Single-cell sequencing on PBMCs from patients with HA and HB with inhibitors reveals different immune responses to FVIII and FIX.

Inhibitors are the most severe complication of replacement therapy in patients with hemophilia. Previous studies, along with our clinical observations, have identified distinct incidence rates and clinical manifestations of factor VIII (FVIII) and FIX inhibitors in patients with severe hemophilia A (HA) and HB. To explore different immune responses to FVIII and FIX in patients with HA and HB and elucidate the mechanisms underlying the varying clinical manifestations of these patients, we performed single-cell sequencing on peripheral blood mononuclear cells (PBMCs) collected from 5 patients with HA and 5 with HB with inhibitors. After quality control, a total of 75 051 cells were clustered into 19 subsets. Transcriptome analysis revealed differences in the composition of lymphocyte subsets and the functional status of immune cells between the HA and HB groups. Additionally, immune repertoire analysis indicated variations in the diversity of B- and T-cell clones between the 2 groups. HA group exhibited a relatively higher proportion of B cells and more active B cells, whereas HB group demonstrated a higher proportion of T cells, with more active CD4+ T helper cells. Our study provides insights into the distinct biological processes underlying the distinct immune responses to therapeutic FVIII and FIX in patients with HA and HB, as revealed through single-cell sequencing of PBMCs from patients with hemophilia with inhibitors. The data generated will serve as a valuable resource for future research on how the immune system recognizes and initiates responses to antigens with varying molecular characteristics.