Embryonic Stem Cells Used to Make Laboratory-Created Thymus


Medical researchesr from UC San Francisco have used embryonic stem cells to construct a functioning mouse thymus in the laboratory. When implanted into a living mouse, this laboratory-made thymus can successfully foster the development of T cells, which the body needs to fight infections and prevent autoimmune reactions.

This achievement marks a significant step toward developing new treatments for autoimmune disorders such as type 1 diabetes and other autoimmune diseases, such as systemic lupus erythematosis and ulcerative colitis.

This research team was led by immunologist Mark Anderson and stem cell researcher Matthias Hebrok. They used a unique combination of growth factors to push the embryonic stem cells into a particular developmental trajectory. After a period of trial and error, they eventually found a formula that produced functional thymus tissue.

In our bodies, the thymus lies just over the top of our heart, and it serves to instruct T lymphocytes (a type of white blood cell) what to attack and what to leave alone. Because T cells serve a vital role in the immune response, the thymus serves a vital function.

thymus

Typically, each T cell attacks a foreign substance that it identifies by binding the foreign substance to its cell surface receptor. This T cell-specific receptor is made in each T cell by a set of genes that are randomly shuffled, and therefore, each T cell has a unique cell receptor that can bind particular foreign molecules. Thus each T cell recognizes and attacks a different foreign substance.

With in the thymus, T cells that attack the body’s own proteins are eliminated. Thymic cells express major proteins from elsewhere in the body. The T cells that enter the thymus first undergo “Positive Selection” in which the T cell comes in contact with self-expressed proteins that are found in almost every cell of the body and are used to tell “you” from something that is not from “you.” In order to destroy cells that do not bear these self-expressed proteins, they must be able to properly identify them. If T cells that enter the thymus cannot properly recognize those self-expressed proteins (known as MHC or major histocompatibility complex proteins for those who are interested), the thymus destroys them. Second, T cells undergo “Negative Selection” in which if the T cell receptor binds to self MHC proteins, that T cell is destroyed to avoid autoimmunity.

The thymus tissue grown in the laboratory in this experiment was able to nurture the growth and development of T cells. It could act as a model system to study patients with fatal diseases from which there are no effective treatments, according the Mark Anderson.

As an example, DiGeorge Syndrome is caused by a small deletion of a small portion of chromosome 22 and infants born with DiGeorge Syndrome are born without a thymus and they usually die during infancy.

Other applications include manipulating the immune system to accept transplanted tissues such as implanted stem cells or organs from donors that are not a match to the recipient.

Anderson said, “The thymus is an environment in which T cells mature and where they also are instructed on the difference between self and nonself.” Some T cells are prepared by the thymus to attack foreign invaders and that includes transplanted tissue. Other T cells that would potentially attack our own tissues are eliminated by the thymus.

Laboratory-induced thymus tissue could be used to retrain the immune system in autoimmune diseases so that the T cells responsible for the autoimmune response eventually ignore the native tissues they are attacking.

Hebrok warns that he and his team have not perfectly replicated a thymus. Only about 15% of the cells are successfully directed to become thymus tissue with the protocols used in this study. Nevertheless, Anderson asserted, “We now have developed a tool that allows us to modulate the immune system in a manner that we never had before.”

Synthetic Silicate Stimulates Stem Cells to Form Bone Cells


Researchers from Boston, MA have used synthetic silicate nanoplatelest or layered clay to induce bone cell formation from stem cells in the absence of other bone-inducing factors.

Synthetic silicates are composed of either simple or complex salts of silicic acid (SiH4O4).  Silicic acids have been used extensively in commercial and industrial applications that include food additives, glass and ceramic filler materials, and anti-caking agents.

In this study, novel silicate nanoplatelets were constructed that stimulated human mesenchymal stem cells to differentiate into bone-making cells in the absence of any bone-inducing growth factors or cytokines.  The presence of the silicate triggers a set of events inside the mesenchymal stem cells that re-enacts the steps cell normally take during development when they form become bone cells.  These exciting findings illustrate how the use of these silicate nanoplatelets in designing bioactive scaffolds for tissue engineering can lead to the formation of clinically useful bone tissues.

