Transplantation of low-dose of splenic T cells from anti-DR3–pretreated donors protected osteoblasts and partially rescued impaired BM B-cell development in cGVHD. B10.BR mice were transplanted with BM only or BM and T cells from B6 donor mice injected with either anti-DR3 mAb (4C12, 0.5 mg/kg) or isotype control IgG (NTK888) 3 days prior to the procedure. (A) Representative flow cytometry plots demonstrating frequency of donor-derived CLP cells in Lin⁻c-Kit^intSca-1^int and total number of donor-derived CLP cells. Combined data from 2 independent experiments are shown. *P < .05, **P < .01 (Mann-Whitney U test); n = 6 in each group. (B) Representative flow cytometry plots demonstrating frequency of pre-pro–B, pro-B, pre-B, and immature B cells in the BM (numbers indicates frequency of parental gate). (C-D) Frequency of total BM (C) and total number (D) of donor-derived pre-pro–B (B220⁺CD43⁺CD19⁻IgM⁻), pro B (B220⁺CD43⁺CD19⁺IgM⁻), pre B (B220⁺CD43⁻CD19⁺IgM⁻) and immature B cells (B220⁺CD43⁻CD19⁺IgM⁺) isolated from BM of transplanted mice. Combined data from 4 independent experiments are shown. *P < .05; **P < .01 (Mann-Whitney U test); n = 18 and n = 24 for BM plus T cells (iso) and BM plus T cells (anti-DR3), respectively. (E) Frequency of osteoblast isolated from tibiae and femurs (percentage of Ter119⁻CD31⁻CD51⁺cells in the CD45⁻ gate). Combined data from 2 independent experiments are shown. Mann-Whitney U test; n = 8 for BM only and BM plus T cells, and n = 6 for BM plus T cells (anti-DR3). (F-G) Frequency of infiltrating donor-derived CD4⁺ T cells (F) and CD4⁺CD25⁺FoxP3^GFP+ T_regs (G) in the BM. The BM-only group was not included in this analysis due to lack donor-derived FoxP3-GFP–expressing T_regs. Combined data from 3 independent experiments are shown. Mann-Whitney U test; n = 10 for all groups. Bars represent standard error of the mean.