Abstract PR12: Early TCRα expression during T cell development for the generation of enhanced-affinity TCRs for TCR gene therapy.

Abstract

Abstract Thymic selection eliminates T cells expressing TCRs with a high affinity for self-antigen. However, many of the most promising tumor antigens for T cell-based cancer immunotherapies are unmodified self-antigens. Therefore, tumor-specific T cells often have a low avidity for tumor antigens, thus limiting the efficacy of this approach. TCR gene therapy using TCR genes that have been modified for increased affinity can overcome this limitation. The generation of enhanced affinity TCRs generally involves saturation mutagenesis targeting the complementarity determining regions of the TCR genes to be modified. However, this approach requires considerable trial and error, and is still not always successful at generating a higher affinity TCR without promiscuous off-target activity. We have developed a system for selecting high affinity tumor antigen-specific TCRs from a population of T cells selected by agonist signaling during T cell development in vitro. The αβ/γδ lineage choice is in part dictated by the strength of TCR/pre-TCR signaling during early T cell development, such that the pre-TCR provides a weak signal that drives αβ T cell development while the mature γδ TCR provides a stronger signal that drives γδ T cell development. In TCR transgenic mice, early expression of the transgenic TCRα chain prior to β-selection can also provide a stronger γδ-like signal through the mature αβ TCR, leading to the development of lineage redirected TCRαβ+ CD4/CD8 double negative (DN) γδ wanna-be” cells. The development of these DN TCRαβ+ cells is enhanced in the presence of cognate antigen or TCR crosslinking; suggesting that early expression of an antigen-specific TCRα chain before β-selection could promote the generation of DN TCRαβ+ cells in the presence of antigen, through a process in which the introduced TCRα chain pairs with an endogenous TCRβ chain to produce an αβ TCR with high affinity for the target antigen. To test this hypothesis, the TCRα chain from a tumor antigen-specific TCR was transduced into hematopoietic progenitor cells and a library of TCRβ chains was isolated from the lineage redirected DN TCRαβ+ T cells that developed. Several TCRβchains of varying CDR3 lengths were isolated that confer enhanced affinity for the target antigen when paired with the introduced TCRα chain. This abstract is also presented as Poster A13. Citation Format: Thomas M. Schmitt, Philip D. Greenberg, David H. Aggen, David Kranz, Sebastian Ochsenreither. Early TCRα expression during T cell development for the generation of enhanced-affinity TCRs for TCR gene therapy. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr PR12.