LAG3 limits the diabetogenicity of intra-islet CD8 T cells

Abstract

Abstract Tight control of effector T cells is necessary to limit autoimmune diabetes (AD). One mechanism by which this is achieved is through inhibitory receptor (IR) expression. Lymphocyte Activating Gene 3 (LAG3) is one critical IR that limits disease progression and incidence of AD. Using a mouse model in which LAG3 deletion is restricted to CD8+ T cells, Lag3L/L-YFPE8iCRE-GFP.NOD, and wild type (WT) controls, E8iCRE-GFP.NOD, we find that CD8+ T cell-restricted deletion of LAG3 is sufficient to accelerate diabetes incidence and insulitis. Interestingly, we see Lag3L/L-YFPE8iCRE-GFP.NOD mice have an increased intra-islet CD8:Treg ratio, and increased tetramer (Nrpv7, IGRP mimotope) staining. These observations drive our hypothesis that LAG3 limits those autoreactive CD8+ T cell. 5′ single cell RNAseq in conjunction with TCRseq reveals that LAG3-deficient (Lag3−/−) intra-islet CD8+ T cells are transcriptionally unique compared to WT controls, exhibiting a more activated phenotype along with lower geneset enrichment for markers of exhaustion. This was validated by flow cytometry in which WT CD8+ T cells possess an expanded PD1Hi, Tox+ population, while Lag3−/− CD8+ T cells have an expanded PD1mid population, express more CD44, KLRG1, BrdU, Ki67, and less aCasp3. This indicates that WT CD8+ T cells are able to appropriately upregulate PD1 and Tox in response to chronic self-antigen stimulation, while Lag3−/− CD8+ T cells maintain a more activated population. Strikingly, LAG3 deletion on CD8+ T cells appears to be sufficient to overcome a normal “exhaustion-like” program in intra-islet CD8+ T cells, resulting in accelerated diabetes incidence. These data highlight an important role for LAG3 and CD8+ T cell exhaustion programs in AD.