Conference Coverage

Sickle cell disease gene therapy seen advancing



Experimental gene therapies for sickle cell disease and thalassemia appear to be advancing, with BCL11A among the most promising targets in this field, researchers said at Sickle Cell in Focus, a conference held by the National Institutes of Health.

Dr. Alexis A. Thompson, Northwestern University, Chicago

Dr. Alexis A. Thompson

Several highly anticipated presentations on the topic are expected for December meeting of the American Society of Hematology.

Alexis A. Thompson, MD, of Northwestern University, Chicago, reviewed highlights from a study in which the majority of patients given a gene therapy for transfusion dependent beta-thalassemia didn’t need subsequent blood transfusions. The New England Journal of Medicine in April published the results of this work done with Bluebird Bio’s LentiGlobin gene therapy (N Engl J Med. 2018; 378:1479-93).

Of the 22 patients in this trial, 15 have become transfusion independent, Dr. Thompson said in her presentation. Those patients that did not have this positive outcome still appear to have been helped by the gene therapy, she said. They had a median of 60% reduction in their transfusion volumes and nearly 60% in their number of transfusions.

“Whether it was transfusion independence or reduction in their transfusion volume or number, the vast majority of individuals in this first large-scale study had clinical benefit” from the therapy, said Dr. Thompson, who was the lead author of the study.

Dr. Thompson, the current president of the American Society of Hematology (ASH), said she’s looking forward to presentations on some of the most advanced gene therapies for sickle cell disease and thalassemia at the group’s annual meeting in December. The ASH presentations include those of John F. Tisdale, MD, who will report the latest data on LentiGlobin gene therapy in sickle cell disease, and Punam Malik, MD, of Cincinnati Children’s Hospital, who has developed a gamma globin lentivirus vector. There also will be a first readout on a particularly novel approach taken by researchers at Boston Children’s Hospital, led by David Williams, MD.

The development of CRISPR-Cas9 “has really opened up the field” of gene therapy, aiding researchers at Boston Children’s in their efforts to develop a treatment to maintain fetal hemoglobin production, Daniel E. Bauer, MD, PhD, of Boston Children’s Hospital, said during his presentation at the NIH conference.

Dr. Daniel E. Bauer is a blood disorders researcher at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center.

Dr. Daniel E. Bauer

Dr. Bauer provided an update on the BCL11A research that seeks to block what amounts to a genetic “off switch” for production of fetal hemoglobin. It’s long been known that erythrocytes of newborns with sickle cell disease are protected from sickling by high levels of fetal hemoglobin. Clinical manifestations of sickle cell disease then emerge in the first year of life as fetal hemoglobin levels decline.

“A main goal in hematology has been to understand how is it that these alternative fetal hemoglobin genes get silenced and how can we turn them back on,” said Dr. Bauer, a staff physician in pediatric hematology/oncology.

The gene BCL11A also plays key roles in the development of the central nervous system, B lymphatic lymphocyte maturation, and hematopoietic stem cell self-renewal. That led the researchers to hone in on targeting sequences around the BCL11A gene that act as erythroid enhancers, intending to limit potential complications by creating a very specific therapy for sickle cell disease.

In a related clinical trial, using lentiviral gene therapy rather than gene editing, researchers at Boston Children’s began an open-label, nonrandomized, single-center pilot study that involves a single infusion of autologous bone marrow derived CD34+ HSC cells transduced by a vector containing a short-hairpin segment of RNA targeting the gene BCL11A.

The study has a maximum accrual of seven evaluable patients, according to the NIH’s clinical trials website. The protocol is similar to bone marrow transplant, in that native blood stem cells are eliminated by myeloablative conditioning therapy. In this gene therapy, the patient’s own blood stem cells are then infused after the new genetic material has been added to counter the normal BCL11A off switch.

Swee Lay Thein, MBBS, an organizer of the NIH’s sickle cell conference, said in an interview that the “gene therapy side is really looking very optimistic.”

Dr. Thein, a senior investigator for sickle-cell genetics at the National Heart, Lung, and Blood Institute, earlier in her career discovered segments of DNA, including the BCL11A gene. She said that gaining greater understanding about genomic variation might someday aid in determining which people need more intense intervention for their sickle cell disease.

“You would be able to predict who will have more severe disease; we could monitor them more closely and perhaps even advocate for gene therapy or bone marrow transplant before complications have occurred rather than waiting for them to occur,” Dr. Thein said.

She referred to this as her “dream” for care of people with sickle cell disease. “This is still far off in the horizon.”

The NHLBI in September 2018 launched its Cure Sickle Cell Initiative. The agency estimates that it spends about $100 million on sickle cell disease research each year. The inherited blood disorder affects about 100,000 people in the United States and 20 million individuals worldwide. In sickle cell disease, a single genetic mutation causes red blood cells to form abnormal, sickle shapes that can clog the blood vessels and deprive cells of oxygen.

Dr. Thompson reported research funding and consulting agreements with Biomarin, Bluebird Bio, Celgene, Novartis, and Shire. Dr. Bauer reported patents related to BCL11A enhancer editing, consulting agreements with Merck and Pfizer, and research support from Bioverativ.

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