Donor immunization with WT1 peptide augments antileukemic activity after MHC-matched bone marrow transplantation

Abstract 1896 The curative potential of MHC-matched allogeneic bone marrow transplantation (BMT) is in part due to immunologic graft-versus-tumor (GvT) reactions mediated by donor T cells that recognize host minor histocompatibility antigens. Immunization with leukemia-associated antigens, such as Wilm's Tumor 1 (WT1) peptides, induces a T cell population that is tumor antigen specific. We determined whether BMT combined with immunotherapy using WT1 peptide vaccination of donors induced more potent anti-tumor activity when combined with allotransplantation. WT1 peptide vaccinations of healthy syngeneic or allogeneic donor mice with a 9-mer WT1 peptide (amino acids 126–134, the WT1 9-mer which has the highest binding affinity for H-2Db) and Incomplete Freund's Adjuvant induced CD8+ T cells that were specifically reactive to WT1-expressing FBL3 leukemia cells. We found that compared to vaccination with IFA alone, four weekly WT1 vaccinations induced an increased percentage of WT1-tetramer+CD8 T-cells (0.15% vs. 1%) in the peripheral blood 28 days following the first vaccination (Figure A *p Disclosures: No relevant conflicts of interest to declare.