Selective cell removal may tame stem cell Transplant's dangerous side effect

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

Inclusion Criteria: * Considered appropriate candidate for allogeneic HCT following low dose (4Gy) TBI containing-conditioning and have one of the following diagnoses: A) BMF B)Hemoglobinopathies C)PID D) Autoimmune cytopenias E) Immune dysregulation F) HLH G) Other NMD treatable by HCT and NMD that is not clearly defined (a patient with a NMD for whom genetic testing has been done and a genetic mutation responsible for their NMD phenotype has not been identified) are eligible for the study following discussion with and approval by the protocol PI * Patients aged 6 months- 5 years old (inclusive) at the time of informed consent * Patient with suitable HCT donor (see inclusion criteria below) * Recipient informed consent/assent (13 years and older), and/or legal guardian permission must be obtained Exclusion Criteria: * Patient with aplastic anemia * Patients with severe combined immunodeficiency (SCID) * Fanconi anemia * Dyskeratosis congenita * Patient weight \> 100 kg * Patients who are positive for HIV-1, HIV-2 * Patients with current neoplastic disorders * Patients with uncontrolled infections for whom HCT is considered contraindicated by the consulting infectious disease physician. * Patients with organ dysfunction including A) Renal insufficiency B) Impaired cardiac function C)Impaired pulmonary function D) Liver dysfunction * Patients who are pregnant or breast-feeding * Patients on other experimental protocols for prevention of GVHD * Patients of childbearing age who are presumed to be fertile and are unwilling to use an effective birth control method or refrain from sexual intercourse during and for 12 months post-HCT * Patients with any other significant medical conditions that would make them unsuitable for transplantation, as determined by the PI * Patients with a known hypersensitivity to tacrolimus or MMF