The lead author of this work, Ali Khademhosseini from the division of biomedical engineering at Brigham and Woman’s Hospital, thinks that silicic acid derivatives might be useful in engineering bone. “With an aging population in the U.S., injuries and degenerative conditions are subsequently on the rise,” said Khademhosseini. This means that there is also an increased demand for therapies to repair damaged tissues. Forming such tissues requires protocols to direct stem cell differentiation so that the cells can form new tissues and biomaterials. According to Khademhosseini, “Silicate nanoplatelets have the potential to address this need in medicine and biotechnology.”

“Based on the strong preliminary studies, we believe that these highly bioactive nanoplatelets may be utilized to develop devices such as injectable tissue repair matrixes, bioactive filters, or therapeutic agents for stimulating specific cellular responses in bone-related tissue engineering,” said Akhilesh Gaharwar, first author of this present study.

Future mechanistic studies are necessary to elucidate those underlying pathways that govern the induction of bone differentiation by materials like silicates. Such studies should lead to a better understanding of how particular strategies can be adjusted to improve the performance of lab constructed biomaterials, and accelerate patient recovery time.

For Treating Heart Attacks, Satellite Cells Lacking MyoD are Superior to Those With MyoD


Atsushi Asakura and his colleagues at the University of Minnesota Stem Cell Institute have extended some of their earlier findings in a paper that appeared in PLoS One last year. This paper is almost a year old by now, but its results are fascinating and are definitely worth examining.

In 2007, Asakura published a paper with the Canadian researcher Michael A. Rudnicki in the Proceedings of the National Academy of Sciences. In this paper, Asakura and his colleagues examined the ability of muscle satellite cells from MyoD- mice to integrate into injured muscle. I realize that last sentence just sounded like gobbledygook, to some of you, but I will try to put the cookies on a lower shelf.

Satellite cells constitute a stem cell population within skeletal muscle. They are a small population of muscle-making stem cells found in skeletal muscle and they express a whole host of muscle-specific genes (e.g., desmin, Pax7, MyoD, Myf5, and M-cadherin). Satellite cells are responsible for muscle repair, but previous work has shown that there are at least two populations of satellite cells in skeletal muscle. One population rapidly contributes to muscle repair, whereas the other population is more stem cell-like and remains longer in an undifferentiated state in the recipient muscle (see Beauchamp JR , et al (1999) J Cell Biol 144:1113–1122; Kuang S , et al (2007) Cell 129:999–1010). Presently, it is not clear which population is more efficient in repairing continuously degenerating muscle.

MyoD is a gene that encodes a protein that binds to DNA and activates the expression of particular genes. It plays a vital role in regulating muscle differentiation, and belongs to a family of proteins known as myogenic regulatory factors or MRFs. All MRFs are bHLH or basic helix loop helix transcription factors, and they act sequentially in muscle differentiation. MRF family members include MyoD, Myf5, myogenin, and MRF4 (Myf6). MyoD is one of the earliest genes that indicates a cell has committed to become a muscle cell. MyoD is expressed in activated satellite cells, but not in quiescent (sleeping) satellite cells. Strangely, even though MyoD marks myoblast commitment, muscle development is not dramatically prevented in mouse mutants that lack the MyoD gene. However, this is likely to result from functional redundancy from Myf5. Nevertheless, the combination of MyoD and Myf5 is vital to the success of muscle production.

MyoD
MyoD

Therefore, Asakura and his crew decided to isolated muscle satellite cells from mice that lacked functional copies of the MyoD gene. Making such mice is labor intensive, but doable with mouse embryonic stem cell technology. When such MyoD- mice were made, Asakura and others isolated the satellite cells from these mice and characterized them. They discovered in their 2007 paper, that the satellite cells from the MyoD- mice were much more stem cell-like than satellite cells from MyoD+ mice. The MyoD- satellite cells grew better in culture, integrated into injured muscles better and survived better than their MyoD+ counterparts.

Why is this important? Because when it comes to treating degenerative muscle diseases like muscular dystrophy, finding the best cell is crucial. MyoD+ satellite cells have been used, but they are limited in the amount of muscle repair they provide. MyoD- cells might be a better option for treating a disease like muscular dystrophy.

