Lentiviral Gene Transfer for Treatment of Children Older Than Two Years of Age With X-Linked Severe Combined Immunodeficiency (XSCID)

This is a non-randomized clinical trial of gene transfer using a self-inactivating,
insulated, lentiviral gene transfer vector to treat 13 patients with X-linked severe combined
immunodeficiency (XSCID, also called SCID-X1) who are between 2 and 40 years of age; who do
not have a tissue matched sibling who can donate bone marrow for a transplant; who may have
failed to obtain sufficient benefit from a previous half-tissue matched bone marrow
transplant; and who have clinically significant impairment of immunity. A patient s own
precursor cells (also called blood stem cells) that give rise in the marrow to blood and
immune cells will have been or will be collected from the patient s blood or bone marrow. A
patient will not proceed to gene transfer treatment in this protocol until there are at least
3 million blood stem cells per kilogram body weight collected from the patient. At the NIH
the patient blood stem cells will be collected from either the blood or bone marrow under
another protocol (NIH protocol 94-1-0073 or a successor approved protocol) that is specific
for collection of such cells. In most cases the harvested blood stem cells are put into
frozen storage before use in this protocol. When the patient enrolled in this protocol has
the required number of blood stem cells harvested, then the patient s blood stem cells will
be grown in tissue culture and exposed to the lentiviral gene transfer vector containing the
corrective gene. These gene corrected blood stem cells will be administered by vein to the
patient. To increase engraftment of the corrected blood stem cells, patients will receive on
2 days before the gene transfer treatment a chemotherapy drug called busulfan at a total dose
of 6 mg/kilogram body weight (3 mg/kilogram body weight/daily times 2 days) that is a little
more than one-third the dose used in many standard bone marrow transplants. Patients will
also be given another drug called palifermin that helps prevent the main side effect from the
busulfan that is a type of inflammation the mouth, stomach and bowels called mucositis. After
this treatment, patients will be monitored to see if the treatment is safe and whether their
immune system improves. Patients will be followed at frequent intervals for the first 2
years, and less frequently thereafter so that the effectiveness in restoration of immune
function and the safety of the treatment can be evaluated.

XSCID is a genetic disease caused by defects in common gamma chain, a protein found at the
surface of immune cells called lymphocytes and necessary to their growth and function. XSCID
patients cannot make T-lymphocytes necessary to fight infections, and their B-cells fail to
make essential antibodies. Without normal T- and B-lymphocyte function patients develop fatal
infections in infancy unless they are rescued by a bone marrow transplant from a healthy
donor. The best type of transplant is from a tissue matched healthy brother or sister, but
most XSCID patients do not have a tissue matched sibling, and are treated with a transplant
from a parent who is only half-matched by tissue typing. While a half-matched transplant from
a parent can be life-saving for an infant with XSCID, a subset of patients fail to achieve
sufficient long lasting restoration of immunity to prevent infections and other chronic
problems.

Recent trials of gene transfer treatments using mouse retrovirus vectors for infants with
XSCID have been performed and have demonstrated that this type of gene transfer can be an
alternate approach for significantly restoring immunity to infants with XSCID. However, among
the 18 infants with XSCID benefiting long term from the gene transfer treatment, 5 developed
T-lymphocyte leukemia and 1 died of this leukemia. Furthermore, when older children with
XSCID were treated with gene transfer, the restoration of immunity was very much less than
seen in the infants. These observations of gene transfer treatments using mouse retrovirus
vectors to treat infants and older patients with XSCID suggests that safer and more effective
vectors were needed, and that there also may be a need to give chemotherapy conditioning to
increase engraftment in the marrow of the gene corrected blood stem cells. Our data and other
published studies suggest that lentivectors that are derived from the human immunodeficiency
virus and have the properties of our highly modified vector called CL20-4i-EF1alpha-
HgammaC-OPT have a reduced interaction with nearby genes and therefore less of a tendency to
activate genes that may lead to cancer formation. Also, this type of lentivector may work
better at getting into blood stem cells.

The study purpose is to evaluate safety and effectiveness of lentiviral gene transfer
treatment at restoring immune function to 13 XSCID patients who are 2 to 40 years of age, and
have significant impairment of immunity. Early evidence for effectiveness will be defined by
appearance and expansion in the circulation of the patient s own gene corrected T-lymphocytes
with a functional gammac gene and improved laboratory measures of immune function. The
primary endpoint for efficacy will be at 2 years after treatment, and will include these
laboratory parameters plus evidence for clinical benefit. Evidence for safety will focus on
maintenance of a diversity of gene marked cells and no occurrence of abnormal pattern of
production of blood cells or any leukemia or other cancer. The primary study endpoints for
all laboratory and clinical measures of efficacy and safety will occur at 2 years after gene
transfer treatment. However, data collection regarding efficacy will occur at frequent
intervals during the 2 years leading up to the endpoint analysis, and long term safety and
efficacy evaluation will continue at intervals during the long term follow-up required by
regulation in gene transfer treatment studies.

- INCLUSION CRITERIA:

- A proven mutation in the common gamma chain gene as defined by direct sequencing of
patient DNA

- HLA typing of the patient will have been performed before enrollment

- No available HLA matched sibling donor as determined before enrollment.

