New drug could make stem cell transplants safer for rare immune disorder

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

* INCLUSION CRITERIA: * Age \>= 6 and \<= 70 years old * Germline mutation in the GATA binding protein 2 (GATA2) gene, predicted to be deleterious or previously reported in GATA2 deficiency as determined by targeted GATA2 sequencing performed at the National Institutes of Health (NIH) * Clinical manifestation(s) consistent with a diagnosis of GATA2 deficiency, including any of the following (Note: only one clinical manifestation is required): * History of severe, disfiguring, and/or recurrent infections * Low monocyte (\< 190 cells/microL), B cell (\< 61 cells/microL) and/or Natural Killer (NK) cell (\< 126 cells/microL) counts * Myelodysplastic syndrome by World Health Organization (WHO) criteria * "Early stage" GATA2 deficiency defined as a hypocellular for age bone marrow with less than 5% blasts and normal cytogenetics or favorable cytogenetics (defined as "good" or "very good" cytogenetics risk groups plus trisomy 8) * Availability of an 8/8 HLA-matched related or unrelated donor, a 7/8 HLA-matched unrelated donor or a haploidentical related donor * Lansky (for participants \< 16 years of age) or Karnofsky (for participants \>=16 years of age) performance status of \>= 40% * Left ventricular ejection fraction \> 40%, preferably by 2-D echocardiogram (echo) obtained within 90 days prior to treatment initiation * Participants must have adequate organ function as defined below: * Total bilirubin \<=2.5 x upper limit of normal (ULN) * Alanine transaminase (ALT) and aspartate aminotransferase (AST) \<= 5 x ULN * Creatinine: Adult participants: \<=2.0 mg/dl and creatinine clearance \>= 30 ml/min. Pediatric participants (\<18 years old): creatinine \<1.5 mg/dL and a creatinine clearance using the Schwartz Formula \> 30 mL/min/1.73m\^2 * Pulmonary function tests (PFT)s: Forced expiratory volume in 1 second (FEV1) and adjusted diffusing capacity of the lungs for carbon monoxide (DLCO) \>30%. Children who are unable to cooperate for pulmonary function tests (PFTs) due to age are still eligible if no evidence of dyspnea at rest and no need for supplemental oxygen * Women of childbearing potential (WOCBP) and men must agree to use highly effective contraception (hormonal, intrauterine device (IUD), abstinence, tubal ligation, partner has had the previous vasectomy) at the study entry, for the duration of study treatment, and for at least one-year post-allogeneic HCT or 12 months after completion of chemotherapy preparative administration if HCT is not performed for women and for 4 months for the same for men. * Breastfeeding participants must be willing to discontinue breastfeeding * Willingness to remain in the NIH hospital or, if discharged, stay close to the NIH (60 minutes' drive), for a minimum of 100 days after transplant or longer if there are complications. The participants must commit to having an adult caregiver with them during the first 100 days after transplant in case of discharging from the hospital before 100 days verified by social worker * Participants with hepatitis B virus (HBV) or hepatitis C virus (HCV) antibody-positive testing are allowed if HBV DNA \<100 IU/m or HCV RNA level is undetectable. Additionally, transplantation must be approved by a hepatology consult for these participants * Participants or parents/guardians must be able to understand and willing to sign a written informed consent document EXCLUSION CRITERIA: * Participants with a Hematopoietic Cell Transplantation-Comorbidity Index (HCT-CI) score \>8 * Participants who have received any investigational agents within 4 weeks before treatment initiation with the exception of virus-specific T cells for the treatment of viral infection/reactivation prior to allogeneic HCT * Participants with a history of hematologic malignancy (e.g., Acute Myeloid Leukemia (AML), Chronic Myelomonocytic Leukemia (CMML). Note: participants with Myelodysplastic Syndromes (MDS) are included * History of allergic reactions attributed to compounds of similar chemical or biologic composition to agents (fludarabine, cyclophosphamide, tacrolimus, mycophenolate mofetil, granulocyte-colony stimulating factor (G-CSF)) used in the study * Presence of active malignancy. Note: participants with malignancy driven by viruses (e.g., human papillomavirus (HPV) or HPV or Epstein-Barr virus (EBV)) are allowed as the immune reconstitution after transplant may control the malignancy and participants with MDS are allowed * Human immunodeficiency virus (HIV)-infected participants * Pregnancy (confirmed with Beta-Human Chorionic Gonadotropin (HCG) serum or urine pregnancy test performed in WOCBP at screening) * Uncontrolled intercurrent illness or social situations (as determined by social work consult) that would limit compliance with study requirements