Or for that matter, what about the heart? Finding the right cell to treat the heart after a heart attack has proven difficult. There are some things bone marrow cells do well, and other things they do not do well when it comes to regenerating the heart. Likewise, there are some things mesenchymal do well and other things they do not do well when placed in a damaged heart. Can MyoD- satellite cells do a better job than either of these types of stem cells?

That was the question addressed in the 2012 Nakamura paper that was published in PLoS One. Clinical trials that have treated heart attack patients with injections of MyoD+ satellite cells into the heart have shown that such treatments can improve heart function, but usually only transiently. They also prevent remodeling of the heart after a heart attack. However, two larger studies failed to produce significant improvements in heart function compared to the placebo, and patients who received the satellite cell transplants were also susceptible to very fast heart beats (tachycardia). Because of these downsides, the excitement for transplanting muscle satellite cells into the heart has waned.

So how did MyoD- satellite cells do? All the laboratory animals used in this experiment (BALB/c mice) were given heart attacks, and injected with either MyoD+ or MyoD- satellite cells. The hearts of animals injected with MyoD- satellite cells were compared with animals whose hearts were injected with MyoD+ satellite cells.

In culture, the MyoD- satellite cells grew better than the MyoD+ cells. When injected into the heart, the MyoD- cells integrated into the heart muscle and spread throughout the heart muscle much more robustly than the MyoD+ cells. The MyoD- cells were also much less susceptible to cell death and survived better than their MyoD+ counterparts.

(A) These panels show MI induced by left coronary artery ligation. Wild-type and MyoD−/− myoblasts were directly injected into the peri-infarct regions of LV. After 1 week, X-gal staining of whole heart indicated that more MyoD−/− myoblasts engrafted than wild-type myoblasts (arrows). Arrowheads indicate left coronary artery ligation points. X-gal staining of cross sections indicated that more MyoD−/− myoblasts than wild-type myoblasts engrafted in both injured and uninjured areas of the heart. Arrows indicate engrafted lacZ+ wild-type and MyoD−/− myoblasts. Scale bars = 1 mm.
(A) These panels show MI induced by left coronary artery ligation. Wild-type and MyoD−/− myoblasts were directly injected into the peri-infarct regions of LV. After 1 week, X-gal staining of whole heart indicated that more MyoD−/− myoblasts engrafted than wild-type myoblasts (arrows). Arrowheads indicate left coronary artery ligation points. X-gal staining of cross sections indicated that more MyoD−/− myoblasts than wild-type myoblasts engrafted in both injured and uninjured areas of the heart. Arrows indicate engrafted lacZ+ wild-type and MyoD−/− myoblasts. Scale bars = 1 mm.

Functionally speaking for the heart, animals that had received transplantations of MyoD- satellite cells had higher ejection fractions, small areas of dead heart tissue, lower end systolic and end diastolic volumes, and more normal echocardiograms. Even though MyoD- cells differentiated into skeletal muscle and not heart muscle (no surprise there), the MyoD- cells induced a very substantial quantity of new blood vessels to sprout in the scar area.

(A) Two weeks post-transplantation, immunofluorescence staining of heart cross sections showed that the progeny of lacZ+ wild-type and MyoD−/− myoblasts formed nestin+ multinucleated skeletal myotubes. Laminin (red) indicates cardiomyocytes and skeletal myotubes. Arrows indicate lacZ+ donor cell-derived nuclei in nestin+ myotubes. (B) Comparison of the relative numbers of lacZ+/nestin+ myotubes for wild-type and MyoD−/− myoblasts 2 weeks after injection (n = 3).
(A) Two weeks post-transplantation, immunofluorescence staining of heart cross sections showed that the progeny of lacZ+ wild-type and MyoD−/− myoblasts formed nestin+ multinucleated skeletal myotubes. Laminin (red) indicates cardiomyocytes and skeletal myotubes. Arrows indicate lacZ+ donor cell-derived nuclei in nestin+ myotubes. (B) Comparison of the relative numbers of lacZ+/nestin+ myotubes for wild-type and MyoD−/− myoblasts 2 weeks after injection (n = 3).

