Clinical and immune responses of WT1-peptide vaccination in patients with acute myeloid leukemia

Abstract

2511 Background: The transcription factor Wilms tumor protein (WT) 1 belongs to a new generation of tumor antigens, as it is essential for tumor cell proliferation. WT1 is highly expressed both in myeloid leukemias and many carcinomas. This phase 2 proof-of-concept trial was initiated to determine immunogenicity and toxicity of vaccination with a novel HLA-A2-restricted WT1 peptide vaccine. Methods: Sixteen HLA-A2-positive patients with acute myeloid leukemia and one patient with myelodysplasia received 3–18 vaccinations (median 8) of WT1. 126–134 peptide (0.2 mg) together with the T helper protein keyhole limpet hemocyanin (1 mg) and in addition GM-CSF (75 mcg for four days) and. Twelve patients had elevated blast counts at study entry and 5 patients complete remission with high risk for relapse. Results: Six of 12 patients with presence of leukemic blasts had evidence of antileukemic activity. One patient achieved complete remission for 12 months. The patient with myelodysplasia RAEB II had a major response of neutrophils and platelets. Two patients had minor responses with transient clearance of peripheral blasts or improvement of hematopoiesis, and two patients achieved disease stabilization for 3 and 14 months. WT1 transcripts as molecular disease marker decreased in 5 of these 6 patients and also in 4 of 5 high-risk patients. No significant toxicity occurred. The generation of a WT1-specific T cell response in peripheral blood and bone marrow was detected in 9 of 13 patients by tetramer analysis and 8 of 13 patients by intracellular cytokine staining. Conclusion: These results show that WT1 vaccination can induce functional T cell responses associated with antileukemic activity and warrant trials of WT1 vaccination in patients at high risk of relapse and with WT1-expressing carcinomas. No significant financial relationships to disclose.