In vitro and in vivo analysis of bone marrow-derived CD3+, CD4-, CD8-, NK1.1+ cell lines.

The development of methods of avoiding graft-versus-host disease (GVHD) while retaining the alloengraftment-promoting and anti-leukemic effects of allogeneic T cells is a major goal of research in bone marrow transplantation (BMT). We have recently obtained evidence suggesting that natural suppressor (NS) cells derived from T cell-depleted (TCD) syngeneic marrow can protect against GVHD while permitting alloengraftment. We have now attempted to enrich and then propagate NS cells in vitro, with the goal of obtaining an enhanced anti-GVHD effect by adoptive transfer in vivo. Two long-term cell lines were generated culturing BMC depleted of Mac1-positive cells and of Mac1-positive plus Thy1-positive cells in high concentrations of IL-2. Both cell lines showed anti-GVHD effects when administered along with a GVHD-producing inoculum, while permitting complete allogeneic reconstitution. A clone derived from Mac1-depleted BMC protected completely against a more chronic pattern of GVHD. These cell lines demonstrated suppressive activity in vitro, cytolytic activity against a broad range of natural killer (NK)-sensitive and NK-resistant targets, and a novel cell surface phenotype, with characteristics of both alpha beta-TcR-bearing T cells and of NK cells. In some respects, these cells resemble LAK cells and differ from fresh NS cells, and from the cloned NS cells derived from spleens of total lymphoid irradiation (TLI)-treated mice and neonatal mice. To our knowledge, this is the first detailed phenotypic analysis of cell lines with in vivo anti-GVHD activity. If applicability can be demonstrated in large animal models, the ability to use bone marrow as a source of such protective cell lines might also have potential utility in clinical BMT.

Interleukin 2 prevents graft-versus-host disease while preserving the graft-versus-leukemia effect of allogeneic T cells.

We have recently demonstrated that interleukin 2 (IL-2), when administered in high doses for several days beginning on the day of allogeneic bone marrow transplantation (BMT), markedly diminishes graft-versus-host disease (GVHD) mortality in lethally irradiated mice. An optimal anti-GVHD effect was attained by coadministering T-cell-depleted (TCD) syngeneic marrow. We demonstrate here that the full graft-versus-leukemia effect of allogeneic T lymphocytes is obtained even when GVHD is markedly diminished by the coadministration of IL-2 and TCD syngeneic marrow. This methodology represents an approach to the treatment of leukemia in which the beneficial effects of allogeneic T cells can be exploited while their major deleterious effect, GVHD, is avoided. These results may thus have an impact on the clinical use of BMT for the treatment of hematologic malignancies.

In vivo administration of interleukin 2 plus T cell-depleted syngeneic marrow prevents graft-versus-host disease mortality and permits alloengraftment.

Previous work from this laboratory has demonstrated that T cell-depleted (TCD) syngeneic marrow can delay, but not prevent, the mortality from acute graft-vs.-host disease (GVHD) caused by MHC-mismatched lymphoid cells administered to lethally irradiated mice. We demonstrate here that a protective effect against GVHD is also observed after in vivo treatment with IL-2. Administration of 10,000-50,000 U of IL-2 twice daily for the first 5 d after bone marrow transplantation markedly reduced the mortality from both acute and chronic GVHD induced across complete MHC barriers in lethally irradiated mice, and frequently led to long-term survival. Complete allogeneic reconstitution was demonstrated in all long-term survivors of this treatment regimen. While either IL-2 or TCD syngeneic marrow administered alone was protective in some experiments, the maximal protective effect was observed after administration of both IL-2 and TCD syngeneic marrow, especially when the effects of IL-2 were suboptimal. The timing of IL-2 administration was critical to this beneficial effect, since a delay of 7 d in commencing IL-2 treatment was associated with accelerated GVHD mortality. This new approach to the prevention of GVHD permits the administration of allogeneic T cells, and may therefore avoid the increased incidence of graft failure and loss of antileukemic effects associated with the T cell depletion of allogeneic marrow, which is otherwise required for the prevention of GVHD.

Effects of T cell depletion in radiation bone marrow chimeras. III. Characterization of allogeneic bone marrow cell populations that increase allogeneic chimerism independently of graft-vs-host disease in mixed marrow recipients.

The opposing problems of graft-vs-host disease vs failure of alloengraftment severely limit the success of allogeneic bone marrow transplantation as a therapeutic modality. We have recently used a murine bone marrow transplantation model involving reconstitution of lethally irradiated mice with mixtures of allogeneic and syngeneic marrow to demonstrate that an allogeneic bone marrow subpopulation, removed by T cell depletion with rabbit anti-mouse brain serum and complement (RAMB/C), is capable of increasing levels of allogeneic chimerism. This effect was observed in an F1 into parent genetic combination lacking the potential for graft-vs-host disease, and radiation protection studies suggested that it was not due to depletion of stem cells by RAMB/C. We have now attempted to characterize the cell population responsible for increasing allogeneic chimerism in this model. The results indicate that neither mature T cells nor NK cells are responsible for this activity. However, an assay involving mixed marrow reconstitution in an Ly-5 congenic strain combination was found to be more sensitive to small degrees of stem cell depletion than radiation protection assays using three-fold titrations of bone marrow cells. Using this assay, we were able to detect some degree of stem cell depletion by treatment with RAMB/C, but not with anti-T cell mAb. Nevertheless, if the effects of alloresistance observed in this model are considered, the degree of stem cell depletion detected by such mixing studies in insufficient to account for the effects of RAMB/C depletion on levels of allogeneic chimerism, suggesting that another cell population with this property remains to be identified.