Ischemic AKI Modifies Expression of Immune Checkpoint Inhibitor TIGIT Ligands and Co-signaling Partners

Background: T cell immunoreceptor with Ig and ITIM domains (TIGIT) increases in kidney T cells following ischemic AKI and participates in the pathogenesis of AKI in mice. To explore how TIGIT mediates AKI, we investigated the effects of ischemic AKI on TIGIT interacting ligands (CD155, CD112, CD113) and co-signaling molecules (CD226, CD96, CD127, PD1) Methods: C57BL6 mice underwent bilateral ischemia reperfusion (IR) injury. TIGIT ligand/co-signaling molecule expression was initially measured with western blotting at 24h and 18 days post-AKI. Flow cytometry was performed to identify the cell types that express TIGIT ligands and co-signaling partners at baseline and 24h post-IR. TIGIT positive (TIGIT+) and TIGIT negative (TIGIT-) cells were analyzed to examine TIGIT relationship with these molecules Results: Western blotting showed enhanced expression of CD155 (5.6±0.5 fold; P<0.001) and CD112 (2.4±0.5 fold; P<0.01) 24h after AKI. At 18 days, CD155 expression returned to normal levels however, CD112 remained elevated (2.7-fold). CD113 expression was reduced 24h after AKI (0.7±0.2 fold; P=0.04) with normalization at 18 days. CD155 expression by FACS increased significantly in CD11b+ cells at 24h (26.7±4.7 vs 1.5±0.3% P<0.0001) compared to control. Conversely, TIGIT co-stimulatory counterpart CD226 decreased in CD4 (67.1±19.0 vs 46.0±10.3%; P<0.05), double negative (DN) (92.1±5.1 vs 61.4±10.8%; P<0.001) and NKT (91.2±3.5 vs 71.2±5.9%; P<0.001) cells at 24h. CD96 expression was not affected by IR injury. Analysis of TIGIT+ cells showed significant decrease in CD155 (22.4±19.7 vs 6.8±8.6%, P<0.05) and CD127 (42.6±20.3 vs 10.7±6.5%, P<0.05) in NK cells from post-IR kidneys. TIGIT+ cells expressed PD1 both at baseline and after IR injury in CD4 (52.1±12.6 and 66.7±7.1%), CD8 (76.3±18.2 and 84.1±8.5%) and DN T (42.9±17.7 and 47.4±15.3%) cells. PD1 significantly increased at 24h in TIGIT+ CD4 (66.7±7.1 vs 16.5± 4.6%; P<0.001), CD8 (84.10±8.5 vs 12.3± 6.0%, P<0.01) and DN T cells (47.4±15.4 vs 16.6±7.4%; P<0.01) compared to TIGIT- cells. Conclusion: Ischemic AKI leads to increased TIGIT ligands CD155 and CD112, and modulates TIGIT co-signaling molecules CD226 and CD127.TIGIT and PD1 are co-expressed by a subset of kidney T cells at baseline and during AKI. TIGIT ligand/signaling molecule interactions likely underlie TIGIT effects on AKI Funding: NIDDK Support