A high avidity WT1 reactive T cell receptor mediates recognition of peptide and processed antigen but not naturally occurring WT1 positive tumor cells

摘要

Wilms’ Tumor Gene 1 (WT1) is an attractive target antigen for cancer immunotherapy because it is overexpressed in many hematologic malignancies and solid tumors but has limited, low-level expression in normal adult tissues. Multiple HLA class I and class II restricted epitopes have been identified in WT1, and multiple investigators are pursuing the treatment of cancer patients with WT1 based vaccines and adoptively transferred WT1 reactive T cells. Here we isolated an HLA-A*0201 restricted WT1 reactive T cell receptor (TCR) by stimulating PBL of healthy donors with the peptide WT1:126-134 in vitro. This TCR mediated peptide recognition down to a concentration of ~0.1 ng/ml when pulsed onto T2 cells as well as recognition of HLA-A*0201+ target cells transfected with full-length WT1 cDNA. However, it did not mediate consistent recognition of many HLA-A*0201+ tumor cell lines or freshly isolated leukemia cells that endogeneously expressed WT1. We dissected this pattern of recognition further and observed that WT1:126-134 was more efficiently processed by immunoproteasomes compared to standard proteasomes. However, pretreatment of WT1+ tumor cell lines with Interferon gamma (IFNγ) did not appreciably enhance recognition by our TCR. In addition, we highly overexpressed WT1 in several leukemia cell lines by electroporation with full-length WT1 cDNA. Some of these lines were still not recognized by our TCR suggesting possible antigen processing defects in some leukemias. These results suggest WT1:126-134 may not be a suitable target for T cell based tumor immunotherapies.