Patients with steroid-resistant GVHD display a selective and persistent increase of circulating plasmablasts. (A) Heatmap of B-cell subclusters with annotation numbers corresponding to data shown in (B-C). (B) Hierarchical stochastic neighbor embedding (HSNE) map of B-cell subclusters (left). Right panel shows the same HSNE map as depicted on the left, but subclusters are color annotated according to the patient group in which they are most prevalent. (C) Boxplots (median and interquartile range) showing frequencies of B-cell subclusters that are increased significantly or decreased in refractory patients with aGVHD (HSCT patients with steroid-refractory aGVHD nonresponsive to MSC-based second-line therapy [GVHD-NR]). GVHD-CR, HSCT patients with steroid-refractory aGVHD responsive to MSC-based second-line therapy; Healthy ctr, healthy control participants; HSCT ctr, patients who underwent HSCT without aGVHD; Steroid-CR, HSCT patients with steroid-responsive aGVHD. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001.