Donor blood stem cells and T cells could help patients wean off immunosuppressive drugs after organ transplant

Dr. Samuel Strober is refining a process that eliminates the need for the many immunosuppresant drugs normally required after a transplant.
Image credit: Stanford Medicine News Center

In 2019, there were over 23,000 kidney transplants in the United States, according to figures from the United Network for Organ Sharing (UNOS). These transplants can be lifesaving, but the donated organ can be perceived as a foreign invader by the patient’s immune system and attacked. In order to protect the organ from attack, transplant recipients are required to take numerous drugs that suppress the immune system, which are referred to as immunosupressive (IS) drugs. Unfortunately, these drugs, while helping protect the organ, can also cause long term problems such as hypertension, diabetes, heart disease, infection, a high concentration of fats in the blood, and cancer.

To address this problem, Dr. Samuel Strober and his team at Stanford University are conducting a CIRM-funded clinical trial that gives patients getting a kidney transplant a mixture of their own blood cells and cells from the kidney donor, a process called mixed chimerism.

Pairing patients and donors for transplants is done via Human Leukocyte Antigen (HLA) matching. HLA are markers on most cells in your body and are used by your immune system to recognize which cells belong to the body. If you are fully HLA matched that means your cells and the donor cells are immunologically compatible, and so less likely to be rejected. If they are HLA haplotypes, it means they are close but not fully matched so rejection is more likely.

In the trial, fifty-one patients with end stage renal failure that had just received a kidney transplant were infused with blood stem cells (cells that can give rise to different kind of blood cells) and T cells (a cell that plays a role in the immune response) obtained from the donor to achieve a mixed chimerism. Of the 51 patients 29 were fully HLA matched, and 22 were HLA haplotype matched.

Standard IS drugs were administered to all the patients after transplantation and the patients were monitored from six to twelve months to ensure there was no organ rejection or graft vs host disease (GVHD), a condition where donated blood stem cells attack the body.

After this period, the patients were taken off the IS drugs and the results of this trial are very promising. Twenty-four of the fully HLA matched patients with a persistent mixed chimerism for at least six months were able to stop taking the IS drugs without evidence of rejection for at least two years. Ten HLA haplotype matched patients with a persistent mixed chimerism for at least twelve months were able to stop taking some of the IS drugs without rejection.

This is encouraging news for patients undergoing any kind of transplant, leading to hope that one day all patients might be able to get a life-saving organ without having to take the IS drugs forever.

The full results of this study were published in Science Translational Medicine.

Stories that caught our eye: How dying cells could help save lives; could modified blood stem cells reverse diabetes?; and FDA has good news for patients, bad news for rogue clinics

Gunsmoke

Growing up I loved watching old cowboy movies. Invariably the hero, even though mortally wounded, would manage to save the day and rescue the heroine and/or the town.

Now it seems some stem cells perform the same function, dying in order to save the lives of others.

Researchers at Kings College in London were trying to better understand Graft vs Host Disease (GvHD), a potentially fatal complication that can occur when a patient receives a blood stem cell transplant. In cases of GvHD, the transplanted donor cells turn on the patient and attack their healthy cells and tissues.

Some previous research had found that using bone marrow cells called mesenchymal stem cells (MSCs) had some success in combating GvHD. But it was unpredictable who it helped and why.

Working with mice, the Kings College team found that the MSCs were only effective if they died after being transplanted. It appears that it is only as they are dying that the MSCs engage with the individual’s immune system, telling it to stop attacking healthy tissues. The team also found that if they kill the MSCs just before transplanting them into mice, they were just as effective.

In a news article on HealthCanal, lead researcher Professor Francesco Dazzi, said the next step is to see if this will apply to, and help, people:

“The side effects of a stem cell transplant can be fatal and this factor is a serious consideration in deciding whether some people are suitable to undergo one. If we can be more confident that we can control these lethal complications in all patients, more people will be able to receive this life saving procedure. The next step will be to introduce clinical trials for patients with GvHD, either using the procedure only in patients with immune systems capable of killing mesenchymal stem cells, or killing these cells before they are infused into the patient, to see if this does indeed improve the success of treatment.”

The study is published in Science Translational Medicine.

Genetically modified blood stem cells reverse diabetes in mice (Todd Dubnicoff)

When functioning properly, the T cells of our immune system keep us healthy by detecting and killing off infected, damaged or cancerous cells in our body. But in the case of type 1 diabetes, a person’s own T cells turn against the body by mistakenly targeting and destroying perfectly normal islet cells in the pancreas, which are responsible for producing insulin. As a result, the insulin-dependent delivery of blood sugar to the energy-hungry organs is disrupted leading to many serious complications. Blood stem cell transplants have been performed to treat the disease by attempting to restart the immune system. The results have failed to provide a cure.

Now a new study, published in Science Translational Medicine, appears to explain why those previous attempts failed and how some genetic rejiggering could lead to a successful treatment for type 1 diabetes.

An analysis of the gene activity inside the blood stem cells of diabetic mice and humans reveals that these cells lack a protein called PD-L1. This protein is known to play an important role in putting the brakes on T cell activity. Because T cells are potent cell killers, it’s important for proteins like PD-L1 to keep the activated T cells in check.

Cell based image for t 1 diabetes

Credit: Andrea Panigada/Nancy Fliesler

Researchers from Boston Children’s Hospital hypothesized that adding back PD-L1 may prevent T cells from the indiscriminate killing of the body’s own insulin-producing cells. To test this idea, the research team genetically engineered mouse blood stem cells to produce the PD-L1 protein. Experiments with the cells in a petri dish showed that the addition of PD-L1 did indeed block the attack-on-self activity. And when these blood stem cells were transplanted into a diabetic mouse strain, the disease was reversed in most of the animals over the short term while a third of the mice had long-lasting benefits.

The researchers hope this targeting of PD-L1 production – which the researchers could also stimulate with pharmacological drugs – will contribute to a cure for type 1 diabetes.

FDA’s new guidelines for stem cell treatments

Gottlieb

FDA Commissioner Scott Gottlieb

Yesterday Scott Gottlieb, the Commissioner at the US Food and Drug Administration (FDA), laid out some new guidelines for the way the agency regulates stem cells and regenerative medicine. The news was good for patients, not so good for clinics offering unproven treatments.

First the good. Gottlieb announced new guidelines encouraging innovation in the development of stem cell therapies, and faster pathways for therapies, that show they are both safe and effective, to reach the patient.

At the same time, he detailed new rules that provide greater clarity about what clinics can do with stem cells without incurring the wrath of the FDA. Those guidelines detail the limits on the kinds of procedures clinics can offer and what ways they can “manipulate” those cells. Clinics that go beyond those limits could be in trouble.

In making the announcement Gottlieb said:

“To be clear, we remain committed to ensuring that patients have access to safe and effective regenerative medicine products as efficiently as possible. We are also committed to making sure we take action against products being unlawfully marketed that pose a potential significant risk to their safety. The framework we’re announcing today gives us the solid platform we need to continue to take enforcement action against a small number of clearly unscrupulous actors.”

Many of the details in the announcement match what CIRM has been pushing for some years. Randy Mills, our previous President and CEO, called for many of these changes in an Op Ed he co-wrote with former US Senator Bill Frist.

Our hope now is that the FDA continues to follow this promising path and turns these draft proposals into hard policy.