Spleen Cells from Antithymocyte Serum Pretreated Mice Do Not Induce GVHD but Exert Increased Repopulating Activity in Irradiated Semiallogeneic Recipients

Graft-versus-host disease (GVHD) due to allogeneic bone marrow transplantation can be prevented by depleting the T cells from the marrow graft in vitro . However, the elimination of the donor T cells results in a higher frequency of graft failure, secondary infections and, in case of leukaemia, relapse. We found, that, in contrast to normal spleen cells, spleen cells from A or B10 donor mice pretreated with xenogeneic antithymocyte serum (ATS) in vivo did not induce GVHD in non-irradiated (B10 x A)F₁ hybrids. Spleen cells of ATS-pretreated A donors did not cause GVHD in allogeneic CBA mice made neonataily tolerant to the A donor strain either. Furthermore, spleen cells from ATS-treated donors did not cause GVHD in irradiated F₁ hybrid recipients, moreover, they decreased the lethal effect of irradiation. The in vivo ATS pretreatment improved the repopulating capacity of spleen cells in irradiated syngeneic recipients, too. The effect of the ATS treatment does not rely solely upon the elimination of T cells, since flow cytofluorometric analysis revealed only a partial depletion of both the CD4₊ and CD8₊ T cells of the ATS-pretreated animals. These observations may also have clinical relevance.