- Must be between 2 and 40 years of age and weigh greater than or equal to 10 kg

- If previously transplanted, must be greater than or equal to 18 months post
haploidentical HSCT

- Expected survival of at least 120 days.

- Documented to be negative for HIV infection by genome PCR

- The patient must be judged by the primary evaluating physician to have a suitable
family and social situation consistent with ability to comply with protocol procedures
and the long-term follow-up requirements.

- Medical lab data (historical) of severe B cell dysfunction (low or absent IgG levels,
failed immune response to vaccines); OR demonstrated requirement for intravenous gamma
globulin (IVIG) (significant drop over 3 to 6 weeks between peak and trough IgG
levels).

- Must be willing to have blood and tissue samples stored

IN ADDITION, patients must satisfy the following Laboratory Criteria AND Clinical Criteria

Laboratory Criteria: (greater than or equal to 1 must be present)

i. CD4+ lymphocytes: absolute number less than or equal to 50 percent of the lower limit of
normal (LLN)

ii. CD4 plus CD45RA+ lymphocytes: absolute number less than or equal to 50 percent of the
LLN OR T-cell receptor excision circles (TRECs)squared less than or equal to 5 percent of
normal for age.

iii. Memory B Cells: absolute numberless than or equal to 50percent of LLN

iv. If serum IgM
v. NK cells: absolute number less than or equal to 50 percent of LLN

vi. Lymphocyte proliferative response to each of 2 mitogens, phytohemagglutinin (PHA) and
concanavalin A (ConA), is squared 25 percent with a normal control.

vii. Molecular spectratype analysis- absent or very oligoclonal (1-3 dominant peaks) in
greater than or equal to 6 of the 24 V- Beta T-cell receptor families.

Clinical Criteria: (greater than or equal to 1 must be present):

i Infections (not including molluscum, warts or mucocutaneous candidiasis; see vii and viii
below): greater than or equal to 3 significant new or chronic active infections during the
12 months preceding evaluation for enrollment.

Infections are defined as an objective sign of infection (fever greater than 38.3 degrees C
[101 degrees F] or neutrophilia or pain/redness/swelling or radiologic/ultrasound imaging
evidence or typical lesion or histology or new severe diarrhea or cough with sputum
production). In addition to one or more of these signs/symptoms of possible infection,
there also must be at least 1 of the following criteria as evidence of the attending
physician s intent to treat a significant infection (a. and b.) or objective evidence for a
specific pathogen causing the infection (c.)

-Treatment (not prophylaxis) with systemic antibacterial, antifungal or antiviral
antibiotics greater than or equal to 14 days

OR

-Hospitalization of any duration for infection

OR

-Isolation of a bacteria, fungus, or virus from biopsy, skin lesion, blood, nasal washing,
bronchoscopy, cerebrospinal fluid or stool likely to be an etiologic agent of infection

ii Chronic pulmonary disease as defined by:

-Bronchiectasis by x-ray computerized tomography

OR

-Pulmonary function test (PFT) evidence for restrictive or obstructive disease that is less
than or equal to 60 percent of Predicted for Age

OR

-Pulse oximetry less than or equal to 94 percent in room air (if patient is too young to
comply with performance of PFTs).

iii Gastrointestinal enteropathy:

-Diarrhea-watery stools greater than or equal to 3 times per day (of at least 3 months
duration that is not a result of infection as defined in criterion above)

OR

-Endoscopic evidence (gross and histologic) for enteropathy (endoscopy will only be
performed if medically indicated)

OR

-Other evidence of enteropathy or bacterial overgrowth syndrome: including malabsorption of
fat soluble vitamin(s), abnormal D-xylose absorption, abnormal hydrogen breath test,
evidence of protein losing enteropathy (for example increasingly high or frequent dosing of
intravenous gamma globulin supplement required to maintain blood IgG level).

iv Poor nutrition: Requires G-tube or intravenous feeding supplement to maintain weight or
nutrition.

v Auto- or allo-immunity: Examples must include objective physical findings that include,
but are not limited to any one of alopecia, severe rashes, uveitis, joint pain with redness
or swelling or limitation of movement that is not a result of infection, lupus-like
lesions, and granulomas (Does not include auto- or allo-immune enteropathy which is
criterion iii). Where possible and appropriate, diagnosis will be supported by
histopathology or other diagnostic modality.

vi Failure to grow in height: less than or equal to 3 rd percentile for age

vii Skin molluscum contagiosum OR warts (this criterion is satisfied if molluscum consists
of greater than or equal to 10 lesions or there are two or more lesions at each of two or
more widely separated anatomic sites; or there are greater than or equal to 3 warts at
different anatomic sites at the same time; or the patient has both molluscum and warts)

viii Mucocutaneous candidiasis (chronic oral thrush or candida esophagitis or candida
intertriginous infection or candida nail infections; must be culture positive to satisfy
this criterion)

EXCLUSION CRITERIA:

- Any current or pre-existing hematologic malignancy

- Current treatment with any chemotherapeutic agent (becomes eligible if not on
treatment for at least 3 months)

- Documented HIV-1 infection

- Documented active Hepatitis B infection

- Childhood malignancy (occurring before 18 years of age) in the patient or a first
degree relative, or previously diagnosed known genotype of the subject conferring a
predisposition to cancer (no DNA or other testing for cancer predisposition genes will
be performed as part of the screen for this protocol)