Splenomegaly May Increase the Risk of Rejection in Low-Risk Matched Related Donor Transplant for Thalassemia, This Risk Can Be Partially Overcome by Additional Immunosuppression during Conditioning

Severe thalassemia syndromes (ST) are highly curable by bone marrow transplant (BMT), but rejection may still occur. We retrospectively analyzed our fully matched related donor transplants to establish if isolated splenomegaly is an independent risk factor for rejection and if this risk can be reduced by modifying the conditioning protocol. In this study, we compared rejection rates between patients with and without splenomegaly in 189 consecutive low-risk ST transplants across 2 sequential conditioning regimens: regimen A (August 2013 to December 2016): busulfan (14 mg/kg oral, not adjusted to serum levels), cyclophosphamide (200 mg/kg), and anti-thymocyte globulin (ATG) (Genzyme (Sanofi, Paris, France) 4 mg/kg or Fresenius (Grafalon, Neovii Biotech GmbH, Gräfelfing Germany) 16 mg/kg on days –12 to –10), and regimen B: same backbone as regimen A except fludarabine total dose of 150 mg was added upfront and ATG dose was increased to 7 mg/kg in case of splenomegaly and/or sex-mismatched transplants (January 2017 to September 2018). Compared with regimen A, in regimen B, both overall rejection rates (RRs) (16% versus 6.5%, P = .023) and treatment-related mortality (TRM) (9.9% versus 2.8%, P = .038) improved significantly. By Cox regression analysis, the improvement in RR between the 2 protocols was particularly significant in patients with splenomegaly (RR 54.5% versus 6.5%, P = .00015; TRM 18.2% versus 6.5%, P = .25) (hazard ratio, 4.13; confidence interval, 1.61 to 10.6; P = .003). The increased risk of rejection related to splenomegaly can be overcome by adding fludarabine to the standard ATG-Busulfan- Cyclophosphamide (ATG-Bu-Cy) protocol without significantly increasing transplant-related morbidity and mortality or resorting to splenectomy pre-BMT.