Mechanisms of MAIT tissue repair properties – MAIT-repair

scRNA-seq, scATAC-seq, CrisprCas9-based technology, bone-marrow chimeras, drug inhibitors, blocking antibodies, genetic inactivation, in vivo mouse model, flow cytometry, cell sorting, cell culture.

1- We obtained results in order to better understand how tissues and environmental cues determine MAIT cells location and properties:
- We assessed thymic development of MAIT cells to elucidate the molecular pathways involved in the choice of MAIT1 versus MAIT17 pathways. We were able: i) to enrich immature and intermediary clusters, ii) to capture cycling MAIT1 cells, and iii) to better define the transcriptional trajectory development of MAIT1 and MAIT17 effectors. The resulting trajectories led to the identification of new molecular candidates involved in the MAIT1 cells lineage commitment.
- We generated single-cell RNAseq data from sorted MR1:5-OP-RU tetramer+ thymocytes from human, rat, mouse, cattle, sheep and opossum. We found a core transcriptional program for MAIT cells that is conserved along evolution and acquired either in the thymus or in the gut.
- We demonstrated that MAIT cells directly monitor a bacterial metabolism associated with oxidative stress and provide host protection in return. MAIT cells produced amphiregulin, IFN?, IL17 and IL22 during colitis, suggesting a beneficial effect on the epithelial barrier. MR1-/- mice showed increased epithelial damage, inflammatory cell infiltrates and weight loss as compared with MR1+ counterparts during chronic colitis, which indicates that MAIT cells protect against intestinal inflammation.
- Using single cell transcriptomic analysis, we showed that lung MAIT cells express a tissue repair program at steady state despite no sign of TCR triggering. Type I IFN signaling is triggered in a subset of MAIT cells, both in the lung and in the mediastinal lymph nodes.
- We have established the colony of germ-free CAST/CAST MR1+/+ mice.
- We have successfully colonized breeding pairs of this mouse strain with a wild-type, antibiotic sensitive, E. coli strain. Experimental animals from this newly established gnotobiotic colony (F1 generation) will be available in Q3 2022.

2- We analyzed MAIT cell functions and associated mechanisms involved during skin wound healing:
- Skin MAIT cells release various effector molecules according to the context of stimulation. We uncover the parameters determining MAIT cell dynamics in the skin and highlight functions underlying their ability to promote skin wound healing. We found that MAIT cells promote wound healing repair by comparing MR1+ and MR1- B6-MAITCAST mice. Expression of molecules involved in pathogen clearance and angiogenesis in the wound were increased in the presence of MAIT cells. We evidenced that, contrary to the resident ?dT cells, MAIT cells are rapidly recruited into the inflamed site and that this recruitment was MR1-independent. Instead, the recruitment relied on the chemokine receptor CXCR6. Our work shows how skin MAIT dynamics promotes tissue repair and provides potential mechanisms supporting this function.

The project progresses smoothly according to the working plan.

Several oral presentations have been made. One paper is in revision in a leading immunology journal. Two other papers will be submitted before the end of the year.