From these experiments, it seems that the MyoD- satellite cells are superior to the MyoD+ satellite cells for treating heart after a heart attack. These cells secrete a whole host of factors that aid the heart in healing and also structurally support the heart and prevent remodeling.

Might it be possible to use such cells in human trials? Asakura notes that engineering MyoD- satellite cells would be impractical for human clinical purposes, but it might be possible to downregulate MyoD expression with drugs (bromodeoxyuridine) or other reagents (RNAi or Id protein transformation).

This work shows that there is a better way to use muscle satellite cells for heart treatments. It simply requires you to remove MyoD function, and the cells will grow and spread throughout the heart better, and more robustly augment heart function and healing.

See NakamuraY, et al PLoS One 7(7) 2012:e41736.

Umbilical Cord Blood Stem Cells Revive Child From Persistent Vegetative State


Physicians from Ruhr-Universitaet-Bochum (RUB) have successfully treated cerebral palsy in a 2.5-year old boy with his own cord blood.

“Our findings, along with those from a Korean study, dispel the long-held doubts about the effectiveness of the new therapy,” says Dr. Arne Jensen of the Campus Clinic gynaecology. Jensen collaborated with his colleague Prof. Dr. Eckard Hamelmann of the Department of Pediatrics at the Catholic Hospital Bochum (University Clinic of the RUB). This case study was published in the journal Case Reports in Transplantation.

At the end of November 2008, a young child’s heart stopped (cardiac arrest), and his brain suffered oxygen deprivation, and, consequently, severe brain damage. He was in a persistent vegetative state, and his body was completely paralyzed. This condition, infantile cerebral palsy, until now, has no recognized treatment. Typically, the prognosis of children with infantile cerebral palsy is rather grim, since the chances of survival miniscule and months after suffering severe brain damage, the surviving children usually only exhibit minimal signs of consciousness. According to the physicians at RUB, “The prognosis for the little patient was threatening if not hopeless.”

However, this child’s persistent parents scoured the literature for alternative therapies to infantile cerebral palsy. Arne Jensen explains. “They contacted us and asked about the possibilities of using their son’s cord blood, frozen at his birth.”

Nine weeks after suffering brain damage, on 27 January 2009, Jensen and his colleagues administered the child’s prepared cord blood intravenously. They studied the child’s progressive recovery at 2, 5, 12, 24, 30, and 40 months after treatment.

After the cord blood therapy, the patient, however, recovered quickly. Within two months, the child’s spasms decreased significantly. He was able to see, sit, smile, and to speak simple words again. Forty months after treatment, the child was able to eat independently, walk with assistance, and form four-word sentences. “Of course, on the basis of these results, we cannot clearly say what the cause of the recovery is,” Jensen says. “It is, however, very difficult to explain these remarkable effects by purely symptomatic treatment during active rehabilitation.”

Just listen to the description of the child’s recovery from this paper:

After two years, there was independent eating and speech competence of eight words (pronunciation slurred, mimicking prosody) with broad understanding. The patient moved from a prone to a free sitting position and crawled without cross-pattern, but using the arms. Independent passive standing, walking with support, and independent locomotion in a gait trainer was possible (video S5). He played imaginative games, and recognized colours, animals, and objects, assigning them correctly. Fine motor control improved to such an extent that he managed to steer a remote control car (video S6). At 30 months, he formed two-word-sentences using 80 words.

After 40 months, there was further improvement in both receptive and expressive speech competence (four-word-sentences, 200 words), walking (Crocodile Retrowalker), crawling with cross-pattern, and getting into vertical position.

And this is from a child who was a in a persistent vegetative state, who could neither speak, nor eat on his own, nor talk.

In animal studies, scientists have examined the therapeutic potential of cord blood. In a previous study with rats, RUB researchers revealed that cord blood cells migrate to the damaged area of the brain in large numbers within 24 hours of administration.  Umbilical cord stem cells are also known to secrete gobs of neurotropic molecules that stimulate neuron growth and differentiation, promote neuron survival, quell inflammation, staunch star formation in the brain (gliosis), and stimulate the growth and formation of blood vessels.

In March 2013, in a controlled study of one hundred children, Korean doctors reported for the first time that they had successfully treated cerebral palsy with someone else’s cord blood.

