CD4^LVFOXP3 in Participants With IPEX

Inclusion Criteria:

* Body weight greater than 8 kg, unless assessed as able to tolerate leukapheresis
* FOXP3 gene mutation
* Medical history of progressive symptoms of IPEX with persistency of some symptoms and/or signs requiring immune suppressive medication. The participant may or may not be on immunosuppression at time of starting the study.
* Uncontrolled IPEX disease but unable to tolerate immune suppressive medication
* Recurrent IPEX symptoms, requiring immune suppressive medications, in participants who have had prior allogeneic (allo) blood stem cell transplantation (HSCT).
* ≥ 50% Performance rating on Lansky/Karnofsky Scale
* Organ and marrow function within acceptable levels of function
* Absence of ongoing infections
* Must be able to consent if an adult

Exclusion Criteria:

* Medical instability
* Less than 6 months life expectancy
* Inability to meet limits for steroid dosing
* Eligible for an HLA matched sibling or matched unrelated donor blood stem cell transplant, and be willing to undergo transplant.
* Unrelated or comorbid cardiac, renal, pulmonary, liver, or hematologic disease
* Allergy to any study medication, product, or intervention
* Currently receiving another experimental treatment
* History of malignancy, unless disease free for at least 2 years, with the exception of non melanoma skin cancer or carcinoma in situ