Prevention of lethal graft‐vs.‐host disease by a single low dose injection of anti‐T cell monoclonal antibody to the allograft recipients

We investigated the capacity of monoclonal antibody (mAb) treatment to prevent graft‐vs.‐host disease (GVHD) in lethally irradiated, allogeneically reconstituted mice, employing anti‐T cell (subset) mAb and a fully allogeneic strain combination. In this strain combination, purified CD4⁺ cells were able to induce a lethal GVH reaction, whereas purified CD8⁺ cells were not. In the same strain combination, a single intraperitoneal injection of IgG_2b anti‐Thy‐1 mAb, one day after reconstitution, caused a dose‐dependent improvement of the survival. A single injection of a dose as low as 12.5 μg per mouse was already effective. Intravenous and intraperitoneal administration of the mAb appeared equally effective. For effective prevention of GVHD the treatment could be postponed until the 4th day after transplantation, but treatment delayed until day 6 was no longer effective. Treatment with IgG_2b mAb specific for either helper or cytotoxic T cells also led to improvement of GVHD and survival, but was less effective than treatment with anti‐Thy‐1 mAb. Clinically, there was a difference in the effectiveness of anti‐CD4 and anti‐CD8 treatment, since symptoms of GVHD started earlier in the anti‐CD8 treated group and the survival was better in the anti‐CD4 treated group. These results press for prospective clinical studies employing anti‐T cell mAb treatment early after allogeneic bone marrow transplantation, especially in HLA mismatched cases.