Safety and Efficacy of Abatacept for Treating Chronic Cytopenia in Cytotoxic T-Lymphocyte Antigen 4 (CTLA4) Haploinsufficiency

Inclusion Criteria

• •Individuals must meet all of the following criteria to be eligible for study participation:
• •1. Age 8-65 years.
• •2. Documented CTLA4 mutation (requires documentation of confirmed mutation via Sanger sequencing at a laboratory approved by the Clinical Laboratory Improvement Amendments \[CLIA\]).
• •3. At least one of the following established hematologic abnormalities during the past 6 months (including results from outside CLIA-certified laboratories) prior to screening:
• •* ANC \< 750 cells/microL.
• •* Platelet count \< 75,000 cells/microL.
• •* Hemoglobin \< 7.5 g/dL.
• •4. The above mentioned hematologic abnormalities should require active treatment with steroids, immunomodulatory agents (e.g., mycophenolate mofetil, cyclosporine, tacrolimus, mercaptopurine, methotrexate, sirolimus, high dose intravenous immunoglobulin \[IVIG\]), and/or other agents (e.g., TPO agonists) for at least 60 days prior to screening.
• •5. The dose of any concomitant medication(s) aimed at treating cytopenia should be stable in the 60 days prior to screening. Stable is defined as:
• •* No new concomitant medications for cytopenia were initiated.
• •* No dose increase of the medication was required.
• •6. Did not receive blood product transfusions within 30 days prior to screening.
• •7. Did not receive abatacept within 60 days prior to screening.
• •8. Did not receive rituximab within 3060 days of screening.
• •9. Did not receive alemtuzumab at any time.
• •10. Has access to healthcare provider at home.
• •11. Able to provide informed consent.
• •12. Willing to allow storage of biological specimens for future use in medical research.
• •13. Females of childbearing potential must agree to use appropriate birth control methods when engaging in sexual activities that can result in pregnancy, beginning Day -30 through 30 days after the last dose of study agent. Appropriate methods should include 2 forms of contraception, one from each of the following categories:
• •* Hormonal contraception or placement of an intrauterine device or intrauterine system.
• •* Barrier method: Condom or occlusive cap (diaphragm or cervical/vault cap) with a spermicide.