“Ex Vivo Retroviral Gene Transfer for Treatment of X-linked Severe Combined

Immunodeficiency (XSCID)”

Treatment of patients with persistent immune defects despite allogeneic bone

marrow transplantation

Harry L. Malech, MD and Jennifer M. Puck, MDNational Institute of Allergy and Infectious Diseases

and National Human Genome Research InstituteNational Institutes of Health

Bethesda, Maryland

Current Standard Therapy for SCID

Bone marrow transplantation60-90% survivalBetter outcome with HLA-matched sibling donor

(available to only 25% of patients)Less success with haploidentical (from parent)

or matched unrelated donorBetter outcome with diagnosis and transplant by

3 months of age

Limitations of Haploidential BMT

• Graft vs. host disease

• Incomplete immune reconstitution or graft loss:

Poor B cell function (IVIG dependence)

Immune dysregulation, autoimmunity

Recurrent infections

Growth retardation, nutritional problems, and chronic lung disease

NIH XSCID Gene Therapy ProtocolDesign:

Up to 6 XSCID patients, 2-20 years old with persistent immune defects despite BMT

Ex vivo retrovirus gene transfer to cytokine mobilized autologous CD34+ peripheral blood hematopoietic stem cells

Single infusion of gene corrected CD34+ cells with no marrow conditioning to enhance engraftment (no radiation, no chemotherapy)

Long term follow up of immune reconstitution, vector marking, and changes in clinical status

Protocol DesignSubjects:An important feature of our study is

that all subjects have already received one or more allogeneic bone marrow transplants, but demonstrate persistent immune defects which result in IVIG dependence, recurrent infections, growth failure, chronic gastrointestinal problems, chronic inflammatory skin conditions and chronic lung disease.

Patient Selection: Pre-enrollment Evaluation

No patients have yet enrolled in this gene therapy protocol.

We have studied 8 post-BMT XSCID patients dependent on IVIG who have a variety of persistent clinical problems.

8 Post-haploidentical BMT XSCID Patients Referred to NIH all > 3 yrs (range 3-11 yrs) from Last BMT

Age(yrs)

#BMTs

Weight Percenti

le

HeightPercentil

e

5 1 90% 95-97%

7 2 90% 25%

8 2 10-25% 25%

8 2 <3% <3%

9 2 <3% <3%

10 4 <3% <3%

11 1 <3% <3%

19 2 <3% <3%

Post-BMT XSCID Patients Referred to NIH for Evaluation

    Chronic Conditions    

Age(yrs) Skin

EarInfections

SinusitisLungs:

Infections √;Chronic Dis.

ElevatedLiver

Enzymes

Gastrointestinaldisease Psychosocial

factors

5 Molluscum √ √ √      

7 Eczema   √ √; Reactive airway

√ Intravenous feed;

Gastric tube;Diarrhea

Speech therapy;Special

education

8   √   √   Diarrhea Delayed speech;Special

education

8     √ √ Bronchiectasis;

Reactive airway;

√ Gastric tube  

9 Alopecia   √ √; Reactive airway;

√ Gastric tube;Diarrhea;

Malabsorption

Not enteredschool;

Separationanxiety

10 Alopecia;Eczema;Impetigo

√ √ √; Reactive airway; Fibrosis

√ Esophagealstenosis;

Chronic colitis

Frequent schoolabsences

11 Flat warts;Nail

infections

√ √ √; Bronchiectasis;Reactive airway

√    

19 Flat warts     √; Atelectasis;Fibrosis

√ Diarrhea;Hepatomegaly

Frequent schoolabsences

Immunologic Data from Post-BMT XSCID Patients Referred to NIH

Immunophenotyping* Antibody levels Proliferation  

Age(yrs)

CD3/ul CD19/ul NK/ul IgA mg/dL

IgM mg/dL

mitogens PHA/ConA/PWM

antigens Tetanus / Candida

5 1478 417 6 28 83 normal normal

7 504 132 29 <10 11 low-normal very low

8 980 232 63 20 25 normal low

8 527 153 5 <10 42 low low-normal

9 96 435 0 <10 25 low low

10 135 263 9 <10 17 very low none

11 3279 71 17 <10 44 low low-normal

19 2411 44 5 <10 21 low low-none

Bold = low for age

T cellsB cells

Granulocytes

224

70

239

101

82

34

62

104

0

10

20

30

40

50

60

70

80

90

100

Perc

en

t

Patients

Engraftment post BMTMicrosatellite PCR Chimerism Assay of Blood Cells

Perc

ent D

onor

Cel

ls

T-cells B-cells Granulocytes5 7

8 8

9

10 11

1 9

Pati

ent A

ge (y

rs)

Host (cells/ul)

Donor (%)224

70

82

34

62

104

0

10

20

30

40

50

60

70

80

90

100

Patients

CD34 Mobilization and OriginMobilization and Source of Peripheral Blood CD34+ Cells

5 7

9

10

11 1 9

Patient A

ge (yrs)

Mob

ilize

d C

D34

+ ce

ll pe

r ul

Host Donor

Conclusions About Post-BMT XSCID Patients Referred to NIH

• Some XSCID patients have persistent immune deficiency despite one or more prior haploidentical T-depleted BMTs.

