Neutrophil granule proteins as targets of leukemia-specific immune responses

Purpose of review. Recent progress in the identification of leukemia antigens has stimulated the development of vaccines to treat hematological malignancies. Here we review the identification and characterization of the myeloid leukemia-specific antigens proteinase 3 and neutrophil elastase found in the primary (azurophil) granule proteins of granulocytes and their precursors. A peptide 'PR1' derived from these proteins induces powerful HLA-A0201 restricted CD8 T-cell proliferation. PR1-specific T cells are cytotoxic to leukemia and myelodysplastic syndrome progenitors, and occur at low frequencies in normal individuals, Frequencies are higher in patients with myeloid leukemias, and highest in patients with chronic myeloid leukemia entering molecular remission after allogeneic stem cell transplantation. Recent findings. These observations, together with the known association of autoimmunity to proteinase 3 and neutrophil elastase in Wegener's granulomatosis, support the concept that there is a natural immunity to primary granule proteins which can be boosted to enhance immunity to leukemia. Preliminary reports indicate that PR1 peptide vaccination induces significant increases in PR1-specific cytotoxic T cells with rapid and durable remissions in some patients with advanced myeloid leukemias. Summary. These promising developments in antileukemia vaccines have stimulated research to optimize vaccine delivery and modify regulation of natural T-cell immunity to primary granule proteins to improve treatment of otherwise refractory myeloid leukemias and myelodysplastic syndrome.