These results show that cord blood has tremendous therapeutic potential for pediatric neurological conditions.  This remarkable recovery is seemingly miraculous.  Certainly this merits more work and excitement.

Treating the Heart with Mesenchymal Stem Cells: Timing and Dosage


Stephen Worthley from the Cardiovascular Investigation Unit at the Royal Adelaide Hospital in Adelaide, Australia and his colleagues have conducted a timely experiment with rodents that examines the effects of dosage and timing on stem cell treatments in the heart after a heart attack.

Mesenchymal stem cells from bone marrow and other sources have been used to treat the heart of laboratory animals and humans after a heart attack. The optimal timing for such a treatment remains uncertain despite a respectable amount of work on this topic. Early intervention (one week) seems offer the best hope for preserving cardiac function, but the heart at this stage is highly inflamed and cell survival is poor. If treatment is delayed (2-3 weeks after the heart attack), the prospects for cell survival are better, but the heart at this time is undergoing remodeling and scar formation. Therefore, stem cell therapy at this time seems unlikely to work. Human clinical trials seem to suggest that mesenchymal stem cell treatment 2-3 weeks after a heart attack does no good (see Traverse JH, et al JAMA 2011;306:2110-9). The efficacy of the delivering mesenchymal stem cells to the heart at these different times has also not been compared.

If that degree of uncertainty is not enough, dosage is also a mystery. Rodent studies have used doses of one million cells, but studies have not established a linear relationship between efficacy and dose, and higher dosages seem to plateau in effectiveness (see Dixon JA, et al Circulation 2009;120(11 Suppl):S220-9). High doses might even be deleterious.

So what is the best time to administer after a heart attack, and how much should be administered? These are not trivial questions. Therefore a systematic study is required and laboratory animals such as rodents are required.

In this study, five groups of rats were given heart attacks by ligation of the left anterior descending artery, and two groups of rats received bone marrow-derived mesenchymal stem cells immediately after the heart attack. The first group received a low dose (one million cells) and the second group received twice as many cells. The three other groups received their treatments one week after the heart attack. The third group received the low dose of stem cells received the low dose of cells (one million cells), and the fourth group received the higher dose (two million cells). The fifth group received no such cell treatment.

All mesenchymal stem cells were conditioned before injection by growing them under low oxygen conditions. Such pretreatments increase the viability of the stem cells in the heart.

The results were interesting to say the least. when assayed four weeks after the heart attacks, the hearts of the control animals showed a left ventricular function that tanked. The ejection fraction fell to 1/3rd the original ejection fraction (~60% to ~20%) and stayed there. The early high dose animals showed the lowest decrease in ejection fraction (-8%). The early low dose group showed a greater decrease in ejection fraction. Clearly dose made a difference in the early-treated animals with a higher dose working better than a lower dose.

In the later-treated animals, dose made little difference and the recovery was better than the early low dose animals. when ejection fraction alone was considered. However, when other measures were considered, the picture becomes much more complex. End diastolic and end systolic volumes were all least increased in the early high dose animals, but all four groups show significantly lower increases than the controls. The mass of the heart, however, was highest in the late high-dose animals as was ventricular wall thickness.

When the movement of the heart walls were considered, the early-treated animals showed the best repair of those territories of the heart near the site of injection, but the later-treated animals showed better repair at a distance from the site of injection. The same held for blood vessel density: higher density in the injected area in the early-treated animals, and higher blood vessel density in those areas further from the site of injection in the later-treated animals.

The size of the heart scar clearly favored the early injected animals, which the lower amount of scarring in the early high dose animals. Finally when migration of the mesenchymal stem cells throughout the heart was determined by using green fluorescent protein-labeled mesenchymal stem cells, the later injected mesenchymal stem cells were much more numerous at remote locations from the site of injection, and the early treated animals only had mesenchymal stem cells at the site of injection and close to it.

These results show that the later doses of mesenchymal stem cells improve the myocardium further from the site of the infarction and the early treatment improve the myocardium at the site of the infraction. Cell dosage is important in the early treatments favoring a higher dose, but not nearly as important in the later treatments, where, if anything, the data favors a lower dose of cells.

