Patients with late onset of B-cell reconstitution display increased numbers of BM-infiltrating T cells associated with reduced numbers of osteoblasts. (A) Histological sections of BM trephines obtained 3 to 4 weeks after allo-HSCT were analyzed for the number of CD3⁺ T cells and osteoblasts. Graphs show representative examples for the staining of formalin-fixed sections from patients with (upper) early or (lower) late onset of B-cell reconstitution. CD3 immunostaining (brown) is shown in the left graphs and evaluation of osteoblast number and morphology on hematoxylin and eosin-stained sections is shown in the center graphs (arrows indicate osteoblasts). In the right graphs, osteoblasts are indicated with arrows on CD3 antibody-stained (brown) sections. T cells are marked with triangles. (B) The percentage of patients displaying <5% (gray), 5% to 9% (light blue), and ≥10% (dark blue) T-cell infiltration in the analyzed BM compartment is shown for patients within the (left) early and (right) late onset group. (C) The percentages of patients with only few and inactive (blue) and of patients with several and activated (gray) osteoblasts within the patient groups displaying (left) <5%, (center) 5% to 9%, or (right) ≥10% T-cell infiltration are depicted. Numbers in the pie charts indicate the percentage of patients within the respective group.