A novel T cell receptor single-chain signaling complex mediates antigen-specific T cell activity and tumor control

Abstract

Adoptive transfer of genetically modified T cells to treat cancer has shown promise in several clinical trials. Two main strategies have been applied to redirect T cells against cancer: 1) introduction of a full-length T cell receptor (TCR) specific for a tumor-associated peptide-MHC, or 2) introduction of a chimeric antigen receptor (CAR), including an antibody fragment specific for a tumor cell surface antigen, linked intracellularly to T cell signaling domains. Each strategy has advantages and disadvantages for clinical applications. Here, we present data on the in vitro and in vivo effectiveness of a single-chain signaling receptor incorporating a TCR variable fragment as the targeting element (referred to as TCR-SCS). This receptor contained a single-chain TCR (Vβ-linker-Vα) from a high-affinity TCR called m33, linked to the intracellular signaling domains of CD28 and CD3ζ. This format avoided mispairing with endogenous TCR chains, and mediated specific T cell activity when expressed in either CD4 or CD8 T cells. TCR-SCS-transduced CD8-negative cells showed an intriguing sensitivity, compared to full-length TCRs, to higher densities of less stable pepMHC targets. T cells that expressed this peptide-specific receptor persisted in vivo, and exhibited polyfunctional responses. Growth of metastatic antigen-positive tumors was significantly inhibited by T cells that expressed this receptor, and tumor cells that escaped were antigen loss variants. TCR-SCS receptors represent an alternative targeting receptor strategy that combines the advantages of single-chain expression, avoidance of TCR chain mispairing, and targeting of intracellular antigens presented in complex with MHC proteins.

An Engineered Switch in T Cell Receptor Specificity Leads to an Unusual but Functional Binding Geometry

“…Retroviral supernatants were harvested after 48 h and 58 −/− cells were transduced as described previously (Stone et al, 2014). After cells were transduced they were sorted via FACS for binding to MART1/HLA-A2 tetramer to obtain a positive staining population.…”

Adoptive T Cell Therapies: A Comparison of T Cell Receptors and Chimeric Antigen Receptors

“…While the many parameters that differ between TCRs and CARs (affinity, ligand structure, and ligand density) have made it difficult to compare directly, a system has been developed that allows comparisons by using the analog of a scFv, a single-chain TCR (Vβ-linker-Vα) as a CAR-like receptor [76,77]. This allows the same V regions to be used in a conventional full-length αβ TCR for comparison with the CAR, where the affinity of the cell-associated forms, the ligand (pepMHC), and ligand density are identical.…”

“…This system also allowed the direct measurement of CAR affinity using typical monomeric pepMHC antigens, and it enables the rapid analysis of the effects of antigen density by simply ‘loading’ different concentrations of peptides onto MHC-positive target cells. Using a high-affinity variant of the 2C TCR called m33 (K d of the TCR and CAR on T cells was identical), it was observed that, in primary CD4 + T cells, the full-length TCR had greater sensitivity to pepMHC than the CAR format (with either CD28 or 4-1BB, and CD3ζ), even though the CAR format was expressed at higher densities on the surface of T cells [77]. Thus, even in the absence of the CD8 coreceptor, the TCR machinery has greater sensitivity.…”

TCR affinity for p/MHC formed by tumor antigens that are self-proteins: impact on efficacy and toxicity

“…K D values of 1 µM or less) are required to mediate activation in CD4 + T cells as compared to CD8 + T cells, where CD8 can co-engage the class I MHC molecule. Effector CD4 + T cells with higher affinity TCRs have mediated significant tumor control, and in some cases rejections, in mouse models [11,17–19]. TCRs with increased affinity against MART1/HLA-A2 [8], NY-ESO-1/HLA-A2 [20], MAGE-A3/HLA-A2 [21], and MAGE-A3/HLA-A1 [22], and ability to mediate in vitro CD4 + T cell activity, have been evaluated in adoptive T cell transfer studies.…”