Ex vivo immunological evaluation of stable mixed chimeric patients after matched related donor allogeneic transplantation in sickle cell disease

Favorable outcome of non-myeloablative allogeneic transplantation in adult patients with severe sickle cell disease: A single center experience of 200 patients

Allogeneic hematopoietic stem cell transplant (HSCT) for adults with severe sickle cell disease (SCD) is potentially curative but not commonly utilized therapy due to complications such as graft failure (GF) and organ toxicity. Herein, we are reporting our long-term outcome data of non-myeloablative (NMA) HSCT in adults with severe SCD with emphasis on factors predicting event free survival (EFS). Adults with severe SCD undergoing NMA match-related donor allogeneic HSCT from 2015 to 2021 with at least 12 months of follow-up were included. A total of 200 patients were included with a median age of 26 years (14-43) and 56% were male. The median infused CD34 dose was 13.7 (5.07-25.8), respectively. Median absolute neutrophil count engraftment was 19 (13-39) days with 51% of patients receiving GCSF to expedite recovery. A total of 17 patients experienced GF; 3 as primary and 14 as secondary within a median time of 204 days (40-905). A 76% successfully discontinued sirolimus at the last follow-up. Median follow-up for the cohort is 29.2 (2.1-71.4) months. Estimated 3-year EFS and OS were 88.2% (81.9-92.5) and 94.6% (89.2-97.3). At multivariable analysis, minor ABC incompatibility hazard ratio (HR) 4 (1.3-12.1; 0.014) and allo-antibody against non-ABO donor antigens HR 4.3 (1.3-14.1; 0.016) were significant for EFS. No clonal evolution or myeloid malignancies were seen. This largest single-center report of NMA HSCT in adults with severe SCD further delineated its feasibility, potential toxicities, and fertility outcomes. GF remains a major impediment and appears dependent on ABO matching and non-ABO antibodies.

Non-myeloablative human leukocyte antigen-matched related donor transplantation in sickle cell disease: outcomes from three independent centres

Non-myeloablative haematopoietic progenitor cell transplantation (HPCT) from matched related donors (MRD) has been increasingly utilized in sickle cell disease (SCD). A total of 122 patients received 300 cGy of total body irradiation (TBI), alemtuzumab, unmanipulated filgrastim-mobilized peripheral blood HPC and sirolimus. The median follow-up was four years; median age at HPCT was 29 years. Median neutrophil and platelet engraftment occurred on day 22 and 19 respectively; 41 patients required no platelet transfusions. Overall and sickle-free survival at one and five years were 93% and 85% respectively. Age, sex, pre-HPCT sickle complications, ferritin and infused HPC numbers were similar between graft failure and engrafted patients. Mean donor myeloid chimaerism at one and five years post HPCT were 84% and 88%, and CD3 was 48% and 53% respectively. Two patients developed grade 1 and 2 skin graft-versus-host disease (GVHD) with no chronic GVHD. Median days of recipients taking immunosuppression were 489; 83% of engrafted patients have discontinued immunosuppression. Haemoglobin, haemolytic parameters and hepatic iron levels improved post HPCT. Pulmonary function testing, hepatic histology and neurovascular imaging remained stable, suggesting cessation of further sickle-related injury. Fourteen patients had children. In this largest group of adult SCD patients, this regimen was highly efficacious, well-tolerated despite compromised organ functions pre HPCT, and without clinically significant GVHD.