A New Target for Treating Stroke: The Spleen

If the blood vessels of the brain become plugged as a result of a clot or some other obstructive event, then the brain suffers a trans-ischemic attack (TIA), which is more commonly known as a stroke. The initial stroke starves brain cells of oxygen, which causes cell death by suffocation. However, dying brain cells  often spill enormous amounts of lethal material into the surrounding area, which kills off even more brain cells. Worse still, these dead or dying called can induce inflammation in the brain, which continues to kill off brain cells.

New work, however, from the laboratory of César Borlongan at the University of Southern Florida in Tampa, indicates that the spleen may be a target for treating the stroke-induced chronic inflammation that continues to kill brain cells after the initial stroke.

At the University of Florida Center of Excellence for Aging and Brain Repair, a study found that the intravenous administration of human bone marrow stem cells to post-stroke rats reduced the inflammatory-plagued secondary cell death associated with stroke progression in the brain. The intravenously administered cells preferentially migrated to the spleen where they reduced this post-stroke inflammation.

This study answers some of the perplexing questions surrounding animal experiments that used stem cells to treat stroke. Typically, stem cell administration to animals that suffered an artificially-induced stroke causes some functional recovery, but when their brains are examined for the stem cells that were implanted into them, very few surviving cells are observed.

“Our findings suggest that even if stem cells do not enter the brain or survive there, as long as the transplanted cells survive in the spleen the anti-inflammatory effect they promote may be sufficient enough to therapeutically benefit the stroke brain,” said César Borlongan, principal investigator of this study.

Stroke is the leading cause of death and the number one cause of chronic disability in the United States, yet treatment options are limited.

Stem cell therapy has emerged as a potential treatment for ischemic stroke, but most pre-clinical studies have examined the effects of stem cells transplanted during acute stroke (one hour to three hours aster the onset of the stroke).

In the wake of an acute stroke, an initial brain lesion forms from the lack of blood flow to the brain. The blood-brain barrier is also breached and this allows the infiltration of inflammatory molecules that trigger secondary brain cell death in the weeks and months that follow. This expanded inflammation is the hallmark of chronic stroke.

In this study, Borlongan and his colleagues intravenously administered human bone marrow stem cells 60 days after the onset of a stroke. Thus these animals were well into the chronic stroke stage.

The transplanted stem cells predominantly homes to the spleen. In fact, Borlongan and his crew found 30-times more cells in the spleens of the animals than in the brain.

While in the spleen, the stem cells squelched the production of a protein called tumor necrosis factor, which is a major inflammatory signal that increases in concentration after a stroke. The reduction of the tumor necrosis factor signal prevented the macrophages and other immune cells from leaving the spleen and going to the brain. This reduced systemic inflammation and decreased the size of the lesions in the brain caused by the stroke. There was also a trend toward reduced neuronal death and smaller decreases in learning and memory in the laboratory animals.

Borlongan explained that during the chronic stage of stroke, macrophages seem to fuel inflammation. “If we can find a way to effectively block the fuel with stem cells, then we may prevent the spread of damage in the brain and ameliorate the disabling symptoms many stroke patients live with,” said Borlongan.

Borlongan and his team hope to test whether transplanting human bone marrow stem cells directly into the spleen will lead to behavioral recovery in post-stroke rats.

One drug that has been approved for the emergency treatment of stroke is tPA or tissue plasminogen activating factor, which activates the blood-based protein plasminogen to form the highly active enzyme, plasmin. Plasmin is a powerful dissolved of clots, but tPA must be administered less than 4.5 hours after the onset of ischemic stroke, and benefits only three to four percent of patients.

Even though more work needs to be done, evidence from the USF group and other neurobiology groups indicates that stem fells may provide a more effective treatment for stroke over a wider time frame.

Targeting the spleen with stem cells or the anti-inflammatory molecules they sec rate offers hope for treating chronic neurodegenerative diseases like stroke at later stages.

This study, which was published in the journal Stroke, shows that it is possible to arrest the chronic inflammation that characterizes chronic stroke 60 days after the initial stroke. If such a result can be replicated in human patients, it will indeed be a powerful thing, according the Sandra Acosta, the first author on this paper.

