TofBs inhibit priming of T cells during immune responses in vivo. (A-C) In a hapten hypersensitivity assay, Balb/C mice were sensitized against DNFB by epicutaneous application on the back. Ears were challenged with DNFB 5 days later and ear swelling was measured 48 hours after challenge. T cells primed by different APCs loaded with T-cell antigen–specific, hapten-unrelated, peptide (pOVA) were intravenously applied at different time points to modulate ear swelling. Ear swelling response is expressed as the difference (μm, mean ± SD) between the thickness of the challenged ear and the vehicle-treated ear. *, P less than.05; ***, P less than .005 versus positive control. (A) Adoptive transfer of primed TofDCs, and TofBs at 24 hours before challenge. Transferred cells were unable to modulate the ear swelling induced by the challenge. (B) In contrast, when T cells were transferred before priming (at d −1), a specific inhibitory effect of TofBs could be seen. The transfer of TofBs but not of TofDCs resulted in a decreased immune response post challenge. (C) TofBs are functioning at 10 days after transfer yet require specific antigen restimulation. The suppressive effect shown after transfer at d −1 (as in panel B) is lost when cells were transferred already at d −10 before priming. However, when hapten priming and specific antigen restimulation (pOVA) occurred together, TofBs were rescued to suppress. In contrast, the application of an unspecific control antigen (pHA; Hemagglutinin peptide) had no effect. (D) In ectopic allogeneic heart transplantation in the mouse model, TofBs effectively inhibit organ rejection. At d −1 before ectopic transplantation of C57BL/6 donor hearts, Balb/c recipients of the treatment group were injected with TofBs, while the control group received only a saline injection. No other immunosuppressive treatment was administered. Graft function was assessed by daily palpation. Rejection was defined as the lack of palpable cardiac contraction. **, P less than.01 vs. control group.