Type 1 diabetes (T1D) exhibits significant heterogeneity in disease progression, driven in part by variable immune-mediated destruction of insulin-producing β cells. This project focuses on Programmed Death-Ligand 1 (PD-L1), a critical immune checkpoint protein that protects β cells by suppressing autoimmune responses via interaction with PD-1 on immune cells [1]. β cells also release PD-L1 via extracellular vesicles (EVs), which may regulate immune activity beyond the islet microenvironment [2].
Our previous work revealed that exposure to interferons—a hallmark of the inflamed islet microenvironment—upregulates PD-L1 on both β cells and their EVs [2]. Using nPOD slice perifusates, we observed heterogenous elevations in EV PD-L1 levels isolated from pancreatic slice perfusates of T1D donors compared to controls. Within this group, EV PD-L1 correlated with preserved insulin secretion in situ, suggesting its potential as a biomarker for residual β cell function. However, mechanisms underlying variability in EV PD-L1 across individuals remain unclear.
Our preliminary data indicate that interferon exposure also induces an alternative splicing variant of PD-L1 lacking exon 3 (PD-L1Δ3). This variant is poorly incorporated into EVs and may reduce the protective PD-L1 cargo in these vesicles. We hypothesize that increased β-cell production of PD-L1Δ3 in some individuals impairs EV PD-L1 trafficking, leading to variable immune protection and increased β-cell vulnerability.
To investigate this, we will analyze panceatic sections using advanced single-molecule in situ hybridizaton (BaseScope assay) to detect PD-L1Δ3 variant in β cells from donors with, at-risk, and without T1D. By correlating these findings with existing EV PD-L1 data from perifusates, we aim to understand how alternative splicing alters PD-L1 trafficking and impacts β-cell survival. This research could uncover novel biomarkers and therapeutic targets to preserve β-cell function and slow T1D progression.