Multipotent Adult Progenitor Cells Prevent Rejection of Transplanted Tissue

Solid organ transplantation is a procedure that has saved untold millions of lives. Unfortunately, the tendency for an organ to be rejected by the immune system of the organ recipient is a formidable problem that is addressed in two ways. One of these is through tissue matching of the organ to the recipient. The other is through the use of immunosuppressive drugs that suppress the immune system. Neither one of these strategies is without caveats.

Tissue typing begins with a blood test to determine the organ recipient’s blood type. If the organ contains a blood type that is incompatible with the immune system of the organ recipient, the result will be catastrophic. Hyperacute rejection is the name given to organ rejection that occurs minutes to hours after the organ was transplanted. Hyperacute rejection occurs because the recipient has pre-existing antibodies in their body that recognizes and begins to destroy the graft. These antibodies can result from prior blood transfusions, multiple pregnancies, prior transplantation, or xenografts against which humans already have antibodies. Massive blood clotting within the capillaries of the organ clog the blood vessels and prevent perfusion of the graft with blood. The organ must come out or the patient will die.

Human cells have on their surfaces particular proteins that are encoded by genes located on the short arm of chromosome 6 called the major histocompatibility complex or MHC. the MHC genes encode human leukocyte antigens or HLAs. HLA proteins are extremely variable from person to person, and this seems to be the case because the more variation we have in our HLA proteins, the better job the immune system does recognizing foreign invaders.

Each individual expresses MHC genes from each chromosome. Therefore, your cells contain a mosaic of surface proteins, some of which are encoded by the HLAs encoded by the chromosome you inherited from your father and others of which are encoded by the chromosome your inherited from your mother.

The MHC molecules are divided into 2 classes. Class I molecules are normally expressed on all nucleated cells, but class II molecules are expressed only on the so-called “professional antigen-presenting cells” or APCs. APCs include cells that have names like dendritic cells, activated macrophages, and B cells. T lymphocytes only recognize foreign substances when they are bound to an MHC protein. Class I molecules present antigens from within the cell, which includes bits from viruses, tumors and things like that. Class II molecules present extracellular antigens such as extracellular bacteria and so on to a subclass of T cells called T helper cells, which express a molecule called “CD4” on their cell surface.


All this might seem very confusing, but it is vital to ensuring that the organ is properly received by the organ recipient. Some types of MHC are very different and will elicit robust immune responses against them, but others are not as different and can be rather well tolerated. How does the doctor which are which? Through three tests: 1) Blood type is the first one. If this does not match, you are out of luck; 2) lymphocytotoxicity assay in which blood from a patient is tested to determine if it reacts with lymphocytes from the blood of the donor. A positive crossmatch is a contraindication to transplantation because of the risk of hyperacute rejection. This is used mainly in kidney transplantation; 3) Panel-reactive antibody (PRA) screens in which the the serum of a patient is screened for antibodies against the lymphocytes from the donor. The presence of such antibodies is contraindicated for transplantation. Finally, there is a test that is not used a great called the mixed lymphocyte reaction test that uses lymphocytes from the blood of the organ donor and the organ recipient to see if they activate one another. This test takes a long time and can be difficult to interpret.

Once the patient receives the transplant, they are usually put on immunosuppressive drugs. These drugs include cyclosporine, tacrolimus, sirolimus, mycophenolate, and azathioprine. Each of these drugs has a boatload of side effects that range from hair loss, diabetes mellitus, nerve problems, increased risk of illness and tumors, and so on. None of these side effects are desirable, especially since the drug must be taken for the rest of your life after you receive the transplant.

Enter a new paper from University Hospital in Regensburg, Germany from the laboratory of Marc Dahkle that used particular stem cells from bone marrow to induce toleration of grafted heart tissue in laboratory animals without any drugs. This paper was published in Stem Cells Translational Medicine and is potentially landmark in what it shows.

