A New Gene-Editing Trial Reported a 96% “Functional Cure” Rate — Here’s What That Means

An investigational CRISPR-based gene-editing therapy called reni-cel (short for renizgamglogene autogedtemcel) produced a functional cure in 96% of adolescent and adult patients with severe sickle cell disease, according to results from the RUBY Trial published in the New England Journal of Medicine this spring.

Like the already-approved therapy Casgevy, reni-cel works by editing a patient’s own blood-forming stem cells outside the body, then reinfusing them so the body starts producing protective fetal hemoglobin again instead of the sickle-shaped form. Pediatric hematologist Dr. Christopher McKinney of Children’s Hospital Colorado, a co-author on the study, has described the approach as designed to prevent sickle cell complications at their source rather than simply managing them after the fact.

The 96% figure refers to patients who were free of the disease’s defining pain crises after treatment — a remarkable result for a condition that, until recently, had no fix beyond a well-matched bone marrow transplant, an option unavailable to most patients because of how difficult a genetic match is to find.

What “functional cure” actually means

It’s worth being precise about what “functional cure” means here: patients still carry the underlying sickle cell gene, but the edited cells produce enough healthy hemoglobin that the disease’s worst complications don’t manifest. It’s not the same as removing the trait from a person’s DNA, but for someone who has spent years cycling through emergency rooms, the practical difference can be life-changing.

Reni-cel is still investigational, meaning it hasn’t yet been formally approved the way Casgevy and Lyfgenia have. But results like this add to a growing body of evidence that CRISPR-based approaches to sickle cell disease are not a one-off success story — they’re becoming a genuine treatment category, with multiple companies and research groups now racing to refine the approach, reduce its cost, and extend its reach.