Utility of transplant conditioning intensity score in allogeneic haematopoietic stem cell transplantation for genetic disorders

In allogeneic haematopoietic stem cell transplantation (allo-HSCT) for genetic disorders (GDs), predicting outcomes using the currently used myeloablative/reduced-intensity conditioning classification is challenging. We examined the utility of the transplant conditioning intensity (TCI) score in allo-HSCT for GDs. We retrospectively analysed 1077 patients who underwent first allo-HSCT for GDs between 1987 and 2018. While no significant difference was observed in 3-year non-relapse mortality (NRM) between the myeloablative and reduced-intensity conditioning group, 3-year NRM in the TCI score ≥4.0 (TCI-high) group (17.3%) was higher than that in the TCI score 0.5-3.5 (TCI-low/intermediate) group (11.6%, p = 0.013). Multivariate analysis identified a high TCI score as a significant factor for NRM (HR 1.56, p = 0.011). Infection-related mortalities were more prevalent in the TCI-high group (7.9%) compared with the TCI-low/intermediate group (3.2%). In contrast, patients in the TCI-high group achieved a significantly higher rate of complete donor chimerism (71.7%) than those in the TCI-low/intermediate group (62.2%, p = 0.022). TCI score is a valuable tool for predicting outcomes after allo-HSCT for GDs as well as for guiding the selection of conditioning regimens tailored to the unique characteristics of GDs.