In this paper, Dahkle and his colleagues used stem cells from the bone marrow known as multipotential adult progenitor cells or MAPCs. MAPCs have been thought to be a subtype of mesenchymal stem cell in the bone marrow because they have several cell surface markers in common. However, there are some subtle differences between these two types of cells. First of all, the MAPCs are larger than their mesenchymal stem cell counterparts. Secondly, MAPCs can be cultured more long-term, which increases the attractiveness of these cells for therapeutic purposes.

In this paper, the Dahkle group transplanted heart tissue from two unrelated strains of rats. Four days before the transplantation, the donor rats received an infusion of MAPCs into their tail veins. There were a whole slew of control rats that were used as well, but the upshot of all this is that the rats that received the MAPCs before the transplantation plus a very low dose of the immunosuppressive drug mycophenolate did not show any signs of rejection of the transplanted heart tissue. If that wasn’t enough, when the transplanted heart tissue was then extirpated and re-transplanted into another rat, those grafts that came from MAPC-treated rats survived without any drugs, but those that came from non-MAPC-treated rats did not.

Because control experiments showed that the rats treated with cyclosporine did not reject their grafts, Dahkle and others used this system to determine the mechanism by which MAPCs prevent immune rejection of the grafted tissue. They discovered that the MAPCs seem to work though a white blood cell called a macrophage. Somehow, the MAPCs signal to the macrophages to suppress rejection of the graft. If a drug (clodronate) that obliterates the macrophages was given to the rats with the MAPCs, the stem cells were unable to suppress the immunological rejection of the graft.

In this paper, the authors conclude that “When these data are taken together, our current approach advances the concept of cell-based immunomodulation in solid organ transplantation by demonstrating that third-party, adherent, adult stem cells from the bone marrow are capable of acting as a universal cell product that mediates long-term survival of fully allogeneic organ grafts.” Revolutionary is a good word for this findings of this paper.  Hopefully, further pre-clinical trials will eventually give way to clinical trials in human patients that will allow human patients to have their lives saved by an organ transplant without the curse of taking immunosuppressive drugs for the rest of their lives.

Treating a Rare Immune Disorder with Mesenchymal Stem Cells

In the journal Stem Cells and Development, there is a case report from the University Hospital at Karolinska Institutet in Stockholm, Sweden of a 21-year-old man who suffered from a rare immune disorder and was treated with an infusion of mesenchymal stem cells (MSCs) from a donor.

This patient was seen in October, 2010 and had been suffering from a fever for 2 months. He had had a previous gastrointestinal infection that had resolved, but the inflammation that resulted from the infection refused to go away. He was diagnosed with hemophagic lymphohistiocytosis (HLH). This is a mouthful, but it is a relatively rare immune disorder that results in pronounced systemic hyperinflammation. This hyperinflammation essentially results from some sort of infection that causes inflammation, but the inflammation does not turn off when the infection resolves. The condition causes the spleen to enlarge and the number of blood cells to decrease to abnormally low levels and the patient has a constant, burning fever.

The medical team that treated this poor soul used steroids, and that worked from about a week. Then they tried the HLH-94 treatment protocol, which involves treating the patient with a combination of powerful immunosuppressive drugs; etoposide, (VP-16), corticosteroids, CyclosporinA, and, in some patients, intrathecal methotrexate, before the patient is given a bone marrow transplant. The HLH-94 protocol returned the patient to normal – for about 2 months, and then the patient was back to square one.

At this point, the medical team needed a Hail Mary, if you will. Therefore, they decided to use MSCs from a healthy donor. The patient was given a total of 124 million bone marrow-derived MSCs, and within 24 hours, the patient’s fever was gone and his blood work normalized.

Unfortunately, the poor chap contracted a nasty fungal infection that, in his weakened state, spread throughout his whole body and killed him. However, postmortem examinations showed that the MSCs had mobilized a whole gaggle of special white blood cells called macrophages, and these MSC-recruited macrophages suppressed the over-active immune response of this HLH patient. The fungal infection was contracted before the administration of the MSCs, therefore, the stem cell treatment had no causal relationship to the fungal infection.

However, this case study suggests that MSCs have a future in the treatment of immune disorders. Furthermore, the use of MSCs from donors can also provide therapeutic material for the treatment of immune disorders.