Graft-versus-host (GVH) disease can result in a beneficial graft-versus leukemia (GVL) effect after bone marrow transplantation in patients with malignant disease. In this report, we used bacteria-free AKR (H-2k) mice bearing advanced spontaneous T cell leukemia/lymphoma as a moel to evaluate the GVH and GVL effects of bone marrow transplantation using fully incompatible SJL (H-2k) donors. A therapeutic GVL effec, accompanied by increased leukemia-free survival, was obtained only when 0.5x106 allogeneic lymphocytes (lymph node cells) were added to the marrow inoculum. Transplantation of allogeneic bone marrow without added lymph node cells (or use of syngeneic cells) resulted in a significant increase in leukemia relapse; increasing the dose of allogeneic lymph node cells to 2.0x106 resulted in significantly higher GVH-associated mortality. Survival and therapeutic benefits were obtained only when the intensity of the GVH reaction was carefully controlled by manipulation of alloreactive lymphocytes present in the marrow. These results suggest, indirectly, that T cell depletion may abolish any GVL effect of marrow transplantation, even if the donor is mismatched with the host at the major histocompatibility complex.
The frequency in the spleen of cytotoxic T lymphocytes (CTL) reactive against host alloantigens was estimated using limiting-dilution microcytotoxicity assays at various times after transplantation of allogeneic bone marrow with and without added lymph node cells. The average frequency of CTL was highest in mice that were given marrow plus lymph node cells and tested within the first four weeks after transplantation. The level of CTL activity measured in vitro was dependent on the dose of lymphocytes injected and correlated with both the GVL and GVH effects in vivo. Down-regulation of CTL activity against host, but not third-party, alloantigens in vitro was observed under limiting dilution assay conditions, leading to the suggestion that host-specific regulatory cells may be present in these allogeneic bone marrow chimeras.