HLA-A*0201 Restricted Killing Activity of WT1-Specific CTL Generated From the Peripheral Blood Lymphocytes of Normal Healthy Donors.

Abstract 3026

Poster Board II-1002

The Wilms' tumor antigen (WT1) is over-expressed on several human leukemia and solid tumors, and thus is considered as a potential target for cancer immunotherapy. Combating leukemia by targeting WT1 expressing leukemic cells using in vitro generated WT1-specific CTL is one potential approach, but it is difficult to generate an immune response against WT1 due to low T cell precursor frequency in normal healthy individuals. Earlier studies have shown the generation of WT1-A*0201 peptide specific CTL from CD8⁺ T cells by cloning. Another study reported the production of IFN- γ by WT-1 specific CD8⁺ T cells. However, the cytolytic killing ability of these IFN- γ producing cells was not further characterized. Here, we demonstrate the generation of WT1-A*0201 specific CTL from the peripheral blood lymphocytes (PBL) of normal healthy donors using CD137 selection. The PBL were stimulated once with RMFPNAPYL (WT1-A*0201 peptide) pulsed autologous dendritic cells and twice with WT1-A*0201 peptide pulsed irradiated peripheral blood mononuclear cells (PBMC). Following three stimulations, the PBL were selected for CD137⁺ expression and rapidly expanded with OKT3 and IL-2. The WT1-A*0201 specific CTL showed killing of target cells and production of IFN-γ in an antigen-specific manner. The percent killing of WT1-A*0201 peptide pulsed T2 cells (TAP⁻, HLA- A2⁺) and autologous B blast (BB) were significantly higher when compared with their control targets. T2 cells and BB either pulsed with an irrelevant A*0201 peptide or un-pulsed served as the control. We have observed similar results with WT1-A*0201 specific CTL generated from normal donor CD8⁺ cells. However, the efficiency of WT1-A*0201 CTL generated from PBL to kill target cells and produce IFN- γ was higher than CTL from CD8⁺ cells. The CTL generated from PBL killed BA25, a WT1 expressing A2⁺ leukemia cell line but failed to kill Molt-4, a WT1 expressing A2⁻ cell line, clearly indicating HLA-A2 restricted CTL activity. The specificity of the generated CTL were further confirmed by staining with WT1-HLA-A*0201 tetramer. The percentage of WT1-specific CD3⁺CD8⁺Tetramer⁺ cells either remained same or higher in CTL generated from PBL when compared with those generated from CD8⁺ cells. CD137 selection leads to the generation of significant number of CTL in a shorter time when compared to conventional cloning methods. In addition, generation of WT1-A*0201 specific CTL from PBL avoids CD8⁺ selection. Currently, we are aiming to generate WT1-specific CTL using an overlapping WT1 peptide-mix in order to widen our ability to treat patients with different HLA types. This study has implications for cellular immunotherapy in leukemia patients who relapse following allogeneic stem cell transplantation.