The MAIT cell TCR and MR1 are highly conserved across mammalian evolution, presenting a unique immunological interface that has been historically challenging to target with traditional immunisation protocols. Indeed, although anti-MR1 antibodies have been successfully generated, antibodies with fine specificity for the MAIT TCR remain elusive.
Here, we combined a panel of recombinant TCR and MR1 proteins, paired with in vitro yeast display to generate two unique nanobody clones; Nb-01 and Nb-02. Nb-01 binds with high specificity to the MAIT TCR and can be used in flow cytometry to isolate MAIT cells in both humans and mice, outperforming conventional surrogate identification approaches (e.g. anti-Va7.2 paired with CD161). Nb-01 furthermore functions as a MAIT TCR agonist, inducing activation and proliferation in human and mouse MAIT cells. In contrast, Nb-02 binds selectively to MR1 in complex with its prototypical ligand 5-OP-RU and potently blocks MAIT cell activity in vitro and in vivo.
In this presentation, we detail the development of Nb-01 and Nb-02, supported by structural and functional analyses. We describe their selection, provide a molecular basis for their specificity, and demonstrate their bioactivity and application in human and murine settings.
We anticipate that these two novel nanobodies will be helpful reagents for the field, allowing researchers to readily identify MAIT cells in humans and mice, and to manipulate their function in various experimental settings. Their specificity coupled with agonist or antagonist properties offer a modular strategy to manipulate the MR1/MAIT cell axis in therapeutic settings.