A San Francisco company says it has rewritten the single faulty letter of DNA that causes sickle cell disease in three patients, and that all three no longer need blood transfusions. Kamau Therapeutics announced the results on November 4, 2026, ahead of a talk at the yearly meeting of the American Society of Hematology (ASH), the main gathering of blood specialists, in New Orleans in December1. The data come from the company and have not yet been presented in full or reviewed by outside scientists.
What happened
Kamau describes itself as a company making medicines by precisely engineering patients’ own blood stem cells, the cells in bone marrow that make all blood cells1. Its treatment, called nula-cel, is being tested in a trial named RESTORE in people with severe sickle cell disease1. The trial is a combined Phase 1/2 study, an early test mainly meant to check safety and find the right approach before larger trials1.
The new results cover three patients treated with a revised way of making the product, which the company calls version 2.0. Two of them have been followed for more than six months1. The announcement also includes an update on the first patient ever given nula-cel, made with the older process, who is now four years past treatment1.
According to the company, all three patients on the new process stopped needing transfusions before they left hospital, and no patient has had a vaso-occlusive event since treatment1. Vaso-occlusive events are the sudden, severe pain episodes that happen when stiff, sickled red blood cells block small blood vessels2.
The evidence so far
Sickle cell disease comes from a change in the beta-globin gene, which carries the instructions for part of hemoglobin, the protein in red blood cells that carries oxygen. The change produces an abnormal form called hemoglobin S, or sickle hemoglobin3. Kamau’s approach uses a repair method known as homology-directed repair to convert the sickle letter directly back to the normal adult sequence, so the cells make ordinary adult hemoglobin, also called hemoglobin A1.
The company reported these measurements from the trial’s abstract, the short summary accepted for the conference1:
- Blood counts: in the two patients followed past six months, total hemoglobin was 10.2 and 11.1 grams per deciliter1.
- Less sickle protein: sickle hemoglobin made up 17.6% of the total at 12 months in one patient and 19.1% at 8 months in the other1.
- More normal protein: normal adult hemoglobin made up 76.8% and 66.8% at those same time points1.
- Edited cells taking hold: about 20% of the gene copies in the bone marrow carried the correction and stayed at that level, which the company said is consistent with the corrected stem cells settling in for the long term1.
- Protected red cells: tests of single cells showed more than 90% of red blood cells in circulation had protective levels of hemoglobin that resists sickling1.
- Recovery: white blood cells called neutrophils recovered a median of 21 days after treatment, with a range of 19 to 32 days1.
On safety, the company said no serious side effects linked to nula-cel or the editing were seen in the three newest patients. The side effects that did occur matched those expected from busulfan, a strong chemotherapy given beforehand to clear the bone marrow, and from a transplant of a person’s own stem cells1. It said unintended edits elsewhere in the DNA stayed low and unchanged1.
The company also reported on manufacturing. In all three products, between 32% and 38% of gene copies carried the correction, above its 20% target. Collecting enough stem cells from the blood took a median of one collection session, with a range of one to three1.
What it does not show yet
These are early numbers from very few people. Three patients were treated with the new process, and only two have more than six months of follow-up1. The trial has no comparison group, so the results cannot show how the treatment stacks up against other options. The full data have not been presented, and the findings have not appeared in a peer-reviewed journal.
The doctor who will present the work said as much. John F. DiPersio of Washington University School of Medicine, who is not described as a Kamau employee in the announcement, called the results an encouraging early signal1:
“These are early data in a small number of patients, and longer follow-up will be essential, but they support continued evaluation of this approach.”
Long-term safety and durability are open questions across gene therapies for sickle cell disease, and possible risks include unintended genetic changes3. The treatment also still depends on chemotherapy before the cells go back in, a step that can be hard on patients and may not suit everyone3. The announcement does not give prices, and cost has been a major barrier for gene therapies in this disease4.
Who is behind it
All of the results come from Kamau’s own announcement. Vali Barsan, the company’s co-founder and chief executive, framed the treatment as a correction rather than a workaround1:
“Sickle cell disease has a single root cause, one letter in the β-globin gene, and nula-cel is designed to correct it rather than work around it.”
Barsan also said these are the first patients in whom correction has been shown, a claim made by the company, and added that “results and a process built to repeat them are not the same thing”1. Matthew Porteus, Kamau’s co-founder and head of research and development, said the findings “provide early clinical evidence that precise HDR-mediated correction of the native HBB gene is feasible”1. The announcement does not describe the company’s funding.
How it fits the field
Sickle cell disease affects an estimated 100,000 people in the United States and occurs in about 1 in every 365 Black or African American births, according to a 2026 treatment overview2. Roughly 7.7 million people live with it worldwide2. Research cited in that overview found people born with the disease can expect to live an average of 52.6 years, compared with 73.5 to 79.3 years in the general US population2.
For decades, care has relied on transfusions, pain treatment and drugs such as hydroxyurea, which manage symptoms but do not address the genetic cause3. Gene treatments fall into two broad groups: adding a working copy of the gene, or editing the patient’s own DNA3.
The best-known edited treatment, Casgevy, uses the CRISPR tool to switch off a gene called BCL11A, which raises fetal hemoglobin, a form of the protein that does not sickle4. In 2026 it was expanded to children aged 2 and older2. Kamau’s approach is different: instead of turning up a backup protein, it aims to fix the original error so the body makes normal adult hemoglobin under its own controls1. Researchers have long seen direct correction of the gene as a goal, including through newer methods such as prime editing that are still being studied4.
What to watch next
DiPersio is set to present the data at the ASH meeting on December 14, 2026, from 2:45 to 3:00 p.m. Central Time1. The talk, titled as the first clinical results of precise gene correction in patients with severe sickle cell disease, covers the safety and early effects from the first part of the RESTORE study1. Points to watch include whether more patients are treated with the new process, whether the corrected cells and freedom from transfusions hold up over longer follow-up, and whether outside experts reviewing the full data reach the same reading as the company.
