-INCLUSION CRITERIA:

1. Age greater than or equal to 18 years
2. CD4 T cell count less than 300 cells/microL or less than 20% of total T lymphocytes on 2 occasions at least 6 weeks apart in the absence of any illness accounting for CD4 lymphocytopenia

3. ICL diagnosis that indicates a risk for disease progression, defined as one or both of the following:

   • CD8 T cell lymphocytopenia (less than 180 cells/microL)
   • History of opportunistic or otherwise significant infection (e.g., AIDS-defining or highly morbid illnesses, such as Cryptococcus or Mycobacteria infection, severe herpes zoster, JC virus causing progressive multifocal leukoencephalopathy, Kaposi's sarcoma, or severe human papilloma virus condylomata)
4. HIV-1 and HIV-2 seronegativity and below detection of HIV-1 viral load
5. HTLV-1 and HTLV-2 seronegativity
6. Adequate venous access, as determined by the study team, although participants unable to undergo leukapheresis will not be excluded
7. Normal thyroid-stimulating hormone (TSH)
8. Negative serum or urine pregnancy test at time of study enrollment for women of childbearing potential
9. Ability to understand and give informed consent
10. Capacity and willingness to adhere to study procedures, including scheduled follow-up visits
11. Willingness to allow blood and tissue sample storage
12. Established primary care provider

EXCLUSION CRITERIA:

1. History of prior cytotoxic, chemotherapeutic, immunosuppressant (e.g., systemic corticosteroids), immunomodulatory (e.g., IL-2, IL-7, interferon-gama), or growth factor therapy within the last 6 months
2. History of prior participation in another investigational intervention study within the last 6 months
3. Active uncontrolled opportunistic infection at the time of enrollment
4. Current or recent history (less than 28 days prior to screening) of a viral, bacterial, parasitic or fungal infection requiring hospitalization and/or systemic treatment, other than long-term maintenance pharmacotherapy
5. Serious illness requiring systemic treatment and/or hospitalization within 56 days (8 weeks) of screening, unless the patient is clinically stable, in the opinion of the Principal Investigator, and has completed therapy or has been on appropriate therapy for greater than 28 days (4 weeks) prior to screening
6. Current or history of hematologic or lymphoid (lymphoma) malignancy
7. Established or planned pregnancies or refusal to use effective birth control (e.g., barrier methods, oral contraceptives, intrauterine devices) for the duration of study involvement, regardless of gender
8. Concurrent breastfeeding
9. Renal insufficiency (e.g., estimated glomerular filtration rate less than 60 mL/min/1.73 m(2))
10. Any of the following screening laboratory abnormalities: platelets less than 100,000 cells/microL; lipase greater than 1.5 times the ULN; AST, ALT, or alkaline phosphatase greater than 2.5 times the ULN; total bilirubin greater than 1.5 times the ULN
11. History of splenectomy or hematologic disease associated with hypersplenism, such as alpha- or beta-thalassemia, hereditary spherocytosis, Gaucher's disease, or autoimmune hemolytic anemia
12. Cirrhosis of any origin, including alcoholic or non-alcoholic steatohepatitis, either suspected by history or histologically proven
13. History of hepatitis B or C infection, i.e., positive hepatitis B surface antigen, positive anti-hepatitis B core antibody with a detectable hepatitis B DNA viral load, positive anti-hepatitis C antibody and/or detectable hepatitis C RNA viral load (patients who became negative for hepatitis B DNA or hepatitis C RNA following anti-viral treatment will not qualify for study treatment)
14. Need for anticoagulant medication (e.g., warfarin, heparin), other than aspirin, clopidogrel, or other antiplatelet agent as CYT107 may co-precipitate with heparin if taken together.
15. Active drug or alcohol use or dependence that, in the opinion of the investigator, would interfere with adherence to study requirements (participants must agree to refrain from substance abuse use during the entire course of the study)
16. Past or current psychiatric illness that, in the opinion of the investigator, would interfere with protocol adherence or the ability and willingness to give written informed consent
17. Current autoimmune conditions requiring systemic (oral, injection, or other parenteral) therapy, as well as psoriasis and optic neuritis regardless of treatment, as rhIL-7 may carry some risk of uncontrolled lymphocyte proliferation, potentially leading to a break in immune tolerance to self-antigens and contributing to exacerbations of autoimmune phenomena
18. Cardiac, pulmonary, thyroid, renal, hepatic, neurological (central or peripheral) disease or disorder of hemostasis requiring therapy and considered to be significant by the protocol team
19. History of cardiovascular disease, arrhythmias, or clinically significant ECG abnormalities, including a corrected QT interval (QTc) greater than or equal to 470 milliseconds
20. Family history of sudden cardiac death
21. Uncontrolled hypertension (i.e., resting systolic blood pressure greater than140 mmHg or resting diastolic blood pressure greater than 90 mmHg), despite pharmacologic antihypertensive treatment, confirmed with a second blood pressure measurement done later in the same day.
22. Evidence of circulating neutralizing anti-IL-7 antibodies (prior to initial rhIL-7 administration)