Suppression of graft-versus-host reactivity by a single host-specific blood transfusion to prospective donors of hemopoietic cells

Delayed-type hypersensitivity responses against recipient’s histocompatibility antigens can occur early in the course of a graft-versus-host reaction in lethally irradiated allogeneically reconstituted mice. This reactivity could be suppressed by a single host-specific blood transfusion to the prospective donors of allogeneic spleen cells. Maximum suppression was found when the blood transfusion was given 4 or 5 days before the mice were used to reconstitute lethally irradiated hosts. Whole blood and purified white blood cells were capable of inducing suppression, whereas purified red blood cells, plasma, and serum were not. Suppression was already detectable after administration of 1 µ1 of whole blood and virtually complete at a dose of 1.0 ml. Irradiation of the blood reduced but did not abrogate its capacity to induce suppression. Purified B and purified T lymphocytes appeared equally effective in inducing suppression. Two helper T cell clones, a Thl and a Th2 clone, were able to induce suppression as well. A high dose of recombinant IL-2, injected daily for 5 days after reconstitution, did not abrogate or reduce the suppression. Suppression could be induced by H-2 as well as non-H-2 alloantigens, separately or together. A pure H- 2-incompatible transfusion was more effective in inducing suppression than a pure non-H-2-incompatible one. Suppression appeared to be a dominant phenomenon and was mediated by a Thy-1⁺, CD4⁺, CD8⁻ spleen cell population. This T cell population had its origin in the transfused donor, which excludes the possible involvement of blood-derived “veto-cells.”.