April 1, 2016 (Vol. 36, No. 7)
Alex Philippidis Senior News Editor Genetic Engineering & Biotechnology News
Co-Leader of the Seminal Study Says Team “Basically Showed That You Could Do This”
When she was just two days old, Ashanti DeSilva developed an infection. It turned out to be the first of many infections that would baffle her parents and doctors until she turned 26 months old, when she was finally diagnosed with adenosine deaminase (ADA) deficiency, a form of severe combined immunodeficiency disease (SCID).
Like other children with the disorder, DeSilva was started on pegylated ADA (PEG-ADA), an enzyme therapy that emerged in the 1980s. The treatment worked well enough for her to gain weight, develop a normal peripheral T-cell count, and experience fewer infections. Yet her immune deficiency persisted.
At the age of four years, DeSilva made history at 12:52 p.m. on September 14, 1990, as the first patient to undergo an approved application of gene therapy. She was part of a trial authorized by the FDA and the NIH’s Recombinant DNA Advisory Committee (RAC). The trial included just one other patient, Cynthia Cutshall (now Kisik). Cynthia began treatment January 31, 1991, when she was nine years old.
Researchers drew blood from both girls, inducing the T cells from their blood to replicate in culture. Retroviral vectors infused with functional ADA genes were transferred into the cultured T cells. The gene-corrected T cells were reinfused back into the girls about 12 days after blood was drawn. DeSilva received 11 infusions over approximately two years, compared with 12 infusions over 18 months for Cutshall.
The trial, which took place at the NIH’s Clinical Center, was led by W. French Anderson, M.D., then of the NIH’s National Heart, Lung, and Blood Institute; R. Michael Blaese, M.D., then chief of the Cellular Immunology Section of the NIH’s National Cancer Institute (NCI); and Kenneth W. Culver, M.D., also then of the NCI, in Dr. Blaese’s laboratory. The researchers used an ADA retroviral vector constructed and provided by A. Dusty Miller, Ph.D., of the Fred Hutchinson Cancer Center in Seattle.
“We basically showed that you could do this, you could do it safely, and you could have a positive impact on patients,” Dr. Blaese, who was also deputy chief of the NCI’s Metabolism Branch, told GEN. “It wasn’t a curative trial, but it was certainly an effective treatment, and I think it did open the door for some very successful trials that have cured patients of a number of diseases.”
Delivering the Gene
A key to the success of the 1990 trial, Dr. Blaese said, was figuring out how to get the corrected gene into patients. As a molecular hematologist, Dr. Anderson focused on placing the corrected gene in stem cells in the patient’s bone marrow, so the disease could be corrected through stem cell transplantation. But that turned out to be much harder than first thought.
“Getting it into the bone marrow stem cell, and getting that stem cell then to differentiate to become a mature T cell that expressed the gene, just kept eluding us,” Dr. Blaese recalled. “We could get it at low levels, but it was never at a level that was going to be therapeutically useful.”
While considering how to overcome this difficulty, Dr. Blaese made a critical observation. He saw that another NCI colleague had used a different retrovirus to immortalize T cells. The colleague hoped to advance the study drugs that would make T cells resistant to HIV infection, but Dr. Blaese had a different idea. “I realized,” he said, “that maybe we could use that same trick to immortalize T cells from some of these children with ADA deficiency.”
Drs. Blaese and Anderson began working in 1985 to correct cells from patients with ADA deficiency in tissue culture, using a retrovirus to carry the corrected ADA gene to the cells. After transfers into bone marrow didn’t produce enough cells for an effective treatment, the researchers opted for T cells, resulting in a far larger number of corrected genes taken up by the cells.
Borrowing from Immuno-Oncology
The researchers also reached out to the NCI’s chief of surgery, Steven A. Rosenberg, M.D., Ph.D. He was using infusions of autologous tumor infiltrating lymphocytes (TILs) as a form of immunotherapy.
“At my request, Steve agreed to incorporate a retroviral marker gene to track the distribution and survival of the infused TILs in his cancer patients,’” Dr. Blaese said.
Working with Dr. Rosenberg, Drs. Blaese and Anderson grew TILs from five patients with malignant melanoma, then used the LNL6 retroviral vector to put a DNA marker into those cells. The marked TILs allowed researchers to learn which ones worked best for fighting cancer—but equally important, that the engineered virus could be used safely in humans.
Drs. Blaese, Anderson and Rosenberg submitted the TIL marker gene protocol as their first formal protocol to the RAC’s Human Gene Therapy Subcommittee, then to the full RAC and the FDA. When that review proved the retroviral gene transfer technology to be safe and effective, the researchers were ready to submit the ADA T cell protocol, Dr. Blaese said.
Refining the ADA Protocol
The ADA protocol was reviewed a dozen times by seven regulatory committees before it was finally approved by the RAC in July 1990, and by the FDA two months later.
Maria Grazia Roncarolo, M.D., chief of the Division of Pediatric Stem Cell Transplantation and Regenerative Medicine at Stanford Medicine, told GEN that among the lessons learned by her research team from the 1990 trial was that inserting a gene in mature T cells was not sufficient to produce enough enzyme.
“To cure the patient, we needed to correct the gene at the level of the blood stem cells, to have the corrected gene in more than one cell lineage and to create space for the corrected stem cells in the patient bone marrow,” she explained. “Researchers learned that if we want to do in vivo gene therapy, to inject the vectors directly into the patient, we have to be very, very careful about the dose—and also the purity of the vector.”
‘Here I stand’: First Patient Recalls Successful 1990 Trial
Ashanti DeSilva, the first patient for whom treatment with gene therapy was authorized by the FDA and NIH’s RAC, has few memories of her gene therapy in 1990, but many of R. Michael Blaese, M.D., who co-led the landmark trial, treated her for years after the trial, and with whom she has stayed in touch into adulthood.
“He was the kindest man, but I remember him saying once that I have to remain on these injections for the rest of my life as a precaution. And I just remember tearing up, even though injections had never really bothered me,” DeSilva said.
In learning of her SCID diagnosis, DeSilva shared last year on her blog, “my parents finally received an answer as to why I couldn’t walk more than a few feet without collapsing, and why I was constantly catching infections without full recovery.”
“The gene therapy was not the cure we had all hoped for, but my cell counts continued to increase,” she added. “If you ask my parents or myself, it worked, because my fate was written with my diagnosis, yet here I stand today.”
DeSilva went on to earn a master’s degree in public administration from The Ohio State University, then began pursuing a career in genetic counseling. That required taking science courses, which gave her a better understanding of her disease—and made her comfortable enough to talk publicly about SCID and her gene therapy, starting at IDF’s 2013 National Conference.
Today DeSilva is married and living in Chicago as a genetic counselor. She raises awareness for primary immune deficiencies through the Immune Deficiency Foundation (IDF), a national nonprofit patient organization focused on primary immunodeficiency diseases, while sharing her experiences on a blog for Global Genes Project, a rare and genetic disease advocacy organization.
DeSilva credits family and friends with helping her face the challenge of balancing the need to continue follow-up treatments and respond to illnesses as they arose, with her desire to maintain as normal a life as she could.
“Many, many times, I’d have news cameras following me at school. And I was extremely self-conscious,” DeSilva recalled. “I had to take a lot of time off from school. If I had to be hospitalized, I would just tell them to put the IV in my left hand because I’m right handed, and my parents would bring my work, and I’d do my homework, and come back as if I didn’t miss a day.
“It is a bit hard for anyone with a chronic condition to have to sort-of defend your illness constantly if you have to miss school or work, but you do the best you can. Some people are more understanding than others,” DeSilva said.