Flt-3L expansion of recipient CD8{alpha}+ dendritic cells deletes alloreactive donor T cells and represents an alternative to post-transplant cyclophosphamide for the prevention of GVHD

Purpose: Allogeneic bone marrow transplantation (BMT) provides curative therapy for leukemia via immunological graft-versus-leukemia (GVL) effects. In practice, this must be balanced against life threatening pathology induced by graft-versus-host disease (GVHD). Recipient dendritic cells (DC) are thought to be important in the induction of GVL and GVHD. Experimental Design: We have utilized preclinical models of allogeneic BMT to dissect the role and modulation of recipient DC in controlling donor T cell mediated GVHD and GVL. Results: We demonstrate that recipient CD8a+ DC promote activation-induced clonal deletion of allospecific donor T cells after BMT. We compared pre-transplant fms-like tyrosine kinase-3 ligand (Flt-3L) treatment to the current clinical strategy of post-transplant cyclophosphamide (PT-Cy) therapy. Our results demonstrate superior protection from GVHD with the immunomodulatory Flt-3L approach, and similar attenuation of GVL responses with both strategies. Strikingly, Flt-3L treatment permitted maintenance of the donor polyclonal T cell pool, where PT-Cy did not. Conclusions: These data highlight pre-transplant Flt-3L therapy as a potent new therapeutic strategy to delete alloreactive T cells and prevent GVHD, which appears particularly well suited to haploidentical BMT where the control of infection and the prevention of GVHD are paramount.

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