T Cell Activation by Antibody-Like Immunoreceptors: The Position of the Binding Epitope within the Target Molecule Determines the Efficiency of Activation of Redirected T Cells

Abstract

Recombinant TCRs confer specificity to T cells and trigger their activation. Receptors with Ab-derived binding domains have the advantages of MHC-independent Ag recognition and of targeting a variety of chemically different molecules. We explored the impact of the position of a defined epitope within the target molecule on the efficacy of receptor-mediated T cell activation. T cells were grafted with recombinant immunoreceptors that recognize either the membrane distal N or the proximal A3 domain of carcinoembryonic Ag (CEA). Upon binding to isolated, solid-phase immobilized CEA, receptor-mediated T cell activation correlates with the binding efficiency, irrespectively, of the epitope position. Upon binding to CEA expressed on the cell membrane, in contrast, the A3 epitope mediates more efficiently T cell activation than the N epitope, although the N epitope is bound with higher affinity. The CEA N epitope when expressed in a more membrane proximal position, however, activated receptor grafted T cells with higher efficiency than in the distal position. The position of the targeted epitope within the molecule obviously has major impact on the efficacy of T cell activation independently of the binding efficiency of the immunoreceptor.

Antigen Sensitivity of CD22-Specific Chimeric TCR Is Modulated by Target Epitope Distance from the Cell Membrane

“…This is consistent with studies examining primary T cells and T cell hybridomas responding to pMHC ligands of varying size (20), in which ligands exceeding the native TCR:pMHC dimensions severely diminished signaling in primary T cells. Recently, a similar correlation was shown between cTCR:ligand pair size and signaling efficiency with cTCR targeting membrane-proximal or -distal epitopes of carcinoembryonic Ag (22). However, the diminution in lytic potential was less pronounced in that system than in ours, suggesting that differential flexibility of target molecule extracellular domains may modulate this phenomenon.…”

“…This loss of phosphatase exclusion can then lead to inefficient phosphorylation of the TCR complex and result in inefficient signaling (21). It has also recently been shown that chimeric immunoreceptors exhibit diminished signaling efficiency as the distance of the epitope from the target cell membrane increases, albeit to a lesser extent than seen with canonical TCR (22). These results suggest that the choice of epitope targeted on the CD22 molecule might influence signaling efficiency and potential therapeutic activity.…”

CD28 cosignalling does not affect the activation threshold in a chimeric antigen receptor-redirected T-cell attack

“…28 We previously explored the situation by redirecting T cells against the membrane distal and the proximal domain of carcinoembryonic antigen. The membrane-proximal carcinoembryonic antigen epitope more efficiently mediates CARredirected T-cell activation than the distal epitope.…”

CAR Mechanics: Driving T Cells into the MUC of Cancer

“…When CARs bind antigen at a membrane-proximal location, potent T-cell activation is generally the result. By contrast, weak activation is commonly observed when membranedistal epitopes are targeted (15)(16)(17), although function may be enhanced by removal of the CAR spacer domain (15). Intriguingly, however, if epitope is coexpressed at membrane-distal and membrane-proximal locations in separate molecules, potent T-cell activation ensues (17).…”