Generation and expression of high affinity, tumor antigen-specific mouse and human T cell receptors to genetically modify CD8p+s T cells for adoptive immunotherapy of cancer

Abstract

Adoptive T cell immunotherapy has shown promise in treating some cancers, but the challenge of isolating T cells with high avidity for tumor antigens limits large-scale applicability. T cell receptor (TCR) gene transfer employing high affinity TCRs recognizing defined tumor-associated antigens can potentially circumvent these challenges. Using a well-characterized murine model of adoptive T cell immunotherapy for established malignancy, we have demonstrated the feasibility of eliminating disseminated leukemia using T cells genetically modified by TCR gene transfer.We next examined the potential of targeting a clinically relevant tumor antigen, the transcription factor WT1, for which the expression patterns in normal and malignant cells are similar in mouse and man. WT1 is overexpressed in most leukemias and many solid tumors and its expression contributes to the malignant phenotype. The RMFPNAPYL peptide from WT1 is presented by HLA-A2 in humans, as well as by H-2Db in C57BL/6 mice, and has been shown to be the target of WT1-specific responses in both species. Like many tumor-associated antigens, generating robust immune responses to the WT1 protein has been difficult as endogenous WT1 expression may delete or render anergic most of the high avidity T cell repertoire capable of recognizing WT1 expressing tumors. We hypothesized that in vitro engineering to increase TCR affinity would improve tumor cell recognition, although the potential for such high affinity TCRs to recognize normal tissues expressing low levels of WT1 would need to be assessed.To test this hypothesis, we characterized the murine and human T cell responses elicited to WT1RMFPNAPYL. Mice immunized with this peptide generate a diverse T cell response, recruiting T cells of multiple TCR Vbeta families and encompassing an avidity range of three logs. However, none of the T cells isolated recognized murine tumors endogenously expressing WT1. We also isolated two human T cell clones specific for WT1RMFPNAPYL, one of which recognizes human tumors expressing this antigen. The TCRs from these T cells are being used as templates for in vitro mutagenesis and selection of higher affinity TCRs by yeast display to determine the threshold required for efficient tumor recognition without targeting normal tissues.