EZN-2279 in Patients With ADA-SCID

Inclusion Criteria:

1. Diagnosis of ADA-deficient combined immunodeficiency

2. Stable clinical status while receiving therapy with Adagen®. Patients previously
receiving gene therapy or undergoing hematopoietic stem cell transplantation who still
require Adagen® treatment are eligible. The dose of Adagen® must be stable for at
least 3 months prior to study entry.

3. Have both during the Adagen® Lead-in phase of the study:

1. Trough plasma ADA activity >15 μmol/h/mL while receiving Adagen®

2. Total erythrocyte dAXP ≤0.02 μmol/mL from a trough blood sample

4. Patients or parent/guardian must be capable of understanding the protocol requirements
and risks and providing written informed assent/consent

Exclusion Criteria:

1. Autoimmunity requiring immunosuppressive treatment

2. Patients with neutralizing anti-Adagen® antibodies at screening evaluation.

3. Severe thrombocytopenia (platelet count <50 x 109/L)

4. Current participation in other therapeutic protocols for ADA-deficient combined
immunodeficiency

5. Current or prior participation in another clinical study with an investigational agent
and/or use of an investigational drug in the 30 days before study entry.

6. Known planned participation in a gene-therapy study for the planned duration of this
study

7. Any condition that, in the opinion of the PI or Sigma-Tau, makes the patient
unsuitable for the study

8. Inability or unwillingness to administer Adagen® or EZN-2279 on a one time per week
regimen

9. Inability to comply with the study protocol

10. Female patients who are pregnant or lactating

11. Female patients who are breast-feeding

12. Female subjects of childbearing potential who are not using an FDA approved birth
control method