Stem Cell Transplants for SCID
DURHAM, N.C. -- When performed within the first 28 days of
birth, stem cell transplants have a 95 percent success rate in
treating newborn babies with severe combined immunodeficiency
(SCID), according to a long-term study by Duke University
Medical Center researchers.
Additionally, when babies who receive these early
transplants are compared with those who received the same
transplants after the first four weeks of life, the earlier
transplants appear to stimulate a more robust and effective
immune system. This enhanced response may be due to reduced
stresses on the thymus, an organ responsible for "training"
immature immune cells to fight off disease, said the
The results of the Duke study, which was supported by the
National Institutes of Health (NIH), were published today (Jan.
24) in the February issue of the journal Blood.
SCID is a rare disorder in which babies are essentially born
with little or no immune system, leaving them unable to defend
themselves from potentially life-threatening infections. The
stem cells used for transplant are obtained from the bone
marrow of related donors and infused into the baby to generate
a "new" immune system.
During the past 19 years, the Duke team has performed stem
cell transplants on 117 SCID patients. Of the 21 babies who
received their transplants within the first 28 days of life, 20
are still alive and leading normal lives, the oldest being 19
years old, said the Duke researchers. For those 96 babies who
received their transplants after 28 days, the survival rate is
"By transplanting these children very early, we were able to
provide an immune system to protect them from opportunistic
infections," said Duke pediatric immunologist Dr. Laurie Myers
and lead author of the new analysis. "We have shown that by
transplanting early, we can improve the survival rates of an
already highly effective therapy.
"Twenty years ago, all of these babies would have died,"
Myers added. "A pathogen that would have little effect on a
healthy baby could kill one with SCID."
The key to improving the chances of a baby with SCID lies in
early detection. According to Myers, all that is required is a
simple test after birth in which researchers count the number
of lymphocytes, a type of white blood cell, in a blood sample.
However, she added, since the incidence of SCID ranges from one
in 50,000 to 100,000 births, most pediatricians do not
routinely order lymphocyte counts for this rare disorder.
"If, however, there is a family history of SCID, most
parents want their baby tested," Myers said. "In our study, we
identified nine of the 21 babies before birth and 12
immediately after, and in all cases there was a family history,
so we were able to do the transplant shortly after birth."
On average, babies are first diagnosed with SCID after the
age of 6 months. By that time the baby has probably suffered
many infections and has not thrived as healthy babies would,
Myers said. One effect of these repeated infections, the
researchers believe, is undue stress on the thymus.
The thymus is critical in the development of key immune
system cells known as T cells. These potent cells begin life in
the bone marrow as stem cells, then migrate to the thymus where
they divide, mature and receive their "marching orders" for the
defense of the body.
"Researchers believe babies with SCID who are transplanted
earlier have a thymus that hasn't been stressed by infections
and so can turn the donated stem cells into functioning T
cells," Myers said. "In the babies with early transplants, we
saw a significantly higher number of T cells, and this was most
evident from three months to three years after transplantation,
a critical time in the development of defenses against common
The transplant itself is relatively straightforward.
Physicians begin by removing bone marrow cells from the donor's
hip. Researchers then remove the donor's mature T cells to
avoid a condition known as graft-vs.-host disease, in which the
donor's immune cells attack the recipient. The resulting stem
cells are then infused into the baby.
"The cells know where to go, and eventually go to the
thymus," Myers explained. "Within one month, we can see a
significant increase in the number of new immune cells, and by
three months, the levels are normal. Those who received the
transplants in the first 28 days had more T cells earlier."
The Duke SCID program, which is one of the few in the
country specializing in this treatment, was developed and is
led by Dr. Rebecca Buckley, chief of pediatric allergy and
Other authors on the paper were Duke's Dr. Dhavalkumar Patel
and Dr. Jennifer Puck of the NIH.