• These patients have immune defects, poor growth, and chronic medical conditions.

• Engraftment of donor T cells was detected in 6 of 8 patients, but no patient had any donor B cells, granulocytes, or monocytes.

• 6 of 6 patients mobilized with G-CSF to collect CD34+ cells as part of a clinical evaluation protocol had no CD34+ cells of donor origin.

NIH XSCID Protocol Vector

Vector: GALV pseudotyped MFGS-gamma chain

MFGS vector contains only the open reading frame of IL2RG (common gamma chain of the IL2 receptor).

MFGS differs from MFG by only 3 nucleotides in the truncated gag region, further reducing the potential for production of gag peptide through recombination events.

Our replication incompetent vector was packaged by the PG13 cell line, and supernatant for clinical use was collected from confluent cultures of a stable, highly characterized producer clone.

NIH XSCID Protocol Ex Vivo Transduction

1-10 x 106 autologous mobilized peripheral blood CD34+ cells will be subjected to 4 daily transductions ex vivo with GALV pseudotyped, replication-defective MFGS-gc.

Transductions will occur in flexible gas-permeable plastic containers using serum-free medium with 1% human serum albumin and 5 recombinant growth factors (50 ng/ml Flt3-L, 50 ng/ml SCF, 50 ng/ml TPO, 25 ng/ml IL-6, and 5 ng/ml IL-3).

Expected transduction efficiency is 40-60%, based on testing of the clinical vector.

NIH XSCID Protocol Treatment and Follow up

Subjects will receive a single infusion of transduced autologous CD34+ cells.

Subjects will be monitored for:

• gene marking in blood cell lineages

• changes in numbers of T-, B- and NK cells

• changes in T-, B-, and NK cell function.

• changes in clinical status (growth, chronic conditions and quality of life).

NIH XSCID Protocol Safety Considerations

The first 3 subjects will be treated at least one month apart and there must be appearance of gene marked T-cells in at least one of these 3 patients before additional patients can be enrolled.

Safety studies include:

• monitoring for replication competent virus in blood cells.

• evaluation of hematologic, kidney, liver, neurologic and other organ function.

Proposed Modifications of NIH XSCID Protocol in Response to the Adverse Event in the

French Study

Subjects: Further limit enrollment to patients with immune defects, growth impairment, and recurrent infections post-haploidentical transplant who have no detectable engraftment in B-cells, NK cells, myeloid cells or CD34+ cells. Exclude subjects with a history of leukemia or childhood cancers in first degree relatives.

Proposed Modifications of NIH XSCID Protocol in Response to the Adverse Event in the

French Study

Informed consent: Full disclosure in the informed consent document of everything known about the severe adverse event in the French study.

Proposed Modifications of NIH XSCID Protocol in Response to the Adverse Event in the

French StudyInsert site analysis: Following appearance of

marked cells in peripheral blood, determine insertion sites by inverse PCR and sequencing at 6 month intervals, from blood lineages and from clones of T-cells grown ex vivo. Using that information, quantify the persistence and changes in relative proportion of particular inserts in different lineages over time. Insert site analysis in the bulk ex vivo tranduced CD34+ cells is not proposed as this is highly unlikely to reveal the predominant clones in the rare cells which actually engraft long term.

Proposed Modifications of NIH XSCID Protocol in Response to the Adverse Event in the

French Study

Analysis of T-cell subsets: Closely follow numbers of gamma/delta T-cells and other subtypes including T-cell receptor analyses

Proposed Modifications of NIH XSCID Protocol in Response to the Adverse Event in the

French Study

Infection treatment: Early interventional treatment of all infections, particularly virus infections with specific therapies where approved therapies are available (antibiotics, anti-virus agents and/or specific immune globulin where appropriate).

The subset of patients with XSCID who have persistent immune defects and chronic medical problems despite allogeneic bone marrow transplantation do not have other treatment options and may benefit from ex vivo gene therapy.

The risk/benefit assessment for gene therapy treatment of these patients should take into account the degree of impairment of their immune function and quality of life, and the lack of alternative therapies.