Flow cytometric gating algorithm demonstrating circulating B-cell subpopulations in patients with cGVHD. Whole blood was analyzed by multicolor flow cytometry, and CD19⁺ B cells were further stained in various combinations for CD21, CD27, CD38, CD10, IgM, and IgD. Immature, transitional, naive, non–class-switched and class-switched memory B cells were enumerated, which were different between healthy donors and patients with cGVHD.