Stem Cell Gene Therapy for Sickle Cell Disease

Sickle cell disease (SCD) affects ~90,000 people in the U.S. who suffer significant
neurological, lung, and kidney damage, as well as severe chronic pain episodes that adversely
impact on quality of life. While current medical therapies for SCD can reduce short-term
morbidity, the inevitable progressive deterioration in organ function results in a
significant decrease in quality of health with early mortality. Allogeneic hematopoietic stem
cell transplant (HSCT) can benefit patients with SCD, by providing a source for life-long
production of normal red blood cells. However, allogeneic HSCT is limited by the availability
of well-matched donors and immunological complications, especially for the more than 80% of
patients who lack an HLA-identical sibling donor. Autologous HSCT using a patient's own bone
marrow stem cells that have been corrected by transfer of a modified human beta-globin gene
that inhibits polymerization of the HbS (stem cell gene therapy) may provide a better
therapeutic alternative, as it would avoid the immunologic complications and donor
limitations of allogeneic HSCT.

Up to 6 subjects with SCD lacking matched sibling donors and meeting eligibility criteria for
disease severity and adequacy of organ function will be enrolled. .

Following informed consent, enrolled subjects will be screened to confirm full eligibility
for participation. A chronic red blood cell transfusions regimen will be given prior to stem
cell collection and transplant. Subjects will undergo peripheral blood stem cell collection
using plerixafor mobilization and apheresis. A portion of their stem cells will be
cryopreserved as "back-up," with the remaining portion used to prepare the gene-modified
Final Cellular Product: autologous peripheral blood CD34+ cells transduced ex vivo by the
Lenti/G-βAS3-FB lentiviral vector to express an anti-sickling (βAS3) gene. The subject will
receive marrow cytoreduction with busulfan prior to infusion of the gene-modified cells. The
follow-up period will include an initial 2 years of active follow-up, where the subjects will
be seen at intervals of no more than 3 months, followed by offer for enrollment into a
long-term follow-up study during years 3-15.

The primary objectives of the Phase I study are to assess safety and feasibility, with
secondary objectives to assess efficacy (engraftment, βAS3-globin gene expression, and
effects on red blood cells function and clinical hematologic and disease parameters).

Inclusion Criteria:

- Age ≥18 by time of enrollment

- Diagnosis of SCD documented by phenotype (Hb electrophoresis) or genetic analysis
(S/S, S/β-thalassemia-zero)

- Must not have medically eligible and available HLA-identical sibling donor or 10/10
allele-matched unrelated donor

- Inadequate clinical response to hydroxyurea (HU), defined as any one of the following
outcomes, while on HU for at least 3 months:

- 2 or more acute sickle pain crises requiring hospitalization

- no rise in Hb >1.5 gm/dl from pre-HU baseline or requires transfusion to maintain
Hb > 6.0 gm/dL

- Has an episode of acute chest syndrome despite adequate supportive care measures.

- Or medical decision for other therapy (e.g. chronic transfusion program), or
subject refusal to take HU.

- The patient must be off HU for at least 90 days (+/- 5 days) before enrolling in the
trial.

- Must have one or more of the following clinical complications demonstrating disease
severity:

- Clinically-significant neurologic event: stroke or any central nervous system
deficit lasting >24 hours.

- Abnormal head CT or brain MRI demonstrating previous stroke

- Administration of regular RBC transfusions for equal or longer than 1 year to
prevent vaso-occlusive crises or other sickle cell disease complications or to
maintain Hb >6.

- Pulmonary arterial hypertension with tricuspid regurgitant jet velocity > 2.5
m/sec.

- At least one episode of acute chest syndrome that required hospitalization,
intubation, and mechanical ventilation support within the 2 years prior to
enrollment

- At least 2 acute sickle pain crises requiring hospitalization within the 2 years
prior to enrollment

- Osteonecrosis requiring joint replacement

- History of acute dactylitis during childhood

- Recurrent priapism (2 or more episodes)

- Karnofsky performance score ≥60%

Exclusion Criteria:

- Patient has a medically eligible and available HLA-identical sibling donor or 10/10
allele-matched unrelated donor (after at least 3 months search)

- Cardiac evaluation: left ventricular ejection fraction (LVEF) < 40% or LV shortening
fraction < 26% by cardiac echocardiogram or by MUGA scan,

- Poorly-controlled hypertension as determined by history of recorded BP in previous
year with systolic >135 or diastolic >95 mmHg.

- Pulmonary evaluation: baseline oxygen saturation of <85% or DLCO< 40% (corrected for
Hb).

- Renal evaluation: serum creatinine >1.5x upper limit of normal for age or GFR<60
mL/min/1.73 m2

- Hepatic evaluation: serum conjugated (direct) bilirubin > 2x upper limit of normal for
age as per local laboratory or ALT and AST > 5 times upper limit of normal as per
local laboratory

- Hematologic evaluation: Leukopenia (WBC< 3x103/uL) or neutropenia (ANC < 1.0x103/uL)
or thrombocytopenia (platelet count < 100x103/uL)

- PT/INR or PTT >1.5x upper limit of normal or other clinically significant bleeding
disorder

- Serum ferritin >1,000 ng/ml. (Potential subjects with serum ferritin >1,000 will be
referred back to their physician for more specific evaluation {e.g. MRI or liver
biopsy}, and consideration of iron chelation therapy, if indicated. If successful and
serum ferritin comes below 1,000 ng/ml, subjects may be reconsidered for enrollment).

- Seropositivity for HIV (Human Immunodeficiency Virus), HCV (Hepatitis C Virus), HTLV-1
(Human T-Lymphotropic Virus), or active Hepatitis B Virus, or active infection by CMV
or parvovirus B19, based on positive blood PCR

- Psychiatric evaluation: psychiatric disorder or neurologic disease that would impair
the informed consent process or cooperation with the clinical trial performance

- Pregnancy

- Cancer or other malignant disease.