Allogeneic Hematopoietic Stem Cell Transplantation With Briquilimab-Based Conditioning in Participants With GATA2 Deficiency

Overview

Background: People with GATA2 deficiency have a mutation on the GATA2 gene. This gene affects immune function. People with this disease are prone to serious infections; in time, they may develop blood cancers. A hematopoietic stem cell (HSC) transplant can cure GATA2 deficiency, but using stem cells donated by other people can cause serious side effects. Objective: To test a new drug (Briquilimab) to see if it can make HSC transplants safer. Eligibility: People aged 6 to 70 years who have GATA2 deficiency. Design: Participants will be screened. They will have a physical exam, with blood and urine tests. They will have tests of their heart and lung function. They may have a bone marrow biopsy: Their hip will be numbed; a large needle will be inserted to draw out tissue from inside the pelvis. Participants will have a central venous catheter placed in a vein of the neck or chest. This will be used to draw blood and administer drugs. Briquilimab will be given through the catheter about 11 days before the transplant. This is part of conditioning: preparing the body to receive the new stem cells. Conditioning also includes other medications and total body irradiation. Donor stem cells will be administered through the catheter. Participants will receive other approved drugs to help prevent side effects. Participants will stay in the hospital from the beginning of the conditioning until several weeks after the transplant. They will remain in the local area for 100 days after discharge; they will come to the clinic at least once a week during this time. Follow-up visits will continue for 3 years....

Background: * GATA2 deficiency, an immunodeficiency and bone marrow failure disorder due to inherited or sporadic mutations in or loss of one allele of the GATA2 gene, is characterized by: 1) nontuberculous mycobacteria (NTM) and other opportunistic infections, 2) deficiency of monocytes, B lymphocytes, and Natural Killer (NK) cells in the peripheral blood, and 3) progression to myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML), and acute myelogenous leukemia (AML). * Allogeneic hematopoietic cell transplantation (HCT) appears to be curative, and interim results from protocol #13-C-0132, NCT01861106, demonstrated a 2-year event-free survival rate of 83% for 59 participants with GATA2 deficiency who underwent HCT with a busulfan-based conditioning regimen. * However, traditional HCT approaches using alkylating agents such as busulfan continue to place recipients at risk for potentially life-threatening, transplant-related toxicities as well as late effects such as infertility and secondary malignancy. * Briquilimab is a humanized, glycosylated IgG1 monoclonal antibody that targets CD117 (human c-Kit) present on endogenous hematopoietic stem cells (HSC). Briquilimab has been shown in pre-clinical and early clinical studies to safely deplete human and non-human primate HSC with minimal toxicity. Primary Objective: -To determine whether allogeneic hematopoietic cell transplantation with Briquilimab-based conditioning results in sustained donor engraftment by 100 days post-transplant in participants with GATA2 deficiency Eligibility: * Recipients aged 6-70 years old with pathogenic germline mutations in GATA2 and clinical manifestations consistent with a diagnosis of GATA2 deficiency * Have an 8/8 Human leukocyte antigen (HLA)-matched related or unrelated donor or a 7/8 HLA-matched unrelated donor or haploidentical related donor * Have "early stage" GATA2 deficiency defined as a hypocellular for age bone marrow with less than 5% blasts and normal or favorable cytogenetics (defined as "good" or "very good" cytogenetics risk groups plus trisomy 8) Design: * All participants with GATA2 deficiency will receive a pre-transplant conditioning regimen consisting of Briquilimab administered as a single intravenous (IV) infusion on day -11 (range day -13 to -10) with pharmacokinetics, followed by fludarabine or fludarabine/cyclophosphamide IV infusions (3 or 5 days depending on the donor) and 200 cGy total body irradiation (TBI) on day -1. HCT will be infused on day 0. * Participants with an 8/8 HLA-matched related or unrelated donor assigned to Arm A will receive a fludarabine for three days on days -4, -3, and -2. * Participants with a 7/8 HLA-matched unrelated donor or a haploidentical related donor assigned to Arm B will receive a fludarabine for five days on days -6, -5, -4, -3, and -2, cyclophosphamide for 2 days on days -6 and -5 * Post-transplant immunosuppression for Graft Versus Host Disease (GVHD) prophylaxis for recipients of Arms A and B will consist of cyclophosphamide for 2 days on days +3 and +4, along with mycophenolate mofetil from day +5 to approximately day +35 and tacrolimus from day +5 to approximately day +180. If there is no evidence of GVHD, tacrolimus will be stopped or tapered at approximately day +180