When the polar vortex froze out residents in much the United States in January, it also sent chills through the U.S. blood system, especially for people who needed platelets.
“If you are safely able to leave your house, please consider giving blood for hospital patients,” tweeted the Red Cross of Massachusetts. “Polar vortex blamed for critically low blood supply,” reported Minnesota’s Northwest Community Television.
The record cold exposed a key problem underlying our nation’s blood donation system. It relies exclusively on volunteer donors to provide blood for transfusion. But bad weather routinely keeps potential donors away — as do good weather and holidays.
That means we are constantly dealing with shortages of lifesaving blood components. Platelets are needed more than others because they are so perishable. Red blood cells that carry oxygen can be refrigerated and used for up to 42 days. Plasma, the straw-colored liquid that carries cells, can be frozen for as long as a year. But platelets — the Band-Aids of the body that stop bleeding — have a shelf life of only two days after they are screened for disease.
That means blood drives are often really platelet drives.
Platelets are made by large cells called megakaryocytes that live in bone marrow. These cells extend long arms into nearby blood vessels. When those tentacles encounter the force of flowing blood, bits of them bud off. Those bits are platelets. Once in circulation, a platelet can last for as long as 10 days.
Who needs platelets? Trauma victims, anyone undergoing surgery, women giving birth, and others can require units of platelets to live. But most platelets go to people with cancer. That’s because individuals undergoing chemotherapy and radiation therapy typically lose the ability to make platelets in their bone marrow. They need regular donations of platelets to prevent life-threatening bleeding.
But there are never enough platelets to help everyone who needs them, largely because of their ephemeral nature. Donated platelets, when separated from the other blood components, are a mix of young and old cells. After testing for bacterial and viral pathogens, their life span drops to about two days. Chilling or freezing destroys platelets.
The result is not only continual platelet shortages, but platelet deserts: Outside of large and medium-sized cities, platelets are often unavailable. It’s worse in developing countries.
The current blood donation system is vulnerable to disruption. Given their short shelf life, platelets must be screened for bacteria and viruses quickly, and immediately delivered to individuals who need them. Natural disasters wreak havoc on the carefully choreographed supply chain.
One way of addressing this problem would be to get more people to donate blood, although I’m not sure how realistic that is. About 7 million people already donate blood in the U.S. each year. But with 7,000 units of platelets needed every day, the supply can’t keep up with demand. Whenever the supply spikes, so does the demand, suggesting that we are nowhere near meeting current needs.
The real solution to this endemic shortage is a new way of thinking about sourcing and delivery.
Not long ago, if you needed a cab in the city, you walked to a major street and waved your arm until a cab pulled over. Often, though, there were more riders than cabs, and you could wait for awhile before spotting an empty cab. Now, with ride-hailing services, drivers are usually available on demand.
What if we could make platelets on demand? Several groups, including Platelet BioGenesis, the company I co-founded, are working to turn that concept into reality.
My group is developing a bioreactor that can make platelets from human stem cells. These platelets would be safer than those supplied by donations because of their inherent sterility and would be manufactured on demand. They would also last longer than donated platelets, because they are all freshly made, and so have their full 10-day lives ahead of them.
We aren’t alone in trying to improve the supply of platelets.
Cedric Ghevaert and colleagues at the University of Cambridge are among academic groups developing a different method of making platelets from stem cells that holds substantial promise. While my group is exposing stem cells to “outside-in” signals that help direct their differentiation toward platelets, Ghevaert’s team is boosting the expression of key genes in the stem cells to effect “inside-out” signaling to drive the same differentiation process. The two approaches aren’t mutually exclusive and could potentially be combined to improve overall platelet yield and quality.
William Miller and colleagues at Northwestern University are among another group of academic researchers performing computational fluid dynamic modeling to explore how changing shear forces and flow patterns can trigger platelet generation.
A number of companies in the U.S. and abroad are exploring ways to extend the life span of platelets in storage. Grifols S.A., Fenwal Inc., Baxter International, and Terumo Medical are investigating improved solutions in which to store platelets, while Fresenius Kabi and Haemonetics Corp. are working to re-engineer platelet storage bags. This work would also support donor-independent sources of platelets for transfusion.
These efforts aren’t meant to replace blood donations, which will always be necessary and valuable, but to complement them. Some individuals with rare diseases need precisely matched transfusions that come from specific donors. And the volunteer donor system works well for red cells and plasma, which last much longer than platelets.
But continuing with the current system of volunteer platelet donations ensures continued shortages, more frequent public service announcements to persuade potential donors, and suboptimal outcomes for patients who are kept waiting for platelet transfusions, or who simply don’t get them when they are needed. We can and must do better.
Jonathan Thon, Ph.D., is the co-founder and CEO of Platelet BioGenesis, based in Cambridge, Mass., and a lecturer at Harvard Medical School in Boston.