A CRISPR therapy that attempted to cure a man of HIV has failed, but proved safe for the patient.

The patient was diagnosed with HIV/AIDs and acute lymphoblastic leukemia. He was being treated with chemotherapy for the leukemia and anti-viral drugs for HIV, which reduce the amount of virus in the blood but do not eliminate it from cells.

A Possible Cure for HIV

12 years ago, a patient was cured of both HIV and leukemia after receiving a bone marrow transplant from a healthy donor. It was later discovered that the donor had a mutation in their CCR5 gene. The CCR5 gene codes for a membrane protein that the HIV virus can use to infiltrate cells, but the CCR5 gene mutation alters the protein’s shape so the virus can no longer enter.

As the current patient was due to have a bone marrow transplant to treat his leukemia, researchers wondered if the CCR5 gene donor’s bone marrow stem cells could be edited with CRISPR. This would hopefully cure his HIV and leukemia in one treatment, effectively killing two birds with one stone.

CRISPR Treatment Comes with Risks

However, there are legitimate concerns of treating patients with CRISPR. It is possible the CRISPR can edit mutations in the genes that it is not designed to edit, known as off target mutations. These mutations could go on to cause diseases such as cancer. It was hoped that these effects would be avoided by editing the donor’s stem cells instead of the patient’s body cells.

The stem cells from the healthy donor were edited with a CRISPR system to knock out the CCR5 gene. However, analysis revealed that only 17.8% of the stem cells had been edited successfully. The stem cells were then implanted into the patient. The transplant cured the patients leukemia, but when they stopped taking anti-viral medication their HIV levels rose in the blood, demonstrating that the CRISPR technique had not cured the patient of HIV.

Treatment is Safe but Ineffective

Possible reasons for the treatment failure include the low proportion of cells that were edited successfully with CRISPR, and the low survival rate of the cells that were. The CCR5 mutation also only prevents a particular strain of HIV from entering cells, meaning that other strains could still enter cells using alternative methods.

However, the patient did survive and has apparently not suffered any other genetic alterations from the CRISPR treatment, which suggests that the CRISPR can be used safely on patients in the future.