TGF-β neutralization augments donor T-cell proliferation and expansion to host antigens late after SCT. (A) Lethally irradiated B6D2F1 recipients underwent transplantation with G-CSF-treated B6 splenocytes and received anti-TGF-β (n = 5) or control antibody (n = 5) on day 0 and then 3 times weekly. On day+14, splenocytes from transplant recipients were pooled within the treatment group (numbers of CD3⁺ cells were equilibrated between the groups based on the CD3 staining of the input cells) and were stimulated with irradiated B6D2F1 peritoneal macrophages. Proliferation was measured at 48 hours by standard [³H]-thymidine incorporation assay, as described in “Materials and methods.” □ indicates allogeneic plus anti-TGF-β antibody; ○, allogeneic plus control antibody. Proliferation of nonstimulated splenocytes was 1157 ± 43.32 cpm and 1197 ± 90.39 cpm (allo plus anti-TGF-β antibody and allo plus control antibody, respectively). Results from one of 2 identical experiments. (B) Recipients received anti-TGF-β (□, n = 5-9) or control antibody (▪, n = 5-10), as in panel A. The absolute numbers of lineage and donor (H2b^pos/H2d^neg) cells were determined per spleen (× 10⁶) 14 days after SCT. ^*P < .05; anti-TGF-β compared with control antibody. Pooled data from 2 experiments, expressed as mean ± SE. (C) B6D2F1 recipients underwent transplantation with G-CSF-treated donor B6 or B6D2F1 splenocytes and received anti-TGF-β (□, n = 5) or control antibody (▪, n = 5), as described in “Materials and methods.” Syngeneic recipients (, n = 4) received control antibody. IFN-γ and TNF-α were determined in the sera of animals 5 and 14 days, respectively, after SCT by enzyme-linked immunosorbent assay (ELISA). GI tract abnormalities were determined 14 days after transplantation by semiquantitative histologic examination, as described in “Materials and methods.” Data are presented as mean ± SE.