Got “golden” blood?

Fewer than 50 people on Earth do. Their veins carry Rh-null, an ultra-rare blood type experts say could help save countless lives.

Now scientists are racing to grow it in a lab — a breakthrough that could transform blood transfusions around the world.

Researchers want to increase the supply of Rh-null blood for transfusions by growing it in a lab.
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The American Red Cross considers a blood type “rare” when it occurs in fewer than 1 in 1,000 people. At roughly 1 in 6 million, Rh-null is the rarest of them all.

But to understand why it’s so extraordinary, you first need to know how blood types are classified.

Blood types are determined by antigens, the proteins and sugars on red blood cells that signal to the immune system what blood belongs in the body and what doesn’t.

“If you get transfused with donor blood that contains different antigens to your own blood, you’ll make antibodies to that blood and attack it,” Ash Toye, professor of cell biology at the University of Bristol, told the BBC. “If you get transfused with that blood again, it can be life threatening.”

The two blood group systems that trigger the strongest immune responses are ABO and Rhesus (Rh).

The ABO system determines whether someone has A, B, both or neither antigen on their red blood cells, while the Rh system checks if they are “positive” or “negative” for the RhD protein.

Together, these systems determine whether a person has one of the eight main blood types: A+, A-, B+, B-, AB+, AB-, O+ or O-.

Blood group systems are essential for blood transfusions, as our bodies reject blood group antigens that they perceive as foreign.

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O-negative blood is often called a universal donor type because it lacks A, B and Rh-D antigens, making it safe for most transfusions.

But the Rh system includes more than just the D antigen. In fact, it has more than 50.

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“We test for RhD because it’s the one that’s most likely to trigger an immune reaction,” Dr. Zaher Otrock, a transfusion medicine physician, told the Cleveland Clinic.

“In that sense, it’s the most important and clinically significant of the Rh antigens. But it’s definitely not the only one to consider.”

People with Rh-null blood have none of these antigens, meaning even a transfusion with O-negative blood can trigger a dangerous immune response.

As a result, people with Rh-null blood can only receive transfusions from donors with the same rare type, making their pool of donors extremely limited.

Yet scientists see Rh-null as extremely valuable because it can be safely transfused into anyone with a rare Rh blood type, including those with uncommon blood disorders.

For this reason, Rh-null has earned the nickname “golden blood.”

People with Rh null blood cannot receive transfusions from any other blood type.
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Because so few people carry Rh-null naturally, scientists are working to grow it in the lab to increase the supply for transfusions.

Back in 2018, Toye and his team recreated the rare blood type using the gene-editing technique CRISPR-Cas9. However, the technology is controversial and tightly regulated, so it will likely be years before lab-grown Rh-null could be used in humans.

In the meantime, Toye is co-leading the RESTORE trial, the first study testing lab-grown red blood cells — developed from donor stem cells — when transfused into humans.

“At the moment, taking blood out of somebody’s arm is so much more efficient and cost effective, and so we will need blood donors for the foreseeable future,” he told the BBC.

“But for people with rare blood types where there’s very few other donors, if we can grow them more blood, that would be really exciting.”