Gene therapy restores immunity in Artemis-deficient severe combined immunodeficiency

Infants with Artemis-deficient severe combined immunodeficiency improved after corrected genes in their stem cells enabled them to grow their own T cells and B cells, according to a study published in The New England Journal of Medicine.

Mutations in the DNA cross-link repair 1C (DCLRE1C) gene lead to Artemis-deficient severe combined immunodeficiency (ART-SCID), which is characterized by a lack of T lymphocytes with a lack of or nonfunctional B lymphocytes.

ART-SCID responds poorly to typical SCID treatment, allogenic hematopoietic stem cell transplantation (HSCT), even when it involves sibling donors with matching human leukocyte antigens (HLA), according to the researchers.

This defect in their DNA also makes them more sensitive to chemotherapy and radiation therapy than other patients, Morton J. Cowan, MD, pediatric immunologist at UCSF Benioff Children’s Hospital, told Healio.

Morton J. Cowan

“These patients are more likely to reject a bone marrow graft from another person, have a higher incidence and severity of graft-versus-host disease — a potentially fatal reaction when donor T cells react to recipient or host tissues — and fail to fully reconstitute T- and B-cell immunity,” Cowan said.

“Gene therapy, which uses the patient’s own bone marrow stems cells for the correction, eliminates many of these major issues associated with standard bone marrow transplants,” Cowan continued.

Without treatment to provide a new, durable immune system, patients with SCID die of infections in infancy, Jennifer Puck, MD, pediatric immunologist at UCSF Benioff Children’s Hospital, told Healio.

Jennifer Puck

“Gene therapy, achieved by adding a correct copy of the Artemis gene to the patient’s own blood-forming stem cells harvested from their bone marrow, avoids the complications of rejection and graft-versus-host disease and offers patients with ART-SCID the chance for a long and healthy life,” Puck said.

Study design

The study involved 10 infants (60% boys) who did not have an HLA-matched sibling enrolled and treated at UCSF Benioff Children’s Hospital for newly diagnosed ART-SCID between June 2018 and September 2021.

Clinicians manufactured, cryopreserved and performed quality-control testing of the patients’ gene-transduced autologous CD34+ cells, which in effect included corrected copies of the DCLRE1C gene.

The patients then received IV busulfan including these cells over a period of 2 days. The median age at infusion of gene-transduced cells was 2.7 months (range, 2.3-13.3).

The researchers began measuring the patients’ immune reconstitution and gene marking 4 weeks after infusion and T-cell receptor (TCR) diversity and vector insertion-site analysis 12 weeks after infusion. Patients underwent monthly evaluations through month 6, then every 3 months through month 24.

Results

Median follow-up was 31.2 months (range, 10-48.9).

The researchers detected gene-marked CD3+ cells at a median of 12 weeks (range, 6-16) in all 10 infants. Five of six patients who were followed for at least 24 months experienced cellular immune reconstruction at a median of 12 months (range, 6-24).

Also, there was an increase in levels of CD3+, CD4+ and CD8+ T cells, naive CD4+ T cells and regulatory T cells for a 9-month period following infusion. At 3 to 6 months after infusion, researchers detected TCR excision circles that increased in parallel with naive T cells.

All patients except for one with an ongoing cytomegalovirus infection had normal lymphocyte proliferation in response to phytohemagglutinin by 9 months. The researchers reported improved TCR beta diversity as well, with levels observed similar to those of health adults.

Flow cytometry and gene marking detected B cells in all 10 patients at a median of 6 weeks (range, 4-10), although levels subsequently declined in one patient. At 24 months after infusion, three patients had normal IgM concentrations and immunization responses, with a fourth beginning immunization.

Researchers observed 40 nonserious adverse events that were possibly, probably or definitely related to the treatment, including 23 grade 1 or 2 and 17 grade 3 or 4 events, the latter of which included 16 cytopenias and one case of autoimmune hemolytic anemia (AIHA).

AIHA is not unique to gene therapy as it is a complication of HSCT, Cowan said, especially when mismatched donors, cord blood or unrelated donors are used.

Four patients overall developed AIHA that resolved following T-cell immunity reconstitution between 4 and 11 months after infusion, the researchers said, adding that all 10 patients were healthy at the time of their report, at home and living normal lives.

Conclusions, next steps

Cowan called the therapy’s ability to reconstitute T-cell immunity in all the patients and B-cell immunity in many with no adverse effects from the low-dose chemotherapy “very gratifying and significant.”

“While we expected T lymphocyte recovery, we were surprised and pleased to see gene-corrected B lymphocytes appear in all 10 of the patients treated, and several have been able to produce their own antibodies and stop relying on antibody infusions,” Puck added.

Puck also called the successful use of the natural human Artemis promoter sequence in their vector to achieve the right amount of Artemis protein at the right time for proper T- and B-cell development a significant aspect of this therapy.

“Other gene therapies to date have used generic promoters,” Puck said.

The precisely targeted very low dose of busulfan also proved adequate in making space in the patient’s bone marrow for engraftment of the gene-corrected cells, which was another significant achievement, Puck continued.

“So far, we have not seen adverse side effects from this despite the known difficulty hat Artemis SCID patients have in repairing DNA damage,” Puck said.

Further, Puck noted that the researchers expected to enroll some infants of Navajo and Apache Native American background due to the recognized founder mutation in these populations, adding that their study population was very diverse and, in addition to Navajo and Apache Native Americans included patients of white, Hispanic, Japanese, Vietnamese and Middle Eastern background.

“Thus, while considered ultra-rare, Artemis-deficient SCID occurs in diverse populations worldwide,” Puck said.

To obtain FDA approval, the researchers need to continue this trial, Cowan said.

“Meanwhile, we’re investigating next-generation gene therapy approaches including targeting a specific safe site in the genomic DNA of the stem cell, editing the mutation specifically and identifying nonchemotherapeutic approaches to making marrow space,” Cowan said.

Eventually, Cowan said that the researchers would like to be able to administer this therapy in vivo by injecting the vector intravenously, which would eliminate the need for any chemotherapy conditioning and make the therapy much easier to export to other countries.

Also, this treatment is new, so patients need to be followed longer to determine if it is safe and durably effective, Puck said, adding that the researchers plan on 15 years of follow-up. They also plan on extending the trial to enroll further patients and hope to offer treatment at other sites.

“We also are enrolling older Artemis SCID patients who do not have satisfactory immunity despite prior transplants from healthy donors,” Puck said.

Reference:

• Infant gene therapy is a breakthrough for Artemis-SCID patients. https://www.eurekalert.org/news-releases/974668. Published Dec. 21, 2022. Accessed Dec. 21, 2022.

For more information:

Morton J. Cowan, MD, can be reached at mort.cowan@ucsf.edu.

Jennifer Puck, MD, can be reached at jennifer.puck@ucsf.edu.