Potential Increase in Graft Failure Risk after Reduced Intensity Conditioning Stem Cell Transplant (RIT) Using Umbilical Cord Blood for Children with Primary Immunodeficiency.
Authors: Guarino Jessica , Kletzel Morris , Duerst Reggie , Jacobsohn David , Schneiderman Jennifer , Tse William T. 
Published: April 2020

Abstract
Allogeneic stem cell transplantation is curative for patients with primary immunodeficiency. A unique reduced intensity conditioning regimen has been developed to maximize cure rate and minimize transplant-related toxicity. Between 2000 and 2007, we performed 16 RIT in patients with hyper-IgM syndrome (n=2), severe combined immune deficiency (SCID) (n=10), immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) (n=2), Wiskott-Aldrich syndrome (n=1), and X-linked lymphoproliferative disease (n=1). There were 12 males and 4 females, with a median age at the time of RIT of 8.0 months (range 1.1 months to 8.9 years). Donor sources included peripheral blood stem cells (PBSCs) from matched related donors (n=7) or unrelated donors (n=2), and cord blood units (CBUs) (n=7). The median cell dose was 8.55 × 108 total nucleated cells (TNC)/kg and 6.7 × 106 CD34+cells/kg for the PBSC group, and 1.99 × 108 TNC/kg and 0.71 × 106 CD34+cells/kg for the CBU group. The conditioning regimen consisted of Fludarabine (Flu), days -10 through -5, intravenous Busulfan (Bu), days -5 and -4, and Anti-thymocyte globulin (ATG), days -4 through -1. GVHD prophylaxis included tacrolimus/prednisone (n=1), cyclosporine A (CSA) alone (n=2), and CSA/mycophenolate mofetil (n=13). All patients who received PBSCs from related and unrelated donors engrafted (9/9), whereas only 4/7 (57%) patients who received CBUs engrafted. The 3 patients who experienced primary graft failure had the following diagnoses; IPEX, T−B−NK+ SCID and T−B+NK+ SCID. Their cord blood doses were 0.78, 1.19 and 1.99 × 108 TNC/kg, and 0.11, 0.69, and 0.55 × 106 CD34+cells/kg, respectively. For the 13 patients who engrafted, median time to absolute neutrophil count (ANC) &gt;1000 was 19 days (range 4 to 53) and median time to platelets &gt;50K was 23 days (range 14 to 90). The ANC never dropped &lt;500 for 8/13 (62%) patients, and platelets never dropped &lt;20K for 9/13 (69%) patients who engrafted. VNTR analysis of donor cell contribution showed that full donor chimerism was achieved in 8/16 patients (50%; 6 received PBSCs and 2 received CBUs), and, partial donor chimerism was achieved in 5/16 patients (31%; 3 received PBSCs and 2 received CBUs). Toxicities within 100 days post-RIT included bacteremia (n=8), candidemia (n=1), and viral infection (n=6). All infections were effectively treated and patients fully recovered. No episodes of seizure or veno-occlusive disease were experienced. No mucositis or severe nausea/vomiting was reported. No grade III/IV acute graft-versus-host disease (GVHD) or chronic GVHD was seen. Three patients died within 100 days post-RIT from causes related to primary or secondary graft failure. The overall survival was 81.0% at 2 year post-RIT (95% CI 89.5–71.5). All deceased patients received CBUs as the donor source. One of these patients were considered high-risk with pre-RIT Lansky score =30%. If this patient was excluded from analysis, the 100 day RIT related mortality was 13.3%. This retrospective analysis revealed that RIT with Flu/Bu/ATG conditioning is well tolerated in children with primary immunodeficiency. The use of CBUs, however, appeared to increase the risk of graft failure. A larger study of the use of RIT in primary immunodeficiency could further examine this hypothesis.