CD4+ Peptide Epitopes from the WT1 Oncoprotein Stimulate CD4+ and CD8+ T Cells That Recognize and Kill Leukemia and Solid Tumor Cells.

Wilms tumor protein 1 (WT1) is a transcription factor over-expressed in several types of leukemias and solid tumors, making it an ideal target for immunotherapy. A number of class I binding WT1 peptides have been identified and shown to stimulate CD8+ T cells. These peptides are being tested as potential cancer vaccine candidates in a variety of clinical trials. However, the induction and maintenance of a robust memory CD8+ cytotoxic T cell response requires CD4+ T cell help. Herein we report the identification of three HLA Class II peptide epitopes of WT1 using the SYFPEITHI and RANKPEP predictive algorithms. Peptides 328–349 and 423–441 are able to stimulate a peptide specific CD4+ response that can recognize WT1 positive tumor cells in multiple HLA-DRB*1 settings, as determined by IFN-gamma ELISPOT assays. Due to the highly polymorphic nature of the HLA class II alleles, such broad reactivity is critical in the development of a universal therapeutic. In addition, we identified a WT1 CD4+ peptide epitope (122–140) that lies within close proximity to a previously identified CD8+ peptide epitope (126–134). Residue 126 was mutated from an Arginine (R) to a Tyrosine (Y) thereby embedding a synthetic immunogenic analog CD8+ peptide that was previously designed to improve immunogenicity and induce a potent CD8+ response. Mutated peptide 122–140 is able to induce a CD4+ and cytotoxic CD8+ WT1 specific T cell response that can recognize the native WT1 epitopes on the surface of human CML and solid tumor cells. Cross-priming experiments demonstrated that APCs pulsed with either CML or mesothelioma tumor lysates can process and present each of the CD4+ peptides identified. These studies provide the rationale for using the three WT1 CD4+ peptides in conjunction with CD8+ peptide epitopes to vaccinate patients with WT1 expressing cancers.