Engraftment of gene-modified umbilical cord blood cells in
neonates with adenosine deaminase deficiency
Donald B. Kohn1, Kenneth I. Weinberg1, Jan A. Nolta1, Linda N. Heiss1, Carl Lenarsky1,
Gay M. Crooks1, Mary E. Hanley1, Geralyn Annett1, Judith S. Brooks1, Anthony El-
Khoureiy1, Kim Lawrence1, Susie Wells1, Robert C. Moen2, John Bastian3, Debora E.
Williams-Herman4, Melissa Elder4, Diane Wara4, Thomas Bowen5, Michael S. Hershfield6,
Craig A. Mullen7, R. Michael Blaese7, and Robertson Parkman1
1Division of Research Immunology/Bone Marrow Transplantation, Childrens Hospital, Los
Angeles, University of Southern California School of Medicine, 4650 Sunset Boulevard, Los
Angeles, California 90027, USA
2Genetic Therapy, Inc., 938 Clopper Road, Gaithersburg, Maryland 20878, USA
3Children's Hospital and Health Center, San Diego, California 92123, USA
4Department of Pediatrics, University of California at San Francisco, San Francisco, California
94143, USA
51842 Oak Bay, Victoria, BC, Canada, V8R 1C2
6Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
7National Center for Human Genome Research, National Institutes of Health, Building 49, Room
2A03, 4900 Convent Drive, Bethesda, Maryland 20892-4430, USA
Abstract
Haematopoietic stem cells in umbilical cord blood are an attractive target for gene therapy of
inborn errors of metabolism. Three neonates with severe combined immunodeficiency were
treated by retroviral-mediated transduction of the CD34+ cells from their umbilical cord blood
with a normal human adenosine deaminase complementary DNA followed by autologous
transplantation. The continued presence and expression of the introduced gene in leukocytes from
bone marrow and peripheral blood for 18 months demonstrates that umbilical cord blood cells
may be genetically modified with retroviral vectors and engrafted in neonates for gene therapy.
Inherited deficiency of adenosine deaminase (ADA) is the cause of approximately onequarter
of the cases of severe combined immunodeficiency (SCID)1,2. Based on the
successful treatment of ADA-deficient SCID by allogeneic bone marrow transplantation and
the cloning of the normal human ADA complementary DNA, ADA-deficiency has been a
major target for gene therapy3,4. Theoretically, genetically corrected autologous Tlymphoid
precursors should have a selective survival advantage over non-corrected ADAdeficient
cells. A broad level of expression by an inserted ADA gene (from one-tenth to
above normal) should be beneficial without adverse consequences, although there is no
specific information about consequences of vast overexpression of ADA in cells of all
haematopoietic lineages. Thus, even with the currently modest capabilities to efficiently
© 1995 Nature Publishing Group
Correspondence should be addressed to D.B.K. C.A.M. present address: Department of Experimental Pediatrics, Univeristy of Texas
M.D. Anderson Cancer Center, Box 88, Room AC6.004, 1515 Holcombe Boulevard, Houston, Texas, 77030, USA.
NIH Public Access
Author Manuscript
Nat Med. Author manuscript; available in PMC 2011 January 3.
Published in final edited form as:
Nat Med. 1995 October ; 1(10): 1017–1023.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
transfer genes into primary haematopoietic cells and an inability to control gene expression
in a precise manner, ADA-deficient SCID may respond to gene therapy.
The first clinical trial of gene therapy involved two young girls with ADA deficiency, using
their peripheral blood T lymphocytes as the target for ADA gene transfer5,6. Multiple
courses of leukopheresis, transduction and re-infusion of T lymphocytes led to increased
numbers of T lymphocytes and improved T-Iymphocyte function, with attainment in one of
the two patients of circulating leukocyte ADA levels equivalent to a quarter of those in
normal individuals. Despite these encouraging results with mature T lymphocytes, the
genetic correction of haematopoietic stem cells may create a more long-lasting source of
ADA-expressing T lymphocytes. Information gained from the treatment of ADA deficiency
would be applicable to the use of haematopoietic stem cells for gene therapy for other
aetiologic forms of SCID and to other genetic diseases affecting haematopoietic and
lymphoid cells.
In the spring of 1993, three women who were known to be heterozygous for ADA
deficiency were identified to be carrying ADA-deficient fetuses. After independent genetic
counseling, each family elected to carry its respective pregnancy to term. Because of the
prenatal diagnosis, the unique opportunity was afforded to attempt gene therapy for the
neonates using their umbilical cord blood as a source of haematopoietic stem cells.
