INHIBITION OF THE GRAFT-VERSUS-HOST REACTION: I. Reduction of the Graft-Versus-Host Potential of Mouse Spleen Cells (with a Sparing of Stem Cells) by Treatment with Antilymphocyte Globulin-Derived Fab Fragments

Abstract

Injection of parental strain spleen cells into 8-day-old hybrid mice produced splenomegaly associated with graft-versus-host (GVH) reaction. The GVH reactivity of parental spleen cells was prevented by pretreatment of the cells with antilymphocyte globulin (ALG). This treatment, however, rendered lymphoid cells nonviable and destroyed colony-forming hemopoietic stem cells. Papain digestion of ALG results in the formation of Fab fragments which retain immunological specificity but are no longer cytotoxic. These Fab fragments of ALG significantly inhibited the ability of parental strain spleen cells to produce splenomegaly in F1 hybrid recipients, but unlike ALG did not destroy the hemopoietic colony-forming stem cells of normal bone marrow and had no cytotoxic effect on lymphoid cells. Thus, noncytotoxie fragments of papain-digested ALG are capable of reducing the GVH reactivity of allogeneic parental spleen cells.