First stem cell drug to market-Prochymal

I've mentioned many times on this blog that stem cell-based drugs are not yet ready for prime time. Well, I was wrong. Prochymal has achieved the distinction of being the world's first stem cell drug to jump through all the regulatory hoops and is approved for market...in Canada. But thanks to the Expanded Access Program (EAP), it is available in eight countries including the US. In case you're wondering, EAP is designed to make investigational drug accessible to patients with very serious or terminal conditions--basically as a last resort.

Currently, Prochymal is approved to treat acute graft-vs-host disease, which is a complication that occurs after bone marrow transplant when the newly transplanted cells attack the host's body and cause life-threatening inflammation. Prochymal has been shown to control inflammation, stimulate regeneration, and decrease scarring. And yes, we're talking about live cells given to the patients intravenously. Several clinical trials are underway to see if Prochymal may be useful for treating other diseases. It's currently at Phase III (confirming efficacy) for Crohn's disease (intestinal inflammation), at Phase II (determining efficacy) for type 1 diabetes (autoimmune disease), and at Phase I (determining safety) for preserving functional tissues after heart attacks.

So what is Prochymal. Well, it's essential mesenchymal stem cells (or bone marrow stem cells) obtained from the bone marrow of healthy adults that are purified and enriched in a lab. Mesenchymal stem cells were one of the first three adult stem cell populations identified; the others being hematopoietic stem cells (from blood), and neural stem cells (from the brain). Nowadays it seems like regenerative cells can be found in almost every organ, if you believe what's in the literature. Mesenchymal stem cells have long been known to reduce inflammation and suppress the immune response. They were also known to impart regenerative properties to damaged tissues. However, nobody really knows how they do that.

The interplay between injury and regeneration is a hard one to define. When cells or tissues are damaged, they release chemical signals (cytokines) as a cry out for help and inflammation occurs, which in turn recruit immune cells to help repair the damage and fight off invaders. The louder the cry, the more inflammation there is, and the more immune cells appear to do their thing. A critical decision is reached based on these molecular cries. Is the damage severe enough to just seal it off and leave it to die, if it would keep the rest of the body alive? In which case, the tissue dies and is replaced by scar tissue, which doesn't do much more than retain an organ's structure. Or is the damage minor enough to worth salvaging? In this case, the body may try to heal the damage and grow new tissues. Researchers are basically trying to pick apart how a human body decides this because regeneration requires that the body thinks the damage isn't too bad, and that means keeping inflammation down. Molecularly speaking, we can either muffle those chemical cries, or block those cries from reaching certain ears. Mesenchymal stem cells appear to do both by decreasing the secretion of certain pro-inflammatory cytokines, and by altering the receptors expressed on the surface of immune cells. The tricky part now is to figure out which receptors and cytokines control this delicate balance between regeneration and willful destruction.

The door is certainly open now for similar stem cell-based products, assuming they too can show that they are sufficiently safe and effective. That begs the question "Who sets the bar, and will it move?"

First stem cell drug to market-Prochymal

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