Immature dendritic cells (DCs) are deficient in surface co-stimulatory molecules and have been shown to exhibit a 'tolerogenic' potential. We investigated the allostimulatory activity of immature DCs in one-way mixed leukocyte reactions and their capacity to inhibit anti-donor cytolytic activity in the sponge matrix allograft model. Immature DCs (CD80 and CD86 deficient) were derived from bone marrow cells propagated in GM-CSF and TGF-beta1. Mature DCs (CD80+ and CD86+) were derived from bone marrow cells propagated in GM-CSF and IL-4. Either 2 x 10(6) DBA/2J (DBA, H-2d) immature DCs or 2 x 10(6) mature DCs were injected intravenously into C57BL/6J (B6, H-2b) mice 7 days prior to sponge matrix allograft implantation. On day 12, the sponge was harvested and the graft-infiltrating cells were tested in vitro for cytotoxic T lymphocyte (CTL) activity. Immature dendritic cell (DC) infused significantly and markedly inhibited intra-graft CTL activity compared to mature DCs and syngeneic bone marrow control cells. The administration of immature DCs directly into the sponge allograft failed to induce hyporeactivity. Thus, the only systemic infusion of immature donor DCs was able to recapitulate the donor-specific transfusion effect, and the capacity of donor bone marrow cells to induce donor-specific hyporeactivity in the sponge allograft model.