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 The technique replaces a defective version of a gene the body needs
to build cells that seek out and destroy invading germs. Earlier
versions of the treatment have been less efficient and also posed a
risk of triggering leukemia.
The doctors said they have skirted the leukemia problem by
implanting "insulators" around the replaced gene, preventing the
treatment from accidentally activating adjacent genes and causing
cancer.
Three months after treatment, non-defective immune cells appeared in
all but one of the treated children. That child was successfully
treated with a second round of gene therapy 12 months after his
initial therapy.
All have normal growth and development, and any infections they had
suffered because of their disabled immune system have disappeared.
There have been no signs of leukemia.
"The kids are cured because for the first time we are able to
restore all three types of cells that constitute a full immune
system," lead author Dr. Ewelina Mamcarz of the bone marrow
transplantation and cellular therapy center at St. Jude Children's
Research Hospital in Memphis, Tennessee, said at a news conference.
"Our patients are able to generate a healthy, fully-functional
immune system and are now responding to vaccinations, and that's a
first for a gene therapy trial."
Results from the first eight babies treated at St. Jude and the
University of California, San Francisco Benioff Children's Hospital
through September 30 appear in the New England Journal of Medicine.
Those children, treated when they were 2 to 14 months old, have only
been followed for 7 to 25 months, so further study will be needed to
determine if there are any long-term problems.
The 10th child is due to be released from the hospital this week,
about four months after treatment. It typically takes three or four
months for the corrected cells to sufficiently build up the immune
system to allow a child to leave isolation.
Based on the results so far, said St. Jude president Dr. James
Downing, "we're comfortable at this point stating this is cure."
"Only time will say if this is a durable lifelong cure," said Dr.
Alain Fischer, a professor at the College of France who is also with
the Unit of Pediatric Immunology, Hematology and Rheumatology at
Necker Hospital for Sick Children in Paris. He was not involved in
the new treatment, but helped develop an initial gene therapy for
the condition 20 years ago.
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The new work "is a significant step forward in the development of
gene therapy and specifically for these diseases," Fischer told
Reuters Health in a telephone interview.
Earlier treatments were less efficient and less safe, although the
first patient Fischer's team treated remains alive 20 years later
and is still doing well.
Bubble boy disease, formally known as X-linked severe combined
immunodeficiency or SCID-X1, is a rare genetic defect that leaves
the baby defenseless against infection. Treatment usually requires
getting stem cells from a donor, which can be dangerous if the donor
isn't a closely-matched brother or sister. Sibling donors are
usually available in fewer than 20 percent of cases.
The new technique, developed at St. Jude, involves taking some of
the baby's bone marrow and using an AIDS-type virus to inject a
working copy of a gene known as IL2RG into cells. The gene makes a
protein essential to building a properly-functioning immune system.
The treatment cannot cause AIDS.
Mamcarz noted that "any genetic disorder with a known genetic defect
is amenable to this approach."
Some previous attempts to cure bubble boy disease have only produced
temporary results. She said this treatment doesn't seem to have that
problem.
"In previous trials, waning of the immune system was observed much,
much earlier - within the first year," Mamcarz said. One patient
treated with the new technique has been followed for more than two
and a half years with no sign that the benefits are fading.
SOURCE: https://bit.ly/2UQI5Ar The New England Journal of Medicine,
online April 17, 2019.
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