An Efficient Method for Converting Fat Cells to Liver Cells


I have a friend whose wife has systemic lupus erythematosis, and her liver has taken a beating as a result of this disease. She has never had a drop of alcohol for decades and yet she has a liver that looks like the liver of a 70-year-old alcoholic. The scarring of the liver as result of repeated damage and healing has seriously compromised her liver function. She is now a candidate for a liver transplant. Wouldn’t it be nice to simply give her liver cells to heal her liver?

This dream came a little closer to becoming reality in October of this year when scientists at Stanford University developed a fast and efficient way to convert fat cells isolated from routine liposuction into liver cells. Even though these experiments used mice, the stem cells were isolated from human liposuction procedures.

This experiment did not use embryonic stem cells or induced pluripotent stem cells to generate liver cells. Instead it used adult stem cells from fat.

Fat-based stem cells

The liver builds complex molecules, filters and breaks down waste products and toxic substances that might otherwise accumulate to dangerous concentrations.

The liver, unlike other organs, has a capacity to regenerate itself to a significant extent, but the liver’s regenerative abilities cannot overcome the consequences of acute liver poisoning, or chronic damage to the liver, as a result of hepatitis, alcoholism, or drug abuse.

For example, acetaminophen (Tylenol) is a popular pain-reliever, but abusing acetaminophen can badly damage the liver. About 500 people die each year from abuse of acetaminophen, and some 60,000 emergency-room visits and more than 25,000 hospitalizations annually are due to acetaminophen abuse. Other environmental toxins, such as poisonous mushrooms, contribute more cases of liver damage.

Fortunately, the fat-to-liver protocol is readily adaptable to human patients, according to Gary Peltz, professor of anesthesia and senior author of this study. The procedure takes about nine days, which is easily fast enough to treat someone suffering from acute liver poisoning, who might die within a few weeks without a liver transplant.

Some 6,300 liver transplants are performed annually in he United States, and approximately 16,000 patients are on the waiting list for a liver. Every year more than 1,400 people die before a suitable liver can be found for them.

Even though liver transplantations save the lives of patients, the procedure is complicated, not without risks, and even when successful, is fraught with after effects. The largest problem is the immunosuppressant drugs that live patients must take in order to prevent their immune system from rejecting the transplanted liver. Acute rejection is an ongoing risk in any solid organ transplant, and improvements in immunosuppressive therapy have reduced rejection rates and improved graft survival. However, acute rejection still develops in 25% to 50% of liver transplant patients treated with immunosuppressants. Chronic rejection is somewhat less frequent and is declining and occurs in approximately 4% of adult liver transplant patients.

Peltz said, “We believe our method will be transferable to the clinic, and because the new liver tissue is derived from a person’s own cells, we do not expect that immunosuppressants will be needed.”

Peltz also noted that fat-based stem cells do not normally differentiate into liver cells. However, in 2006, a Japanese laboratory developed a technique for converting fat-based stem cells into induced liver cells (called “i-Heps” for short). This method, however, is inefficient, takes 30 days, and relies on chemical stimulation. In short, this technique would not provide enough material to regenerate a liver.

The Stanford University group built upon the Japanese work and improved it. Peltz’s group used a spherical culture and were able to convert fat-bases stem cells into i-Heps in nine days and with 37% efficiency (the Japanese group only saw a 12% rate). Since the publication of their paper, Peltz said that workers in his laboratory have increased the efficiency to 50%.

Dan Xu, a postdoctoral scholar and the lead author of this study, adapted the spherical culture methodology from early embryonic-stem-cell literature. However, instead of growing on flat surfaces in a laboratory dish, the harvested fat cells are cultured in a liquid suspension in which they form spheroids. Peltz noted that the cells were much happier when they were grown in small spheres.

Once they had enough cells, Peltz and his co-workers injected them into immune-deficient laboratory mice that accept human grafts. These mice were bioengineered in 2007 as a result of a collaboration between Peltz and Toshihiko Nishimura from the Tokyo-based Central Institute for Experimental Animals. These mice had a viral thymidine kinase gene inserted into their genomes and when treated with the drug gancyclovir, the mice experienced extensive liver damage.

After gancyclovir treatment, Peltz and his coworkers injected 5 million i-Heps into the livers of these mice, using ultrasound-guided injection procedures, which is typically used for biopsies.

Four weeks later, the mice expressed human blood proteins and 10-20 percent of the mouse livers were repopulated with human liver cells. Blood tests also showed that the mouse livers, which were greatly damaged previous to the transplantation, were processing nitrogenous wastes properly. Structurally, the mouse livers contained human cells that made human bile ducts, and expressed mature human liver cells.

Other tests established that the i-Heps made from fat-based stem cells were more liver-like than i-Heps made from induced pluripotent stem cells.

Two months are injection of the i-Heps, there was no evidence of tumor formation.

Peltz said, “To be successful, we must regenerate about half of the damaged liver’s original cell count.” With the spherical culture, Peltz is able to produce close to one billion injectable i-Heps from 1 liter of liposuction aspirate. The cell replication that occurs after injection expands that number further to over 100 billion i-Heps.

If this is possible, then this procedure could potentially replace liver transplants. Stanford University’s Office of Technology Licensing has filed a patent on the use of spherical culture for hepatocyte (liver cell) induction. Peltz’s group is optimizing this culture and injection techniques,talking to the US Food and Drug Administration, and gearing up for safety tests on large animals. Barring setbacks, the new method could be ready for clinical trials within two to three years, according the estimations by Peltz.

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.

MHC-Class-I-Topology_3mhc_class2

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.