators from the University of Texas, Houston, MD Anderson Cancer Center, Amgen, and Blood Systems Research Institute (San Francisco) used MSCs to staunch the increased permeability the BBB after a traumatic brain injury.

They used a mouse model in these experiments and induced traumatic brain injuries in these mice. Then they gave MSCs to some, and soluble TIMP3 to others, and buffer to another group as a control. They discovered that the MSCs mitigated BBB damage after a traumatic brain injury. However, they also found that soluble TIMP3 could also protect the BBB approximately as well as MSCs. This suggested that the TIMP3 secretion by MSCs is the main mechanism by which MSCs protect the BBB after a traumatic brain injury.

To test this hypothesis, Pati and his colleagues administered MSCs to mice that had experienced traumatic brain injury, but they also co-administered a soluble inhibitor to TIMP3. They discovered that this inhibitor completely abolished the ability of MSCs to protect the BBB after a traumatic brain injury. They also found that the main target of TIMP3 was vascular endothelial growth factor. Apparently after a traumatic brain injury, massive release of vascular endothelial growth factor causes the breakdown of BBB structures. TIMP3 degrades vascular endothelial growth factor, which prevents BBB breakdown.

These findings suggest that administration of recombinant proteins such as TIMP3 after a traumatic brain injury can protect the BBB and decrease brain damage. Clinical trial anyone?

Highly Efficient Method for Converting Blood Stem Cells into Induced Pluripotent Stem Cells Without Viruses


A research group from Johns Hopkins University has designed a protocol that reliably converts stem cells from umbilical cord blood into a primitive stem cell state. From this primitive state, these cells can differentiate into any other type of cell in the body.

This paper was published in the August 8th issue of Public Library of Science (PLoS), and serves as the second publication in an ongoing effort to efficiently and consistently convert umbilical cord blood stem cells and other types of stem cells into stem cells that are usable for use in clinical and research settings in place of human embryonic stem cells, according to Elias Zambidis, M.D., Ph.D., who is an assistant professor of oncology and pediatrics at the Johns Hopkins Institute for Cell Engineering and the Kimmel Cancer Center.

Zambidis said: “Taking a cell from an adult and converting it all the way back to the way it was when that person was a 6-day-old embryo creates a completely new biology toward our understanding of how cells age and what happens when things go wrong, as in cancer development.”

The first paper that is sometimes designated ‘Chapter One‘ of this work was published last spring in PLoS One. In this paper, Zambidis’ group described the successful use of a method that safely transformed several different types of human pluripotent stem cells into heart muscle cells. In the latest experiments, Zambidis and his colleagues describe methods that convert umbilical cord blood stem cells into induced-pluripotent stem cells (iPS), which are adult or fetal cells reprogrammed to an embryonic like state.

According to Zambidis, he and his team developed a “super-efficient, virus-free” method for making iPS cells. This overcomes some troubling difficulties for those scientists who work with iPS cells; namely, the vast inefficiency of making iPS cells from adult cells and the use of mutation-causing viruses to introduce those genes into adult cells required to convert adult cells into iPS cells. Generally, out of hundreds of blood cells, only one or two typically revert into iPS cells. However, with Zambidis’ method, 50-60% of blood cells were engineered into iPS cells.

To circumvent the use of viruses to deliver genes, Zambidis’ team used plasmids, or small circles of DNA that replicate briefly inside cells and then degrade. By using plasmids, the cells receive the genes required to drive adult cells into the iPS state, but because these genes are only required transiently, the plasmids do their job and then go away. Therefore, the production of mutations by viral DNAs that insert themselves into the host cell genome is not a problem with this method from Zambidis’ laboratory.

In order to introduce the genes into the cells, Zambidis’ team used a technique called electroporation. They treated the umbilical cord blood cells with the plasmids and then delivered an electrical pulse to the cells, which made tiny holes in the surface through which the plasmids could slip to the cell interior. Once inside, the plasmids triggered the cells to revert to a more primitive cell state. After genetic engineering, the blood cells were also given an additional new step in which they were stimulated with their natural bone-marrow environment. To do this, the Johns Hopkins team took some of the treated cells in a dish alone, and cultured them together with irradiated bone-marrow cells.

When iPS cells made from umbilical cord blood were compared to iPS cells made from hair cells and from skin cells, they found that the most superior iPS cells came from those made from blood stem cells treated with just four genes and cultured with the bone marrow cells. These cells reverted to a primitive stem cell state within seven to 14 days. Their techniques also successfully converted blood stem cells from adult bone marrow and from circulating blood into iPS cells.

In ongoing studies, Zambidis and colleagues are testing the quality of their newly formed iPS cells. They are also interested in the ability of these iPS cells to differentiate into other cell types, as compared with iPS cells made by other methods. These efficient methods to produce virus-free iPS cells will hopefully speed research to develop stem cell therapies that use nearly all cell types, and may provide a more accurate picture of cell development and biology.

Prosthetic Retina Restores Sight In Mice


A pair of neuroscientists have designed a prosthesis that partially restores sight in mice. To get this device to work, they had to decipher the code by which the retina tells the brain what the eye has seen. They hope to adapt the device to test in human patients.

