“This is the first scientific report of patients with a human genetic disease treated successfully with CRISPR-Cas9.”
So reported Dr. Selim Corbacioglu on behalf of an international team of researchers on June 12 at the 25th annual meeting — virtual, of course — of the European Hematology Association.
Wow.
A Mississippi woman named Victoria Gray, under the treatment of Dr. Haydar Frangoul of the Sarah Cannon Research Institute (Nashville, Tenn.), had such a severe case of sickle-cell anemia that at any given time a good majority of her red blood cells were malformed.
Cases like Gray’s are debilitating and extremely painful. Oxygen just can’t circulate well at all, so even walking up stairs can be crushingly difficult.
But thanks to a truly amazing cascade of many years of research, with one discovery compounding upon another, some of it by curious winnowers who didn’t understand the nature of what they were finding, and some of it by savvy innovators with clear targets in their sights, Victoria Gray at long last is feeling good.
So, a quick reminder of what sickle-cell anemia is: it’s basically defective hemoglobin. Hemoglobin is a protein that carries oxygen throughout your blood to deliver it everywhere energy is needed. No oxygen means no respiration, no endpoint for your metabolism. You know how painful it is to work your biceps to exhaustion by carrying a heavy box for way too long. Lactic acid builds up because there’s no oxygen left in there. You’ve just got to put that thing down. Imagine your whole body feeling like that whenever you try to exert even modest activity.
Hemoglobin, like all your other proteins, is encoded by a gene, and just one incorrect letter (nucleotide) in that gene can mean sickle-cell trait. If both copies of your hemoglobin gene are like that, you have a real problem. Your hemoglobin proteins clump up, they have trouble carrying oxygen, and they cause malformed red blood cells:
So you might wonder how CRISPR could possibly fix that. How are we going to change a single DNA letter specifically into another? Well, CRISPR technology isn’t quite so … crisp just yet, though it’s getting there. (If you want a good general introduction to it, go here.)
What CRISPR can robustly do is find a particular sequence within a gene, and snip the gene in half right at that spot like a pair of scissors. This quite literally snips an entire chromosome in half, so the cell needs to fix that right away. It usually does so in a haphazard way, just anything to put the chromosome back together, and the gene that was targeted ends up mutated and not functional anymore. You can’t do that to the hemoglobin gene, or you’re in even bigger trouble. So what the heck is CRISPR going to do for us?
Well, this is where the cool cascade of discoveries comes in. It’s been known for some time that fetuses and young babies have a different form of hemoglobin altogether than adults do. It’s called “fetal hemoglobin” (abbreviated HbF), and it has a higher affinity for oxygen than the adult form (HbA), so that baby can snag oxygen from mommy:
But at a few months of age, a switch comes on and tells the red blood cells to stop making HbF and start making HbA. That switch generally stays on for the rest of your life, and everything is good.
Some people, though, never stop making HbF because something in their switching mechanism isn’t right. Those people are totally fine, because HbF works pretty well. They just walk around with a lot more HbF than most people have. But those rare people enabled us to find the switch. It’s a regulator protein called BCA11L.
Some even rarer people have sickle-cell anemia AND a defective switch, and guess what? They make HbF, and it makes up for their sickle-cell anemia, and they have very mild symptoms, if any at all.
Hmmm…….
It was later found that a particular region of the BCA11L gene, outside of the part that actually codes the protein, is responsible for making the switch from HbF to HbA, but that region is expendable for all of BCA11L’s other functions. So if that region could just be disrupted somehow… Oh, now we’re on to something!
This is what did it for Victoria Gray: They took out some of her red bone marrow, and isolated the hematopoietic stem cells (HSCs). Those cells are what divide to make all the red blood cells in your body, loads of them. They CRISPR-edited those HSCs very efficiently (which took a lot of work to figure out exactly how to do, because HSCs are stubborn that way) with a disruption of the BCA11L gene. That disruption turned out, due to the DNA-repair whims of HSCs, to most often be the addition of one extra letter to the BCA11L gene. And that little change was enough to make BCA11L a defective switch for HbF to HbA. Gray’s edited bone marrow cells, it was hoped, would proliferate with the CRISPR fix. No BCA11L function would mean they’d start cranking out HbF, divide into red blood cells, and fix the problem all throughout her blood.
So they reinjected the edited red marrow back into Gray’s bones and waited. They drew blood once a month and checked on what kinds of hemoglobin were there. And on June 12 they gave us this very nice graph. A revolutionary one, you might say:
Victoria Gray’s graph is on the right (and a thalassemia patient who also was treated successfully is on the left). Blue bars represent fetal hemoglobin, and red bars are sickle-cell hemoglobin. You can see that Gray was in bad shape at the beginning — a lot of red — but as you go from left to right (0 to 6 months), look at all that blue HbF she developed and has stably kept making! Life-changing:
"It's hard to put into words the joy that I feel — being grateful for a change this big. It's been amazing," said Gray, 34, who lives in Forest, Miss.
In many ways, it's a change that came just in time, Gray said. In the fall, the National Guard deployed her husband to Washington. And then, the coronavirus pandemic triggered a national lockdown. Gray was suddenly home alone with three of her kids.
Her great-aunt as well as the pastor of her childhood church died of COVID-19. Friends at her current church have been getting sick.
And then George Floyd was killed by police in Minnesota.
"I feel like everything happened so fast," she said. "It hasn't been easy."
If she hadn't had the treatment, Gray said she doesn't know how she'd be coping. She would have been too weak to care for her children and probably would have been hospitalized at a time when hospitals feel especially unsafe.
"Since my treatment I've been able to do everything for myself, everything for my kids. And so it's been joy not only for me but for the people around me that's in my life," she said.
One other woman named Jennelle Stephenson, also with severe sickle-cell anemia, has been successfully treated recently (read her story, too; it’s great) using another method where a fully correct adult hemoglobin gene was engineered into her HSCs with the help of a semi-disabled form of HIV. That type of therapy strikes me as more risky because you don’t know where that corrected hemoglobin gene is going to land within the genome; it could be harmful by disrupting something it shouldn’t, but evidently that didn’t happen to Stephenson, because for her part, she has gone from debilitating pain to an active jiu jitsu student!
But back to Victoria Gray: think about all that had to go right to get to this point. It’s like a highlight-reel hockey play with about 15 passes and a brilliant finish:
First you have the discovery that some adults keep making HbF in the first place (pre-1960’s) and the discovery of the genes involved (1980’s). Then you have the discovery that BCL11A regulates HbF (2008). Then the discovery that a certain region of BCL11A is responsible for repressing BCL11A but isn’t needed in other cells — so, a specific target to go after (2013). Then the discovery of CRISPR/Cas9 by people who had no idea what the heck it was (going all the way back to 1987). Then figuring out what it was (2005). Then re-engineering it to edit DNA (2012). Then the ability to deliver it and use it efficiently in HSCs (2019).
And instead of fixing the hemoglobin gene itself, we tap into another form that isn’t even supposed to be there by finding the switch that controls it, so we bypass the defective hemoglobin entirely. A pretty behind-the-back pass:
This is just the beginning for these kinds of therapies, and there will be fits and starts, and more bumps along the way, but make no mistake about it: this is a tremendous advance. We’re getting better at this. The results are starting to come in.
"High school graduations, college graduations, weddings, grandkids — I thought I wouldn't see none of that," Gray said.
"Now I'll be there to help my daughters pick out their wedding dresses. And we'll be able to take family vacations," she says. "And they'll have their mom every step of the way."