Neutralization of TGF-β attenuates GVL. (A) Leukemia development in a GVL model whereby recipients underwent transplantation with allogeneic (n = 10 per group) or allogeneic TCD (n = 3) splenocytes in conjunction with host-type P815 and control antibody or anti-TGF-β antibody, as described in “Materials and methods.” ^***P < .001; all groups. (B) Xenogen biophotonic imaging of leukemia development in allogeneic (T-cell replete) and TCD recipients after cotransplantation of a lower dose of P815 transfected with a luciferase reporter gene, as described in “Materials and methods.” All TCD recipients developed leukemia on day 11 and required humane killing regardless of whether they received anti-TGF-β or control antibody. Allogeneic recipients receiving anti-TGF-β had evidence of leukemia by day 18, as demonstrated by biophotonic imaging. No leukemia was visualized in allogeneic recipients receiving control antibody. □ indicates TCD plus control Ab; ▪, allo plus control Ab; and •, allo plus anti-TGF-β Ab.