posed to even th e most innocu-
ous germs can acquire infections
that turn deadly. As soon as Om-
arion tested positive for the dis-
order, an ambulance carried him
to Cincinnati Children’s Hospital
in nearby Ohio and placed him
in isolation, where he remained
for the next few months. “I had
no idea what would happen to
him,” his mother recalled.
Approximately one in 40,000
to 100,000 infants is born with
SCID, according to the Centers
for Disease Control and Preven-
tion. Only about 20 to 50 new
cases of the SCID-X1 mutation—
which accounts for about half of
all SCID cases—appear in the United States each year. For years, the
best treatments for SCID-X1 have been bone marrow or blood stem
cell transplantations from a matched sibling donor. But fewer than 20
percent of patients have had this option. And Omarion, an only child,
was not among them.
As it happened, medical scientists at St. Jude Children’s Research
Hospital in Memphis, Tennessee, were then developing a bold new
procedure. The strategy: introduce a normal copy of the faulty gene,
designated IL2RG, into a patient’s own stem cells, which then go on
to produce the immune system components needed to fi ght infec-
tion. Simpson enrolled Omarion in the clinical study and Cincinnati
Children’s Hospital arranged a private jet to transport her and her
son to the research hospital, where they stayed for fi ve months.
St. Jude wasn’t the fi rst to try gene therapy for SCID-X1. Nearly 20
years ago, researchers in France reported successfully recondition-
ing immune systems in SCID-X1 patients using a particular virus to
deliver the correct gene to cells. But when a quarter of the patients
in that study developed leukemia, because the modifi ed virus also
disrupted the functioning of normal genes, the study was halted and
scientists interested in gene therapy for the disorder hit the brakes.
At St. Jude, experts led by the late Brian Sorrentino, a hematol-
ogist and gene therapy researcher, set out to engineer a virus de-
livery vehicle that wouldn’t have side eff ects. They started with a
modifi ed HIV vector emptied of the virus and its original contents,
and fi lled it with a normal copy of the IL2RG gene. They engineered
this vector to include “insulators” to prevent the vector from dis-
turbing other genes once it integrated into the human genome.
The goal was to insert the gene into stem cells that had come from
the patients’ own bone marrow , and those cells would then go on
to produce working immune system cells. It was crucial for the vi-
ral vector to not deliver the gene to other kinds of cells—and that’s
what the researchers observed. “After gene therapy, for example,
brain cells do not have a correct copy of the gene,” explained Ste-
phen Gottschalk, who chairs St. Jude’s Department of Bone Marrow
Transplantation and Cellular Therapy.
BYLINESJessica Ravitz, a longtime features reporter for CNN Digital, is
now a freelance writer living in Atlanta.
Editorial and commercial photographer John David Pittman, an
Arkansas native, is a fi rst-time contributor to Smithsonian.LIFE SCIENCES
Ewelina Mamcarz and
Stephen Gottschalk
Developed a treatment for
babies born without an
immune system