In vitro stimulation with WT1 peptide-loaded Epstein-Barr virus-positive B cells elicits high frequencies of WT1 peptide-specific T cells with in vitro and in vivo tumoricidal activity

The Wilms tumor protein (WT1) is overexpressed in most acute and chronic leukemias. To develop a practicable, clinically applicable approach for generation of WT1-speciric T cells and to comparatively evaluate the immunogenicity of WT1 in normal individuals, we sensitized T cells from 13 HLA-AO201(+) and 5 HLA-A2402(+) donors with autologous EBV-transformed B cells or cytokine-activated monocytes, loaded with the HLA-A0201-binding WT1 peptides (126-134)RMFPNAPYL or (187-195)SLGEQQYSV or a newly identified HLA-A2402-binding WT1 peptide (301-310)RVPGVAPTL. WT1-specific T cells were regularly generated from each donor. T cells sensitized with peptide-loaded EBV-transformed B cells generated higher numbers of WT1-specific T cells than peptide-loaded cytokine-activated monocytes. Contrary to expectations, the frequencies of WT1 peptide-specific T cells were equivalent to those generated against individual highly immunogenic HLA-A0201-binding EBV peptides. Each of these T-cell lines specifically killed WT1(+) leukemias and solid tumors in an HLA-restricted manner but did not lyse autologous or HLA-matched normal CD34(+) hematopoietic progenitor cells or reduce their yield of colony-forming unit-granulocytemacrophage (CFU-GM), burst-forming unit erythroid (BFU-E), or mixed colonies (CFU-mix). Furthermore, WT1 peptide-specific T cells after adoptive transfer into nonobese diabetic-severe combined immunodeficient mice bearing subcutaneous xenografts of WT1(+) and WT1(-) HLA-A0201(+) leukemias preferentially accumulated in and induced regressions of WT1(+) leukemias that expressed the restricting HLA allele. Such cells are clinically applicable and may prove useful for adoptive cell therapy of WT1(+) malignant diseases in humans.