i2TCR-Research: Immunotherapies inspired by TCR Research

• Applicant: Privatdozentin Dr. Susana Minguet, Ph.D.
• Subject Area: Immunology
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501436442

Since the discovery of the T cell receptor (TCR) in the 1980s, known before as the "Holy Grail of Immunology", thousands of publications have aimed to elucidate the structure, functioning and signaling of this receptor. The TCR is one of the most complex membrane receptors known; indeed, a clear structural pathway from ligand binding to the initial signaling events at the cytoplasmic side remains to be decoded. The TCR is composed of the ligand-binding αβTCR and the signal-transducing CD3εγ, CD3εδ and CD3ζζ dimers. Each CD3 subunit has one cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM), while CD3ζ has three ITAMs. The accessibility of the ITAMs to the Src-family kinase LCK is regulated by conformational changes within the αβTCR, which in turn controls CD3 phosphorylation (Minguet and Schamel, 2008; Minguet et al., 2007; Swamy et al., 2016). We have shown that pMHC binding stabilizes the αβTCR in the active conformation, which in turn recruits LCK by direct binding of its SH3 domain to the CD3ε cytoplasmic tail prior to any receptor phosphorylation (Hartl et al., 2020). We discovered a novel motif (RK motif, RKxQRxxY) within the CD3ε cytoplasmic tail that mediates a non-canonical binding to the SH3 domain of LCK. Thus, LCK and the adaptor molecule NCK are recruited to the CD3ε cytoplasmic tail to cooperatively orchestrate TCR signaling (Hartl et al., 2021). These findings provide a novel paradigm in T cell biology and rewrite the current textbook model for how TCR signaling is initiated following ligand binding. Excitingly, we translated these fundamental insights by grafting this signaling motif into chimeric antigen receptors (CARs), which significantly enhanced the antitumor activity of CAR T cells. This research has demonstrated that translating basic knowledge on the functioning of the TCR into CAR-T cell design is an excellent strategy to improve anti-cancer immunotherapies and has potential for the development of innovative immunotherapeutics. In this proposal, we aim at following this rationale by investigating the initial steps resulting in TCR phosphorylation. Our specific goals are to selectively modulate LCK recruitment to the TCR and to translate this information into novel T cell-based immunotherapies. References: Hartl, Nat. Immunol. 2020. Hartl, Cells 2021. Minguet, Trends in Biochemical Sciences 2008. Minguet, Immunity 2007. Swamy, Immunity 2016.

• DFG Programme: Research Grants