Transcriptomic profile and endothelial changes during differentiation syndrome in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is curable with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), but differentiation syndrome (DS) remains a potentially life-threatening complication, with poorly understood pathogenesis. We investigated clinical, molecular and functional determinants of DS in APL. Two independent cohorts of APL patients were analyzed, including a real-life series (n = 34) and a cohort from the APL0406 trial (n = 18). Baseline and sequential RNA sequencing, and cytokine profiling were performed on PB samples. In vitro assays on human pulmonary microvascular endothelial cells were also performed (HPMECs). DS occurred in 47% of patients included in this study. Red blood cell (RBC) transfusion burden during induction phase was significantly associated with DS occurrence (median 9 vs 3 RBC units, p = 0.002), and retained independent significance in multivariable analysis. Cytokine profiling showed increased IL-6 levels, with a trend towards higher levels at DS onset. Transcriptomic analysis identified 93 differentially expressed genes in patients who developed DS (DS +), with enrichment of pathways related to hematopoietic stem cell differentiation and erythroid maturation. Functionally, ATRA/ATO treatment induced marked morphological changes and increased permeability in HPMECs, consistent with a capillary leak phenotype, which was significantly attenuated by dexamethasone. Our findings support a model in which erythroid dysregulation and endothelial dysfunction contribute to DS pathogenesis, together with an inflammatory environment. RBC transfusion burden may represent an early and accessible biomarker to identify patients at higher risk, with potential implications for risk stratification and early therapeutic intervention.