Globally, some 20 million people blind from retinal disease that cause degeneration of retinal cells. The retina is a thin tissue at the back of the eye that actually is composed of multiple cell layers that help convert electromagnetic energy in the form of visible light into a neural signal. Presently, there is only one prosthetic device that has been approved for treatment of such conditions. This device consists of an array of surgically implanted electrodes that directly stimulate the optic nerve in response to light. It allows patients to discern edges and letters, but patients cannot recognize faces or perform many everyday tasks.

Sheila Nirenberg, a physiologist at the Weill Medical College at Cornell University in New York, thinks that the reason the present prosthetic devices work poorly is that they do not properly code the light energy into a form that the brain can interpret. The retina contains several layers of nerves that seem to translate light energy into encoded neural signals. According to Nirenberg, “The thing is, nobody knew the code.” Without knowing this retinal coding system, Nirenberg believes that visual prostheses will never be able to create images that the brain can easily recognize.

In light of this, Nirenberg and her student, Chethan Pandarinath, have devised a code and developed a device that uses it to restore some sight in blind mice.

They began their work by injecting nerve cells into the retinas of mice with a genetically engineered virus. This virus had been designed to insert a gene that causes the cells to produce a light-sensitive protein normally found in algae. When a beam of light was then projected into the eye, the algal protein triggered the nerve cells to send a signal to the brain. By engineering the neural cells in this fashion, the ganglion cells that normally receive the message from the photoreceptors cells, which directly respond to light, sent neural signals directly to the brain and performs in a manner similar to healthy rod and cone cells.

This experiment is not unique, since Zhuo-Hua Pan’s laboratory at Wayne State University School of Medicine had published a similar result in 2006 (here). However, Nirenberg and Pandarinath went a step further. Instead of feeding the visual signals directly into the eye, they processed these signals using a code that they had developed by watching how a healthy retina responds to stimuli. After the ganglion cells that received the encoded input, the mice were able to track moving stripes, which is something that they hadn’t been able to do before. Then Nirenberg and Pandarinath examined the neural signals that the mice were producing and they a used a different, ‘untranslate’, code to determine what the brain would have been seeing. The encoded image was clearer and more recognizable than the non-encoded one (see image).

A prosthetic retina that can translate an image into neural signals was tested using a picture of a baby’s face. A is the original image. B is the image after it passes through the coding software. C is after it has been processed by the retinal cells. D is the processed image without coding.

Researchers attempting to design visual prostheses have debated the importance of encoding. Some think that it will be crucial, but others think the brain can adapt to an unprocessed signal. James Weiland, an ophthalmologist at the University of Southern California in Los Angeles, notes that Nirenberg and Pandarinath have shown that encoding provides an advantage, but how effective it is in human patients is completely unknown until the technique is tried out in people. Weiland probably speaks for the entire field when he commented that “You can’t say for sure until you have the patient telling you ‘yes I see it. It’s better when you do that.'”

Nirenberg hopes to test her system in human trials soon. The encoding is relatively simple and can be done by a microchip. The combination of the microchip with a small video camera could fit onto a pair of glasses. The camera would record a signal and the encoder would then flash it directly onto the genetically treated nerve cells in the eye. If this prosthesis works, the technique is simple enough that it could be done in a doctor’s office. “We would like to [try it] in patients in the next one or two years,” she says.

Getting Genes into Stem Cells Without Viruses


Genetic engineering of cells and, in particular, of stem cells has the ability to adjust the functional capacities of cells. Unfortunately, genetically engineering cells requires the use of viruses that introduce genes into cells and, by doing so, produce mutations in cells.

However, there are new ways to put genes into cells without the use of viruses. By surrounding DNA that encodes the genes you want to put into cells with positively-charged lipids, you have made a structure called a liposome. Liposomes can fuse with the membranes of cells and deliver the genes to cells without viruses that can cause mutations.

A paper that has appeared in the journal Stem Cells and Development examined the use of liposomes to introduce genes into blood cell-making stem cells (HSCs). They used commercially-available systems to transfer genes into these stem cells, but they found that their own lab-designed system did a better job than the commercially-available systems.

The lead author of this paper is Hilal Gul-Uludag and the senior author is Jie Chen from the University of Alberta in Edmonton, Alberta, Canada. In this paper, Chen’s research group isolated blood cell-making stem cells from umbilical cord blood. Then they used liposomes to insert the CXCR4 gene. The CXCR4 gene encodes a receptor for “stromal cell-derived factor-1alpha” (SDF-1alpha). When cells bind to SDF-1alpha, they move towards the source of SDF-1alpha.

Interestingly, one of the best sources of SDF-1alpha is the bone marrow. If HSCs could be engineered to make CXCR4, then they would readily move into the bone marrow. This means that implanted HSCs would only need to be introduced into the peripheral blood and not into the bone. This would increase the efficiency of bone marrow or umbilical cord transplants.

Chen’s group showed the feasibility of such experiments, and that these treatments are not toxic in any way to the HSCs. Thus, such a strategy could potentially increase the efficiency of bone marrow and umbilical cord blood transplantation.