Three people with the inherited blood diseases sickle cell and beta thalassemia remain free of burdensome blood transfusions and their worst symptoms, months after receiving an infusion of genetically modified stem cells.

One of the three, a young woman with a severe form of beta thalassemia, has now been followed for over a year since she was treated, while the second, a woman in her 30s with sickle cell disease, is more than nine months removed from her infusion. They are the first two patients in pioneering studies of a therapy, developed by CRISPR Therapeutics and Vertex, that's based on the gene editing technology known as CRISPR.

Both patients continue to respond to treatment, bolstering evidence of genetic medicine's potential to permanently alter the course of devastating hereditary conditions like sickle cell and transfusion-dependent beta thalassemia. A gene therapy developed by Bluebird Bio has shown similar potential.

First results from the two studies, disclosed last November, were "taking the promise of CRISPR and turning that into a reality," said Samarth Kulkarni, CRISPR Therapeutics' CEO, in an interview. The additional data and follow-up now available "show these effects can be long-lasting and durable."

And in beta thalassemia, the first patient's experience is now supported by results from another patient who was treated about five months ago. This individual has also been able to stop receiving blood transfusions.

Taken together, the two patients responses are "proof of concept," CRISPR Therapeutics and Vertex claim, that their approach to treating beta thalassemia has the potential to be curative.

In sickle cell, the companies are also hopeful. The one patient for whom they have data has not had a vaso-occlusive crisis, a painful episode caused by the disease's characteristic sickling of red blood cells, since her treatment.

"The clinical manifestation of the disease is different, but we see consistent outcomes across both diseases," said Bastiano Sanna, Vertex's head of cell and genetic therapies, in an interview.

Three other beta thalassemia patients and one other sickle cell disease patient have been treated in the two studies of CRISPR Therapeutics and Vertex's therapy, dubbed CTX001. If results continue to look positive, CTX001 could be another powerful way to help people for whom treatment options have long been limited.

CRISPR, an easy-to-use method of genetic surgery that's derived from a bacterial defense system, has become a mainstay in labs across the world for all types of experiments. Its potential use as a human therapeutic has drawn closer as companies harnessing the technology CRISPR Therapeutics, Editas Medicine and Intellia Therapeutics have advanced their research. CRISPR Therapeutics is the first of the three to deliver results from a clinical trial.

CRISPR and Vertex unveiled their updated results at the European Hematology Association's virtual meeting on Friday. Also being presented were the latest data from Bluebird's gene therapy, known as LentiGlobin.

Bluebird is much further along, having treated 60 patients with beta thalassemia and 37 with sickle cell disease across six different studies.

Updated results from three of those studies showed 23 of 27 evaluable patients with beta thalassemia were transfusion independent for at least a year following treatment. And in sickle cell, no serious vaso-occlusive crises were observed in the 18 patients who had at least six months of follow-up. An episode was previously reported in one patient several months after LentiGlobin treatment, but was judged to be non-serious.

One sickle cell patient died suddenly 20 months following infusion with LentiGlobin, Bluebird reported Friday. Both the treating physician and an independent study committee concluded the death, ruled to be cardiovascular in nature, was unlikely to be related to the gene therapy.

Both beta thalassemia and sickle cell are diseases caused by mutations in the beta globin gene, faulty DNA that results in either absent or warped hemoglobin. Without enough hemoglobin, patients' red blood cells can't carry needed oxygen throughout the body. And those with sickle cell have abnormal hemoglobin that makes red blood cells fragile and stiff, causing them to stick in blood vessels.

Both diseases require chronic blood transfusions, and can lead to organ damage and reduced lifespans. Treatment options are limited, although that's now changing. The Food and Drug Administration, over the past few years, has approved Reblozyl, for beta thalassemia, and Oxbryta and Adakveo, for sickle cell.

Adakveo reduces the frequency of vaso-occlusive crises, while Reblozyl and Oxbryta are chronic medicines meant to boost patients' hemoglobin levels.

CRISPR Therapeutics and Vertex, along with Bluebird, are trying to accomplish the same goal but in more dramatic fashion: raising hemoglobin levels high enough so patients can stop blood transfusions and, in sickle cell, avoid pain crises altogether.

CRISPR and Vertex use CRISPR/cas9 gene editing to modify the DNA of stem cells extracted from a patient's bone marrow. The cells are engineered to produce a type of hemoglobin that's present at birth but normally replaced soon after. Once returned to the body and engrafted in the bone marrow, these CRISPR'd cells substitute this so-called fetal hemoglobin for the missing adult hemoglobin.

In the three patients treated so far, that appears to be what's happened. Both beta thalassemia patients are producing hemoglobin at levels considered normal. The sickle cell patient now has enough fetal hemoglobin to dilute the effects of sickled hemoglobin, potentially helping to preserve red blood cells.

Crucially, CRISPR and Vertex shared data for the first time indicating a high percentage of edited cells are present in each patient's bone marrow, supporting their confidence that the effects of treatment might last.

Bluebird, by contrast, doesn't edit the DNA of extracted stem cells, but rather inserts a modified gene into those cells. Once infused and engrafted in a patient, the cells can produce gene therapy-derived hemoglobin.

In most beta thalassemia and sickle cell patients treated with Bluebird's LentiGlobin, hemoglobin levels rose to normal or near-normal levels.

LentiGlobin is already approved for certain beta thalassemia patients in Europe as Zynteglo. In the U.S., Bluebird has hit delays and pushed back when it expects to submit an application to the middle of next year. A filing for an accelerated approval in sickle cell would likely follow sometime in the second half of 2021.

CRISPR and Vertex, meanwhile, plan to enroll more patients into their two studies, which they hope could serve as sufficient for an approval application if positive, Kulkarni said.

Read more:
New CRISPR, gene therapy results strengthen potential for treatment of blood diseases - BioPharma Dive