Mesenchymal stem cells affect the heart muscle by secreting growth factors and other molecules that aids and abets healing and decreases inflammation. However, research on these cells pretty clearly shows that they modulate their secretions under different environmental conditions (see for example, Thangarajah H et al Stem Cells 2009;27:266-74). Therefore, the cells almost certainly secrete different molecules under these conditions.

In order to confirm these results, similar experiments in larger animals are warranted, since the rodent heart is a relatively poor model for the human heart as it beats much faster than human hearts.

See James Richardson, et al Journal of Cardiac Failure 2013;19(5):342-53.

Muscle-Derived Stem Cells And Platelet-Rich Plasma Improve Cartilage Formation


Skeletal muscle contains a stem cell population called muscle derived stem cells or MDSCs that might have tremendous therapeutic potential. MDSCs have been isolated from skeletal muscle by means of their ability to adhere to culture flasks coated with collagen. Samples of muscle taken from a biopsy are mechanically mashed and then treated with enzymes the separate the cells. These cells are plated onto collagen-coated dishes and the cells either adhere quickly (fibroblasts and myoblasts), or slowly (MDSC-enriched fraction).

Skeletal muscle contains another cell population known as satellite cells. Satellite cells can divide and form muscle progenitor cells known as myoblasts that fuse to form myotubes. MDSCs, however, as distinct from satellite cells. They express different sets of genes: satellite cells typically express Pax7, whereas MDSCs are more heterogeneous but express Sca-1 consistently and often express CD34.

Studies in culture and in living animals have established that MDSCs can self-renew and differentiate into multiple lineages. They also have the potential to regenerate various adult tissues. See Usas A, et al Medicina (Kaunas) 2011;47:469–479; Cao B, et al Nat Cell Biol. 2003;5:640–646; Deasy BM, et al Blood Cells Mol Dis. 2001;27:924–933.

MDSCs also display a superior regenerative capacity relative to satellite cells following transplantation into mice with a form of rodent muscular dystrophy (mdx mice). MDSCs are at least partially invisible to the immune system. When transplanted into mdx mice and left for at least 3 months, no sign of immune rejection was detected.

The laboratory of Johnny Huard at the University of Pittsburgh has been genetically engineering MDSCs from mouse for use as cartilage making cells to treat rodents with osteoarthritis. In 2009, Huard’s group published an intriguing paper in the journal Arthritis and Rheumatism in which they genetically engineered MDSCs with two genes: Bone Morphogenetic Protein 4 (BMP-4) and Soluble Flt-1. If you are wondering what the heck these two genes encode, then you are not alone. BMP-4 is a secreted signaling protein that is very important for bone healing, but it also plays a central role in helping cartilage-making cells (chondrocytes) survive and divide. Flt-1 is one of the receptor proteins that binds the growth factor VEGF (vascular endothelial growth factor).  Normally, VEGF forms blood vessels and remodels existing blood vessels.  However, when it comes to cartilage, VEGF tends to cause cartilage to die back.  Therefore, Huard’s group used a soluble version of Flt-1, which scavenged the available VEGF in the environment and bound it up.

In their 2009 paper, Huard and others showed that BMP-4/soluble Flt-1-expressing MDSCs did a remarkable job of making new cartilage and repairing damage joint cartilage in rodents.  See Tomoyuki Matsumoto, et al ARTHRITIS & RHEUMATISM Vol. 60, No. 5, May 2009, pp 1390–1405.

