Background and Importance Allogeneic haematopoietic stem cell transplantation (allo-HCT) is the only curative therapy in patients with sickle cell disease (SCD). Conditioning regimens traditionally were busulfan based. Treosulfan shows advantages such as intense immunosuppressive activity, low extramedullary toxicity and linear pharmacokinetics that decreases variability.

Aim and Objectives To evaluate safety and potential complications associated to allo-HCT after treosulfan-based conditioning regimen in children with SCD.

Material and Methods Retrospective, observational, unicentric study. Inclusion criteria comprised paediatric patients diagnosed with SCD who had undergone allo-HCT at a tertiary hospital between April 2015 and September 2022. Conditioning regimen included thiotepa, treosulfan, fuldarabine and anti-thymocyte globulin. Variables: gender, age, age of diagnosis, age of allo-HCT, type of HCT, graft versus host disease (GvHD) prophylaxis, seizure prophylaxis, veno-occlusive disease (VOD) prophylaxis, cumulative incidence of GvHD, non-haematological toxicity (potentially associated to conditioning regimen) during the first 30 days after HCT, graft failure, peripheral blood chimerism data collected and death related to HCT. Disease-free survival and overall survival after HCT were also measured.

Results 31 patients were included in the study (17 female, 14 male). Median age of diagnostics was 2 months (2–120) and median age of allo-HCT was 64 months (25–154). Median time between diagnostic and HCT was 4 years (1.9–12.5). Transplantation was the first for all children except for one (graft failure after a previous allo-TPH). All donors were human leucocyte antigen (HLA)-matched siblings. Double-therapy immunosuppression was used in GvHD prophylaxis (21/31 cyclosporine with mycophenolate mofetil and 10/31 tacrolimus with mycophenolate mofetil). All received levetiracetam and ursodeoxycholic acid for seizure and VOD prophylaxis, respectively.11/31 developed cutaneous GvHD (10 grade I-II and 1 grade III-IV) and 2/31 grade I-II hepatic GvHD. 4/31 developed grade I-II mucositis and 4/31 grade III-IV mucositis. 3/31 cases of mild diarrhoea, 5/31 neurological toxicities (seizures and encephalopathy) and 1/31 case of hepatomegaly (not associated to VOD) were registered. All resolved adequately. 25/31 children showed complete chimerism in peripheral blood at the end of follow-up. Immunosuppression was enhanced in case of mixed chimerism .There were no graft failures. All children are alive and remain disease-free after median follow-up of 47 months (12–78).

Conclusion and Relevance Treosulfan-based conditioning shows clinically manageable toxicity profile and low morbidity and mortality.

Conflict of Interest No conflict of interest