T-cell responses directed against multiple HLA-A*0201-restricted epitopes derived from Wilms' tumor 1 protein in patients with leukemia and healthy donors: Identification, quantification, and characterization

University of Oxford, Oxford, England, United Kingdom
Clinical Cancer Research (Impact Factor: 8.19). 01/2006; 11(24 Pt 1):8799-807. DOI: 10.1158/1078-0432.CCR-05-1314
Source: PubMed

ABSTRACT Antigens derived from the Wilms' tumor (WT1) protein, which is overexpressed in leukemias, are attractive targets for immunotherapy. Four HLA-A*0201-restricted WT1-derived epitopes have been identified: WT37, WT126, WT187, and WT235. We determined the natural immunogenecity of these antigens in patients with hematologic malignancies and healthy donor.
To detect very low frequencies of WT1-specific CD8+ T cells, we used quantitative reverse transcription-PCR to measure IFN-gamma mRNA production by WT1 peptide-pulsed CD8+ T cells from 12 healthy donors, 8 patients with chronic myelogenous leukemia, 6 patients with acute myelogenous leukemia, and 8 patients with acute lymphoblastic leukemia.
Responses were detected in 5 of 8 chronic myelogenous leukemia patients, 4 of 6 patients with acute myelogenous leukemia, and 7 of 12 healthy donors. No responses were detected in patients with acute lymphoblastic leukemia. The magnitude and extent of these CD8+ T-cell responses was greater in patients with myeloid leukemias than in healthy donors. Clonotypic analysis of WT1-specific CD8+ T cells directly ex vivo in one case showed that this naturally occurring population was oligoclonal. Using fluorescent peptide-MHC class I tetramers incorporating mutations in the alpha3 domain (D227K/T228A) that abrogate binding to the CD8 coreceptor, we were able to confirm the presence of high-avidity T-cell clones within the antigen-specific repertoire.
The natural occurrence of high-avidity WT1-specific CD8+ T cells in the periphery could facilitate vaccination strategies to expand immune responses against myeloid leukemias.

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    • "Although WT1 is expressed in normal tissues during embryogenesis, immunological tolerance to WT1 is not complete: WT1-specific CTLs have been detected and expanded following exposure to the peptide both in healthy donors (Rezvani et al, 2003) and in patients with AML (Scheibenbogen et al, 2002). Recent studies have shown immune and clinical responses with peptide vaccinations against single epitopes of WT1 (Oka et al, 2004; Keilholz et al, 2009); however, naturally occurring CD8 + T cell responses against myeloid leukaemias target multiple epitopes , potentially enhancing the strength and diversity of these responses (Gannag e et al, 2005; Rezvani et al, 2005). We have identified two distinct peptide epitopes of WT1 that are presented by HLA-A0201 (A2) and function as targets for leukaemia-reactive CD8 + CTL: pWT126 and pWT235 (Bellantuono et al, 2002). "
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    • "As at least one study has shown clonal diversity in the CD8+ T cell response to WT1 126 antigen (Rezvani et al., 2005), the structural differences observed here suggest caution in the use of the R1Y variant of the WT1 126 antigen as a therapeutic vaccine. Expanded studies are likely to reveal differences in TCR binding properties and thus the sets of T cells that respond to the two peptides. "
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