A and B, Macroscopic (A) and histologic (B) evaluation of representative joints from rats injected with muscle-derived stem cells (MDSCs) transduced with soluble Flt-1 (sFlt-1) and bone morphogenetic protein 4 (BMP-4 [B4]) (sFlt-1/BMP-4–MDSC), MDSCs transduced with vascular endothelial growth factor (VEGF) and BMP-4 (VEGF/BMP-4–MDSC), MDSCs transduced with BMP-4 alone (BMP-4–MDSC), nontransduced MDSCs (MDSC), or phosphate buffered saline (PBS) alone, 4 and 12 weeks after transplantation. Four weeks after transplantation, the sFlt-1/BMP-4–MDSC and BMP-4–MDSC groups macroscopically and histologically showed smooth joint surface with well-repaired articular cartilage and Safranin O–positive hyaline-like cartilage (red staining in B). However, the other groups showed marked arthritic progression, synovial hypertrophy, and osteophyte formation (arrows). Twelve weeks after transplantation, although the sFlt-1/BMP-4–MDSC group still showed well-repaired articular cartilage, the other groups exhibited more severe arthritis compared with 4 weeks. (Original magnification  100.) C, Semiquantitative histologic scores for all groups, 4 and 12 weeks following transplantation. The sFlt-1/BMP-4–MDSC group had the lowest (best) scores of all groups. Bars show the mean and SEM.   P   0.05 versus all other groups;   P   0.05 versus the VEGF/BMP-4–MDSC, MDSC, and PBS groups.
A and B, Macroscopic (A) and histologic (B) evaluation of representative joints from rats injected with muscle-derived stem cells (MDSCs) transduced with soluble Flt-1 (sFlt-1) and bone morphogenetic protein 4 (BMP-4 [B4]) (sFlt-1/BMP-4–MDSC), MDSCs transduced with vascular endothelial growth factor (VEGF) and BMP-4 (VEGF/BMP-4–MDSC), MDSCs transduced with BMP-4 alone (BMP-4–MDSC), nontransduced MDSCs (MDSC), or phosphate buffered saline (PBS) alone, 4 and 12 weeks after transplantation. Four weeks after transplantation, the sFlt-1/BMP-4–MDSC and BMP-4–MDSC groups macroscopically and histologically showed smooth joint surface with well-repaired articular cartilage and Safranin O–positive hyaline-like cartilage (red staining in B). However, the other groups showed marked arthritic progression, synovial hypertrophy, and osteophyte formation (arrows). Twelve weeks after transplantation, although the sFlt-1/BMP-4–MDSC group still showed well-repaired articular cartilage, the other groups exhibited more severe arthritis compared with 4 weeks. (Original magnification  100.) C, Semiquantitative histologic scores for all groups, 4 and 12 weeks following transplantation. The sFlt-1/BMP-4–MDSC group had the lowest (best) scores of all groups. Bars show the mean and SEM.   =P<0.05 versus all other groups;  =P<0.05 versus the VEGF/BMP-4–MDSC, MDSC, and PBS groups.
In another paper that came out in January of this year, Huard has used platelet-rich plasma with his engineered MDSCs to determine with platelet-rich plasma (PRP) can increase the cartilage-making activity of engineered MDSCs.

Since PRP has been reported to promote the synthesis of collagen and cell proliferation, and increase cartilage repair, it is possible that, when paired with the right stem cells, PRP can enhance cartilage repair.  To test this suspicion, MDSCs expressing BMP-4 and sFlt1 were mixed with PRP and injected into the knees of rats whose immune system did not work properly that had osteoarthritis.  Osteoarthritis can be chemically induced in rats rather easily, and the rats were treated with MDSCs expressing BMP-4 and sFlt1 or MDSCs expressing BMP-4 and sFlt1 plus PRP.  Tissue assessments of the arthritic joints were performed 4 and 12 weeks after cell transplantation.  Other tests conducted in culture determined the cell proliferation, adhesion, migration and cartilage-making capacities of cells in culture.

The results showed that addition of PRP to MDSCs expressing BMP-4 and sFlt1 significantly improved joint cartilage repair at week 4 compared to MDSCs expressing BMP-4 and sFlt1 alone.  The joints showed higher numbers of cells producing type II collagen and lower levels of chondrocyte cell death were observed by MDSCs expressing BMP-4 and sFlt1 and mixed with PRP.  In culture, the addition of PRP promoted proliferation, adhesion and migration of the MDSCs.  When pellets of cells were induced to make cartilage in culture, PRP tended to increase the number of type II collagen producing cells.

From this, Huard and his colleagues concluded that PRP can promote the cartilage-repairing capacities of MDSCs that express BMP-4 and sFlt1.  This enhancement involves the promotion of collagen synthesis, the suppression of chondrocyte cell death, and by enhancing the integration of the transplanted cells in the repair process.

See Mifune Y, et al Osteoarthritis Cartilage. 2013 Jan;21(1):175-85. doi: 10.1016/j.joca.2012.09.018.