Depletion of Naïve Lymphocytes with Fas Ligand Ex Vivo Prevents Graft-versus-Host Disease without Impairing T Cell Support of Engraftment or Graft-versus-Tumor Activity

Graft-versus-host disease (GVHD) can be prevented by Fas-mediated selective depletion of host-sensitized donor lymphocytes ex vivo. We tested the hypothesis that Fas-mediated depletion of lymphocytes in the absence of host-specific antigenic stimulation can alleviate GVHD. Brief exposure (24 hours) of unstimulated donor lymphocytes to Fas ligand (FasL) ex vivo results in balanced apoptosis of CD8+ and CD4+ subsets with preferential depletion of CD62L and CD69, increased T regulatory fractions, and sustained responses to stimulation. This procedure ameliorates weight loss and improves the clinical and histologic score of skin and gastrointestinal GVHD with and without concurrent transplantation of hematopoietic progenitors and irrespective of conditioning-induced tissue injury. Although FasL-resistant donor T cells are less potent effectors of GVHD, they facilitate hematopoietic progenitor engraftment when infused with or after the graft and retain the potential to elaborate graft-versus-tumor reactions. These findings in a preclinical model together with the known trophic effects of FasL on primitive hematopoietic progenitors suggest that brief ex vivo incubation of hematopoietic grafts with FasL may improve the outcome and safety of clinical T cell–replete allogeneic and haploidentical transplants.