Extensive information has been accumulated to indicate that umbilical cord blood contains
haematopoietic stem cells; more than forty patients have had successful haematopoietic
reconstitution by the transplantation of allogeneic cord blood leukocytes following
cytoablative conditioning7,8.
Approval to perform gene transfer into the neonates’ umbilical cord blood followed by the
transplantation of the cells was obtained from the Institutional Review Boards, the
Recombinant DNA Advisory Committee (RAC) of the National Institutes of Health, and the
Food and Drug Administration. The parents of each child gave informed consent for the
collection, transduction and re-infusion of the umbilical cord blood CD34+ cells. After term
delivery of each neonate, umbilical cord blood was collected and processed to isolate the
CD34+ population. The CD34+ cells were transduced with the retroviral vector LASN (ref.
9), which carried a normal human ADA cDNA, and returned to their respective donors by
intravenous infusion on their fourth day of life. Subsequently, we determined the
effectiveness of gene transduction and whether the engraftment of the umbilical cord blood
stem cells had occurred. We report here the results of the first use of umbilical cord blood
cells for clinical gene therapy.
Clinical course
At birth the prenatal diagnosis of ADA-deficiency was confirmed. Fluorescence-activated
cell sorting (FACS) analysis of umbilical cord blood samples demonstrated that the patients
had reduced numbers of T lymphocytes (1.5–2%) compared with those in normal umbilical
cord blood (56.6% ± 12.5). Their levels of serum deoxyadenosine metabolites (dAXP) were
elevated. Following the institution of enzyme replacement therapy with polyethylene glycol
(PEG) combined with ADA on days 1–4 of life (30 U kg-1 twice weekly by intramuscular
injection), there was correction of the metabolic abnormalities, with dAXP levels in
erythrocytes decreasing from 160–302 nmol ml-1 (cord blood red blood cells (RBCs)) to <10
nmol ml-1 within 7–10 weeks. All three patients have remained in good health while
receiving PEG–ADA. Growth and development have been normal with no infectious
complications except for routine upper respiratory tract infections. Prophylaxis with oral
trimethoprim/sulphamethoxazole (TMP/SMX) and intravenous gamma globulin was given
Kohn et al. Page 2
Nat Med. Author manuscript; available in PMC 2011 January 3.
NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
for the first six months to patient 1, patient 2 remains on TMP/SMX, and patient 3 continues
to receive both intravenous gamma globulin and TMP/SMX.
Gene transduction of umbilical cord blood CD34+ cells
Between 60 and 200 ml of umbilical cord blood was obtained from the three infants. FACS
analysis of the umbilical cord leukocytes demonstrated that between 0.7% and 0.9% of the
cells were positive for the stem cell/progenitor antigen, CD34. The cord blood samples were
mixed with biotinylated monoclonal antibody to CD34 and processed through an avidin
immunoaffinlty column. The resulting cell populations were between 32% and 62% CD34
positive, with yields between 24% and 89%.
The enriched CD34+ cells were transduced with three rounds of LASN retroviral vectorcontaining
supernatant in the presence of recombinant haematopoietic growth factors
(interleukin-3 (IL-3), IL-6 and stem cell factor) to enhance gene transfer. After three days of
culture, the total numbers of leukocytes increased by 1.3- to 2.4-fold. The LASN-transduced
umbilical cord blood cells were then infused intravenously into each patient on his fourth
day of life. No toxicities were noted during or after the infusions.
To assess the efficiency of retroviral-mediated transduction of clonogenic myeloid
progenitors contained within the cord blood cells before transplantation, samples were
plated in a colony-forming unit granulocyte-macrophage (CFU-GM) assay, with and without
the selective neomycin analogue, G418. The expression of the neo gene contained in the
LASN vector permits colonies derived from transduced progenitors to survive in G418.
From the three patients, 21.5%, 12.5% and 19.4% of the clonogenic progenitors were G418-
resistant.
Peripheral blood leukocytes
To determine whether the transduced CD34+ cells had engrafted and whether they
contributed to circulating leukocyte populations, we obtained serial peripheral blood
samples at monthly intervals after transplantation. The frequency of peripheral blood
mononuclear cells and granulocytes that contained vector DNA sequences was determined
by semiquantitative polymerase chain reaction (PCR) analysis. PCR primers were designed
to specifically amplify only vector-derived sequences; one primer was complementary to
sequences of the Moloney murine leukaemia virus backbone of the vector and one was
complementary to the human ADA cDNA (Fig. 1a). The intensities of the signals from
leukocyte samples were compared with those of a standard curve to allow an estimation of
the frequency of circulating leukocytes containing the integrated LASN provirus sequ
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